Google's investment in geothermal is the latest string of green initiatives by a company with a stated goal of becoming carbon neutral.

Here is a run-down of Google's recent green investments and initiatives.

Nanosolar: Google invested in this revolutionary thin-film photovoltaic technology, which is solar, but without the need for a panel. Inventors claim this solar technology can generate electricity at a cost point lower than coal generation. Nanosolar is based in San Jose, California.

Geothermal: Google have invested in two companies in the geothermal space, AltaRock Energy Inc, and Potter Drilling Inc. These companies provide a lower cost alternative to conventional geothermal production by pumping water onto hot rocks found beneath the earths surface, and then pumped back up into power plants, where the heat is extracted and used to generate electricity.

Wind: Of all renewable technologies, high altitude wind has the largest amount of energy per square foot. It is estimated that by capturing a small fraction of this energy, using giant kites, this technology could supply the energy needs of the entire planet. Google have invested in Makani Power Inc, based in Alameda, California.

Thermal Solar:  Replaces the need for fuel in a traditional power plant. Aimed at large utilities, this concentrating solar technology also aims to hit a price point lower than coal. Google have invested in eSolar, based in Pasadena, California, and BrightsourceEnergy, in Oakland, California.

Google have also undertaken green initiatives in-house, including evaporative cooling for data centres, replacing incandescent bulbs with higher-efficiency lighting, and building one of the largest corporate solar panel installations in the United States.

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