A California utility company says they’re “bullish” on industrial-scale solar thermal power.

Five centuries ago, Leonardo da Vinci sketched out his idea for harnessing the energy of the sun for industrial purposes: parabolic mirrors designed to heat water or weld copper. This is the basis of solar thermal energy, sometimes called concentrated solar power (CSP).

Unlike solar photovoltaic power, which directly converts light into electrical energy, solar thermal concentrates light to heat into heat. In high temperature solar thermal systems, this heat can then be used to create superheated steam, which drives conventional electric turbines.

Solar thermal is the new hotness

There’s a sexiness to solar thermal. Apart from its overall simplicity, CSP is inherently more efficient than current photovoltaic technology. It’s also easier and far cheaper to store heat than electricity, making it possible to construct solar thermal installations which still produce power overnight, or on cloudy days.

That makes sense to San Francisco-based Pacific Gas and Electric, which has just signed with Oakland’s BrightSource Energy to build three massive solar thermal plants in the Mojave desert. The trio will produce 500 megawatts of power — enough to supply over 375,000 homes. PG&E has also executed options for another 400 megawatts from two additional plants, extending the utility’s capacity to over half a million solar thermal-powered homes.

“We’re bullish on solar thermal,” said Keely Wachs, PG&E’s public policy and environmental communications manager. “While it’s still an emerging technology — not a proven one like wind or geothermal — we think it can make a significant contribution toward our alternative energy goals.”

Wachs told EcoTech Daily that the new BrightSource partnership is the utility’s third foray into solar thermal, following a 553 megawatt contract with Solel and a 177 megawatt project managed by Ausra.

Huge arrays in the desert

The latest venture is based on BrightSource’s DPT 550C technology, developed by Luz II, its Israeli subsidiary. DPT 550C systems use banks of low-cost flat mirrors instead of complex trough or parabolic reflectors. These “heliostats” are arranged around a heating tower, which stands at 60 to 80 meters, depending on local conditions. The mirrors — which can track the sun — focus light on a boiler at the top of each tower.

Temperatures in the boiler can reach 550 to 565 degrees Celsius. This converts locally sourced groundwater into superheated steam, which is then routed to a turbine generator. The expended steam is cooled, and its water captured for reuse.

“Solar thermal is within striking distance of conventional power in terms of cost,” explained Wachs. “As we scale up, we expect it to be come quite competitive.”

California: OPEC of alternative power?

California seems a natural for solar thermal power. Under state law, 20 percent of all generated electricity must come from renewable resources by 2010. But the state is blessed with ample stretches of flat desert, a high percentage of sunny days, and enough water to get the job done.

PG&E has been developing alternative energy strategies for quite a while. The combination of California’s mountain passes and Pacific sea breeze made it an early hub of wind power development.  The state’s famously active geology also means the presence of geothermal energy, and PG&E is also invested in small hydroelectric. Wave and tidal power experiments will be the next additions to PG&E’s green energy portfolio.

The first of BrightSource’s solar thermal clusters are expected to go online in 2011. All three will be located in San Bernadino County: two in the Ivanpah dry lakebed close to the Nevada border, and another on the Broadwell Dry Lake, near Ludlow.

PG&E backs 3 solar plants in the Mojave (SFGate)
PG&E makes huge solar deal (Mercury News)

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