A POTENTIAL BREAKTHROUGH IN HARNESSING THE SUN'S ENERGY

Features

In the high desert of southern Spain, not far from Granada, the Mediterranean sun bounces off large arrays of precisely curved mirrors that cover an area as large as 70 soccer fields.

These parabolic troughs follow the arc of the sun as it moves across the sky, concentrating the sun’s rays onto pipes filled with synthetic oil that can be heated to 750 degrees Fahrenheit. That super-heated oil is used to boil water to power steam turbines, or to pump excess heat into vats of salts, turning them a molten, lava-like consistency.

The salts are just fertilizers — a mix of sodium and potassium nitrate — but they represent a significant advance in the decades-old technology of solar thermal power production, which has traditionally used mirrors to heat water or oil to generate electricity-producing steam. Now, engineers can use the molten salts to store the heat from solar radiation many hours after the sun goes down and then release it at will to drive turbines. That means solar thermal power can be used to generate electricity nearly round-the-clock.

The plant in southern Spain, known as Andasol 1, began operating last November and now provides 50 megawatts of power, enough electricity to supply 50,000 to 60,000 homes year-round. Andasol 2 will come online later this summer, with Andasol 3 already under construction. When the entire Andasol complex is completed in 2011, it is expected to generate enough electricity to power 150,000 households — about 600,000 people.