It seems solar thermal power has quietly grown up, while photovoltaic power has gotten all the attention. It isn’t as though there isn’t a lot to like about photovoltaics – they require almost no maintenance, they last for several decades, they emit zero pollution, and if the claims of companies like Nanosolar are to be believed, they are about to get several times cheaper to make and they will change the world.
In the meantime, however, solar thermal power is probably one of the most cost-effective ways to generate renewable energy; using solar power for water heating is something that countless innovative homes and commercial buildings have already implemented. But by using solar concentrators, where the reflective solar collectors are many times the size of the heat absorber area, transfer fluids can be super-heated to drive turbines to generate electricity.
It isn’t clear why solar thermal power for electricity generation hasn’t taken off in a big way. There are three basic designs – a “power tower” where mirrors tracking the sun surround an absorber tank on a tower in the middle of the array, a parabolic reflector that tracks the sun with its own absorber tank at the focal point of the dish, and “parabolic trough” collectors, where a stationary curved mirror extends in a straight line, with an absorber tube running along the focal point of the trough’s curved surface. For more information on solar concentrator designs, go to Solar Thermal Fact Sheets, or to the solar thermal pages at the Energy Information Agency.
The most cost-effective way to generate electricity using solar thermal power is with the parabolic trough design, which is not as efficient as the other systems, but is far cheaper since the entire array is stationary and doesn’t require tracking systems. One company manufacturing equipment for parabolic trough electric power generating stations is Schott Solar Thermal, who have already supplied solar receivers used in several 100+ megawatt installations.
A surprising fact about solar thermal systems is that the amount of land they require to produce meaningful amounts of electricity is not that great. Our calculations indicate they can produce over 64 megawatt-years of electricity per square mile per year. By contrast, large-scale photovoltaic systems can produce about 93 megawatt-years per square mile per year. As we prove in “Power the Earth with Photovoltaics,” it would only take about 670 square feet of surface for each person on earth allocated to photovoltaic arrays to replace 100% of the energy we currently consume worldwide. By this logic, it would only take about 950 square feet per person, an array 30′ x 30′, for solar thermal systems to replace 100% of the energy currently consumed by humanity. Land, clearly, is not the issue.
Photovoltaic power and solar thermal power have more potential to replace conventional sources of energy than any other clean renewable sources known. Unlike hydro-electric, wind power, or nuclear, there is nothing problematic about their operations and impact. Unlike biofuels, they will not compete for land with agriculture.