GiPV: Building-integrated photovoltaics with partially transparent solar modules – building-integrated photovoltaics

Building-integrated photovoltaics - GiPV (Building-integrated photovoltaics - BIPV) are photovoltaic materials that replace conventional building materials in parts of the building envelope such as the roof, skylights or facade. They are increasingly being integrated into the construction of new buildings as a main or secondary source of electricity, although existing buildings can also be retrofitted with similar technology. The advantage of integrated photovoltaics over the usual non-integrated systems is that the initial costs can be offset by reducing the expenditure on construction materials and labor that would normally be required to construct the part of the building that the BIPV modules replace. In addition, BIPV enables wider adoption of solar installations when the aesthetics of the building are a concern and traditional rack-mounted solar panels would disrupt the intended look of the building.

The term BAPV (Building-applied photovoltaics) for building-integrated photovoltaics is sometimes used to refer to photovoltaic systems that are subsequently integrated into the building. Most building-integrated systems are actually BAPV. Some manufacturers and builders differentiate between BIPV and BAPV for new buildings.

PV applications for buildings emerged in the 1970s. Aluminum framed photovoltaic panels were connected or mounted to buildings, typically located in remote areas without access to an electrical grid. In the 1980s, photovoltaic modules began to be installed on roofs. These PV systems were typically installed on buildings connected to the electrical grid and located in areas with centralized power plants. In the 1990s, BIPV building products specifically designed to be integrated into the building envelope became commercially available. A 1998 doctoral thesis by Patrina Eiffert, entitled An Economic Assessment of BIPV, hypothesized that there would one day be an economic value for trading renewable energy credits (RECs). A 2011 economic assessment and brief review of the history of BIPV by the US National Renewable Energy Laboratory suggests that there are still significant technical challenges to be overcome before BIPV installation costs can compete with those of photovoltaic systems. However, there is a growing consensus that BIPV systems, through their widespread commercialization, will form the backbone of Europe's Zero Energy Building (ZEB) target by 2020. Despite the promising technical possibilities, social barriers to widespread use have also been identified, such as the conservative culture of the construction industry and integration into high-density urban planning. The authors point out that long-term use is likely to depend as much on effective policy decisions as on technical development.

The partially transparent solar modules offer an interesting opportunity to integrate building-integrated photovoltaics (BIPV) into architecture and urban planning. This new type of solar energy generation will most likely be an important part of electricity production worldwide in the future.

Building-integrated photovoltaics with partially transparent solar modules is an attractive option for the construction of energy-efficient buildings. This technology can help reduce energy supply costs while improving the exterior of the building.

In addition, semi-transparent solar modules can be used to direct daylight into the interior of a building. This not only saves energy but also reduces the cost of artificial lighting.

In summary, it can be said that building-integrated photovoltaics is a very efficient and versatile type of renewable energy. It has the potential to sustainably improve the energy supply of buildings.

Solar modules made of crystalline silicon for ground-mounted and rooftop power plants.

Amorphous crystalline silicon thin film solar PV modules, which can be hollow, light, red, blue and yellow, as glass facade and transparent skylight.

CIGS-based (copper-indium-gallium-selenide) thin-film cells on flexible modules that are laminated onto the building envelope element, or the CIGS cells are mounted directly onto the building envelope substrate.

Double glass solar panels with square cells inside.

Flat roofs

The most widely used solution to date is an amorphous thin-film solar cell integrated into a flexible polymer module, which is secured with an adhesive film between the back film of the solar module and the roof waterproofing. Using copper indium gallium selenide (CIGS) technology, a US company can achieve 17% cell efficiency for building-integrated modules in single-layer TPO membranes.

Pitched roofs

Solar roof tiles are (ceramic) roof tiles with integrated solar modules. The ceramic solar roof tile was developed and patented by a Dutch company in 2013.

Modules shaped like several roof tiles.

Solar shingles are panels that look and function like regular shingles but contain a flexible thin-film cell.

They extend the normal lifespan of roofs by protecting insulation and membranes from UV radiation and water damage. Condensation is also prevented as the dew point is kept above the roof membrane.

Metallic pitched roofs (both structural and architectural) are now being equipped with PV capabilities, either by bonding a free-standing flexible module or by heat and vacuum sealing the CIGS cells directly to the substrate.

facade

Facades can be attached to existing buildings and give old buildings a completely new look. These modules are attached to the building's facade over the existing structure, which can increase the building's appeal and its resale value.

glazing

Photovoltaic windows are (semi)transparent modules that can replace a number of architectural elements usually made of glass or similar materials, such as: B. Windows and skylights. Not only do they generate electrical energy, but they can provide further energy savings due to their excellent thermal insulation properties and solar radiation control.

