In a previous Solar Choice blog entry, Prateek Chourdia wrote about some emerging trends in the future of photovoltaic solar technology, including thin-film solar power. This entry will summarise some of the salient points regarding thin-film technologies, otherwise known as flexible photovoltaics, and discuss their possible future direction.
What is a thin-film solar photovoltaic cell?
Unlike the solar panels that you probably imagine when you think of solar power (monocrystalline and polycrystalline), thin-film technology is not composed of highly refined silicon crystals, but is instead one continuous material. There are four basic types of thin-film solar photovoltaics (TFPV), classified by the photovoltaic material that is used. The principle of TFPV, however, is the same as that of crystalline PV: light strikes the material and excites electrons, which then ‘flow’ through some permutation of a p-n junction, generating electricity which is captured and utilised.
Amorphous silicon (aSi) solar PV cells:
Amorphous silicon solar power, discussed briefly in our previous blog entry, was developed in the ’70s and is a made from a non-crystalline form of silicon, which results in lower efficiency per square meter–up to 15% in laboratory conditions, but generally 6-8% in real-life applications. (Compare this to 15-18% in crystalline silicon cells.) However, thanks to its flexible nature and their relatively lower susceptibility to the effects of overheating and shading, aSi has a number of everyday applications: it has already been used for decades in charging solar-powered calculators and watches, and more recently has been developed by a number of companies into solar PV roofing materials such as tiles and shingles.
Cadmium Telluride (CdTe) solar PV cells:
A smaller number of companies have developed solar cells made of Cadmium Telluride, developed in the 1990s, which promises to rival aSi for the place of the most cost-effective means of thin-film solar power generation, with laboratory efficiencies of 16% and 11% in real life. A flexible photovoltaic cell composed of this material with 12.4% efficiency was developed in 2009 by the Swiss Federal for Materials Testing in Switzerland. Cadmium is a relatively cheap and readily available material, but Telluride is one of the rarest elements on earth. (More about First Solar’s CdTe technology.)
Copper indium gallium selenide (CIS or CIGS) solar PV cells:
Copper indium gallium selenide was developed in the ’80s and, in addition to having a high heat tolerance, it also has one of the highest efficiencies for thin-film solar material–20% in lab conditions and 11% in real-life. (More about CIGS technology.)
Organic solar PV cells
Organic solar cells are made of materials that contain carbon. The cost of manufacture of organic cells is less expensive than from inorganic materials such as silicon, but this advantage is significantly offset by the fact that the solar conversion efficiency of these cells is only 8% in the laboratory and 4% in real life, and the fact that they tend to have a short production lifespan of 6 years.
What does the future hold for thin-film solar PV?
There are a number of factors that give promise to the future of thin-film PV. It has numerous applications: it can be used as a building material in the place of awnings, in conjunction with windows, and on walls. It is also useful for smaller, portable devices to be used in areas without readily available electricity: battery chargers in the middle of the desert or in rural areas (or even while camping!). TFPV may be rolled up in some cases and tucked away into a safe sheath or container, to be brought out when needed. In fact, among other organisations, the US military is already making use of portable photovoltaics for operations in areas where grid power is absent. On top of this, with appropriate life-cycle planning, some types of TFPV can be more easily recycled than crystalline cells.
Global Business Intelligence (GBI), a market research firm, predicts that thin-film technologies will become a major force in the solar power market by the year 2020. This realisation of this prediction will be predicated on corporations’ success in ensuring higher solar conversion efficiencies and longer lifespans of these technologies.
In any event, the thin-film PV industry is a rapidly evolving one, and new technologies are being experimented with by a number of different companies all the time. If you are looking to install or use these technologies, be sure to discuss them with the manufacturer, who should know best what the capabilities of each technology are.
Written by James Martin
Solar Choice Analyst
© 2010 Solar Choice Pty Ltd
Resources and Links:
MotherEarthNews.com, “The promise of thin film solar”
GBI Research: “Thin film photovoltaics market analysis to 2020”
SpecialtyFabricsReview.com: “Flexible Photovoltaics”
National Renewable Energy Laboratory, Golden Colorado, “High-efficiency CdTe and CIGS thin-film solar cells: highlights and challenges” (MS Word document)
Japan Pavillion image from TripAdvisor.com
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