Is solar thermal the answer to our energy crisis?
April 3rd, 2008 by Jim JustWhen we think of solar power, we think of photovoltaics. But the most promising mechanism for large scale solar power generation may turn out to be solar thermal power – concentrated sunlight.
But photovoltaics are expensive to produce, and their manufacture requires rare earth elements that are in increasingly short supply. And the best that both thin film and traditional silicon based PV cells have been able to do is approach 20% efficiency – under laboratory conditions.
Big Gav at The Oil Drum: Australia/New Zealand explains that concentrating solar power (CSP) systems use lenses or mirrors combined with tracking systems to focus sunlight which is then used to generate electricity. The primary mechanisms for concentrating sunlight are the parabolic trough, the solar power tower, and the parabolic dish. The high temperatures produced by CSP systems can also be used to provide heat and steam for a variety of applications (cogeneration).
CSP is pretty low-tech. It depends upon direct sunlight to function and works best in really sunny locations. An area of desert around 250 km by 250 km covered with CSP power generation could supply all the world’s current electricity demand.
Proponents claim solar thermal plants could provide more than 90 percent of current U.S. power demand at prices competitive with coal and natural gas. Electricity from solar thermal plants currently costs between $0.13 per kilowatt hour (kWh) and $0.17 per kWh, depending on the location of the plant. Conventional power plants generate electricity for between $0.05 and $0.15 per kilowatt hour (not including any carbon costs) – in most places it’s below $0.10. Wind power generally costs around $0.08 per kWh. Solar thermal costs are expected to fall to as low as six or even 4 cents per kWh as construction of plants is scaled up.
Besides simplicity and cost, another big advantage of solar thermal power over solar photovoltaics is energy storability. Heat energy is more easily and efficiently stored than electricity. Solar thermal plants can combine energy storage into the design to enable around-the-clock, demand-driven electricity generation.
It’s important to remember that generating power isn’t the only way to utilize solar thermal energy. Solar hot water is a very cheap and efficient way of replacing gas or electricity usage with solar energy. And passive solar design – facing your house and windows the right way, with thermal mass, insulating glass, and tight construction – is cheap, low-tech and time-tested.