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UNIVERSITA’ IUAV DI VENEZIA

Dipartimento di Progettazione e pianificazione in ambienti complessi

Corso di Laurea Magistrale: Architettura e Innovazione

Tesi di laurea

A support tool for the early design phase of BiPV towards nearly zero energy districts

Relatore

Prof. Massimiliano Scarpa

Correlatore

Dott. David Moser

Laureanda

Jennifer Adami

Mat. n° 280301

Anno Accademico 2014/2015

A support tool for the early design phase of BiPV towards nearly zero energy districts

Adami Jennifer

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Index

Introduction ........................................................................................................................................... 1

1 BiPV technology to achieve nearly Zero Energy District...................................................................... 4

1.1 From nearly Zero Energy Building towards nearly Zero Energy District ........................................ 5

1.1.1 Nearly Zero Energy District ................................................................................................ 7

1.2 BiPV (Building integrated PhotoVoltaic)..................................................................................... 9

1.2.1 Photovoltaic technology.................................................................................................... 9

1.2.2 BiPV as multifunctional technology...................................................................................14

1.2.3 BiPV “architectural systems” ............................................................................................16

1.2.4 BiPV flexibility .................................................................................................................27

1.2.5 Design stage ....................................................................................................................30

2 New methodology developed to support BiPV design.......................................................................37

2.1 Barriers related to the use of software tools.............................................................................38

2.2 Developed methodology and simulation tools for BiPV design...................................................41

2.2.1 BiPV parametric design process ........................................................................................41

2.2.2 Software tools for BiPV parametric design ........................................................................52

3 Case study .....................................................................................................................................58

3.1 “Druso Est” district project, Bolzano ........................................................................................58

3.1.1 Participative design process .............................................................................................59

3.2 Implementation of the BiPV design process ..............................................................................61

3.2.1 BiPV as shading device .....................................................................................................63

3.2.2 Model construction .........................................................................................................65

3.2.3 Solar irradiation simulation ..............................................................................................69

3.2.4 Economic optimization of the BiPV system ........................................................................72

3.2.5 Thermal energy demand simulation..................................................................................75

3.2.6 Optimization algorithm ....................................................................................................79

3.3 Optimization results................................................................................................................82

4 Conclusions....................................................................................................................................87

4.1 Outlook ..................................................................................................................................89

References ............................................................................................................................................96

Aknowledgement ........................................................................................Error! Bookmark not defined.

A support tool for the early design phase of BiPV

towards nearly zero energy districts Adami Jennifer

1

Introduction

Energy efficiency in buildings is an important objective of energy policy and strategy in Europe.

The reduction of the energy consumption in parallel to an increase in the use of energy from renewable

sources in the building sector are fundamental measures implemented by the European Union in order

to minimize the total final energy use and the carbon dioxide emissions. They represent key parts of

the European regulatory framework. Political statements and directives have the objective to reduce

the building environmental impact on climate and secure future supply of energy. In 2010, the Energy

Performance of Buildings Directive 2010/31/EU (EPBD) recast [1] established several new or

strengthened requirements such as the obligation that all the new buildings should be nearly zero-

energy by the end of 2020. A nearly Zero Energy Building (nZEB) “produces enough renewable energy

to meet its own annual energy consumption requirements” [2]. This definition could represent an

ambitious target to achieve for a single building, especially when referring to existing buildings.

However, enlarging the perspective to a wider system of buildings (cluster of buildings or district), able

to achieve a nearly zero energy balance, can be an effective alternative overcoming the limitations

found at single building level.

From nZEB perspective, the buildings are converted from consumer to energy generator

systems (prosumers). The exploitation of the solar radiation not only can reduce the building energy

needs, through solar passive gains and daylighting, but it can also allow the buildings to become energy

producers. Photovoltaic systems are important solar energy systems towards nZEB in terms of self-

production of electric energy, satisfying part of buildings demand as self-consumption. Moreover, the

photovoltaic technology can play an important role in an nZEB prospective also thanks to its

potentialities in terms of “integrability” into the building envelope. A Building integrated Photovoltaic

(BiPV) element, by definition, becomes part of the building structure as it is integrated into the

envelope, even used in substitution of traditional building components (i.e. roofing systems, buildings

façades, fenestration, overhangs, etc.). BiPV products therefore serve dual roles, being both electricity

generators and part of the building’s construction. As a result, they can be considered as

multifunctional construction materials, having not only to comply electro‐technical requirements, but

also to ensure all the functions of the replaced element (e.g. weather protection, thermal insulation,

shading, noise protection, security). In order to have a suitable integration of a multifunctional

technology such BiPV, constructive and functional quality must be simultaneously preserved without

neglecting an architectural, conceptual perspective, which looks at the building as a formal whole

composition. Integrating photovoltaics into the building envelope changes the role of the building skin



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from a passive barrier towards an active layer where the active role of BiPV represents a crucial issue.

The whole design process of a multifunctional element such a BiPV system is complex where several

considerations from different point of views need to be taken simultaneously into account. Architects

and designers should perform such a comprehensive evaluation from the Early Design Phase (EDP),

when several main decisions can crucially impact the overall building lifecycle, the durability and

performance of any project. In order to better manage the complexities of a design process, designers

should be supported by simple software tools that allow them to evaluate the impact of early design

choices on the building’s efficiency, economic feasibility, appearance, etc. The compelling question is:

are there such easy, flexible and integrated software tools, able to support the first design phase?

The present work aims to provide a strong contribution in this sense. Together with the team

at EURAC, I have developed an innovative design methodology, aimed to provide an effective support

for designers. The method employs specific “integrated” software tools, able to address all issues

related to a project (e.g. energy balance, life‐cycle costs, economic issues, architectural appearance,

etc.) into a single platform. Design and analysis are integrated within a single simulation environment,

where a model is constructed and evaluated according to several target, in order to allow the designer

to provide quick and reliable predictions.

What is most interesting is the parametric approach, which is at the base of the whole system.

The parametric design allows us to characterize a model not by fixing properties, but setting the

constraints where the properties are contained. Users can experiment and explore different designs

by altering the parameters of a model. The parametric design process is developed into the platform

of Grasshopper, a graphical algorithm editor that uses a visual programming language. Based on graphs

that map the flow of relations from parameters through user-defined functions, Grasshopper can

create a parametric model. Connecting with validated environmental data sets and simulation engines

(e.g. EnergyPlus and Radiance) by the plugin Ladybug and Honeybee, it can also provide a wide range

of building and environmental analysis of the parametric system. Developing parametric simulations,

however, is not the main object of the thesis. A genetic algorithm evaluates all the simulation solutions

and finds the best ones, according to one or more targets previously set. This represents the main goal

of the parametric simulation and optimization process, to support designers providing a set of

dominant solutions among which they can choose.

Using the described design method can represent a fundamental step in the design strategy

especially when dealing with complex projects, for which several considerations must be taken into

account. In this work, I have applied an example of parametric design process on a residential district

chosen as demo case considering BiPV technology integrated into the buildings façades. Due to the

“multifunctionality” feature of BiPV, a complex simulations process has been performed to evaluate

https://en.wikipedia.org/wiki/Visual_programming_language



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from different viewpoints some best performing system configurations, based on a parametric model

construction. The BiPV technology proposed is a shading devices system. The photovoltaic overhangs

have been conceived as moveable elements, the tilt angle of which (i.e. the angle between the

overhang and the normal to the façade) represents the dominant parameter. Being a sun control

strategy, their integration into the buildings envelope has been evaluated not only according to the

photovoltaics energy production performance, but also considering all the issues related to the

sunlight entering into the building sites. Therefore the photovoltaics energy yield and the impact on

the solar gain represent the targets to optimize, even taking into account some economic feasibility

considerations. A parametric optimization has been performed, providing some solutions, a set of

integration strategies able to fulfill the initial intent of an effective integration of PV as overhangs

system. Testing the developed method on a real demo case is an useful opportunity to highlight all the

strengths, weaknesses, opportunities and threats of such a complex design process. Each of them will

represent a development key of the methodology proposed, in order to improve its potentialities,

hoping that the present study can represent a starting point for the development of an overall method

for building design.

Chapter 1 defines the BiPV technology as an effective innovative system able to provide a strong

contribution towards nearly zero energy buildings, districts, cities, etc., within an European framework

aimed at achieving specific energy efficiency targets.

Chapter 2 explains in details the new methodology developed through the present thesis work, in

order to provide an useful support to the design process of a complex architectural system such as

BiPV.

Chapter 3 implements on a real demo case the design methodology developed by using specific

software tools. All the main steps of the process are explained. Results are provided to evaluate the

methodology effectiveness and capabilities.

Chapter 4 critically discusses the study results, highlighting identified strengths and weaknesses in

order to provide potential outlooks to improve the developed methodology capabilities.



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1 BiPV technology to achieve nearly Zero Energy District

European legislation has set out a cross-sectional framework of ambitious targets for achieving

high-energy performance in buildings, a sector that accounts an important part of the world’s total

primary energy use and the greenhouse gas emissions. Making buildings (refurbishing and new

developments) more energy-efficient and by using a larger fraction of renewable energy, has been

identified as one of the key issues to reduce the non-renewable energy use and greenhouse gas

emissions. This represents the main objective of the European recast about nZEB requirements [1].

According to nZEB concept, the building has to demonstrate very high-energy performance. Firstly, it

has to use all cost-effective measures to reduce the energy usage, especially non-renewable, through

energy efficiency. Efficient equipment and passive elements such as building orientation, high

insulation, natural daylighting, and ventilation considerably reduce the building energy load. However,

in order to achieve a low energy balance, energy efficiency measures are not enough. The buildings

have to become real energy producers. They have to use renewably energy sources to cover their

energy demand. Several types of localised renewable energy sources are available (i.e. geothermal, air

heat, solar or wind energy), even according to a specific geographic location. Thus, it is necessary to

effectively use active and efficient technologies able to optimize the exploitation of renewables.

Through the current study, the technology of BiPV (Building integrated Photovoltaic) is

presented as an effective option for buildings to optimize the use of the solar energy source. BiPV

systems can play an important role for achieving the nZE target in buildings. Moreover, if integrated in

the urban context, they could enable a supply of renewable energy, helping cities in reaching more

sustainable conditions.



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1.1 From nearly Zero Energy Building towards nearly Zero Energy District

The European Directive 2010/31/EU (EPBD) recast [1] represents a strong engagement in order

to cut energy demand in buildings through increased energy efficiency and wider deployment of

renewable technologies. It establishes that starting from the end of 2020 (2018 for new buildings

occupied and owned by public authorities) all new buildings will have to be nearly Zero Energy

Buildings (nZEBs). According to the directive, nearly Zero Energy Building means a building with “very

high energy performance”, where “nearly zero or very low amount of energy required should be

covered to a very significant extent by energy from renewable sources, including energy from

renewable sources produced on-site or nearby” [1]. In a nutshell, the energy needs of a building has to

be reduced thanks to efficient energy gains and supplying the resulting low energy demand through

renewable energy sources, in order to reach a zero energy balance between annual energy

consumptions and energy supply.

The EPBD neither prescribes a

common approach to implement nearly

Zero Energy Buildings nor describes the

assessment categories in detail. Thus, the

Member States have established

different parameters, both in terms of

quantity and quality. They detailed

application in practice of the definition of

nearly Zero Energy Buildings, reflecting

their national, regional or local

conditions, and included a numerical

indicator of primary energy use

expressed in kWh/m2 per year. Primary

energy factors used for the

determination of the primary energy use

may be based on national or regional yearly average values and may take into account relevant

European standards. To date, according to [3], a definition is available in 15 countries (plus Brussels

Capital Region and Flanders). In other 3 countries, the nZEB requirements have been defined and are

expected to be implemented in the national legislation. In the remaining 9 (plus Norway and the

Figure 1.1 - Status of nZEB definition for new buildings [3]



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Belgian Region of Wallonia), the definition is still under discussion and has not been finalised yet

[Figure 1.1].

With regard to Italian context [4], an nZEB is a building, new construction or existing, that

meets:

- specific technical requirements from 1 January 2019, for public buildings, and from 1 January 2021,

for all the other ones;

- a minimum portion of renewable energy used as set in Annex 3 of DL 28/11.

The Ministerial Decree “Requisiti minimi” [5], approved on 25 March 2015, defines the

methodology to calculate the energy performance of buildings. It refers to specific performance indices

that, taking into account the winter and summer conditioning period, compare the building with a

reference building [4], in order to establish a range for primary energy consumption expressed in

kWh/m2*year, differing according to building type, location and use.

Regardless on the specific definition set by each Member State, generally the first step towards

the nZEB goal is the reduction of the energy demand by means of passive solutions and energy

efficiency and, of course, using sustainable materials for its construction. The second step is

represented by the generation of the energy required by users with renewable energy systems. In

relation to an nZEB design, the possible renewable supply options are several. Energy can be on-site

(PV on a building roof), nearby (wind farm) and off-site (biomass) produced [Figure 1.2].

Figure 1.2 - Renewable energy on-site (a), nearby (b), off-site (c) production (prEN 15603:2013)

However, the focus for the design of nZEBs is to transform the building itself in a production

system. It implies that the energy generation should be within the building property. This represents a

real step-change relative to the current way of building design, both from an architectural and

engineering perspective.



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1.1.1 Nearly Zero Energy District

Achieving a nearly zero energy balance on the scale of a single building is possible when the

energy consumption of the building is low enough and its morphology allows for the optimal

integration of energy generation systems [6]. This is a condition that can not always be met, especially

when dealing with existing building. Consequently, an enlargement of spatial perspective is needed.

The energy balance boundary is thus considered on a broadened scale, looking at the building not only

as a single building, but as a part of a wider system of buildings (district), which itself is part of an even

wider system (the city or the urban context). These considerations lead to the concept of nearly Zero

Energy District (nZED), a complex system of buildings and users, able to achieve a nearly zero energy

balance as a whole. An nZED implies a synergy between buildings, where buildings with a positive

energy balance can compensate those with negative balances.

This approach is possible in the case of new buildings and district design (Example 1), and is

particularly suited for projects on existing buildings or districts (Example 2). In particular, in the case of

interventions on buildings in “dense” urban contexts, where the surfaces for energy generating

systems are limited, very often a single building cannot reach the nZEB balance on its own. The energy

demand may be high, compared to the available surfaces for solar systems, and the effect of shadow

limits the use of the envelope surfaces.



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Two example of nZED concept are shown in [6] and hereunder reported.

1. Plus energy settlement in Freiburg, Germany (new settlement)

The zero energy balance is achieved in the frame of settlement. Some of the 59 built terrace

houses have a positive primary energy balance, others a negative one. The average is clearly

positive. The efficient terrace houses are covered with 3150 m² of roof top integrated PV

generators. The heat is supplied by district heating. The efficiency of the houses is based on

the Passive House concept and a consequent urban planning for shadow -free south

orientation, position and shape of the buildings [6].

