California’s governor Arnold Schwarzenegger recently opened the first solar thermal power plant in the state for nearly 20 years – the new Kimberlina plant in Bakersfield that will generate 5MW of electricity, enough for 3,500 homes. Small though it is, the plant may mark a landmark in a return to sun power in the west. 


While no one is betting that northern Europe can match the desert for heat and light, still the sun beams down enough light every day to provide 5,000 times the world’s energy needs. That single fact makes it seem odd that we don’t harness more of the sun’s power – except that solar energy remains expensive and the technology rudimentary. 


That’s all changing rapidly, however, with one new technology in particular coming to life. Called Solar Thermal, it’s not to be confused with solar photovoltaics, whereby sunlight is converted directly into electricity. Increasingly seen as a commercial-scale green energy source, solar thermal consists of motor-driven, 120m2 mirrors that track the path of the sun through the day, focusing light rays onto a boiler within a central, 100m-tall tower, similar to the effect of a camper focusing sunlight through a magnifying glass to start a fire. These concentrated light rays heat water within the boiler to 550°C, creating steam to drive a turbine, which generates electricity. The steam is then cooled and the water pumped back into the boiler, so that it can be reused. Solúcar, the company operating Europe’s first such plant outside Seville in Southern Spain, claims it generates enough power for 6,000 homes. 


However, there are drawbacks. Solar thermal energy is not cheap to produce at the moment – it’s currently about three times more expensive than conventional energy and requires large upfront investment. “The main problem with solar thermal is one of cost,” says 
Professor Ian Fells, founding chairman of the New and Renewable Energy Centre in Northumberland in the UK, “but as the reality of climate change begins to bite this should start to decrease.” And what happens when the sun goes down? Generation stops, but plants can store power for a couple of hours after sundown and since they use the same steam turbines as other generating stations can be adapted to burn natural gas or other fuels to provide energy through the night. 


Adoption of solar thermal seems to be picking up pace. Increasingly, US states are being compelled to buy a percentage of their energy from renewables including solar, and many of the sunnier states are signing agreements to buy electricity from solar power stations.