Google has announced it is investing $168 million in a project that is set to double the output of solar-generated electricity in the U.S. The commitment is part of the financing that BrightSource Energy needs to build solar power plant in California's Mojave Desert, which will generate 392 MW of clean energy when up and running in 2013. According to Google, that's the equivalent of taking more than 90,000 cars off the road over the projected 25-years lifetime of the plant.

This is the company's largest investment in renewable energy yet. Google has previously put $5 million into a solar photovoltaic farm in Germany, $38.8 million into 169.5 MW worth of wind projects developed by NextEra Energy Resources in North Dakota, and has made a variety of smaller equity investments into clean power startups over the past few years. With the BrightSource deal, the search giant's investments in this sector have now hit $250 million.

Promoting energy that causes less pollution is one of several initiatives championed by Google's co-founders, Page and Brin. But it's also about making smart investments. As Reuters reports, Google has a subsidiary called Google Energy, which the Federal Energy Regulatory Commission approved last year to buy and sell energy on the wholesale markets in exchange for Renewable Energy Certificates (RECs). These are tradeable certificates worth money on certain markets.

Eventually the company will also use these investments to power its huge data centers, which have emerged as major electricity hogs necessary to run the Internet giant's search engine, email and other online services.