Figure 1.3 - Plus seattlement in Freiburg, Germany (Rolf Disch) [6]

2. Renovated district in Bad Aibling, Germany (retrofit project)

New buildings generate an energy surplus to compensate negative balances of refurbished

former military accommodation buildings from the 1930s. Solar thermal and photovoltaic

areas differ significantly from each other. In the shown example, heat is fed into the local

heating grid of the settlements by means of 2000 m2 of solar thermal collectors [6].

Figure 1.4 - Renovated district in Bad Aibling, Gemany (Schankula Architekten) [6]



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1.2 BiPV (Building integrated PhotoVoltaic)

As stated in the previous sections, in the nZEB concept the building is conceived as an integral

and active part of the energy generation system where the consumer becomes prosumer. Therefore,

its design should consider not only the traditional design aspects, but the energy aspect, too. This

translates into the need to design the energy harvesting system for the building together with the

building itself. The energy production should be strictly connected to the buildings structure.

To this end, one of the most promising renewable energy technologies that can be easily

connected with buildings is photovoltaics. Photovoltaics (PV) is an efficient means of producing energy

on site, directly from the sun. It consists of a solid-state device, simply converting electricity out of

sunlight, silently with no much maintenance, limited pollution (depending on the energy used for the

manufacturing of the modules), and limited depletion of materials [7]. PV technology can play an

important role in nZEB perspective, thanks to its potential in terms of “integrability” into the building

envelope.

1.2.1 Photovoltaic technology

A photovoltaic system captures sunlight and converts it into electricity through a simple

principle. It generates electrical power through the photovoltaic effect, using semiconductor

technologies [8]. The photovoltaic effect occurs when light enters a photovoltaic cell, strikes the

semiconductive material, and transfers enough energy to cause the freeing of electrons. A built-in

potential barrier in the cell acts on these electrons to produce a voltage that can be used to drive a

current through an electric circuit [9].

Figure 1.5 - Solar cell structure [8]



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The electricity generated is direct current (DC) and may be stored in batteries, or converted to

alternating current (AC) electricity for general application or connection to the utility grid.

The basic element of a photovoltaic system is the PV module, formed of assembled arrays of

PV cells. Modules are wired together and combined with a set of additional application-dependent

system components. These components include the associated equipment required to convert, use,

and store the electricity (e.g. inverters, batteries, electrical components, and mounting systems) and

differ for “stand-alone” and “grid-connected” systems.

Materials currently used for PV include monocrystalline silicon, polycrystalline silicon,

amorphous silicon, cadmium telluride, and copper indium gallium selenide/sulphide. These

technologies differ in terms of both employed material and structure, with different efficiency of the

energy conversion. The cell types can be grouped in the following categories.

Silicon wafer based crystalline cells

PV products based on crystalline silicon

technology (c-Si) are the most widespread (about 85%

of the cells used) and predominant on the market [10].

Due to the specific material properties of the crystalline-

Si solar cells, the modules available commercially are

mostly rigid, opaque, and flat. Semi-transparent

solutions can be obtained by a specific encapsulation, typically in glass-glass laminates or by

perforating the wafer. Transparency is produced by means of a particular distance set between the

arrays of solar cells, which allows the transmission of light. There is also a range of coloured crystalline

solar cells on the market. Crystalline silicon cells are further subdivided into two main categories:

- Monocrystalline (sc-Si), are produced from silicon wafers, extracted from a square block of single

crystal silicon by cutting slices of approximately 0.2 mm thick. Square cells of around 100 to 160 mm

sides are produced with a homogeneous structure and a dark blue/blackish colour appearance. The

efficiency of monocrystalline cells is currently the highest available on the market, ranging

approximately from 17% to 22%.

- Policrystalline (mc-Si), are produced from the melted silicon, casted into square ingots where it

solidifies into a multitude of crystals with different orientations, which gives the cells their spotted and

shiny surface. Policrystalline cells have an efficiency of around 11% to 17%.

Figure 1.6 - Mono and poli-cristalline cells



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Both the categories offer a good cost-efficiency ratio. However, one important disadvantage

of this technology is known to be the loss of performance at high temperatures and the effect of

shading caused by the surrounding buildings, their chimneys, or other kinds of obstacles. In fact, even

one single partly shaded c-Si module will lead to a significant loss of power, not only in that particular

module, but – in absence of by pass diodes - in all the others modules connected in series within the

same circuit. In the worst case scenario, they could all be affected and reduced to the same power

output as the one that is shaded, and consequently, the whole system could suffer a “cutout”. This

significant issue has to be taken into account when planning with c-Si technology.

Thin‐film solar cells

Thin‐film solar cells are usually categorized according to the photovoltaic material used. The

three main technologies are amorphous silicon (a‐Si), Copper Indium Gallium Selenide (CIS or CIGS)

and Cadmium Telluride (CdTe). The most promising material in the past was amorphous silicon but

due the low improvement in efficiency, attention has moved towards CdTe and CIGS [8].

Figure 1.7 - Solarhaus Darmstadt, Germany. The façade is covered with black CIS thin-film modules [10]

Thin‐film technology consists in a very thin layer of photovoltaic active material deposited

directly on large area substrates, such as glass panels, stainless steel or polymers (square meter sized

and bigger) or foils (several hundred meters long). In relation to the substrate material, thin-film PV

modules exist also in flexible and lightweight forms, as well as opaque or semitransparent. It can be



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seen as a microscopically thin layer of “disordered” photovoltaic material that gives the module

surface a more homogeneous appearance. Modules general surface appearances range from

brown/orange to purple and black, with parallel lines more or less marked.

For standard amorphous silicon cells the efficiency lies among 4% to 8%. However, compared

with c-Si, the efficiency decrease in silicon thin-film cells is less affected by high temperatures and

there are less significant losses of performance under conditions of indirect and hence lower sun

irradiation caused by cloudy weather conditions and shading by trees, other buildings, or chimneys.

The annual energy output of PV modules based on thin-films, in some

conditions provides a higher energy output in kWh/kWp than common

standard screen printed c-Si technology [10]. Nonetheless, when

calculated in terms of kWh/m2, c-Si results always as the best option.

An alternative thin-film technology that can reach higher

efficiencies is CIGS material [Figure 1.8], with around 12%. CIGS modules

tend to exhibit an efficiency increase in the first time of use, leading to higher system performance

ratio. Furthermore its temperature coefficient is noticeably more favourable than that of standard

crystalline silicon [10].

Figure 1.8 - CIGS photovoltaic

technology [11]



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Other cell technologies

Organic Photovoltaics (OPV) technology has interesting

material properties ranging from flexible to semi-transparent and a

reasonable manufacturing costs made possible by roll -to-roll

production techniques. The current limiting factors for OPV are its

still low levels of module efficiency (11.5% under laboratory

conditions) and the absence of products with long lifetime

guarantees [10].

Dye-sensitized Cells (DSC) technology is based on a photochemical system. Its current relatively

low level of efficiency of around 5–6% at module level is offset by the lower cost and other properties,

such as, for example, the potential to be produced in various colours on flexible, rigid, or semi-

transparent substrates in a cost-efficient way [10].

Figure 1.10 - Facade with dye sensitized cell (DSC) technology [10]

Figure 1.9 - OPV on a flexible

substrate [9]



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1.2.2 BiPV as multifunctional technology

Building integrated Photovoltaics (BiPV) refer to photovoltaic cells and modules which can be

integrated into the building envelope as part of the building structure, and therefore can replace

conventional building materials [12]. It represents a “prerequisite for the integrity of the building’s

functionality” [13] and, if dismounted, it would have to be replaced by an appropriate building

component.

According to SUPSI [7], “BiPV definition excludes therefore building independent or overlapped

installations such as PV modules simply placed or mounted on pre-existing roofs or other PV systems

merely attached to parts of the building that do not assume other function than the solar power

generation”. The difference between an “integrated” or “applied” PV system is not always clear. An

accurate analysis of the system functions could be required. A BiPV module, which is used in

substitution of traditional elements of the building envelope, has to ensure all the functions of the

replaced element (e.g. weather protection, thermal insulation, shading, noise protection, security). It

has to comply not only electro‐technical requirements as stated in the low voltage directive

2006/95/IEC or CENELEC standards, related to the module itself, but also a function as defined in the

European Construction Product Directive CPD 89/106/EEC. BiPV must be generally designed and built

in such a way that it does not present risks of accidents or damages in service or in operation for

persons involved throughout the entire lifecycle of the building. It has to satisfy the basic requirements

for building component such as mechanical

resistance and stability, safety in case of fire,

hygiene and health of people, safety and

accessibility in use, protection against noise as

well as energy economy and sustainable use of

natural resources.

Besides these standard building

construction constraints, the integration of PV

implies other issues. It refers also to an

architectural, conceptual perspective, which looks at the building as a formal whole. In this case, BiPV

can be described with regard to the role that it plays in the concept of the envelope composition.

Several architectural criteria have been defined in the framework of the International Energy Agency

project IEA-PVPS Task 7 “Photovoltaic power systems in the built environment” [14] and they are

hereunder summarized.

Figure 1.11 - Glass ceiling with transparent BiPV modules [14]



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Naturally integrated: the PV system is a natural part of the building, it completes the building.

Without PV, the building would be lacking something.

Architecturally pleasing: based on a good design, the PV system adds eye-catching features to the

architecture.

Good composition: the colour and texture of the PV system is in harmony with the other materials.

Grid, harmony and composition: the sizing of the PV system matches the sizing and grid of the

building.

Contextuality: the total image of a building is in harmony with the PV system (e.g. for historic

buildings).

Well-engineered: the elegance of design details is taken into account. All details are well

conceived, the amount of materials is minimized.

Innovative new design: the PV system adds a value to building. The PV is an innovative technology

in the field of architecture, asking for innovative, creative, thinking of architects.

Figure 1.12 - Casa Solara, Laax, Switzerland [15]

Constructive, functional and formal quality must be simultaneously preserved in order to have

a suitable integration of a multifunctional technology such BiPV.



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1.2.3 BiPV “architectural systems”

Photovoltaic modules, available as flat or flexible surfaces, realized with cells or laminates, can

be used together with materials that are common in architecture, such as glass or metal, in opaque as

well as in semitransparent surfaces. They can be integrated into every part of the building envelope,

creating specific “architectural systems”. An architectural system, into the context of this work, refers

to a conceptual model defined by specific structures and components, and associated to specific

physical phenomena. A wide variety of BiPV architectural systems is available today. Several databases

collecting information on existing BiPV products on the market are provided on-line, e.g. in [16] and

[17].

Most of BiPV available can be grouped into three main categories: roofing systems, facade

systems and external devices. These categories will include different technological ways of using PV in

the envelope, which lead to different choices of the PV component.

Roofing system

As a roof element, the PV system is part of the building skin and requires attention to

weatherproofing, structural, and snow accumulation issues. It can displace traditional construction

materials and, depending on the substituted layers, they have to meet different requirements that

influence the choice of the most suitable PV component.

Both crystalline silicon and thin-film technologies are available for BiPV roofing solutions. The former

comfortably dominates the market, whereas the latter is used when chimneys, trees, or neighbouring

buildings cast a shadow or where crystalline modules are excluded because of their rigidity or weight.

Typical bluish or black c-Si solar cell patterns are the most widespread among roof-installed PV

modules. Semi-transparent, wafer-based solutions used as skylights are also an option, especially for

bigger roofs on public, commercial or industrial buildings.

Two first categorizations depending on the tilt of the roof (1) or on its portion dedicated to

BiPV (2) are shown as follows.

1. A pitched roof is made up of angled and sloped parts. It is known as a “discontinuous” roof

due to the presence of small elements (tiles, slates, etc.). Panel installation can be easier than

many other BiPV solutions, but an impermeable roof is required. The most common solutions

is with the use of photovoltaic roof tiles with mono- or polycrystalline solar cells integrated

with the classical roof tiles.



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A flat or curved roof, also known as “continuous roof”, is characterized by an uninterrupted

layer with the main function to be water resistant. Flat roofs have the advantage of good

accessibility and easy installation. On the contrary curved roofs need complex supports and

specific flexible panels, involving added costs. In both cases, care must be taken during the

fixing of the array to preserve the roof integrity. The added weight of the PV array on the

roof must be considered.

2. An in-roof system integrates photovoltaics in a limited portion of the roof, simply replacing

the tiles. In order to perform a good integration, the PV panels are required to be placed with

regard to the surrounding roof tiles. They can be framed into the roof structure or overlap it.

Water tightness has to be guaranteed, for instance, by means of an impermeable interlayer

underneath. Architects consider in-roof systems as a not so attractive option when

photovoltaics are additional and visible materials.

The full roof solution refers to a full solar roof concept, where the roof surface is exclusively

and specifically conceived as a solar collector for energy production. Besides in-roof

installations, a full-roof system is regarded as a more economic and more appealing

alternative choice [10]. All the traditional roof components are substituted and a maximum

surface area is dedicated to energy production.

Figure 1.13 - Full-roof BiPV installation on a 19th century Swiss farmhouse, Uettligen [10]



18

Several categories within roofing system application area include:

- Solar tiles/shingles/slates

This system is usually designed to resemble the conventional ‘”roof tile” with a solar PV tiling.

The panel height is modular to the roof tile’s rows and it can be glazed or foil -based. There are several

varieties, semi-rigid and systems using various thin-film solar cell technologies. Commonly only a part

or the whole roof is used for PV, using the same sub-structure as the mounting system. There are also

smaller panel systems, with module size <0,5 m2,

which are adapted to the conventional roof tile

that becomes itself the PV element. Solar tiles and

solar shingles offer an alternative constructive

and aesthetic approach on account of their

likeness to ordinary roof tiles, but their use could

involve some disadvantages, like for example the

susceptibility to the ingress of water and

humidity, or the lack of compatibility with the multitude of existing different tile types and the

geometric variations. Moreover, in case of PV integration into existing buildings with this solution there

is a need for an additional mounting system and in most cases the reinforcement of the roof structure

due to the additional loads.

- Metal panels

This system consists in mounting flexible laminates PV on building materials such as metal

roofing. BiPV metal roofing can replace an architectural standing seam. The thin film amorphous silicon

PV material is laminated directly onto long metal roofing panels. A

protective waterproof membrane is attached covering the

photovoltaics. A traditional roofer followed by an electrician can

install these metal panels. In an interlocking tongue-and-groove

assembly, the panels are weighed down by pavers that surround

the system to provide access for maintenance and repairs. A cap is

placed over the standing edges to form a seam. This technology can

be used also to redo the roof of an existing building.

Figure 1.15 - PV applied on zinc

standing seam panels [9]

Figure 1.14 - Middle European solar tiles [9]



19

- PV membranes

This technology uses waterproof membrane as a support of flexible laminates PV. The

mounting procedure of the panels on roofs as well as other building structures is different (easier) than

the conventional, rigid ones. The high performance membrane with integrated flexible and lightweight

PV modules can easily be adhesively bonded to roofing materials. This integration system brings along

many advantages like light weight and avoidance of heavy wind loads (because they do not allow wind

beneath them). Moreover, it allows easier planning permission on new build and retrofit projects.

