Search and advertising giant Google is investing $10 million in a relatively new approach to producing electricity from underground heat which could make geothermal power possible in many more areas of the world.

Google's philanthropic arm, Google.org, has recently declared an interest in sustainable technology. It has already pumped tens of millions of dollars into solar thermal and high-altitude wind energy.

Dan Reicher, Google's head of climate and energy initiatives, said that new technology could make extracting heat from beneath the ground a massive contributor to US electricity supplies.

"It's 24-7, it's potentially developable all over the country, all over the world, and for all that we really do think it could be the 'killer app' of the energy world," says Reicher. "Killer app" is a term used in the tech industry to describe an application that revolutionises a field and creates new opportunities.

Hot water

That new "app", called enhanced geothermal systems (EGS), improves upon the century-old technology of tapping geothermal energy from geysers or hot springs to generate electricity. With EGS, engineers drill shafts down to hot rocks and pump in water to create steam to power a turbine.

The bulk of Google's first geothermal investment, $6.25 million, will help finance EGS company AltaRock Energy of Sausalito, California. The firm has also attracted money from some of the best known Silicon Valley venture capitalists.

A further $4 million of Google's money will go to Potter Drilling in Redwood City, California, which has a hard rock drilling technology.

AltaRock hopes to develop technology that can generate electricity in a wider range of geographies than conventional geothermal ones. "If you drill deep enough anywhere you can get to hot rock," says Reicher.

Finding places where hot rocks lie close to the surface can reduce the cost of such projects. Nevada is one such place, Reicher said, while some eastern US states including West Virginia and Pennsylvania also have good geothermal prospects.

Google also awarded nearly $0.5 million to Southern Methodist University's Geothermal Lab in Dallas, Texas, to update geothermal mapping of North America.