Can hybrid solar provide nonstop electricity?

KIBBUTZ SAMAR, Israel Tue Feb 17, 2009 10:37am EST

An Israeli engineer (L) explains an above-ground solar panel to a visitor at Israel's Solel Solar Systems Centre in Bet Shemesh September 20, 2000. REUTERS/Natalie Behring

An Israeli engineer (L) explains an above-ground solar panel to a visitor at Israel's Solel Solar Systems Centre in Bet Shemesh September 20, 2000.

Credit: Reuters/Natalie Behring

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KIBBUTZ SAMAR, Israel (Reuters) - Israeli energy company AORA wants to prove it doesn't have to be sunny for a solar power plant to make electricity. Like weaning a car from total dependence on fuel, the answer, it says, is to go hybrid.

Their idea is to combine traditional fuel such as biomass or diesel with low-carbon solar power, during daylight, to generate uninterrupted electricity.

The approach is a novel answer for handling the variability of solar power, a major challenge which otherwise requires expensive batteries or other forms of storage to provide round-the-clock power.

AORA is constructing its first hybrid solar power station on a half-acre (0.2 hectare) plot in Israel's Negev desert, where companies are competing to create more efficient technologies and tap into the multi-billion dollar clean energy market.

The Negev plant, unveiled to the public this week at an energy conference in Israel's Red Sea resort of Eilat, uses diesel for now.

It will be online next month, producing 100 kilowatts, enough energy to power about 40 houses, said Pinchas Doron, AORA's chief technology officer.

The module looks like a smaller version of solar "power towers" being developed in the United States and Europe, with 30 large mirrors reflecting sunlight onto a generator on top of a 30 meter (90-foot)-high tower.

What is unique in AORA's design is a gas turbine that can handle super-high temperatures and then work off external fuel when sunlight is unable to produce the necessary heat, Doron said. "It can shift seamlessly between using the sun as fuel and a conventional or another renewable fuel."

That is important in off-grid locations where there is no alternative power source. And even where there is a grid, the lack of predictability of solar power is a problem, creating a headache for network operators.

"LOGICAL STEP"

Clean energy experts welcome the new design, though some say the technology has its limitations.

"This was a logical step. In certain contexts, like remote places, this could be the way to go," said Ken Zweibel of the Institute for the Analyses of Solar Energy in Washington, DC.

"It's dispatchable. You can't have that from photovoltaic alone," he said, referring to traditional solar panels.

Israel Kroizer, president of California-based BrightSource Energy Inc, said his company's steam turbine solar tower, which uses hundreds of mirrors, is more efficient than AORA's hybrid gas engine for larger scale production of electricity.

BrightSource last week signed contracts to supply Southern California Edison with 1,300 megawatts of solar thermal power.

One of the main hurdles was creating a generator that could handle concentrated sunlight that reaches nearly 1,000 degrees Celsius (1,832 degrees Fahrenheit), much hotter than any other power tower model, said AORA's operations manager, Yuval Susskind. "Most materials melt in that heat," Susskind said.

Air in a special receiver at the top of the tower capable of handling the high temperature is heated by the concentrated sunlight and shot into a combustion chamber, where it expands and powers a turbine, producing electricity.

A separate route can bypass the solar receiver and use a secondary fuel to power the turbine when necessary, allowing the solar power plant to produce continuous electricity.

The process also creates a by-product of some 170 kw of heat, which can be used to heat water for homes or factories, Susskind said.

"Because each of these units sits on just a half-acre, it can provide electricity in the most remote areas," he said. "You can build one outside a village in Africa or have many together in a desert in California."

A 100 kw plant using traditional photovoltaic panels, which can have up to 15 percent efficiency, would need twice the land, AORA said, than its hybrid-solar plant running at 28 percent solar efficiency.

Susskind said no other plant has hybrid technology at the same scale and efficiency.

AORA said the cost of their electricity is competitive with other solar technologies: between $3,500-$5,000 per installed kilowatt, meaning each 100 kw hybrid plant may cost up to $500,000. Total production costs depend on the price of the external fuel.

A full system prototype constructed in Nanjing, China in 2006 proved the technology worked, the company said, and it expects to begin commercial production later this year.

(Editing by James Jukwey)

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