- Solar glazing

Glazed PV laminates can be used as roof parts, often made by crystalline silicon cells with

adjusted spacing or by laser grooved thin-film which provides filtered vision (skylights).

This integration system is usually one of the most interesting. It combines the advantage of light

diffusion in the building while providing an

unobstructed surface for the installation of PV modules.

PV elements provide both electricity and light to the

building. The amount of light desired to go through the

designed structures can be customized by dimensioning

and adjusting the number and spacing of cells in the

case of crystalline silicon technology or by modifying the

manufacturing process in the case of thin-film. In both

cases the more transparent is the module, the lower is

the energy efficiency. They are also commonly used to

provide sun/wind protection to building surfaces and

interiors. Transparent modules can be used for open

and indoor atria. In both cases the glazing should meet

the standards for mechanical resistance, while in the latter also the thermal requirements of the

envelope. Skylights are used in flat roofs, pitched roofs, and sometimes in the top area of the façade.

They are employed usually for commercial and prestigious buildings, designed to provide a great deal

of natural lightning by using large areas of semitransparent window-like areas.

Figure 1.16 - Solar Glazing system [19]



20

Façade system

The second field of BiPV application is that of façades where solar panels of all technologies

can be integrated as a conventional cladding system for curtain walls and single layer façades . Current

development is aimed at developing more advanced applications like adaptive modular PV façades

and intelligent ways of balancing daylighting and shading [18].

In many cases, standards modules (frame or frameless) are used for such application although the use

of tailored made modules is sometimes requested in order to match the façade specifications. For

example glass PV laminates, replacing conventional cladding material, are basically the same as tinted

glass. They provide long-lasting weather protection and can be tailor-made to any size, shape, pattern

and colour.

Façade applications typically include warm façades, cold façades and solar glazing.

- Warm façade

A warm façade is typically a continuous building envelope system in which the outer walls are

non-structural. A warm façade fulfils all building envelope requirements such as load bearing, thermal

insulation, weatherproofing and noise insulation. Since it is the building skin system, the parameters

related to solar gain control such as thermal and visual

comfort have to be controlled when using highly-glazed

curtain walls. In this case, a warm façade matches a solar

glazing. In general, it can also be represented by an opaque

curtain wall or by an insulating cladding panel (PV + thermal

insulation without an air gap) where there is no ventilation.

A vertical curtain-wall represents a fairly economical and

standard construction strategy, but a sloped one could be

more productive. However, both systems could have

problems with panels’ junctions and sealing. Figure 1.17 - Warm facade systems

with thin film photovoltaic [20]



21

- Cold façade

This facade system typically consists of a load-bearing sub-frame, an air gap and a cladding

panel. The PV panel is used as a cladding element, which has no thermal connection with the wall

warm. It offers weather protection and cooling for the wall. Thanks to the naturally ventilated cavity

heat from the sun is dissipated through bottom and top openings. It provides a good ventilation behind

the modules, which enhances the PV system efficiency.

Figure 1.18 – Cold façade system, 28th Street Apartments, Los Angeles [19]

Some systems make use of vents to optimize the air ventilation. An example is shown in Figure

1.19. Poly-crystalline PV modules are installed in the façade in an integral form such that an air cavity

is created between the PV backside and the building envelope. The system thus constitutes an outer

layer (PV panels) and an inner layer (building envelope). The air gap formed between these two layers

interacts with the indoor environment by means of two vents (dampers), one located in the upper part

and the other located in the lower part of the brick wall. The vents can be controlled manually by the

occupants according to their individual comfort needs and weather conditions [8].



22

Figure 1.19 - Cold facade system with vents [20]

Another possible option for PV integration is the double‐skin façade, a glazed surface that is a

non-load-bearing exterior wall suspended in front of the structural frame and wall elements [Figure

1.20].

Figure 1.20 - GDF Suez, Dijon, France [21]



23

- Solar glazing

Solar glazing systems are often used as

windows or as a curtain wall semi-transparent

system, designed with extruded aluminium frames

(but also steel, woods, etc.) in-filled with glass. Since

it is part of the building envelope, parameters

related to solar gain control, such as thermal and

visual comfort, have to be controlled when using

highly-glazed curtain walls. The transparent

functional layer (glass) is replaced with PV glazed

panes, whilst the load-bearing part is equipped for

the electric wirings passages. The cell pattern and

assembly can provide the proper solar and

daylighting control replacing the traditional external

louvers and defining a particular architectural

appearance of the façade. The most common glass

types used are laminated glass, patterned or fritted

glass and spandrel panels. Some companies sell custom-made BiPV glazing products, available in any

size or dimension and consisting of any PV technology. The architect can indicate the spacing between

solar cells, which will determine the power supply and permit the design of passive solar features by

regulating the amount of daylighting allowed to enter into the building. Standard and custom products

are available in many sizes and in a range of thicknesses [18].

External devices

Photovoltaics can be also integrated into the design as external devices on the building skin.

These accessories may include balconies, shading systems, and several other smaller systems. Shading

systems are the most commonly used accessory [12]. The control of the indoor microclimate, especially

in glazed façade systems, usually requires the use of shading devices aimed to select the solar radiation

for ensuring the thermo-hygrometric and visual wellbeing through a proper use of the natural lighting.

Several types of shading devices are available: applied on roof or façade; external, interposed (for

Figure 1.21 - Solar glazing facade BiPV system [22]



24

example in double skins) or internal; fix or tracking (manually or electrically); vertical, horizontal or

oriented; lamellar, micro-lamellar, sail, grid; curtain or blind; mobile screen [12].

Quite common these are semi‐transparent glass or glass components integrated as canopies

or louvers, but there are also movable shutters with semi‐transparent crystalline or thin film.

Opaque sun protections are also widely used, in most cases with an upper part without cells, to avoid

shading the PV cells when the overhangs overlap.

Figure 1.22 - Hofberg 6/7, Switzerland [22]



25

- Spandrels, balconies parapets

Spandrels and parapet areas are also suitable for photovoltaic integration, mostly using glass

or glass semi-transparent modules made of security glass. Balcony fronts can either be two‐paned

solutions to protect the PV‐cells or single glasses to which the PV‐cell is laminated. In glazed verandas,

the heat generated at the back of the PV can be used to create thermal comfort in spring and autumn,

while the space can be opened for natural ventilation in summer time.

- Shading systems

PV modules of different shapes can be used as shading elements above windows or as part of

an overhead glazing structure. Since many buildings already provide some sort of structure to shade

windows, the use of PV overhangs should not involve any additional load for the building structure.

The exploitation of synergy effects reduces the total costs of such installations and creates added value

to the PV as well as to the building and its shading system. PV shading systems may also use one -way

trackers to tilt the PV array for maximum power while providing a variable degree of shading.

Figure 1.23 - Shading BiPV system [23]



26

The main features of the different BiPV architectural systems described in the current

paragraph are highlighted through the comparative analysis outlined in Table 1.1.

Easy

inst

alla

tio

n

and

rep

airs

Stru

ctu

ral

issu

es

Wat

erp

roo

fin

g is

sues

Ove

rhea

tin

g

issu

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Imp

act

on

day

ligh

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g

Imp

act

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th

erm

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ener

gy d

eman

d

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thet

ic a

dd

ed

valu

e

Hig

her

en

ergy

effi

cien

cy

ROOFING SYSTEMS

Tiles/shingles/slates

Metal panels

PV membranes

Solar glazing

FAÇADE SYSTEMS

Warm façade

Cold façade

Solar glazing

EXTERNAL DEVICES

Shading system

Table 1.1 - Main features of several BiPV solutions commonly used



27

1.2.4 BiPV flexibility

From the building integration point of view,

the market is divided into two main categories: the

standard modules and bespoken products. Both

categories give some formal flexibility in their offer,

but obviously not to the same extent. As PV has to

compete with traditional technologies to generate

electricity at a reasonable price, most producers

have turned to very large factories to mass‐produce

PV modules, achieving economies of scale, but

limiting their offer to a few standard products. Their

fixed sizes and crude frames can make their

integration difficult, as they often do not match the

raster of the project. However, if the PV option is

considered at a very early design stage, an innovative and successful integration can be achieved.

Custom‐made products, developed for special projects for maximum flexibility, can be ordered with

specified formal characteristics (e.g. shape, size, colour, texture, etc.). This freedom usually comes with

an extra cost due to small quantities produced, and attention should be paid to the issue of spare parts,

which should be produced with the main order, to ensure replacement in case of incident.

- Shape and size

The size of standard crystalline photovoltaic modules ranges from 0.2 to 2 m². The small size

of the cells used in crystalline Silicon based modules (10x10 cm to 20x20 cm) gives the dimensional

possible “steps”, as the module will have as dimensions multiples of these cells size. Opaque and

translucent modules, with or without frame, can then be obtained in a large variety of shapes and

sizes, either from existing products or custom made.

About thin-film technology, producers generally offer standard glass modules with specific

size. A set of standardized building dedicated products is also available on the market. Due to the roll‐

to‐roll manufacturing process, there is only flexibility (a set of dimensions to choose from) in the length

of the laminates, that come with a fixed width. Several roofing companies are cooperating with the PV

producers to offer their products (metal roofs, corrugated sheets, insulated panels) with integrated

PV.

Figure 1.24 - SCHOTT Ibèrica SA, Barcelona, Spain [19]



28

Figure 1.25 – Left: GreenPix media wall, Beijing, China [24]; Right: Opera House, Oslo, Norway [8]

- Colour, patterns, textures

The appearance of crystalline modules depends on the appearance and composition of the

cells, and marginally on the colour of the back coating (Tedlar). There is certain flexibility in choosing

the colour, but black or blue cells and black or white Tedlar are largely dominant. Only a few

manufacturers propose coloured cells, so these are quite rare and come with added cost and reduced

efficiency. The standard choice for crystalline modules front glass is an extra‐white, low iron, 3mm

glass, used by most producers. However, there are options for textured or etched extra‐white glass, or

very thick glass for increased static resistance or for combination with a back gl ass.

Figure 1.26 - Poli cristalline silicon wafer with different coloured anti-reflective

Thin-film manufacturers provide basic products in one single colour, brown, blue or black. New

developments offer now also some reddish brown, chocolate‐brown, hepatic and sage green colours.

Laminates are mainly available in dark blue and pinkish shades. Thin-film technology allows for the

possibility to produce semi‐transparent modules with a variety of patterns (point, stroke, stripes), by



29

laser cutting. Some thin-film laminates, like in solar shingles that imitate traditional asphalt roof

shingles, present the general image of a dark blue or magenta cells ribbon, with two empty lateral

areas without cells, where the substrate is visible.

Figure 1.27 - Thin film modules

- Jointing/Framing

The crystalline modules jointing can be made through the aluminium framing, by integration

into curtain‐wall systems with mullion/transom, or modules can be integrated frameless in glazing

systems, with negative jointing. For roof applications, overlapping is often chosen for the horizontal

joint. Custom‐made products can be developed with their own specific fram ing as well, where the

frame becomes part of the module design.

For glass modules, the framing possibilities are the same as for crystalline products. The

jointing and framing of the laminates are defined by their substrate structure. Some laminate

producers are partnering with building component manufacturers to integrate their modules into

existing building products.



30

1.2.5 Design stage

In order to have an effective integration of PV as a real building component, it is hence

necessary to include BiPV from the first design phases. Due to its multifunctional feature [1.2.2], BiPV

integration entails several considerations from different point of views (e.g. weather protection,

thermal insulation, shading, noise protection, security). This might require that the building team,

including architects, building designers, engineers, building owners and utility companies, work

together from the first phase of the project onwards. Some of the factors that must be taken into

account during the first design stages to optimized the performance of a BiPV system, according to

[19] , are reported in the following sections.

Minimizing electric loads

The first consideration in BiPV applications is to maximize efficiency in the building energy

demand or load. Designers should minimize the electricity load by utilizing integrated energy design

strategies such as building envelope improvements, daylighting techniques, natural ventilation

applications, and additionally installing energy-efficient lighting and cooling equipment. The goal is to

minimize the building energy needs and then supplement the remaining loads with the generated

electricity.

Matching electric loads

A BIPV system may produce the same amount of electricity as consumed in the building on a

yearly base, however the simultaneity of production and consumption needs to be evaluated. An

effective strategy to best optimize the PV energy use can be implemented by matching the offer with

the demand. It means that photovoltaics should produce energy when energy is needed with the final

aim to increase the direct self-consumption. The energy demand is defined by the building use.

Different electric load values are measured for example in residential and commercial buildings [25].

Increasing the correlation between the electricity production and the load profile can have a positive

impact on the PV economic case, optimizing the energy use. Designing a BiPV system, therefore,

cannot disregard considerations about load matching.



31

Optimizing system configuration and electricity generation

Decisions regarding where and how to best integrate BiPVs into building designs are greatly

influenced by the potential amount of electricity generated from a specific application and its cost

effectiveness. For example, horizontal applications like roof BiPVs and vertical applications like curtain

walls have different material/installation costs and electrical output curves due to the different

position relative to the sun. The electricity generation widely depend on the solar access, the incidence

of solar radiation that reaches a PV surface at any given time. It is important to note that the availability

of solar radiation changes throughout the day and throughout the year. For maximum energy output,

it is important to determine the orientation, tilt angle, size and location of the BiPV system in relation

to the building site and design. As flexibility exists in the placement of BiPV, this gives a limited degree

of freedom to match the time of day, month, and season when peak solar generation is in close match

with the peak electrical needs of the building [9].

- Tilt. Maximum solar intensity occurs on a flat surface perpendicular to the sun’s rays. Inclining the

panels toward the sun increases the amount of sunlight striking the surface and wil l increase the

output. The sun path sweeps a daily arc that changes seasonally throughout the year. In this way, the

sun follows a prescribed solar position described by an altitude angle (vertical) and azimuth angle

(horizontal). By orienting the BiPV panels to be perpendicular to the sun at certain times of day and

year, it is possible to optimize solar exposure to match loads. As a general rule of thumb in the Northern

Hemisphere, BiPV installations produce the most energy over the course of a year when oriented true

south and tilted at an angle equivalent to the site latitude. However, instantaneous output varies

depending on cloud cover and the sun position. As a panel gets farther from a tilt equivalent to the

site latitude, the total annual output decreases. A vertical surface orientation may produce

approximately 30 percent less electricity, while a horizontal surface orientation may produce

approximately 10 percent less electricity than an optimally inclined installation at our latitudes [9].



