Photovoltaics in an. Architectural Context. Henk Kaan1*,y and Tjerk Reijenga2. 1ECN Energy Research Centre of the Netherlands, P.O. Box 1, ZG Petten. photovoltaics in buildings is not turned into appealing architecture and sound engineering without the concerted professional efforts of several disciplines.
This can lead to constructions in which the modules are applied not applied suing the best orientation, or photovoltaic elements that shade each other, or even the installation of flexible modules on areas with double radius, as well as the application of modules without considering the possibilities associated with the substitution of the bulding skin, with criticizable aesthetic results. The specificity of photovoltaic components as part of construction therefore comes from the numerous possibilities that they offer and, at the same time, from the risks that their installation involves, in which the parameters of their correct application are only partially exploited.
In fact, the primary and fundamental rules and regulations that must be taken into consideration, can be summarized as follows:. Further considerations must then be carried out with regards to the type of module used, since the modules present on the market have mechanical, thermal, and physical characteristics able to carry out diverse technological functions according to the comprised stratifications of material and their method of production. Photovoltaic modules differ essentially as per the production technology used for cells, the layers of materials used for the physical configuration of components, the layout and density of the cells inside the module s.
Diverse applications depend on these characteristics in which the use of a specific module with frame, without frame, opaque, semi-transparent, etc. The most frequently used material for the photovoltaic cells is silicon, even if other materials such as gallium arsenide GaAs , cadmium telluride CdTe , copper indium diselenide CulnSe2 , are also used, above all for the realization of thin films, which differ mainly because of their production and doping process.
Moreover, plastic cells are now in the experimental phase, with rather limited yield at the moment, but if improved could become competitive from the cost point of view. The modules on the market and used in construction at present are mainly those made of mono - crystalline and poly - crystalline silicon and amorphous cells.
From the construction point of view, the biggest difference can be seen between crystalline silicon and amorphous cells. As far as the first sector is concerned, cells made of monocrystalline silicon are made using a single crystal, while those in poly-crystalline silicon come from an ingot created by the solidification of the molten mass of silicon in a parallelepiped-shaped crucible.
The difference between the two types of cells, other than their aesthetic appearance, is also their different yield in terms of conversion of solar radiation and, therefore, of production of electricity. The former have an efficiency that can reach 20 per cent about 15 per cent average , while the latter reach an efficiency of about one or two per cent less.
Cells in amorphous silicon, on the other hand, are produced by the deposition of silicon vapours onto a suitable substrate, in vacuum or controlled atmosphere. In fact, a layer of only a few micron is sufficient to obtain photovoltaic conversion. However, the stabilized average yield is, at about six to nine per cent, considerably less.
It must be noted that amorphous silicon undergoes deterioration in performance during the first months of exposure to sunlight Staebler-Wronsky effect followed by stabilization, but, nevertheless, causing an initial reduction in efficiency conversion that can reach per cent. In the long term, however, amorphous silicon modules can undergo a regeneration of efficiency, proven by experimental data.
A further observation regards the production of thin film cells. This process requires less energy compared to that of the production of crystalline silicon wafers , with consequent reductions in energy and economic costs of amorphous cells compared to crystalline cells, with a positive comparison at equal power, and is a consequence of the smaller amount of material needed.
In fact, the ratio between the amount of material needed for amorphous silicon cells compared to that needed for crystalline silicon cells is from 1 to in favour of the first, also because the production processes of crystalline silicon wafers are affected by the problem of waste product, with consequent increased costs of finished products. There are other materials and technologies at experimental level for the production of cells, which are still not used in the construction market as they are still not completely reliable or because their production is extremely expensive.
Until now, silicon, used in thin crystal layers as in the case of mono-crystalline or poly-crystalline silicon, or deposited by means of particular procedures as in the case of amorphous silicon, has demonstrated stability, efficiency, reliability over time and production costs that have made it preferable compared to other material for photoelectric conversion.
In any case, components made from other materials with photoelectric characteristics are presently undergoing studies and experimentation that include production processes to produce thin films: vacuum deposition per layer and thermal treatments for CIS — copper indium selenite or with gallium CIGS — resulting in laboratory yields of up to 18 per cent , screen printing and electro-deposition for cadmium telluride CdTe , or also hetero-junction cells for copper sulphide Cu2S and cadmium CdS.
As far as thin films are concern ed, polycrystalline layers of gallium arsenide GaAs and gallium arsenide and aluminium GaAlAs , are, at present, not competitive for the construction sector due to their high costs. They are, however, highly reliable and have a good level of conversion theoretical efficiency of single-junction cells of 30 per cent, such as mono- crystalline silicon, which can be improved using multi-junction cells. The stratification of the crystalline silicon photovoltaic modules available on the market include several layers of material creating a sandwich.
The side in direct sunlight is made up of a pane of high-transparency tempered glass, which guarantees the highest passage of solar irradiance along with excellent mechanical resistance. Both external layers are often made of polymeric material and the panel can ifrequired be inserted in a frame with extruded aluminium borders , which are the stiffening support sof the panel.
Amorphous silicon cells, on the other hand, are made up of material deposited on different substrates: rigid glass, for example or flexible also thin transparent laminas which do not need sealant. Regardless of the kind of cells, the type of assembly of the modules is particularly important since the materials used determine the building skin, resistance to atmospheric agents, thermal, acoustic and mechanical behaviour.
Opaque or semitransparent panels can be obtained as per the substrate and positioning of the cells. The transparency of photovoltaic modules can be obtained using transparent closure surfaces and by distancing the cells. Thanks to developments in production systems, some module manufacturers are able to offer architects the possibility of personally deciding the positioning of the cells, thus creating tailor made, versatile components, able to adapt to diverse planning and architectural needs. There are, in fact, diverse methods of interaction between the two systems of application of the component, with integration being just one of the possibilities.
The same difference can be found in the English acronyms PVIB photovoltaics in buildings and BIPV building - integrated photovoltaics used in technical literature, to indicate the different ratio existing between the photovoltaic generator and the building:. Understand how the evolution of political, economic, and environmental factors affect the feasibility of building integrated solar PV 2. Learn about how the utility grid is evolving and how it will affect the practice of building integrated renewable energy 3.
Explore innovations and advancements in building integrated solar PV technology and application 4. Understand how an integrated design process can provide benefits for PV system aesthetics, building energy goals, and constructability 5. At the same time, the project EnergyMatching , addresses the issues related to BIPV energy integration by developing new concepts and technologies in this direction.
In this context, PV integration is irrevocably destined to play an essential role in the years to come and learning from the experience gathered in realized projects, BIPV systems have the potential to play an important role in technological, aesthetic and energy integration.
This should satisfy the well-defined market created by architectural trends, such as a continuous envelope surface with large glass areas between spandrels, b buildings whose activity demands high degrees of daylighting, and c projects located in earthquake and hurricane areas. This will be done through an effective implementation of short and medium-term cost reduction roadmaps addressing the whole BIPV value chain and demonstration of the contribution of the technology towards mass realization of nearly Zero Energy Buildings.
The implementation of this objective is being supported by several initiatives or subtasks looking at developing databases, developing business models, demonstrations and dissemination. Overall, energy integration is becoming increasingly important to meet the new building concept and its energy provision. They are becoming micro energy hubs consuming, generating, storing and supplying energy, thus transforming the EU energy market, moving from centralized, fossil-fuel based, national systems towards a decentralised, renewable, interconnected and variable system.
And the driving role of BIPV to achieve these goals is undeniable. Skip to main content. Sign in. Build Up Home Practices. Share this Post:. Figure 2. Figure 3.