Building-integrated photovoltaics

Building-integrated photovoltaics (BIPV) are photovoltaic materials that are used to replace conventional building materials in parts of the building envelope such as the roof, skylights, or facades. They are increasingly being incorporated into the construction of new buildings as a principal or ancillary source of electrical power, although existing buildings may be retrofitted with similar technology. The advantage of integrated photovoltaics over more common non-integrated systems is that the initial cost can be offset by reducing the amount spent on building materials and labor that would normally be used to construct the part of the building that the BIPV modules replace. These advantages make BIPV one of the fastest growing segments of the photovoltaic industry.

The term building-applied photovoltaics (BAPV) is sometimes used to refer to photovoltaics that are a retrofit – integrated into the building after construction is complete. Most building-integrated installations are actually BAPV. Some manufacturers and builders differentiate new construction BIPV from BAPV.

PV applications for buildings began appearing in the 1970s. Aluminum-framed photovoltaic modules were connected to, or mounted on, buildings that were usually in remote areas without access to an electric power grid. In the 1980s photovoltaic module add-ons to roofs began being demonstrated. These PV systems were usually installed on utility-grid-connected buildings in areas with centralized power stations. In the 1990s BIPV construction products specially designed to be integrated into a building envelope became commercially available. A 1998 doctoral thesis by Patrina Eiffert, entitled An Economic Assessment of BIPV, hypothesized that one day there would an economic value for trading Renewable Energy Credits (RECs). A 2011 economic assessment and brief overview of the history of BIPV by the U.S. National Renewable Energy Laboratory suggests that there may be significant technical challenges to overcome before the installed cost of BIPV is competitive with photovoltaic panels. However, there is a growing consensus that through their widespread commercialization, BIPV systems will become the backbone of the zero energy building (ZEB) European target for 2020. Despite technical promise, social barriers to widespread use have also been identified, such as the conservative culture of the building industry and integration with high-density urban design. These authors suggest enabling long-term use likely depends on effective public policy decisions as much as the technological development.

There are four main types of BIPV products:

Crystalline silicon solar panels for ground-based and rooftop power plant
Amorphous crystalline silicon thin film solar pv modules which could be hollow, light, red blue yellow, as glass curtain wall and transparent skylight
CIGS-based (Copper Indium Gallium Selenide) thin film cells on flexible modules laminated to the building envelope element or the CIGS cells are mounted directly onto the building envelope substrate
Double glass solar panels with square cells inside

Building-Integrated Photovoltaic modules are available in several forms:

Flat roofs
The most widely installed to date is an amorphous thin film solar cell integrated to a flexible polymer module which has been attached to the roofing membrane using an adhesive sheet between the solar module backsheet and the roofing membrane.[clarification needed] Copper Indium Gallium Selenide (CIGS) technology is now able to deliver cell efficiency of 17% as produced by a US-based company and comparable building-integrated module efficiencies in TPO single ply membranes by the fusion of these cells by a UK-based company.

Pitched roofs
Solar roof tiles are (ceramic) roof tiles with integrated solar modules. The ceramic solar roof tile is developed and patented by a Dutch company in 2012.
Modules shaped like multiple roof tiles.
Solar shingles are modules designed to look and act like regular shingles, while incorporating a flexible thin film cell.
It extends normal roof life by protecting insulation and membranes from ultraviolet rays and water degradation. It does this by eliminating condensation because the dew point is kept above the roofing membrane..
Metal pitched roofs (both structural and architectural) are now being integrated with PV functionality either by bonding a free-standing flexible module or by heat and vacuum sealing of the CIGS cells directly onto the substrate

Facades can be installed on existing buildings, giving old buildings a whole new look. These modules are mounted on the facade of the building, over the existing structure, which can increase the appeal of the building and its resale value.

Photovoltaic windows are (semi)transparent modules that can be used to replace a number of architectural elements commonly made with glass or similar materials, such as windows and skylights. In addition to producing electric energy, these can create further energy savings due to superior thermal insulation properties and solar radiation control.

Transparent and translucent photovoltaics
Transparent solar panels use a tin oxide coating on the inner surface of the glass panes to conduct current out of the cell. The cell contains titanium oxide that is coated with a photoelectric dye.

Most conventional solar cells use visible and infrared light to generate electricity. In contrast, the innovative new solar cell also uses ultraviolet radiation. Used to replace conventional window glass, or placed over the glass, the installation surface area could be large, leading to potential uses that take advantage of the combined functions of power generation, lighting and temperature control.

Another name for transparent photovoltaics is “translucent photovoltaics” (they transmit half the light that falls on them). Similar to inorganic photovoltaics, organic photovoltaics are also capable of being translucent.