32

- Orientation. The total amount of energy that strikes

a surface is a function of both tilt and orientation. In

Figure 1.28 is shown the amount of the annual

irradiation evaluated on different orientation in

Bolzano. Vertical surfaces with east/west orientation

have a relevant decrease (around the 60%) of annual

irradiation compared to the optimally inclined

southern orientation. For these east/west

orientations, low sun angles at the beginning and end

of the day account for the majority of the power

generated.

- Sizing. For the selection of a BiPV type and for the sizing of a system, three main factors have to be

considered: energy loads, architectural or aesthetic considerations, and economic factors. To

determine the desired power rating of a BiPV system for a building, the electrical requirements of the

building should be evaluated at first. The optimum power rating of the system can be calculated and

sized, based on the share of the building electricity that will be supplied by the BiPV system.

Architecturally, the size of the BiPV system is physically limited to the dimensions of the building

available surface area. The balance between the amount of power required and the amount of surface

area available can determine the type of PV technology that will be used. Each technology has an

associated range of output in watts per square meter. For example, in order to have a certain energy

output, systems made of amorphous silicon can require a larger surface area than equivalent systems

composed of single crystal solar cells, placed with the same surface tilt and orientation.

- Location. BiPVs should be placed where they have secured long-term solar access. It is critical not to

locate BiPV panels where neighboring landscapes or structures that may cast shadows on the system

are present or planned in the future. Full or partial shading of the panels partially inhibits the

production of electricity. The system performs best if there is homogeneous solar access because the

solar cell with the lowest illumination level determines the operating current for all of the cells wired

in series.

100%

70%

84%

72%

62%

91%

94%

66% 45%

Figure 1.28 - Annual irradiation for different orientation evaluated in Bolzano (PVGIS)



33

Figure 1.29 - Shading due to environmental factors [26]

In the design phase, it is also important to take into account the surface features that surround

the PV system. Their reflection capacity influences the amount of solar irradiati on that hits the PV

system.

Meeting aesthetic criteria

A BiPV solution may be an appropriate option for designers that wish to create aesthetically

appealing buildings. However, from the beginning of the design process, several aesthetic criteria

should be taken into account when designing distinctive “architectural features” [0]. All the formal

characteristic of the project must be architecturally

integrated into the context. This represents a

crucial issue especially when regarding to old

buildings, historical sites, and “protected”

landscapes [27]. The formal acceptance of a PV

integration is a matter of discussion, both in the

private dimension (i.e. willingness to adopt a

specific PV system) and in the public dimension (i.e.

acceptability of specific BiPV applications in the

urban context where the individual lives), as

reported in [28]. Surely, improving the BiPV design

could increase the acceptability of a PV technology. As shown in [1.2.4], the BiPV products already

available on the market today can make visual statements by adding patterns, textures, colours, and

visual notoriety to the roof or façade of a building. The wide flexibility of BiPV appearance can

contribute to achieve a good aesthetic integration level.

Figure 1.30 - Roof integration of PV on historic building, St Silas Church, Pentonville [24]



34

Figure 1.31 – Left: Hotel Renovation, Paris [7]; right: Kollektihuset, Copenhagen, Denmark [29]

The economics of BiPV

While the prices of standards PV modules are very well known in the PV sector [30], when it

comes to BiPV, the subject gets much more complex since a combination of many factors may

contribute to affect the final price of BiPV system. It is important to carry out a comprehensive

economic analysis that evaluate all factors specific to the project. The best way to assess the economic

attractiveness of a building strategy like BiPV is to evaluate the total cost of the system over time [9].

A life-cycle cost (LCC) analysis gives the total cost accounting for all the expenses incurred and the cost

savings gained over the life of the system. It allows the designer to compare the economics of many

different power options as well as determine the most cost effective BiPV system design. Most LCC

analysis includes capital costs, installation costs, maintenance costs, energy costs, replacement costs,

energy cost savings, and salvage value. When using LCC to compare different systems, it is important

that each system configuration performs the same work with the same reliability.

Usually BiPV products are subject to comparison with other building materials since their aim

is to replace those conventional materials and their functionalities [1.2.2]. A review of a recent study

published by SUPSI and SEAC [12] displays the results of the price survey conducted to compare

conventional façade materials with BiPV façade solutions. The price is defined as the end-user price

and measured in €/m², which is the end-user PV system cost calculated over the area that the PV

systems covers on the roof or façade. Figure 1.32 shows a benchmark of the conducted price survey.



35

Figure 1.32 - A benchmark of the conducted price survey, comparing conventional facade materials with BiPV

facade solutions [12]

Conventional façade technologies include fibrocement, brick-ceramic, metal, stone, wood,

window and curtain walls. Prices range all the way from 30-50 €/m2 for a low cost fibre-cement façade

(similar to a traditional plaster) to 1100 €/m2 for a special curtain wall (e.g. self-lighted, interactive

façade, etc.). The price of BiPV solution systems varied from 100-150 €/m2 for a thin-film PV cold façade

(with really simple sub-structures and a low efficiency solar technology) to 750 €/m2 for a high end PV

solar shading system [11].

The survey’s results show that, if considering the materials costs, BiPV systems seem to be

comparable in price with conventional façade materials. However, there is a wide value range, unable

to provide a clear benchmark. Furthermore, into a global costs context, this cost is not so indicative.

When designers have to choose between traditional building materials or photovoltaics, they have to

perform several evaluations. Firstly, they should compare materials with similar conditions, for

instance installation costs, maintainance and disposal costs, architectural integration, impact on the

building thermal balance or on the daylighting, etc. Since the comparison includes a technology that

produce electricity, other crucial issues to evaluate are all the factors connected with the current

electric energy cost and its growth.

A simplified economic analysis can be carried out by calculating what the max imum added cost

should be if the target is a return of investment (ROI) within a 10 year timeframe and represents a

correlation between additional costs, self-consumption and ROI.



36

Assumption: BiPV makes sense if you can directly self-consume in the building (to go towards

nZEB) or in the district (to go towards nZED) (self-consumption can be increased by using early design

tool to place the BiPV modules accordingly using all façade direction/roof or with batteries).

Figure 1.33 - Economic benefits from generated electricity of BiPV modules on facades over a period of 10 years. Assumptions: cost of electricity in 2015, 0.2 Euros/kWh. Self-consumption: 100% in commercial and industrial buildings, 30% in residential buildings. The calculation was carried out for inflation rate of 1% and 3% and for

BiPV system efficiency of 5% and 10% (source: elaboration EURAC)

From the Figure 1.33 can extrapolate the maximal additional cost for two BiPV system

efficiencies of 5% and 10%, for the residential and for the industrial/commercial sector, to have a

return of investment within ten years (only considering self-consumption, energy to the grid is not

valorized). In the building sector price is given per m2. Clearly, the efficiency of PV here has a high

impact in the final figures if the production is calculated over m2 and not as a specific yield in kWh/kWp.

Within the framework of the EU Photovoltaic Technology Platform, EURAC has provided support to

the European Commission in setting future targets for BiPV Figure 1.34.

Figure 1.34 - Targets set by the EU PVTP for BiPV towards the European Commission

Installation year Inflation rate 5% 10% 5% 10%

1% 63 125 84 168

3% 69 137 92 184

1% 66 132 89 177

3% 79 159 107 214

Installation year Inflation rate 5% 10% 5% 10%

1% 19 38 25 50

3% 21 41 28 55

1% 20 40 27 53

3% 24 48 32 64

London

Economic benefits

[Euros/m2/10 years]

Rome

Economic benefits

[Euros/m2/10 years]

Economic benefits

[Euros/m2/10 years]

London Rome

2015

Economic benefits

[Euros/m2/10 years]

2015

2020

2020

Commercial and industrial

buildings

Residential buildings

Efficiency

semi-transparent opaque

Now (end 2015) 150 – 350€ 130 – 250€

2020 50% reduction on today 50% reduction on today

2030 75% reduction on today 75% reduction on today

Facade-integration

Additional cost

(€/m2)



37

2 New methodology developed to support BiPV design

The growing demand for better energy performance in buildings is leading to an ongoing

development of strategies and technologies, involving an increasing complexity of the buildings design.

During the design phase, fundamental decisions are made that have an enormous impact on the whole

building lifecycle, on the durability and performance of any project. Especially the Early Design Phase

(EDP) plays a crucial role. It refers to the “stage of work where initial design ideas are being

conceptualized in tandem with the formulation of the building project requirements” [31]. In order to

achieve an optimal result, designers should be aware of the consequences of these design decisions.

Making informed design decisions requires the management of a large amount of information. An

overview of possible design options and their performance should be created to let the designer

choose the best solution. This can represent a critical task to implement. There is a distinct risk of

missing better design opportunities or obtaining undesirable effects if the design process is not

properly performed [32]. In order to better manage the complexities of a project, therefore, designers

should be supported by computer-based building simulation tools able to make quick and reliable

predictions, which let them evaluate the impact of early design choices on the building efficiency.

Several software tools are currently available. However, as will be explained through the following

sections, their capabilities seem not to satisfy the main designers’ needs. The present study aims to

provide a strong contribution in this sense, attempting to suggest an effective design methodology as

support to the design stage of a complex project.



38

2.1 Barriers related to the use of software tools

There is a broad variety of digital tools that architects are using today. An international survey

of architects carried out within the framework of the IEA SHC Task 41 identified the most used [33].

The software tools reviewed are organized into the following two section.

- Graphical/physical tools section includes solar

charts/sun-path diagrams and physical models tool. They

allow the architect to perform a number of tasks quickly

and accurately such as determining shadows’ cast,

determining spatial relationships between buildings and

sun access to public space or to the internal spaces of

buildings, etc.

- Digital tools section includes CAAD tools (i.e. AutoCAD, ArchiCAD, GoogleSketchup, Revit,

VectorWorks) and Building Performance Simulation (BPS) tools (i.e. Ecotect, Project Vasari, RETScreen,

Radiance, IES VE, SolarBILANZ, bsol, DAYSIM, DPV, Lesosai, Polysun, PVsyst, PV sol, T sol). Digital tools

provide various outputs (e.g. 3D models, pre-sizing, simulation results, etc.) that can be used in

facilitating and improving communication between the actors of the design and construction process,

i.e. architects, clients, engineers, consultants, etc.

Figure 2.2 - Modelling and simulation outputs [33]

Figure 2.1 - Sun-path diagram [31]



39

According to the survey, at the early design phase only some of the tools previously mentioned

are usually used [33]. Graphical/physical tools and CAAD, tools that mostly provide qualitative output

in solar modelling, can be helpful during the first design stage. Other tools, predominantly BPS tools or

specialised tools for sizing active solar components, provide quantitative output, but also require more

detailed and time consuming input. However, some BPS tools are considered acceptable also for the

early design stage. The results reported in [34], about simulation software used per design phase,

indicate Ecotect domination, due to its compatibility with CAD tools, its visual 3D output, its accuracy

at least for the scientific purposes, and capabilities that allows a comparison between various design

proposals. Second place in the acceptance for solar design tools in the early design stage is RETScreen,

which is relatively simple to use, despite of its completely numerical input and output. The following

in order are Radiance, PVSol, Polysun, PVsyst, eQUEST, IES VE, Design Builder, Lesosai, followed by

other software that are considered less compatible with early design phase. A wide review of the

software tools mentioned is available in [31].

Figure 2.3 - Output scenes provided by Radiance (left) [35] and IES VE (right) [36]

As stated by the IEA [34], architects and designers are aspiring to create sustainable built

environment and are taking serious consideration of the use of building performance simulation tools

that improves design reliability of energy efficiency. However, there are current obstacles preventing

architects from using existing methods and tools for solar building design. Although a great number of

digital tools for solar design exist today, they are not necessarily quite adequate for architects and the

EDP. The IEA international survey [34] identifies some barriers related to the use of available tools for

architectural integration of solar design [Figure 2.4].



40

Figure 2.4 - Barriers related to the use of the tools for the architectural integration of solar design [34]

The results indicate that the tools are first of all too complex. Users have more difficulty in

using several tools (e.g. since capacities and software features are not well‐known) and especially in

interpreting the results. Some software tool are not able to provide architects with results that are

presented in a useful form for the EDP: most provide numerical results, as tables or graphs. Moreover,

most software are mainly suited for detailed design phase where extensive information is available

and important design decisions already have been taken. Another crucial barrier identified by the

survey is the lack of interoperability between software. Most of the used tools do not allow data

exchange and importing and exporting features (like 3D models), increasing errors probabilities and

waste of time during design phases. In addition, the lack of a graphical flexible representation to

interact visually instead of entering command lines represent a serious barrier. Users need a dynamic

interface that can respond in real time to their actions, allowing an iterative design process. A graphical

representation can also provide information more easily accessible than results presented in the form

of reports and/or spreadsheets.

Since EDP software tools have to support adequately architects and designers taking in account

all the factors related to a project, there is the need to employ “integrated” software tools, which can

be able to address all issues related to a project (e.g. energy balance, life‐cycle costs, economic issues,

architectural appearance, etc.). The use of multiple platforms for design and simulation not only slows

down the process, but also introduces interoperability issues which include the use of multiple models



41

and interfaces. This represents a crucial problem when referring to the design of a multifunctional

technology like BiPV, which, as explained in [1.2.2], has an impact on several factors related to the

building.

2.2 Developed methodology and simulation tools for BiPV design

In the following paragraphs [2.2.1 and 2.2.2] the new method developed in this work and the

software used for the early design phase of BiPV is described. The methodology proposed aim to

provide a comprehensive evaluation of several issues related to the building integration of a

multifunctional technology as BiPV. It integrates design and analysis within a single parametric

environment, facilitating a smoother, more integrative and efficient workflow.

2.2.1 BiPV parametric design process

The procedure developed in this work evaluates several issues related to the integration of PV

on facades and the architectural system selected for the optimisation is BiPV as overhang. It compares

the output of energy production, shade of thermal gains and shade for daylighting purposes for a set

of different system of BiPV overhangs. Thanks to the aid of parametric design and genetic algorithm,

the three main aspects of the building integration (electricity production, daylighting performance and

thermal performance) are optimized. In the following sections, the main features of the methodology

proposed in this work are presented.



42

Figure 2.5 – Developed BiPV parametric design process



43

Parametric design

The process of parametric design consists in the characterization of a system or object through

a set of dimensions. These can be modified within a certain range of values. In explaining parametric

design, there are a few BiPV examples that deserve to be mentioned.

A glazing system with photovoltaic cells embedded can be described with a technical drawing down to

the smallest detail. Leaving the possibility to change the distance between neighbouring cells, without

changing the design of the element, could open the possibility of variating the overall transparency of

the glazed module. The distance between the cells, in this case, is a parameter. The distance not only

affects the transparency of the glass, but also the peak power per unit area. Analysing a BiPV

ventilated façade, as another example, the distance between the array and the façade could be the

parameter to be optimized. In BiPV overhangs, the type of system used in the following example,

illustrated with the Figure 2.6, the main parameter is the tilt angles. An array of overhangs could be

described with tilt angle, depth and distance between the rows.

