VentureBeat

BrightSource Energy, an Oakland, Calif., solar thermal startup, has landed a hefty $115 million funding round from investors including Google to develop its solar power tower technology.

Solar thermal technology is one the leading hopes for alternative energy. It uses like mirrors and lenses to boil water, the steam of which is harnessed to generate electricity.

This third round was led by Google.org, VantagePoint Venture Partners, BP Alternative Energy, Statoil Hydro Venture and Black River; returning investors included DBL Investors, Draper Fischer Jurvetson and Chevron Technology Ventures. The company has now raised $160 million.

The company recently signed a massive contract with PG&E to supply it with up to 900 megawatts from its plants, whose construction will begin in 2009. Its Distributed Power Tower (DPT) technology is basically an array consisting of thousands of small mirrors, called heliostats, which concentrate sunlight on a single point — in this case, a boiler chamber mounted on top of the tower. Because its heliostats are able to follow the sun in two dimensions, BrightSource claims they are much more efficient than rival solar thermal technologies.

Each field of heliostats, dubbed a Solar Power Cluster (SPC), can produce 20 MW of solar power; a typical BrightSource power plant, made up of five SPCs, is therefore capable of generating up to 100 MW. To reach the 900 MW mark, the company plans on having one 100 MW plant up and running by 2011 and four 200 MW plants up by 2016.

Rivals Ausra, Solel and eSolar use similar technologies to produce electricity, though their specific designs differ. The latter, for example, uses flat mirrors in smaller groupings to produce up to 33 MW at a time –a practical strategy that allows the firm to plug directly into the existing grid and to eschew the burdensome process of obtaining permits. Costs will likely remain the biggest obstacle for these companies, but BrightSource, which is chaired by Arnold Goldman, a man with an extensive background in solar thermal, will be well positioned to handle them.

[See also: CNET Green Tech Blog

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California energy utility PG&E has agreed to buy power from a 177-megawatt solar thermal plant to be built by Silicon Valley company Ausra.

Ausra, of Palo Alto, Calif., is applying for a regulatory permit to build on 640 acres of ranch land in California’s San Luis Obispo county.

The idea behind solar thermal power is focusing mirrors on contained water, which then turns to steam that can drive turbines. We last reported on Ausra two months ago, when it raised $40 million from Khosla Ventures and Kleiner Perkins Caufield & Byers.

Ausra’s execution of the deal, if it goes through will help the company catch up with competitor BrightSource, which just cleared the regulatory hurdle for a 400-megawatt plant in the Mojave Desert last week, according to Green Wombat.

Although PG&E has now committed to buying over a gigawatt of solar thermal energy in coming years, it remains to be seen which startup’s designs are most effective.

Technology used by companies like BrightSource and Solel uses special curved mirrors to focus more light, and thus create more steam than Ausra’s plants. However, the latter’s approach, which uses mass-produced flat mirrors, is cheaper, the company says, potentially bringing the cost for solar thermal energy as low as coal-fired plants.

The technology for solar thermal itself has existed for decades. Photovoltaic cells, which directly capture sunlight, may possibly become cheap enough to be a viable replacement.