Direct steam solar thermal plant fires up

Late last month a new type of solar thermal power plant was inaugurated in Carboneras, Spain. 

The pilot plant, which is the product of a collaboration between German aerospace firm, DLR and Spanish utility company, Endesa, generates steam and stores it in a new way that its creators say is both more efficient and cost-effective.

Like some other solar thermal power plants, this one uses parabolic mirrors to intensely focus sunlight on to receiver tubes.

In typical designs, these receiver tubes are filled with oil, which is superheated to about 390 degrees Celsius (about 734 Fahrenheit) by the sun’s energy. 

That hot oil then heats water, producing steam that drives a turbine which generates electricity. For the plant in Carboneras, DLR says it pulled the oil out of the loop such that the water is heated directly by the sun into steam. 

The receiver tubes are under pressure at up to 120 bar, which helps produce superheated steam reaching 500 degrees Celsius (932 fahrenheit). DLR claims using water directly in the solar collectors results in increased efficiency and, therefore, lower cost solar thermal power.

The plant also uses a new type of salt based latent heat storage system that captures the energy steam creates when it condenses back into water.

According to DLR, at 305 degrees Celsius the salt absorbs energy by transitioning from a solid to a liquid state.

This allows the plant to store large amounts of energy in a small volume and with a minimal temperature change.

The net benefit is more stored energy that will be available at night or in instances where sun is not sufficient.

Researchers plan to use the pilot facility until the end of 2011. DLR researches say that during that time, the plant will provide important performance information about the plant as a whole and its individual parts.

* Caleb Denison, EarthTechling