Solar Energy in Spain .. See How The Spanish Became Leaders ..4

Solar Energy in Spain

Research has focused on technologies to increase the efficiency and decrease the cost of these concentrating solar systems. They’ve refined reflectors and absorber pipes, and worked on improving the coupling between the solar and conventional systems. One technology, the use of molten salt for heat storage, was tested on-site before SENER went ahead with plans to install such a system in the new Andasol facility. Researchers also continue partnering with European companies to develop alternative and even more effective storage systems, which could greatly increase solar thermal’s viability in the marketplace.

The center is currently investigating replacing heating oil in absorber pipes with water, so the steam turbine could be linked to the solar field directly, bypassing a heat exchanger. “Conceptually this seems so simple,” says Zarza, “but that’s not actually the case. Water boils and then turns to steam, and during the transition phase there could be very high temperature differences between the top and bottom of the glass tube, which could cause it to break.” Heating oil, unlike water, remains in liquid form throughout the process.

Scientists have tinkered with tubes to develop one that can withstand these temperature changes, and soon a new 3 MW facility will be built at PSA to test these new tubes.

Fernández of Abengoa’s Solúcar, one of the companies participating in the research project, looks forward to replacing heating oil with water. “Oil is expensive, and in theory you can go to higher temperatures with water and pressurized steam because oil has a heat limit. It’s also more efficient if you can do away with the heat exchanger,” he says.

A significant challenge facing developers of solar concentration plants remains cost – in large part because these plants haven’t been built before. The technology depends on parabolic mirrors made to exacting specifications, and tubes for the oil that consist of a double glass tube with a vacuum between the two layers. There’s currently one mirror manufacturer in Europe and two manufacturers of the glass tubes – one in Israel and another in Germany. “So when there are more manufacturers producing those tubes, and when there’s a larger production in general, you’re going to get more competition and a scale advantage,” says Peter Duprey, director of Acciona North America.

He adds,” I think this is at a fairly early stage in its evolution, and with more money and more people focusing on this energy alternative, I think you’re going to drive costs down, just like what happened with wind. In the 1980s it was 30 cents per kilowatt hour, now it’s down to about 7 cents. I think you’ll see the same thing with concentrating solar.”

Both Abengoa and SENER are working with other Spanish companies to jumpstart the production of parabolic mirrors and glass tubes in Spain, to increase production, competition, and local access to the necessary parts. At least two local companies will soon begin producing mirrors within the year, and another few are investigating developing new absorber pipes.

“Electricity costs are going up – and solar thermal costs are going down. We think they will meet somewhere in the middle,” says Zarza. 

In the US

The first solar thermal power plants in the world, nine in total, were built in Kramer Junction, in dry, sunny southern California, in the 1980s and still harness 350 MW of solar heat. Since the last of those plants was built, however, the technology in the US – as in the rest of the world – halted, with research continuing at American research centers such as the National Renewable Energy Lab (NREL).

This summer, the first new plant, built by Spanish company Acciona with technology from the US’s Solargenix, came on-line outside of Las Vegas in the abundantly sunny Nevada desert.

Acciona acquired 55 percent of Solargenix early 2006 and then began plans to build Nevada Solar One, as the plant is known. The parabolic troughs supply 64 MW, enough to power about 14,000 homes annually. Acciona is also in the permitting stage for two 50 MW concentrating solar plants in Spain.

Duprey, director of Acciona North America, says, “In the southwest of the US we have plenty of land that effectively is unused, and is near grid connection points. That can be developed, and I think we can get gigawatts worth of concentrating solar power over the next ten years.”

Nevada has a renewable portfolio standard that requires its utilities to generate a percentage of their electricity from renewable sources. The wind is weak in southern Nevada, but the sun burns hot – plus the state provided an investment tax credit –– so Acciona took on the project.

This type of technology demands vast amount of land for the parabolic troughs, and the plant is most efficient close to the demand. Conditions in the western US, particularly the southwest, meet both those requirements. The Western Governors’ Association has stated its commitment to increasing the use of solar thermal power in the region.