Figure 2.6 - In yellow the length and angles characterizing the main parameters in an example facade with overhangs

When the behaviour and the physical performance of a building can be simulated, the main

advantage of the parametric design is its possibility of variating certain aspect of a system in order to

obtain maximum performance. The optimum is found by scanning a vast pool of solutions based on

the same basic design but with varying parameters. This gives an obvious advantage for systems such

as BiPV where simulation is essential to achieve design goals, and where performances and efficiency

are considered as key aspects. For the sake of BiPV architectural systems (defined in [1.2.3]), the

integration of photovoltaic has been grouped in few main categories, characterized by specific physical



44

models and specific parameters. Several main solutions of PV integrated in roofs and façades,

accessible and not from within the building, are shown in Figure 2.7.

Figure 2.7 - Schematic subdivision in categories of main BiPV architectural system, each one could be parametrically described [13]



45

Ray Tracing

The irradiation over the designated surfaces is calculated using a method called backward Ray-

Tracing. The procedure allows for the measurement of the irradiance (or illuminance) over specific

points on a surface. In the backward Ray-Tracing method, the light rays are traced in the opposite

direction to that which they naturally follow. As explained in [31], the process starts from the eye (the

viewpoint) and then traces the rays up to the light sources taking into account all physical interactions

(reflection, refraction) with the surfaces of the objects composing the scene. The idea behind

(backward) ray tracing is to simulate individual light rays in space to calculate the luminance

distribution in a room from a given viewpoint. Therefore, rays are emitted from the point of interest

and traced backwards until they hit either a light source or another object. In the former case, the

luminance distribution function of the light source determines the luminance contribution at the

viewpoint. If a ray hits an object other than a light source, the luminance of the object needs to be

calculated by secondary rays that are emitted from the object. Figure 2.8 shows a simplified model of

the Ray Tracing process.

Figure 2.8 - Ray Tracing method [37]

The Ray Tracing process requires as input at least one point associated to at least one vector.

The point will be the precise position where the irradiation is measured, the vector represents the

normal to the surface that should be measured.



46

Weather data and environment modelling

To perform a building´s energy simulation the initial step is to create a model that emulates

the real site environmental condition. This means identifying all critical environmental factors that

influence the building. The main features in the model are the weather conditions and the geometries

and optical properties of the surroundings. In order to build a good model, a weather file should be

used. A weather file contains “typical” data derived from hourly observations at a specific location. It

represents local climatic conditions relative to the building models, such as hourly temperature,

humidity, wind speed and direction, atmospheric pressure and solar radiation or cloud cover

conditions.

Main part of the simulation model is based on the Ray Tracing procedure, using a sky function

as light source. The sky function is represented as a semispherical cap, composed of a system of points,

the luminance of which is determined by their coordinates. The value associated with each specific

point into the sky function can represent the radiation evaluated in a specific moment, when the sun

has a defined position (point in time evaluation) or it can be a total amount of annual radiation

(cumulative evaluation). The sky function, derived from the weather file adopted into the simulation

model, uses the value of direct and diffuse radiation combined with the sun position to generate a sky

vault. The sky function contains shadings determined by far objects. Far shadings usually cast an

instantaneous shadow on the whole simulated building. In order to evaluate the real surroundings

conditions, also close shadings have to be added to the model. The close obstructions, like surrounding

buildings and objects (trees, chimneys, etc.) could cast partial shadows on the simulated building (i.e.

leave some measuring point to the direct irradiation while shadowing others), so they have to be

considered (created or imported into 3D model).

As a last step, the definition of the real radiance properties of all the surrounding materials

(i.e. reflectance, roughness and specularity) is required to complete the environmental model, which

represents an essential input of every energy building simulation.



47

Energy irradiation evaluation and early economic assessment

The developed method allows for an early assessment of the electricity production of the BiPV

system. The Ray-tracing procedure enables a measure of the irradiation over each measuring point of

a specific surface. For the early evaluation of the production and the economic performance of the

system an annual cumulative simulation is performed. For each measuring point, associated with a

single photovoltaic module, an annual cumulative irradiation is retrieved. The irradiation is then

multiplied by the efficiency of the module and by its ownarea, and by the performance ratio of the

system in order to get the system annual energy output. During the simulation every possible PV panel

irradiation is measured, and as results some modules are not worth installing, as their annual

production is low while their price is the same as the best performing ones. The method sorts all the

modules from the most to the least irradiated and calculate the annual electricity production removing

all the modules below a certain threshold with the simplified Equation 1

𝐸𝑡ℎ𝑟 = A ∙ 𝜂 ∙ 𝑃𝑅 ∙ ∑ 𝐻𝑛,

𝑛𝑡ℎ𝑟𝑒𝑠ℎ𝑜𝑙𝑑

𝑛=1

Equation 1 - Annual electricity production for a configuration of modules chosen above a certain threshold of irradiation

where Ethr is the energy output [kWh] for one year, nthreshold is the number installed modules, A is the

area of a PV module [m2], η is the module efficiency, PR is the performance ratio of the system, and Hn

is the cumulative insolation of the nth module [kWh/m2 yr]. The performance ratio is a parameter that

evaluates the performance of a PV system over a certain period of time and it is defined as the ratio

between the final yield (energy produced by 1 kWp of PV system) and the reference yield (incident

energy from the sun divided by 1000 W/m2, irradiance defined as Standard Test Conditions). Typical

values of PR varies from 0.7 (roof mounted) to 0.9 (ground mounted).

Once the power production of the system is estimated, its profitability is accessed through the Net

Present Value (NPV), which is defined as

𝑁𝑃𝑉 = ∑𝐸𝑡ℎ𝑟 ∙ 𝐶𝑝(𝑡) ∙ 𝑃𝐸(𝑡) − 𝑚𝑡ℎ𝑟

(1 + 𝑟)𝑡 − 𝐼0

𝑙𝑖𝑓𝑒

𝑡=1

,

Equation 2 - Net Present Value after a precise time span of the PV system

Ethr is the energy output from Equation 1, Cp(t) is a coefficient of performance defined between 0 (worst

performance) and 1 (best performance), to consider degradation, PE(t) is the price of electricity in the

given year, mthr is the maintenance associated to the number of modules (threshold), I0 is the initial

investment and r is the discount rate, a measure of the future decrease in value of present money.



48

With these two simple formulae, it is possible to evaluate a BiPV system’s annual electricity

production and maximize its NPV within a selected time frame by choosing an adequate threshold for

the minimum irradiation.

Thermal impact evaluation and thermal model

As a multifunctional technology included into the building envelope [1.2.2], BiPV necessarily

influences the building thermal balance. Its resulting impact can be evaluated through an energy

simulation, that, considering all boundary conditions and loads, models the building energy

consumption. Therefore, an optimization of the PV integration can also contribute to optimise the

building energy needs.

Firstly, a building model must be created for the simulation, identifying one or more thermal

zones. A thermal zone is a space within a building that has its own thermostat, served by the same

system and has the same building use. External and internal loads are assigned to the thermal zone.

- External loads come from the weather file. They are influenced by the building envelope: every

thermal zone has specific construction characteristics that condition the building energy

performances. The construction materials employed in the building envelope have their own thermal

properties and characteristics (i.e. thickness, conductivity, density, specific heat, roughness, thermal

absorptance). The external load of the thermal zones are deeply influenced by their boundary

conditions: the determination of the boundary conditions is thus required for the envelope surfaces

as adiabatic, outdoor, or ground exposed.

When the photovoltaics are integrated in the building envelope, they can have a thermal impact on

the building by modifying the external loads. BiPV are geometrically applied to the building model and,

as PV panels integrated in glazing surfaces or as shading elements, they influence solar gain, by varying

their position, size, tilt, transparency level, etc.

- Internal loads depend on the building use: user occupation, devices and type of activity conducted

condition the building energy balance determining the thermal loads. The internal loads are defined

hourly within schedules and assigned to the simulation model.

External and internal loads are employed as input in the Energy Plus simulation that provides hourly,

daily, monthly or annually energy need values (kWh or kWh/m2) for heating, cooling, ventilation,

lighting. These outputs have to be optimized, in favour of a nearly zero building energy balance.



49

Study of daylight impact of BiPV

Daylighting concerns the illumination of the building interiors with sunlight or sky light and is

known to affect visual performance, lighting quality, health, human performance, and energy

efficiency. When the photovoltaic modules are integrated into the building glazed surfaces or as

shading elements, they have an impact on the internal illumination, controlling the solar radiation

reaching the interior of the building.

The daylighting is strictly connected with the human visual comfort as it is meaningful in

relation with the human eye. For this reason, it concerns the portion of the electromagnetic spectrum

included into the visible range of wavelengths (from about 390 to 700 nm). This requires the use of lux

(lumen/m2) as unit of the illuminance intensity in spite of raw irradiance (W/m2). The visual comfort is

related to quantity and distribution of light, it is a condition where people have enough light for their

activities and from the occupant’s viewpoint there is no blinding effect or discomfort glare. It is a

matter of subjective reaction, however there is an agreement about the necessity of glare control, and

about a few strategies for glare assessment in the design phase. One of these is to set a comfort range

of illuminance values on the measuring surface.

A daylighting analysis can be conducted through the Ray Tracing methodology previously

introduced, using a sky function as light source and a system of points and vectors. In this case , we

have to use a point in time evaluation to have hourly illuminance values. This is because the visual

conditions are evaluated calculating the percentage of hours in which the illuminance value is

maintained into the comfort range, so it is connected to the solar illumination level (weather file) and

to the occupancy of the building users (schedules), two factors that change every hour.

To perform a daylighting evaluation, we referred to two validate indices: Daylight Autonomy

(DA) and Simplified Daylight Glare Probability (sDGP), both based on the use of a system of points and

vectors. The first one, DA, is represented by the percentage of annual daytime hours that a given point

in a room is above a specified illumination level. The evaluation

is based on a horizontal point grid set on a specific level, which

could be, for example, the desk height [Figure 2.9]. A vector

indicates the normal to the plane on which the illumination is

measured, a vertical vector is associated to each of the points to

calculate horizontal illuminance.

Table height

Figure 2.9 - Points and vectors

system used in illumination analysis



50

The second one, sDGP, is used for glare probability analysis,

evaluating the percentage of the annual daytime hours when people

are disturbed due to the high level of vertical eye illuminance. This

index also is based on a point evaluation, but in this case the points

are set at eye-level in particular positions where users are supposed

to stay for a long time during the occupied daytime [Figure 2.10]. Four

horizontal vectors with specific directions from each of the positions

have to be set to evaluate vertical illuminance. In cases of a

preferential viewpoint, the directions can be less than four, for

example if the position of the viewer is known there might be a single view direction. The sDGP index

does not sufficiently represent contrast based glare: to this extend it is required to generate luminance

renderings on a time-step basis. This solution is computationally expensive, and anyway cannot

represent the real daylight conditions of a building, as there is no way to foresee optical properties of

equipment and furniture chosen by the occupants. However, using the sDGP index together with

Daylight Autonomy index, it guarantees more details to the daylighting evaluation, revealing

characteristics of the simulated visual environment that cannot be directly inferred from predictions

of the horizontal work plane illuminance. A daylight simulation, with input the weather file, the points

set and the vectors attached to them, calculates these two percentage values, which can be crucial in

determining different design decisions. To avoid arbitrary choices at the end of the process the two

aspects of a minimum illuminance and glare performance were condensed in a DAI ( Daylight

Aggregated Index), described by following equation:

𝐷𝐴𝐼 = 1 − [ 0.5 ∙ (∑ 𝜏𝐸(𝑎)

𝑛𝑝𝑜𝑖𝑛𝑡𝑠

𝑎=1

𝑛𝑝𝑜𝑖𝑛𝑡𝑠+

∑ 𝜏𝐺(𝑏)𝑛𝑣𝑖𝑒𝑤𝑠𝑏=1

𝑛𝑣𝑖𝑒𝑤𝑠

)]

Equation 3 - DAI (Daylight Aggregated Index)

where τE(a) is the percentage of the time, over the total time of use of the building, when minimum

illuminance (300 lux) is not met on the specific ath point, npoints is the total number of measuring points

in the sample, τG(b) is the percentage of time when maximum irradiance (3473 lux) is exceeded on the

specific bth view while nviews is the total number of views in the sample.The DAI value resulting is

included in a range from 0 to 1.

The output of the daylight simulation provides a list of many different configurations with their

associated DAI. A solution might be excellent in avoiding glare while blocking too much daylight or

Eye height

Figure 2.10 - Points and vectors system used in glare

analysis



51

vice-versa without affecting the index. Strongly unbalanced solutions (favouring light penetration or

glare protection) are characterized by lower DAI, while the best solutions are usually balanced.

Optimization algorithms

The core of the process does not lie in the evaluation itself but in the optimization. The method

has to evaluate many different samples with varying parameters and come out with a solution. To find

good performing combination of parameters, genetic algorithms are used. In the single target genetic

optimization, a performance metric (e.g. cumulative annual irradiation over the whole system) is

evaluated for every set of parameters. Each set of parameters can be considered as an individual, and

every single parameter can be considered as one of its genes. After the simulation of a certain number

of individuals (e.g. 100) they are sorted based on their fitness to the performance metric set before.

The low performing ones are excluded while the best performing ones are combined to form new

individuals, in a way passing on their genes to the offspring. In this way, it is possible to find high

performing set of parameters faster than a simple evaluation of every set in the solution space. The

genetic algorithm has as an output a list of individuals ranked from the best performing to the least

ones. In the use of BiPV, considering one simple fitness is not possible because there are, as we saw in

the previous paragraph, at least three criterion for the evaluation (electricity production, daylight

performance, thermal performance). In this case, a multi-target genetic algorithm should be used. The

output of this algorithm is a set of optimized solutions (a curve in case of 2 targets, a surface in case of

3 targets and a hypersurface for higher number of targets). Obviously, this type of output does not

provide the best solution, but a set of dominant solutions among which a choice must be made based

on considerations other than the three fitness metrics.



52

2.2.2 Software tools for BiPV parametric design

The methodology previously explained in [2.2.1] developed in this work to support the design

stage of a BiPV system, is based on the use of validated software, able to provide a wide range of

building and environmental analysis.

Figure 2.11 shows a comprehensive overview of the software employed to develop the BiPV design

process. The main features of the tools proposed are briefly presented through the following sections.

Figure 2.11 - Software tools employed for the developed BiPV parametric design process



53

Grasshopper

Grasshopper is a graphical algorithm editor that uses a visual programming language. It is

integrated with Rhino 3-D modelling software. The Grasshopper plug-in functions by associating

certain parts of a simple geometry with a graphical algorithmic editor. A geometry, created or imported

into Rhino platform, represents a static model. It can be transformed in a dynamic model within

Grasshopper [38]. A parametric transformation of

the geometry is implemented thanks to the “slider”,

a Grasshopper component customized to slide

along a range of numerical values. A slider can be

attached to the geometry, making its properties

parametric values. Every changing of the

parameters gets an instantaneous visual feedback

of the geometric effect in Rhino viewport, allowing

a better direct control of the system. A model based

on a parametric construction is used to perform dynamic evaluations of its performance, providing

different results for every variation of the parameters. In order to run building performance

simulations, Grasshopper is connected with specific validated simulation engines such as Radiance or

EnergyPlus. The model is firstly characterized with its specific properties in Grasshopper. It is then

submitted to the parametric simulations, which provide a dynamic visualization of the effect of the

design.

