Alternatives To C-si In Bipv Glass

By Author: Steve Miller
Total Articles: 3
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In order to move beyond a niche product, building-integrated photovoltaic (BIPV) will need to demonstrate both improved efficiency and lower cost. NanoMarkets believes that BIPV should be able to benefit from the growth that we expect to see in the PV market as a whole, but the degree to which it succeeds will likely depend on advances in technology and choice of PV materials. This may require switching to improved or completely different materials than what is commonly used today. Our latest report on BIPV glass, “BIPV Glass Markets– 2014 and Beyond,” describes PV technologies being used for this application today and analyzes which materials are likely to gain market share in the future.

Crystalline Silicon PV Still Dominates Market

The dominant form of BIPV glass consists of walls of window panes, some of which are crystalline silicon (c-Si) PV panels, and some of which are transparent glass. Because c-Si panels are not transparent, this is really the only way to incorporate it into BIPV glass today. This is a very low form of integration, but c-Si continues to dominate the BIPV market.

NanoMarkets ...
... believes that despite the drawbacks of c-Si, it will remain dominant through the end of the decade. It remains the incumbent PV technology for all applications and has the highest efficiency. Module prices have fallen, spurring growth in all sectors that use c-Si panels. Improvements in c-Si technology will also support its continued use in BIPV glass. According to the forecasts in our recent report, c-Si is expected to lose market share over the forecast period but still retain 75% of the addressable market.

We expect to see increased efforts to overcome the lack of transparency of c-Si panels. Even though c-Si is itself an opaque material, the trend toward thinner and thinner cells (down to as low as 100 μm) may be able to enable semi-transparent solutions. The fact that the busbar width is also reducing from 2 mm to 1 mm should also help with transparency, although it should be noted that at the same time the number of busbars on Si cells are increasing.

Despite advances in c-Si technology, it still has some significant drawbacks as a BIPV material that go beyond the lack of transparency. One issue is aesthetics – many people believe that c-Si panels are ugly, and they often don’t blend in well with the rest of the building.
Performance in situations of indirect or diffuse light is a serious problem because c-Si modules show limited capacity in converting diffused solar irradiation to energy. Shadows naturally fall onto building walls throughout the day, which can lead to loss of power in a shaded c-Si module that extends to all modules connected in series within the same circuit.

Thin Film PV Options

Thin film PV technologies may be able to pave the way toward cheaper BIPV glass, which will be needed in order for BIPV to break into the growing market for zero net energy buildings. TFPV cells offer lighter weight compared to c-Si and many have the advantage of performing equally well in direct sunlight and in shaded environments. This is especially important for applications where BIPV is integrated into building walls rather than skylights.

TFPV technologies are for the most part not mature today, but as the solar sector starts to offer sustained growth, NanoMarkets sees potential for BIPV glass firms to move away from c-Si. They have several options that are compelling, but all have their inherent risks as well:
CIGS: Many CIGS firms disappeared during the solar bust, but some of those who remain are specifically targeting BIPV glass. For example, Manz is involved with BIPV glass and has produced specialty modules with flexibility, color, and design meant to suit the tastes of architects. CIGS is flexible, which allows it to be used on curved building façades, and its high efficiency makes it attractive. NanoMarkets expects CIGS firms to edge their way into the BIPV glass space over the next few years.

CdTe: The CdTe market remains dominated by First Solar who hasn’t expressed interest in BIPV. That said, CdTe has good efficiency, and third parties use CdTe cells from First Solar in BIPV applications, which should help speed up commercialization. CdTe is the only thin-film photovoltaic technology that has surpassed c-Si PV in terms of overall low system cost in multi-kilowatt systems, which gives it a major advantage for BIPV. It does, however, have disadvantages in terms of transparency and the toxicity of cadmium. NanoMarkets believes that these limitations will mean a delay of several years before CdTe emerges as a competitive technology for BIPV glass applications.

DSC: Dye-Sensitized cells (DSC) can be solution processed on a glass substrate, making them very suitable for BIPV glass. In addition, they are quite good when it comes to performance in environments with indirect or diffuse light, and DSC glass can vary in color and transparency, making it very attractive for the BIPV market. Several firms are pursuing DSC for BIPV applications, but currently high prices and limited long-term stability are bottlenecks that make large-scale commercialization a challenge. Current use is limited to trials and pilot production. Until price and reliability improve, that is unlikely to change, but ongoing research and recent investments in this area may yield results that can accelerate commercialization.

OPV: The properties of DSC that make it appealing for BIPV glass also apply to organic PV. Compared to technologies such as CdTe, it is a much “greener” option, which should appeal to those aiming for zero net energy buildings. OPV cells contain no toxic compounds and are potentially disposable and recyclable. Efficiency is currently not great, but it is improving, and will need to continue to do so in order to gain more widespread interest. Heliatek is on the forefront of improving OPV efficiency, and its joint development agreement with AGC Glass Europe is encouraging. Still, OPV is unlikely to resolve efficiency and product durability issues quickly, making it more of a long-term option.

Amorphous silicon: Amorphous silicon (a-Si) was the original TFPV and is a lower cost alternative to c-Si. It is flexible, which is an advantage for curved glass structures. Still, other technologies, such as CIGS, can also claim this benefit and may be more compelling because of higher efficiency. Low performance would appear to make a-Si less desirable than other options, but many Chinese companies are still in this market, keeping it alive, and future product evolution is likely to spur modest growth in the coming years.

Colored Glass

One of the selling points of BIPV compared to traditional rooftop PV panels is aesthetics, so adding color to the glass – so long as it doesn’t adversely affect transparency – is one way BIPV glass suppliers can differentiate themselves in the market and make their products more appealing to building designers. This feature is especially compelling for BIPV glass façades in buildings and may be able to expand the addressable market.

The ability to combine color and aesthetics into solar-panel production is a significant paradigm shift and it will provide glass companies with a significant competitive advantage in an industry dominated by black and blue panels. Partnerships between glass suppliers and PV module manufacturers may enable both players to benefit. One example is the joint venture between SwissINSO and Acomet Solar. The companies recently completed the first installation of light blue PV panels on a building façade, with several other projects contracted in Switzerland and the U.K.

PV technologies that can provide different colors, such as DSC and OPV, are another avenue that can provide the aesthetic appeal that architects are looking for. These technologies thus likely to have a future in BIPV if they can overcome the limitations preventing them from achieving commercial success in the short term.

NanoMarkets expects the BIPV glass market to grow over the next eight years, from just over $800 million in 2014 to around $4.6 billion by 2021. This growth assumes advances in all types of BIPV glass and price reductions that make it appealing to the mass market. This will allow BIPV glass to be used not only in prestige buildings, which currently constitute the largest sources of revenue for BIPV glass, but also in net zero energy buildings, which is a much larger market and should provide a greater source of revenue in the long term.