Oct 17 - McClatchy-Tribune Regional News - Tom Beal The Arizona Daily Star, Tucson

A Tucson solar-energy developer and Arizona Public Service have been awarded a $4.35 million grant to overcome a key obstacle to producing utility-scale solar energy.

The big problem with generating energy from the sun on a large scale is that our demand for electricity doesn't end when the sun goes down -- and electricity is expensive to store.

It is more economical to store heat, which is why utilities are returning to an older technology -- concentrating solar powerby using mirrors to focus the sun on fluid-filled pipes that heat water to run steam turbines. The technology will be installed at a solar thermal plant near Red Rock, north of Tucson.

The grant awarded to APS and US Solar is one of 15 the U.S. Energy Department is granting for research in thermal storage. It is one of only three grants that also involve working models, in this case, two of them -- one that will store the heat in an oil and one that will store it in sand, said Jake Stephens, director of development for US Solar.

US Solar is headquartered in Boise, Idaho, with operations in Denver and Tucson.

"Storage is an absolutely critical component for solar," Stephens said. "The key limitation of solar is the fact that the sun is intermittent. Solar thermal doesn't blink on and off, and it's a lot cheaper than chemical (battery) storage."

Stephens said one of the technologies, which is being developed by the University of Arizona's Department of Aerospace and Mechanical Engineering, will lower the cost of storage by using less of the expensive heat-transferring liquid currently used for thermal storage. The liquid will be stored in a single tank filled with rock, rather than in separate hot and cold tanks, he said.

The other prototype, developed at Georgia Tech, will store the heat in sand. It is "a potential game-changer," Stephens said, and could reduce the cost of thermal storage at a large utility plant by "tens of millions of dollars."

"This is a project with a lot of potential value to the industry, and to the world," he said.

Solar won't replace fossil fuels for generating electricity unless storage can be done more cheaply, Stephens said.

"This project is about making it more financially viable," said APS spokesman Steven Gotfried.

"What's exciting about this is that it's not just a research-and-development project. The one-megawatt plant at Red Rock has no storage currently," he said.

The small plant, called the Saguaro Solar Power Plant, is the perfect test site for the new technology, said Stephens.

APS, meanwhile, is planning Arizona's largest solar-generating plant.

The Solana Generating Station will generate 280 megawatts of power, enough to supply 70,000 of its customers, according to APS. Solana will use molten salt as its thermal-storage medium, said Gotfried. It is being built by Abengoa Solar Inc. at a site near Gila Bend and is expected to be operational by 2011.

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