The BiPV design process I have developed in this work is based on the parametric modelling function of

Grasshopper, creating a complex analysis workflow based on a parametric definition and evaluation of

the BiPV system properties [2.2.1].

Grasshopper was developed by David Rutten at Robert McNeel & Associates [39].

Figure 2.12 - Grasshopper canvas [37]

https://en.wikipedia.org/wiki/Visual_programming_language

https://en.wikipedia.org/wiki/Robert_McNeel_%26_Associates



54

Ladybug

Ladybug is a free and open source environmental plugin for Grasshopper and Rhino. It allows

designer to import standard EnergyPlus Weather files (.EPW) in Grasshopper. As explained in the

previous section [2.2.1], adding a weather file means create an environmental context model that

represents the real climatic condition, defined with hourly data, of a specific project location. It is the

first step to perform a building energy simulation, identifying all critical environmental factors that

influence the building.

Figure 2.13 - Environmental context model provided by Ladybug [40]

Ladybug provides a variety of 2D and 3D designer-friendly interactive graphics to support the

initial stages of a design process. It allows designers to test several initial design options for

implications from radiation and sunlight-hours analyses results, leading to create environmentally

conscious design decisions. Due to the integration of Ladybug into the parametric environment of

Grasshopper, the process of analysis is automated and provides easy to understand graphical

visualizations, showing an instantaneous feedback on design modifications. Ladybug installed

commands are included into the Grasshopper interface as “palettes”. They are dragged onto the

canvas and connected to the simulation components.

Into the BiPV design process, the setting of the local climatic condition allows us to evaluate the

photovoltaics overhangs energy performance for each of the different configurations defined by

varying the set parameters. Evaluating the photovoltaic production and the overhangs impact on the

solar gain must not disregard from the radiation context defined by the weather file.

Ladybug was developed by Mostapha Sadeghipour Roudsari [41].



55

Honeybee

Honeybee is also a free and open source plugin for Grasshopper and Rhino. As extension of

Ladybug, helps designers to explore and evaluate environmental performance. It connects the visual

programming environment of Grasshopper to four validated environmental data sets and simulation

engines (i.e. EnergyPlus, Radiance, Daysim and OpenStudio) which evaluate building energy

consumption, comfort and daylighting [42]. It makes many of the features of these simulation tools

available in a parametric way. At first, Honeybee enables the characterisation of a model with specific

features required as input by an energy simulations.

For example, if considering a building model, it can

automate the process of intersecting the masses

and finding adjacent surfaces; the user only needs

to provide floor heights and use of each space [43].

Construction set, schedules and internal loads are

automatically assigned to the building. Once the

model features are set, Honeybee can run the

simulations from Grasshopper. It directly exports

the input (e.g. scene geometries, climatic context,

materials properties, sensors, etc.) into specific

format to be evaluated by the simulation engines.

The simulations start when all the required inputs are connected to the Honeybee simulation

components. Then, Honeybee re-imports the results of the simulation into Grasshopper, providing

several ways to visualize them.

The design process developed in this work to evaluate a BiPV system uses Honeybee components to

connect the Grasshopper model with Radiance and EnergyPlus engines. Since the BiPV model is based

on a parametric construction, dynamic evaluations of its performance can be performed, in order to

provide output values for each of the system configurations defined by the parameters variation.

Honeybee was developed by Mostapha Sadeghipour Roudsari [41].

Figure 2.14 - Output of a Honeybee energy simulation [42]



56

EnergyPlus

EnergyPlus is an open source building energy simulation software that is widely used to model

the passive performance of an individual building or large communities and the mechanical systems

serving these buildings [44]. It provides both energy consumption results (e.g. for heating, cooling,

ventilation, lighting, and plug and process loads) and water use in buildings. EnergyPlus is a console-

based program that reads input and writes output to text files. It ships with a number of utilities

including IDF-Editor for creating input files using a simple spreadsheet-like interface, EP-Launch for

managing input and output files and performing batch simulations, and EP-Compare for graphically

comparing the results of two or more simulations [45]. The text files used by EnergyPlus (.idf) can be

written through a Honeybee energy simulation. It

contains all the information about the model (e.g.

geometries, materials, climatic data, energy meters,

etc.) connected as input to the Honeybee

component into Grasshopper platform. EnergyPlus

includes a number of innovative simulation features,

such as variable time steps, user-configurable modular systems that are integrated with a heat and

mass balance-based zone simulation. Other planned simulation capabilities include multi-zone airflow,

and electric power and solar thermal and photovoltaic simulation, illuminance and glare calculations

for reporting visual comfort and driving lighting controls, advanced fenestration models [46].

EnergyPlus is used in the parametric design process of BiPV to evaluate the energy demand of the

building simulated. Calculating the amount of energy consumption for heating and cooling allows

to identify the overhangs impact on the solar gain. The simulation provides hourly values for each

variations of the parameters. Once evaluated the shading system performance in increasing or

decreasing the energy demand, its configuration is optimized by the genetic algorithm [2.2.1].

EnergyPlus was funded by the U.S. Department of Energy (DOE) Building Technologies Office

(BTO), and managed by the National Renewable Energy Laboratory (NREL) [45].

Figure 2.15 - Output of an EnergyPlus simulation [45]



57

Radiance

Radiance is a free and open source suite of programs for the analysis and visualization of

lighting in design. It is able to predict internal illuminance and luminance distributions in complex

buildings or boundary spaces under arbitrary sky conditions or electrical lighting. Radiance is based on

a backward ray-tracing algorithm [2.2.1]. The input required for a simulation in Radiance is a

description of the 3D surface geometry, materials,

and light sources in a scene. Geometric input consists

of a boundary representation using N-sided polygons

(concave or convex), spheres, cones, cylinders and

rings. Using Radiance, complex materials (opaque,

transparent or translucent) and different types of

light sources can be modelled. Once a scene

geometry is created, an "octree" data file is

compiled. It allows the ray tracing process to start,

transmitting which surface is intersected by a ray. The output of a Radiance simulation are hourly

values including the radiance, luminance, irradiance, illuminance and glare indices [31]. The results

may be graphically displayed as colour images or provided as numerical values and plots.

The Radiance software plays a crucial rule in the BiPV design process. It is used both to evaluate the

photovoltaic energy production and the overhangs impact on the daylighting. The model defined in

Grasshopper, including geometries, radiation context, meterials properties, points and vectors grid,

is connected to the Honeybee component that writes the text file to provide the geometries data to

Radiance. For every variation of the system parameters, irradiance values on the panels are

calculated in order to analyse the PV yield [2.2.1]. Illuminance values into the buildings, instead, are

provided to evaluate the shading impact on the visual comfort of the buildings users. Once the

Radiance simulations is performed, the provided performance values are optimized by the genetic

algorithm [2.2.1].

Radiance was developed by Greg Ward at the Lawrence Berkeley National Laboratory [31].

Figure 2.16 - Output of a Radiance Simulation

[45]



58

3 Case study

The developed methodology, explained in [2.2], has been implemented in a real demo case.

The process of parametric design and optimization has been applied on a buildings district of Bolzano.

Throughout the study, several issues related to a complex design process have been evaluated. The

following paragraphs show step by step all the phases of the design procedure, from the parametric

construction of the model to the algorithm optimization, with best configuration solutions provided.

One of the optimized BiPV configurations is analysed in terms of ideal and electric energy balance.

3.1 “Druso Est” district project, Bolzano

The case study, matter of the present thesis, is "Druso Est" district. The new neighbourhood

will be built in the city of Bolzano, in an expansion area named “Prati di Gries” along one of the main

roads called “Viale Druso”. An area of 45000

m2 [Figure 3.1] has been assigned to the

construction of the new development. It will

include about 500 apartments, a parking lot,

a park, a large supermarket, small shops and

services (e.g. kindergarten). Different

authorities are involved into the construction

process of the district. Housing cooperatives,

social housing authority and private investors will collaborate in a technical working group. The

cooperatives are allowed to build 224 apartments (11 buildings ranging from 3 to 10 storeys) as well

as approximately 500 m2 of co-housing. The private investors will build seven 10-storeys residential

buildings for a total 35300 m2 and the supermarket. One of the project proposed to be developed in

the Druso Est area is shown in Figure 3.2.

Figure 3.1 - View from Viale Druso (Google Maps)



59

Figure 3.2 - Druso Est district project [47]

3.1.1 Participative design process

The project takes place within a participative process, started in 2015, aimed to create a

cohouser community, where common spaces and services will be shared by the residents. Sharing and

participation are two components that characterize all the project development. From the first process

phases, future cohauser are allowed to cooperate with the technical working group in the definition

of the project. They are supported by a group of sociologists, architects and experts to plan their

common structures [48].

Achieving a high quality from the social viewpoint is a main object of the development; the

energy issue is just as much relevant. Druso Est is an ambitious project that aims to achieve high energy

targets. It is placed within the planning activity set up by the city of Bolzano, following the Copenhagen

Agreement, which requests that local communities have to drastically reduce greenhouse gas

emissions, to reach a neutrality condition within 2030 [49].



60

The implementation plan of the project aims to achieve that goal trough several integrated

actions. The current guideline for the development includes the following concepts:

renewable energy production mainly through Building integrated Photovoltaic panels (BiPV)

on both roofs and façade;

employment of high technical and qualitative standard (CasaClima class A as minimum target

for energy efficiency);

high-rise structures which optimize the solar supply to the buildings envelop;

investment cost reduction to allow great replicability.

Providing a method able to support an effective implementation of such a complex purposes

is one of the main objectives of this study. In the Druso Est demo case, an example of innovative PV

integration is performed to shows all the potentiality of such a multifunctional system and help

designers to explore all the possible design options. Employing an effective design methodology is the

first step to achieve high quality strategies.



61

3.2 Implementation of the BiPV design process

Given the context described in [3.1], the porposed concept is to integrate the BiPV technology

into the buildings envelope. Due to their simple shape, three of the district buildings have been

considered in this study. They are three multi-storey residential buildings (11 storeys), with a gross

floor area of about 400 m2 for storey.

Figure 3.3 - Druso Est 3D model

Through the present section, the developed procedure previously explained [2.2.1] is

implemented. The BiPV technology proposed for Druso Est case study is a shading devices system,

integrated into the buildings façades. Based on the sun control strategy, the integration of the system

is evaluated taking into account not only the electricity production, but also all the issues related to

the sunlight entering into the building sites (i.e. impact on the daylighting and thermal performance).

Through the following paragraphs, the BiPV design process is explained step by step, from the model

construction to the PV integration optimization.



62

Figure 3.4 - Developed BiPV parametric design process applied in the Druso Est case study



63

3.2.1 BiPV as shading device

The use of sun control and shading devices can

represent an important aspect of many energy-efficient

building design strategies. For example in warm, sunny

climates, it can avoid an excess solar gain that may result in

high cooling energy consumption; in cold and temperate

climates it can allow winter sun to enter through south-facing

windows, positively contributing to passive solar heating; and

in nearly all climates it can regulate and diffuse natural

illumination, improving daylighting. So by controlling the

amount of sunlight that it is admitted into a building, the

shading device can reduce building energy requirements and

improve the natural lighting quality of building interiors, increasing the user visual comfort by

controlling glare and reducing contrast ratios. Not least, shading devices offer the opportunity of

differentiating one building facade from another. This can provide interest to an otherwise

undistinguished design [50].

Therefore shading devices appear to have a wide impact on building appearance. This impact

can improve or worsen the situation. According to [50] and [51], several considerations should be

made in designing a shading device. Some of them are reported below.

The design of effective shading devices will depend on the solar orientation of a particular

building façade.

North-facing windows hardly need any shading, since the only time the sun impinges on them

is early in the morning or late in the afternoon in summer, and at those times the angle of

incidence is so great that much of the radiation is reflected from the glass or blocked by the

walls on either side of the window.

To the greatest extent possible, limit the amount of east and west facing windows since it is

harder to shade than south facing windows.

Simple fixed overhangs are very effective at shading south-facing windows in the summer

when sun angles are high. However, the same horizontal device is ineffective at blocking low

morning/evening sun from entering east/west-facing windows during peak heat gain periods

in the summer [Figure 3.6].

Figure 3.5 - Schematic representation of a window with a

overhang



64

Figure 3.6 - Morning and evening solar radiation [52]

Shading has an impact on the daylighting that has to be taken into account.

The optimal length of an overhang depends on the size of the window and the relative

importance of heating and cooling in the building.

Shading strategies that work well at one latitude, may be completely inappropriate for other

sites at different latitudes.

A variety of shading strategies can be implemented, whichever weather conditions and

building features the designer is dealing with. Some example are shown in Figure 3.7.

Figure 3.7 - Examples of shading device systems [53]

As seen in [1.2.2], due to its “multifunctional” rule, a shading device requires during design

phase a general evaluation coming from several point of view (i.e. thermal impact and daylight impact).

Moreover the earlier in the design process that it is considered, the more attractive and well -

integrated in the overall architecture of a project the solution can result.

The following paragraphs show the design process proposed to optimize the integration of a

photovoltaic shading technology into the Druso Est buildings. The whole system is submitted to a

multi-target evaluation that allows the designers to achieve a set of optimized conformations. The



65

pursued goals are simultaneously maximizing the photovoltaic energy production and the positive

impact of the BiPV system on the buildings thermal demand.

3.2.2 Model construction

The parametric construction of the model (including the buildings, the BiPV architectural

elements and the context) represents the first crucial phase to submit the whole system simulated to

the multi-target evaluation that allows to achieve a set of optimized conformations. A 3D model of

Druso Est district is imported into Grasshopper platform and hence developed through the following

stages.

- Buildings and environment modelling

The first step is to create the geometric model of Druso Est district to be submitted to the

simulation. A 3D model of the buildings is created with a CAAD software tool and then simply imported

into the Rhino platform, being careful to maintain the correct model units. In Rhino, the geometries

are selected and set in Grasshopper canvas [Figure 3.8]. The buildings volumes are represented as a

box, with the real dimensions and the effective glazing surfaces, and simulate the real urban

background of Druso Est district. They create close shading conditions that can have a great impact on

the amount of solar irradiation reaching the building facades. The shading scenario is completed

adding to the 3D model the Druso Est weather file (imported from Meteonorm database [54]), which

set the far shadings and places the buildings in own real location, assigning the effective climatic

conditions [2.2.1].



