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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, 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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