Modules used
In order to meet the architectural requirements and the desired multi-functionality, the adaptability of the PV modules in terms of size, shape and materials used is desired. The various mechanical and electrical integration requirements must also be taken into account.

Basically, there are two variants of technologies that can be used for modules for BiPV:

Crystalline Modules
Crystalline modules are based on a plurality of silicon – wafers, mostly in serial connection. The pitch of the variation in size is determined by the size of the wafers and the necessary clearances for the interconnection and isolation. These amount to 15-25 cm. In the case of cell material, a distinction is made between monocrystalline and polycrystalline silicon, which differ in their efficiency. This indicates what percentage of the incoming solar energy is converted into electrical energy. (Mono) Crystalline modules offer today the highest efficiency (15-20%) with optimal alignment. In the BiPV, however, such an optimal orientation (eg facade with vertical orientation) is usually not given. Furthermore, crystalline solutions are very susceptible to shading and a reduction in high temperature performance, which are common in building applications. Therefore, it is advisable to use a simulation software for true energy yield. Crystalline solutions have a high variability in the choice of packaging material, which is very positive for BiPV. Different glass thicknesses, but also plastics can be used, but crystalline cells are very fragile and can not be bent. Semitransparency in simple patterns can also be generated.

Thin-film modules
Thin-film modules are applied to a substrate (usually glass). With the glass substrate variant, a size variance is possible only to a very limited extent. Also, the material selection in this variant of the substrate is very limited, since during the process of PV cell assembly very high temperatures are used, which make certain variations in the glass (for example, safety glass) not possible.

Other thin-film solutions are applied to plastic or metal bands (steel, copper). These solutions currently offer the highest degree of variation in size and packaging and also make it possible to offer flexible and very light solutions (plastic / plastic). Thin-film solutions currently have efficiencies of 6-14% depending on the technology used, have a better yield with sub-optimal alignment (stray light, low light) and are less temperature-dependent in their performance.

Special Promotions
Various policies encourage the use of BiPVs: Driven by the 20-20-20 targets and the desire to promote energy self-sufficient buildings, in some countries (eg Italy, France) in addition to the feed-in tariffs (see Germany EEG) increased tariffs for BiPV offered.

Building Guidelines
A strong driver for the use of BiPV is the successive tightening of guidelines regarding the energetic behavior of buildings (zero energy house, CO 2 footprint). In Germany, the EnEV is a reference based on the EU Directive on the Energy Performance of Buildings. Furthermore, there are country-dependent sustainability- related building assessments with different quality levels, which also promote high energy building quality and low environmental impact. Examples are the US-developed Leadership in Energy and Environmental Design (LEED), BREEAM from the UK or theGerman quality seal sustainable building.

Government subsidies
In some countries, additional incentives, or subsidies, are offered for building-integrated photovoltaics in addition to the existing feed-in tariffs for stand-alone solar systems. Since July 2006 France offered the highest incentive for BIPV, equal to an extra premium of EUR 0.25/kWh paid in addition to the 30 Euro cents for PV systems. These incentives are offered in the form of a rate paid for electricity fed to the grid.

European Union
France €0.25/kWh
Germany €0.05/kWh facade bonus expired in 2009
Italy €0.04–€0.09/kWh
United Kingdom 4.18 p/kWh
Spain, compared with a non- building installation that receives €0.28/kWh (RD 1578/2008):
≤20 kW: €0.34/kWh
>20 kW: €0.31/kWh

USA – Varies by state. Check Database of State Incentives for Renewables & Efficiency for more details.

Further to the announcement of a subsidy program for BIPV projects in March 2009 offering RMB20 per watt for BIPV systems and RMB15/watt for rooftop systems, the Chinese government recently unveiled a photovoltaic energy subsidy program “the Golden Sun Demonstration Project”. The subsidy program aims at supporting the development of photovoltaic electricity generation ventures and the commercialization of PV technology. The Ministry of Finance, the Ministry of Science and Technology and the National Energy Bureau have jointly announced the details of the program in July 2009. Qualified on-grid photovoltaic electricity generation projects including rooftop, BIPV, and ground mounted systems are entitled to receive a subsidy equal to 50% of the total investment of each project, including associated transmission infrastructure. Qualified off-grid independent projects in remote areas will be eligible for subsidies of up to 70% of the total investment. In mid November, China’s finance ministry has selected 294 projects totaling 642 megawatts that come to roughly RMB 20 billion ($3 billion) in costs for its subsidy plan to dramatically boost the country’s solar energy production.

Other integrated photovoltaics
Vehicle-integrated photovoltaics (ViPV) are similar for vehicles. Solar cells could be embedded into panels exposed to sunlight such as the hood, roof and possibly the trunk depending on a car’s design.

Source from Wikipedia