66

Figure 3.8 - Druso Est model visualization in Rhino viewport

- BiPV architectural system

Once this simplified model is created, the BiPV architectural system (i.e. the photovoltaic

overhangs) is added to the buildings [Figure 3.9]. The PV geometries are constructed in Grasshopper

canvas as simple surfaces, with a standard photovoltaic panel size (height=160 cm and weight=90 cm).

They are integrated into the façades of the three high-rise building simulated as shading elements and

parapets. In a preliminary design, the photovoltaics are placed according to several conceptual

statements or strategies (such as those listed in [3.2.1]). The shading photovoltaic panels are

integrated hanging over the windows on south façades and next to the ones towards east and west,

providing the light control especially for the apartments’ living rooms.



67

Figure 3.9 - Druso Est model with the BiPV architectural system

- Setting simulation parameters

As model components, the shading photovoltaics integrated into façades represent an input

that have to be considered to perform a building´s energy simulation. They are conceived as moveable

elements, with tilt angle (i.e. the angle between the overhang and the normal to the façade) that can

vary from 0°, if photovoltaics are perpendicular to the façade, to 90°, if they are parallel to the facade.

They not only rotate but also move. An extra condition is that when tilt angle increases, the panels

distance itself from the windows. The overhangs tilt angle represents a parameter, the variation of

which affects the buildings energy performances. For Druso Est model, the photovoltaic panels are

separated due to their three orientations (east, south, west), therefore the parameters set are three,

one for each panels orientation. In Grasshopper canvas the three parameters are represented as slider

components with a range that spans from 0 to 90, corresponding to the tilt angle allowed variations.



68

Figure 3.10 - Model construction phase in the BiPV parametric design process



69

3.2.3 Solar irradiation simulation

A solar irradiation simulation is performed within the Grasshopper platform, using the

Radiance software through the Honeybee plugin. As previously explained in [2.2.1], it enables a

measure of the solar energy hitting specific surfaces. In this case, the output required is the total

amount of annual radiation (i.e. insolation), a result obtainable through a cumulative evaluation.

To perform an energy simulation, the whole constructed model, including the sky function

(added through Ladybug components) and the geometries created, must be taken into account as

input. All the buildings surfaces are characterized with specific optical properties, setting proper

surface materials (e.g. generic plaster) which can influence the environmental radiation conditions.

The surfaces designated for the evaluation are the photovoltaic panels integrated into the model. The

aim is to quantify the amount of sunlight, direct and diffuse, that can be potentially absorbed by the

photovoltaics and converted into electricity. The method used, the backward ray tracing (explained in

[2.2.1]), requires a set of points to be located on the panels surfaces, one point for each of them. Then

a vector normal to the panel surfaces is associated to each point. Points and vectors are connected

with photovoltaics position and rotation and represent the “sensors” which allow to measure the solar

irradiation amount. They complete the model, ready to be submitted to the energy evaluation. The

inputs, visible within Grasshopper canvas, are connected to

the component able to run the simulation [Figure 3.11]. The

evaluation process provides results in a short computational

time (less than a minute). The output consisted in 657

cumulative annual values of solar irradiation (kWh/m2 year),

one for each photovoltaic panel.

The simulation results are immediately graphically

visible within the Rhino viewport where the 3D model can be

visualized. Furthermore, connecting the values of irradiation

to a multiple coloured gradient component of Grasshopper,

the corresponding photovoltaic panels are coloured, as showed in Figure 3.12. The red panels

represent the most irradiated, the green ones receive less solar radiation.

Figure 3.11 - Radiance simulation Honeybee component



70

Figure 3.12 – Output of the solar irradiation simulation output

The Radiance simulation output are also provided as data in text format. They are available in

an “.ill” file that the software creates once completed the simulation. The file contains 8760 irradiation

map data (one data for each hour of a year) for every photovoltaic panel. Data are provided in a CSL

format, easily importable into Excel.



71

Figure 3.13 - Solar irradiation simulation in the BiPV parametric design process



72

3.2.4 Economic optimization of the BiPV system

To perform the simulation of the annual cumulative irradiation on the photovoltaic surfaces,

all the panels are considered. However, it would not be an effective strategy from an economic point

of view to hang a PV overhang on every window. Especially in the lower floors of the building, in

shadowed conditions, a shaded module would produce little electricity and not benefit the thermal

balance, also burdening the initial investment. An economic evaluation is thus performed to select the

best performing photovoltaic modules. Through the procedure described in [2.2.1], firstly all the panels

are sorted by irradiation from the most irradiated to the least irradiated and an early assessment of

the electricity production is performed with Equation 1. Once all the least performing photovoltaic

modules are removed, the annual electricity production is calculated. In order to estimate the system

production profitability, the Net Present Value (NPV), as defined in Equation 3, is calculated for every

number of panels. Several values related to the photovoltaic system features and the current energy

price are taken into account in the calculations. They are listed into the Table 3.1.

PV panels efficiency 0.12 [8]

PV system performance ratio 75% [55]

Degradation rate 1% /year [56]

PV price 3200 €/kWpeak [10]

Maintenance cost 2% of the initial price [55]

Energy price 0.23 €/kWh [57]

Energy price growth rate 1% [58]

Table 3.1 – Numeric values considered in Equation 1 and Equation 2

The number of photovoltaic panels that

maximized the economic gain in different target time-

frame (i.e. maximum return of the investment in years)

could be chosen. In the Druso Est case study the number

of the photovoltaic overhangs are chosen to maximize

the earnings within 20 years. The best performing panels

are selected conferring to the 3D model a new geometric

configuration [Figure 3.15], with the calculated cash flow

and pay back time shown in Figure 3.14.

Figure 3.14 - Calculated cash flow and pay back time of the economically optimized

BiPV configuration

NPV

Cas

h F

low

(€

)

Year



73

Figure 3.15 – Output of the economic optimization

Usually, in traditional PV design, when designers have to decide where to place the

photovoltaic modules, other simple criteria are fullfilled. Two examples of possible results are shown

below. A possible strategy to follow is to maximize the photovoltaics production. All the panels are

included and integrated on the west-south-east façades. The resulting configuration will entail a very

high initial expenditure and a poor average irradiation, with a consequent long pay back time [ Figure

3.16].

Figure 3.16 - Most productive PV configuration with calculated cash flow and pay back time

Another possible configuration is provided following the simple strategy, frequently used in

traditional PV design, of setting photovoltaics south facing. The few selected panels have a low initial

NPV

Cas

h F

low

(€

)

Year



74

cost and very high average irradiation. Consequently the resulting pay back time decreases. However,

the overall production is low and cannot effectively influence the final energy balance [Figure 3.17].

Figure 3.17 - South facing PV configuration with calculated cash flow and pay back time

Figure 3.18 - Economic optimization phase in the BiPV parametric design process

NPV

Cas

h F

low

(€

)

Year



75

3.2.5 Thermal energy demand simulation

Once the photovoltaic overhang configuration is chosen, their thermal impact is evaluated

through an energy simulation, performed within the Grasshopper platform, using the Energy Plus

software through the Honeybee plugin. As previously explained in [2.2.1], it enables to quantify the

thermal energy demand resulting with a specific building conformation, allowing the designers to

evaluate the impact of the overhangs on heating and cooling demand separately.

The whole model used for Radiance, including the buildings, the BiPV architectural system and

the context, must be taken into account as an input to perform the EnergyPlus simulation.

Furthermore, in this case not only the external loads connected with the local climate condition are

evaluated, but also those produced into the building. The internal loads assigned as input to the

simulation are typical values of residential building used. They refer to the thermal load of equipment,

infiltration and people presence [Table 3.2].

Equipment load 4.14 W/m2

Infiltration rate 0.0004 m3/s*m2

Number of people 0.024 ppl/m2

Table 3.2 - Internal loads values assigned to Druso Est buildings [59]

The internal loads assigned have not the same influence throughout the day on the building

thermal energy balance. To define real conditions, some schedules with hourly profiles are applied to

the simulation process. They contain hourly values of users’ occupancy and activity (EnergyPlus), of

heating and cooling setpoint (EN 15251), of equipment [60] and infiltration [61]. Two examples of

hourly profiles are shown in Figure 3.19.

Figure 3.19 - Left: Occupancy hourly profile (EnergyPlus). Right: Equipment hourly profile [60]

0

0.2

0.4

0.6

0.8

1

00:00 04:00 08:00 12:00 16:00 20:00 00:00

Occupancy profile

0

10

20

30

40

00:00 04:00 08:00 12:00 16:00 20:00 00:00

Equipment profile



76

Internal loads and schedules are assigned to each of the buildings’ thermal zones. To define

the thermal zones the three building simulated are simplified and split into stories. One thermal zone

corresponds to one floor of one building. To limit the computation time, the floors designated to be

evaluated are three for each building (i.e. the two exposed stories and the middle one). Since the

buildings envelope has a crucial rule in controlling internal and external loads that must be considered,

the thermal zones are characterized by specific constructive properties. The construction materials

and components employed have their own thermal properties and characteristics (i.e. thickness,

thermal transmittance (U value), density, specific heat, roughness, thermal absorptance). They are

described in Table 3.3.

EXTERNAL ROOF U = 0.31 W/m2*K EXTERNAL WALL U = 0.26 W/m2*K

- green roof substrate 0.15 m - plaster 0.015 m

- EPS insulation 0.1 m - hollow brick 0.05 m

- reinforced concrete roof slab 0.25 m - reinforced concrete 0.25 m

- plaster 0.015 m - mineral wool insulation 0.13 m

EXTERNAL FLOOR U = 0.26 W/m2*K INTERNAL FLOOR adiabatic surface

- parquet flooring 0.01 m - acoustic ti le 0.02 m

- concrete screed 0.07 m - ceil ing air space resistance

- XPS insulation 0.05 m - l ightweight concrete 0.1 m

- screed 0.08 m WINDOW U = 1.5 W/m2*K

- XPS insulation 0.05 m - glass 3*10-3 m

- concrete floor slab 0.24 m - air 0.01*10-3 m

- plaster 0.015 m - glass 3*10-3 m

Table 3.3 - Druso Est construction materials. Definition of thermal transmittance and thickness

The thermal behaviour of the envelope components is

also characterized by specific boundary conditions. External

walls, floors and roofs are outdoor exposed, while internal floors

are adiabatic surfaces. The model is simplified through the

assumption that the thermal zones cannot exchange heat

among each other.

Once the thermal zone model is completed, it is

connected with the other inputs (i.e. buildings and BiPV

geometries, weather file) to the Grasshopper component able Figure 3.20 - EnergyPlus simulation

honeybee component



77

to run the EnergyPlus simulation [Figure 3.20]. At the end of the evaluation process, several energy

demand values measured in kWh/m2/ y are provided. In this case, the outputs required are monthly

values.

The simulation results are immediately graphically visible within the Rhino viewport. The

thermal zones are coloured based on total energy (either cooling or heating) output data as shown in

Figure 3.21. The red zones represent those with the most energy demand, the blue ones require lower

energy supply.

Figure 3.21 - Thermal energy demand simulation output

The EnergyPlus simulation outputs are also provided as data in text format. They are available

in a “.csv” file that the software creates once completed the simulation. The file contains all the energy

demand data of each of the thermal zones for every month. Data are provided in a CSL format, which

can be edited in Excel.



78

Figure 3.22 - Thermal energy demand simulation in the BiPV parametric design process



79

3.2.6 Optimization algorithm

The energy simulations provide two performance indicators of the BiPV system: the annual

photovoltaics energy production and the impact of the overhangs integration on the annual buildings

energy demand for heating and cooling. These outputs are

connected with a specific BiPV configuration. Each configuration is

characterized by a combination of the three set of tilt angles (i.e. the

three model parameters): west, south and east [Figure 3.23]. A multi-

target genetic optimization algorithms, described in [2.2.1], is

performed to find the best set of angles to obtain specific

performance indicators. The first step is to connect, also into Grasshopper canvas, the performance

indicators and the three parameter to the optimizer component. Once started, the genetic

optimization process evaluates the current configuration and then the other ones, generated by

varying the parameters and each time restarting the simulation process. A genetic selection of the best

performance configurations, located as points on a Pareto curve, provides a set of optimized values of

electricity production and thermal energy demand. Figure 3.24 shows the distribution of the

configurations found by the two objectives optimization.

Figure 3.24 – Output of the genetic algorithm optimization. Each point corresponds to a BiPV configuration

40000

45000

50000

55000

60000

65000

70000

25.3 25.4 25.5 25.6 25.7 25.8 25.9 26

Pro

du

zio

ne

BiP

V (k

Wh)

Fabbisogno energetico (kWh/m2)

Figure 3.23 - Tilt angle Grasshopper sliders



80

The two axis represent the indicators: the horizontal is the energy demand, the vertical is the

photovoltaic energy production. Each point corresponds to a BiPV configuration that have specific

performance values. The best configurations, i.e. those with optimized values of energy production

and/or of energy consumption, are the ones in red closer to the axes, not “dominated” by other

solutions [62]. In this case, the resulted optimized solutions are not so different in performance. The

one optimized for electricity production (on the right) differs by around 1000 kWh/year from the other

configurations. The one optimized for energy consumption (on the left) differs by less than 0.1 kWh/m2

year from the other configurations. The two target, therefore, seem not to be so competitive. The

reason could be found in the initial intelligent integration of the PV overhangs that, increasing the tilt

angle, distance itself from the windows, limiting the shade [3.2.2]. The resulted performance

differences, also, can be included into an estimated error range of 1.9 % (for the PV production) and

0.6% (for energy consumption), attributable to the software. Therefore, the best configurations can

be considered as a single solution. If otherwise (for e.g. with several optimized solutions with very

different performance), it would be left to designers to choose which solution to develop in the

following stage of the design. The choice would depend from the will of giving more weight to

electricity production or energy savings.

The output of the optimization process performed is shown in the following paragraph. A

resulted solution is analysed in terms of energy performances, evaluating the impact of the BiPV on

the total energy balance.



81

Figure 3.25 - Genetic algorithm optimization phase in the BiPV parametric design process



82

3.3 Optimization results

The optimization process provides a set of best solutions. One of them is analysed below. It is

characterized by the following specific combinations of the overhangs tilt angles: 48° on west façades,

36° on south, 56° on east. Figure 3.26 displays the results.

Figure 3.26 - One of the optimized BiPV configurations

The values reported in the following analysis are the output of the monthly EnergyPlus

simulation performed to evaluate an average energy demand of the three high-rise buildings

simulated. The aim is to evaluate the impact of the resulting shading system integration on the

buildings energy balance.

Figure 3.27 and Figure 3.28 show a comparison of energy demand values calculated in kWh/m2,

evaluated in two different buildings configurations. The first (in grey) represents a condition without

any shading system, the other one (in red and blue) is the result of the optimized overhang integration

on buildings façades.



