Amid the fretting over whether the renewable energy business will be dominated by foreign companies, a California venture that creates solar plants that can run around the clock has cut a deal to build a big plant in Spain, a country that is one of the most aggressive users of solar power.
SolarReserve of Santa Monica, Calif., can store heat from the sun in the form of molten salt. A field of mirrors that are aimed by a computer reflect the sun’s light on a black box on top of a central tower. In the box is the molten salt, which the sun heats to more than 1,000 degrees Fahrenheit. The salt can be run through a heat exchanger to make steam to power a conventional turbine and generator.
The advantage is that extra salt can be stored for a rainy day or plain old nighttime so that the plant can continue to make electricity at any hour. That ability is increasingly important as more and more conventional solar farms are set up; ordinary solar cells produce electricity only while the sun is shining, and a system that relies heavily on an intermittent source of power needs storage.
In May, the Energy Department gave the company a promise of a $747 million loan guaranteee for a 110-megawatt plant using that technology in Tonopah, Nev.
Now the Spanish government has chosen SolarReserve to build a plant in Alcázar de San Juan, southeast of Madrid, with a Spanish partner, Preneal. Spain limits solar plants to 50 megawatts, but the field of mirrors will have to be slightly larger there than it would be in Nevada because the sun there is not as strong.
The chairman of SolarReserve, Kevin B. Smith, said that his plants’ energy output was much higher than the rating in megawatts suggests. The Nevada plant will produce more kilowatt-hours than 110 megawatts of solar cells, which convert sunlight directly into electricity, and more kilowatt-hours than other solar thermal plants. Solar thermal plants capture the sun’s light in a different way, using mirrors shaped like a parabolic trough to heat a water-based or oil-based fluid.
“If you looked at a 110-megawatt photovoltaic facility or a trough facility, neither of which have storage, the actual electricity output would be half,’’ Mr. Smith said. “We’re overcollecting, and spreading the energy out a bit.”
Because costs are higher than for conventional energy; a buyer would have to value both the renewable source of the energy and the fact that it can be counted on at an hour of the customer’s choosing. The Nevada plant will have 10 hours of storage, and the Spanish plant, about 16, Mr. Smith said.
Proponents of solar power sometimes argue that sunshine and peak demand coincide because so much of a utility’s peak load is air-conditioning. But utility engineers say this is not precisely accurate. People come home from work around sunset and turn on their home air conditioners, and peak demand continues long after sundown.
In Nevada, Mr. Smith said, the sun can shine roughly from 6 a.m. to 5 p.m. But “peak demand doesn’t start until late morning, maybe noon, and it runs until 10 p.m..” he said.
One solution to that problem is to equip a solar thermal power plant with a supplemental boiler running on natural gas to make steam when the sun cannot. Thus the value of the energy storage depends partly on the price of the gas.
The New York Times