Photovoltaic glass windows: The integration of energy generation technologies into residential and commercial buildings has opened additional areas of research that place greater consideration on the overall aesthetics of the end product. While the goal remains to achieve high efficiency, new developments in photovoltaic windows also aim to provide consumers with an optimal level of glass transparency and/or the ability to choose from a range of colors. Different colored solar panels can be designed to optimally absorb certain wavelength ranges from the broader spectrum. Colored photovoltaic glass has been successfully developed using semi-transparent, perovskite and dye-sensitized solar cells.

• Plasmonic solar cells, which absorb and reflect colored light, were developed using Fabry-Pérot-Etalon technology. These cells consist of “two parallel, reflective metal films and a dielectric cavity film between them.” The two electrodes are made of Ag and the cavity between them is made of Sb2O3. Changing the thickness and refractive index of the dielectric cavity changes the wavelength that is best absorbed. Matching the color of the absorption layer glass to the specific part of the spectrum to which the cell's thickness and refractive index are best matched both improves the aesthetics of the cell by intensifying its color and minimizing photocurrent losses. For the red and blue light devices, a transmittance of 34.7% and 24.6% was achieved, respectively. Blue devices can convert 13.3% of absorbed light into electricity, making them the most efficient of all colored devices developed and tested.
• Perovskite solar cell technology can be tuned to red, green and blue by changing the thickness of the metallic nanowires to 8, 20 and 45 nm, respectively. Maximum power efficiencies of 10.12%, 8.17% and 7.72% were achieved by adjusting the glass reflectance to the wavelength for which each cell is best suited.
• Dye solar cells use liquid electrolytes to capture light and convert it into usable energy; this occurs in a similar way to how natural pigments enable photosynthesis in plants. While chlorophyll is the specific pigment responsible for the green color in leaves, other naturally occurring pigments such as carotenoids and anthocyanins produce variations of orange and purple colors. Researchers at the University of Concepcion have demonstrated the viability of dye-sensitized colored solar cells that both appear and selectively absorb certain wavelengths of light. This cost-effective solution uses natural pigments from maqui fruit, black myrtle and spinach as sensitizers. These natural sensitizers are then placed between two layers of transparent glass. While the efficiency of these particularly low-cost cells is still unclear, previous research in the area of ​​organic dye cells was able to achieve a “high power conversion efficiency of 9.8%.”

Transparent solar cells use a tin oxide coating on the inside of the glass panes to conduct electricity out of the cell. The cell contains titanium oxide 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. When used as a replacement for traditional window glass or placed over the glass, the installation area could be large, leading to potential applications that utilize the combined functions of power generation, lighting and temperature control.

Another name for transparent photovoltaics is “translucent photovoltaics” (they only allow half of the light falling on them to pass through). Similar to inorganic photovoltaics, organic photovoltaics can also be translucent.

Not wavelength selective

Some non-wavelength-selective photovoltaic systems achieve semi-transparency through spatial segmentation of opaque solar cells. This method uses any opaque solar cells and distributes several small cells on a transparent substrate. This division drastically reduces the efficiency of energy conversion and increases transmission.

Another branch of non-wavelength-selective photovoltaics utilize visibly absorbing thin-film semi-conductors with small thicknesses or large enough band gaps that allow light to pass through. These results in semi-transparent photovoltaics with a similar direct trade off between efficiency and transmission as spatially segmented opaque solar cells.

Another branch of non-wavelength-selective photovoltaics uses visibly absorbing thin-film semiconductors with small thicknesses or sufficiently large band gaps that allow light to pass through. This leads to semi-transparent photovoltaics with a similar direct compromise between efficiency and transmission as spatially segmented opaque solar cells.

Wavelength-selective photovoltaics

Wavelength-selective photovoltaics achieves transparency through the use of materials that only absorb UV and/or NIR light and was first introduced in 2011. Despite the higher permeability, energy conversion efficiencies are lower due to a number of problems. These include small exciton diffusion lengths, scaling of transparent electrodes without compromising efficiency, and overall lifetime due to the instability of organic materials used in TPVs in general.

Innovations in transparent and translucent photovoltaics

Early attempts to develop non-wavelength-selective semi-transparent organic photovoltaics with very thin active layers that absorb in the visible spectrum were only able to achieve efficiencies of less than 1%. However, in 2011, transparent organic photovoltaics with an organic chloroaluminum phthalocyanine donor (ClAlPc) and a fullerene acceptor showed absorption in the ultraviolet and near-infrared (NIR) spectrum with efficiencies around 1.3% and visible light transmittance of over 65% . In 2017, MIT researchers developed a method to successfully deposit transparent graphene electrodes on organic solar cells, resulting in 61% visible light transmittance and improved efficiencies of 2.8-4.1%.

Perovskite solar cells, which are very popular as next-generation photovoltaics with efficiencies exceeding 25%, have also shown promise for transparent photovoltaics. In 2015, a semi-transparent perovskite solar cell using a methylammonium lead triiodide perovskite and a silver nanowire grid top electrode demonstrated a transmittance of 79% at a wavelength of 800 nm and an efficiency of about 12.7%.