83

0

1

2

3

4

5

6

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

kWh

/m2

Ideal Heating Demand

Without BiPV

Optimized BiPV

According to the simulations results the effect of the overhangs appears to be beneficial for

the cooling load but has a negative impact on the heating load. This is an expected consequence since

the main function of a shading system is to block part of the incoming sunlight, and so the solar thermal

gain. However for an average increase of heating demand of 0.1 kWh/m2/month (i.e. 1140 kWh per

year for the three whole buildings), the results show an average decrease of cooling demand of 0.2

kWh/ m2/month (i.e. 2280 kWh per year for the three whole buildings). Therefore, the presence of

overhangs is more effective in decreasing the cooling load than increasing the heating load. It means

that BiPV overhangs can have an overall positive impact on the thermal energy balance, although not

much relevant.

Annual values

-without BiPV 16 kWh/m2

-with BiPV 17 kWh/m2

Annual values

-without BiPV 16 kWh/m2

-with BiPV 14 kWh/m2 0

1

2

3

4

5

6


kWh

/m2

Ideal Cooling Demand

Without BiPV

Optimized BiPV

Figure 3.28 - Ideal monthly Cooling Demand

Figure 3.27 - Ideal monthly Heating Demand



84

Despite the comparison of the two different building configurations (without and with shading

BiPVs) in terms of ideal energy demand does not show a relevant improvement, it is not the same if

the electric energy balance is considered assuming that heat pumps are used.Figure 3.29 shows an

annual balance where the energy demand values, measured in kWh, were converted into electric

energy. Once a conversion factors is applied (2.5 for cooling and 3 for heating, supposing an heat pump

generation system and a low temperature emission system), the total electricity consumption was

calculated. For the first buildings configuration (in grey) it represents the amount of cooling and

heating demand values. For the other one (in blue) it was obtained by summing cooling and heating

demand values and subtracting the photovoltaic total energy production (in yellow).

Figure 3.29 - Electric Energy Balance of the district

Considering the total electricity consumption only, the two building configurations do not

show any relevant annual difference. Integrating the shading photovoltaics, the energy demand is

slightlyreduced, from 136500 to 134800 kWh per year. However, if the whole energy balance is

evaluated, the buildings consumption with overhangs integrated is considerably decreased, due to the

photovoltaic production contribution.

The overhangs benefit is clearly visible also at monthly level in the chart of Figure 3.30. In green

are represented values related to the consumptions savings resulting from the shading system

integration. The savings are calculated as the difference between the thermal energy demand (for

cooling and heating) converted in electric energy of the two different buildings configurations (without

and with shading BiPVs). It is relating with the BiPV energy production (in yellow) to provide a measure

of the monthly energy balance (in blue).

-100000

-50000

0

50000

100000

150000

kWh

Electric Energy Balance

Electric Energy Consumptionwith BiPV minus BiPV AnnualProduction

BiPV Annual Production

Electric Energy Consumptionwhitout BiPV



85

Figure 3.30 - BiPV Energy Savings and Electric Energy Balance

As expected, during the heating season the savings values are negative, because the overhnags

are blocking part of the solar gain. On the other hand during cooling period the savings values are

positive, so the shading system has a favourable impact on the energy demand. This output means, as

already highlighted in Figure 3.27 and Figure 3.28, that this specific BiPV solution increases the heating

demand, but less then it decreases the cooling one. Moreover, if the photovoltaic added value of the

energy production is considered, the loss caused during heating season has a low influence on the total

electricity balance.

-2000

0

2000

4000

6000

8000

10000


kWh

BiPV Energy Savings and Electric Energy Balance

Energy savings

BiPV Production

Electric EnergyBalance



86

Figure 3.31 - Optimized models provided by the BiPV parametric design process



87

4 Conclusions

This thesis work shows a methodology able to provide a broad support to design complex

projects integrating BiPV systems from the first design stage. At the beginning, a project is firstly

conceived as a concept, as an idea. Details and strategies are not defined. What is determined is the

final goal. The design process should represent the phase in which the concept evolves in a strategy

and effective solutions. The developed method is an instrument able to support the designers in

realizing their aims, justifying a potential project feasibility. This is enabled by the parametric approach,

which is the main feature of the methodology.

For the Druso Est case study, the developed method was applied to optimize the integration

of a building integrated photovoltaic system (i.e. BiPV overhangs), towards a low energy balance at

district level. The BiPV architectural system is a complex technology whose parameters need a fine

tuning to be optimized. The parameters are involved into a model that is submitted to a comprehensive

evaluation, taking into account all the main concurrent effects such as energy yield, cost analysis,

impact on the building energy demand and on the internal comfort. The simoultaneous consideration

of all these factors is necessary due to the multifunctional feature of the BiPV system. As a

consequence, the optimization does not provide a best solution according to a specific target but a set

of equally good ones. The designer can choose among the solutions according to several additional

considerations. In this case, a designer could choose to focus on the photovoltaic production towards

an optimal energy balance, or he could pursue the goal of minimizing the thermal demand for example

to reduce CO2 emissions, or he could again aim at achieving economic earnings after a given period.

Having a set of defined optimized solutions to select from, can be reflected in an active working

relationship with the customer. The designer can gather the client assessments and considerations,

once showed all the possible options, with peculiarities, limits, pros and cons of each solution. The

customer can see realistic data, previsions justified through a simulation process that, using validated

software tools, creates a model close to the truth. The customer can take advantage of graphic outputs

that make the results obtained more comprehensible and so have a clear representation of what it will

be the result of the project, with an appearance that will be more or less appreciated from an aesthetic

point of view.

One of the main positive aspects of the implemented method is that, after performing a series

of evaluations to determine energy efficient and economically feasible solutions, also aesthetically

good solutions can be considered. These will be solutions where the good appearance will not be

simply an added value but it will keep a “multifunctional” justification inside.



88

The methodology developed and presented through this thesis is based on a specific linear workflow

workflow characterized by some main steps: create a model, test it, analyse the results, approve them or not. If or not. If not, go back to the beginning and, once changed the previous configuration, repeat the process to find

process to find the best solutions. Although it seems to be a simple process, when many inputs or targets to

targets to evaluate are involved into the optimization procedure, some issues connected to the processing processing timeframe could appear. Hence several questions can arise: How to reduce the time needed? How to

needed? How to simplify the process? Maybe limiting the accuracy? Maybe lowering the detail level? This is a This is a complex topic. These questions are of crucial importance for large the project scale. From the simple

simple inclusion of some buildings, it could comprehend a whole district and a city, etc. Implementing a method Implementing a method such as the one applied for the Druso Est district, able to include in a single

single evaluating environment many targets and to provide realistic previsions, could represent a suitable suitable support into a urban, regional, territorial development and energy planning. A suitable key of

development for the methodology could be the nZEB concept, that takes into account several different factors factors (and buildings, if talking about nZED design) into a global energy balance evaluation.

Figure 4.1 shows an example of SWOT analysis reporting strengths, weaknesses, opportunities

and threats, previously explained in the present paragraph, of the developed design methodology.

Figure 4.1 – Developed BiPV parametric design SWOT analysis



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4.1 Outlook

The suggested methodology and tools have been developed to facilitate the design of a

complex element such a BiPV system. However, it can represent a starting point for the development

of an overall method for building design. The previous paragraph highlighted strengths and

weaknesses, opportunities and threats of the developed design process. Each of them could represent

a development key of the methodology, in order to improve its potentiality. The main issues are

discussed below.

Multi-target evaluation

One of the main aspects characterizing the developed methodology is the capability to involve

in a single workflow, and in a single software platform, several different targets. The aim was to equate

them in a comprehensive evaluation to obtain a series of solutions for which economic feasibility,

photovoltaic production and energy demand are simultaneously considered. However, it was proven

to represent a complex purpose.

At the beginning of the optimization process, once the solar irradiation of the PV overhangs is

calculated [3.2.3], the employed procedure proceeds with the economic selection [3.2.4]. This

represents a critical phase. With the aim of guaranteing economically feasible results, the selection

excludes all the panels that, due to their low solar irradiation, do not allow a payback within a certain

timeframe (e.g. twenty years). Some of the discarded overhangs, however, could lead to an energy

saving (of heating or cooling) higher than the amount of the photovoltaics production. Otherwise,

some of the chosen ones could increase the thermal energy demand exceeding the energy generated.

In this case, the economic selection represent a simplification that could exclude some potentially good

solutions.

Several attempts were made to solve the issue. One of them consisted in basing the first

selection on an evaluation of the energy overhangs benefit. This would mean that, once both the

production and consumption simulations were performed, the panels would be selected according to

their impact on the energy demand. The overhangs that, with a specific outdoor temperature, lead to

the use of cooling or heating are preferably removed. This solution, also, is characterized by

simplifications. Considering as an input the heating and cooling consumption hourly values provided

by the thermal energy demand simulation [3.2.5], the dynamic internal gain are instead not taken into

account.



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Finally, the main issue connected with the complex purpose of simultaneously evaluate all the

targets seems to be the problem of simplification. When trying to consider at the same time several

evaluations, it seems complex to keep for each of them a good level of detail. Maybe, starting from a

simplified model to acquire then even more detail throughout the optimization process could be a

solution. Several trials have still to be carried out.

Figure 4.2 - Ideal multi-target BiPV parametric design process



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Daylighting simulation

When shading systems are integrated into the buildings, their impact on the daylighting can

be crucial, as previously seen in [3.2.1]. Optimizing an overhang can be an effective way to guarantee

visual comfort by controlling the glare and allowing enough natural lighting. Therefore, the daylighting

can represent an additional performance indicator to be included into the optimization process,

together with the photovoltaic electricity production and thermal energy building consumption. As

explained in [2.2.1], a daylight analysis uses the same method of the Ray Tracing as the simulation of

PV solar irradiation. However, in this case it is not cumulative but point in time, so the evaluation has

hourly time steps. Being a point grid simulation, it requires a series of points and vectors.

For Druso Est case study a preliminary daylight evaluation was performed. The living rooms of

the three high-rise building are selected to be submitted to the

analysis. Into each of these sites several points were disposed

on an horizontal grid set at desk height to evaluate the

percentage of annual daytime hours that they were above a

specified illumination level. Other three points, for the glare

analysis, were set at eye-level in particular positions where

users are supposed to stay for a long time during the occupied

daytime [Figure 4.3]. The vectors were assigned to each point

according principles already specified in [2.2.1]. Points and

vectors were connected to the Grasshopper component able to

run the Radiance simulation, together with the other input (i.e. 3D model, Druso Est weather file, BiPV

architectural system, users occupation schedule). Once performed the simulation, it provided a set of

values related to the annual percentage of hours in which the illuminance value is maintained into the

comfort range, from 300 [63] to 3473 [64] lux.

Also in this case the output are graphically visible in

Rhino viewport, connecting them to a multiple coloured

gradient component of Grasshopper. An example of a simulated

site, a living room on tenth floor, is shown in Figure 4.4. The

coloured circles are located at the desk level, the visible arrows

represent the vectors set for the glare analysis. The green

elements are indicative of visual comfort, a situation with

enough illumination intensity and an effective glare control.

Figure 4.3 - Points grid and vectors system visualized in Rhino viewport

Figure 4.4 - Daylighting simulation

output



92

In the example shown above, the simulation was a long lasting process. The reason could be

found in the high density of the grid points set, excessively thick to be submitted to a point in time

evaluation. Some grid points could be plainly removed, or some sites can be excluded. Simplifying the

model could be a mean to excessively reduce the evaluation accuracy. Therefore, careful

considerations are needed. However, a potential development of the study could allow to achieve a

correct simplification level in order to include the daylighting simulation into the optimization process.

Figure 4.5 - Daylighting simulation in the BiPV parametric design process



93

Load matching

One of the main goals usually pursued when installing a photovoltaic system is to maximize

the peak production from the installation over a 24-hour period, orienting the PV panel towards south

[65]. However, this could not result in a suitable approach. Often, the time of peak electric gains from

a PV array of southern azimuth does not coincide with peak electricity demand. As exemplified in [65],

if a load needs to be supplied during the second part of the daylight, from 1pm to 7pm, such a choice

does not ensure a correct energy management in the time interval where it is mainly needed. All the

energy extracted in the morning needs to be temporarily stored. It would be more efficient to point

the photovoltaic panels towards West, in order to maximize the energy converted from solar radiation

in the time interval within the load requirement is centred.

Analysing the interaction between the load required by the utility and the output of the PV

system seems to represent a decisive step during the design process. The load matching can widely

increase a PV system performance. It can be an effective strategy to best optimize the PV energy use,

for example reducing the energy cost associated with the storage system (in case of stand-alone

applications) [65] or to minimize the power injected into a grid, avoiding technical and potential

problems with it connected [66].

PV sizing and orientation are two crucial

aspects in conditioning the quality of the load

matching. Figure 4.6 shows the results arose

comparing the power output of two different PV

installation [67]: a single axis tracking systems

rotating from East to West and a fixed axis

system with south azimuth. The first one tracks

the sun throughout the course of each day,

maximizing the power gains during the morning and evening. The second one concentrate the time of

peak solar gain at midday. A clear difference of peak time and total production characterizes the two

applications. It can represent a useful criteria for evaluating which solution can better adapt to specific

buildings, according to the design goals.

A load matching analysis could be therefore included in an optimization process to evaluate a

PV system installation performance. It could result especially suitable in BiPV systems, due to their

several flexible solutions [1.2.3].

Figure 4.6 - Illustrative comparison of tracking PV (horizontal mount, E-W azimuths) to standard fixed

axis PV with South azimuth [50]



94

With regard to Druso Est case study, an assessment of the electric energy consumption was

performed. In Figure 4.7, an hourly definition of the electricity demand profile (in blue) is compared

with the BiPV system production profile (in yellow).

Figure 4.7 - Hourly values of Energy Production and Consumption

The electric energy loads values come from the monitoring of a residential complex composed

of 40 units placed in north Italy [60]. The curve, relating to a typical summer day, shows a considerable

increase during the morning and the evening. Otherwise, the energy production curve is characterized

by a great growth around midday. There is a clear condition of mismatching. This BiPV system

configuration does not provide energy exactly when the buildings need the main electricity supply. The

reason could be that, with the current system solution, the most panels are south facing [Figure 4.8],

so they are especially irradiated around midday. Changing the photovoltaics configuration, for example

adding panels on east and west façades, could represent

the first step to increase the correlation between the

electricity production and the load profile. However, this

improvement of the load matching would have an impact

on other factors (e.g. thermal balance, daylighting, etc.).

Therefore, including the load matching could represent an

interesting development, an additional target to involve

into the design process to improve the optimization

results.

0

10

20

30

40

00:00 04:00 08:00 12:00 16:00 20:00 00:00

kWh

Electric Energy Production and Consumption

BiPV EnergyProduction

Electric EnergyLoads

Figure 4.8 - Resulted BiPV system configuration



95

Figure 4.9 - Load matching integration phase in the BiPV parametric design process



96

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