The speed with which solar PV has taken off has surprised most analysts, with the cost curve coming down far faster than expected as materials technology develops. When people think of solar PV, they tend to think about roof-top panels or large installations in fields or deserts, but imagine if you could integrate photovoltaic cells into ordinary windows…the many buildings that are unsuitable for rooftop panels would suddenly have the ability to generate their own electricity, with enormous potential for modern glass-and-steel office buildings.
Clearly (pun intented!), such a proposition would only be viable if the windows continued to fulfil their original function, ie being transparent / providing daylight (otherwise energy gains would be wasted on lighting, and few people want to live or work in windowless environments). So how real is this technology, and can we expect to be seeing it in practice any time soon?
What is transparent solar PV?
Traditional solar cells generate electricity by absorbing photons and converting them into electrons. By definition, this process is incompatible with transparency because the incoming photons are absorbed by the process. As a result, only low levels of transparency have been achieved with traditional solar PV technology, although even at these levels, they can still be suitable for use in building facades and curtain walls. Spanish company Onyx Solar, has a range of products with transparency levels between 10 and 30% and has installed PV curtain walls, windows, skylights, floors and even furniture in projects around the world, and has an impressive track record with some projects achieving very short payback periods of a year or less and impressive IRRs.
Germany company Heliatek has developed a PV thin film with up to 50% transparency which can be applied to glass building facades, as well as concrete, metal and other substrates. The company claims to hold the world record for cell efficiency for non-transparent organic solar cells, at 13.2%, and has installed its product at a number of sites in Germany, Italy, China, Singapore and Egypt, and is now developing its production processes.