Solar power is an incredibly promising alternative energy technology. However, the problem with converting solar energy directly to solar power via photovoltaics or other designs is that the cost of producing power is simply not cost competitive with nature's designs -- coal or petrol.
The cost issues are not for lack of efficiency. Scientists have milked very high efficiency out of the cells, iteratively raising the yield year by year. However, the high cost of silicon, the primary material for solar panel cells, keeps the costs high even as efficiencies experience dramatic gains.
In order to make solar cost competitive, researchers at University of California, Berkeley, and the Lawrence Berkeley National Laboratory (LBNL) are spearheading the search for a silicon replacement for the solar industry.
The team surveyed 23 promising semiconducting materials and then pared the field down to the 12 that are abundant enough to meet or exceed the world's yearly energy needs. From there 9 were selected, which exhibited significant cost savings in raw material costs over crystalline silicon.
Daniel Kammen, UC Berkeley professor of energy and resources, and colleagues Cyrus Wadia of LBNL and A. Paul Alivisatos of UC Berkeley's Department of Chemistry discovered that some superior solar choices may have been overlooked due to the desire to keep the status-quo of silicon. They believe before solar power can be deployed on a broad scale, the basic science must be reevaluated to ensure that the industry is using the best possible materials, rather than blindly proceeding.
Wadia states, "The reason we started looking at new materials is because people often assume solar will be the dominant energy source of the future. Because the sun is the Earth's most reliable and plentiful resource, solar definitely has that potential, but current solar technology may not get us there in a timeframe that is meaningful, if at all. It's important to be optimistic, but when considering the practicalities of a solar-dominated energy system, we must turn our attention back to basic science research if we are to solve the problem."
Today's top solar materials are crystalline silicon and thin film CdTe (cadmium telluride) and CIGS (copper indium gallium selenide). Silicon is abundant, but costs a great deal to process. The exotic metals like indium used in thin films are cheaper to process, but less abundant. If the world switched to all solar, they would quickly run out. States Professor Kammen, "We believe in a portfolio of technologies and therefore continue to support the commercial development of all photovoltaic technologies. Yet, what we've found is that some leading thin films may be difficult to scale as high as global electricity consumption."
Wadia adds, "It's not to say that these materials won't play a significant role. But rather, if our objective is to supply the majority of electricity in this way, we must quickly consider alternative materials that are Earth-abundant, non-toxic and cheap. These are the materials that can get us to our goals more rapidly."
The team's top candidates for a replacement material are iron pyrite, copper sulfide, and copper oxide. Of them, iron pyrite is the cheapest, being plentiful and easy to process. While nanoscale science has shown that cells of such unconventional materials will experience modest efficiency losses, the researchers say that these costs will be easy offset by the decrease in raw materials and processing costs.
Professor Kammen concludes, "As the U.S. envisions a clean energy future consistent with the vision outlined by President Obama, it is exciting that the range of promising solar cell materials is expanding, ideally just as a national renewable energy strategy takes shape."
The team's research was funded by the U.S. Environmental Protection Agency, the Energy Foundation, the Karsten Family Foundation Endowment of the Renewable and Appropriate Energy Laboratory. It appears in the journal Environmental Science & Technology.