From American Scientist:
Conventional photovoltaic panels will be hard pressed to displace fossil-fuel use anytime soon. But a different kind of solar cell might well do so
...One of the more attractive ways to do so is to use photovoltaic cells, which convert light directly to electricity. These cells are safe, have no moving parts, operate at ambient temperature and last for decades. The obvious roadblock preventing their widespread application is expense: Electricity generated from photovoltaic cells is getting cheaper, but it still costs several times the going rate in most places.
...These studies include, for example, a review of Tucson Electric Power's Springerville photovoltaic plant, which is one of the world's largest such installations, located in eastern Arizona. A careful life-cycle analysis of that plant determined the energy payback time to be 2.78 years.
At first blush, having an energy payback time of three years might not seem so bad. The problem comes when you consider how much the photovoltaic industry would need to grow in size to compete seriously with other forms of electric-power generation. Right now, the installed capacity of photovoltaic cells worldwide is about 6 gigawatts—a drop in the bucket compared with global electricity use, which demands terawatts of power.The photovoltaic industry is, however, growing quite rapidly: Worldwide, the total installed capacity of photovoltaic panels increased by 36 percent in 2006. Alternative-energy advocates would, ideally, like to see such rates maintained so that photovoltaic cells could displace a large fraction of the fossil fuels being used to generate electricity. The rub is that with an energy payback time of three years, growing the industry at this pace requires more energy than all the existing photovoltaic cells produce. That is, even if you could somehow harvest all the energy produced from every last photovoltaic cell in one year, the total wouldn't be sufficient to produce the next year's crop of panels. As Lewis Carroll's Red Queen said in Through the Looking Glass, "Now here, it takes all the running you can do, to keep in the same place."...MORE