BrightSource Energy has finalised $1.6bn in loans, guaranteed by the US Department of Energy (DOE), to finance construction of the world’s largest solar thermal power plant, the Ivanpah complex in the Mojave Desert in California.

Google has also made a $168m equity investment in the project, joining NRG Energy, which committed $300m in October to become the lead investor.

‘Ivanpah will be the largest solar power tower project in the world, able to produce clean electricity at the highest efficiency of any solar thermal plant,’ said Rick Needham, director of green business operations at Google.

‘We hope it can serve as a proof point and spur further investment in this exciting technology.’

The technology works by using an array of rotating mirrors, called heliostats, to focus the sun’s rays at the top of a tower, where the heat generates steam.

Ivanpah’s Power Tower will be approximately 135m (450 ft) tall and will use 173,000 heliostats, each with two mirrors.

Construction began in October 2010 and is expected to be complete by 2013. Power form the project will be purchased by two Californian utilities, Pacific Gas & Electric and Southern California Edison.

‘The loan guarantee from the DOE for the Ivanpah project provides vital support for building this utility-scale solar thermal project,’ said Fong Wan, senior vice president of energy procurement at Pacific Gas & Electric.

The development has been criticised by environmentalists over its impact on the rare desert tortoise. Forty-three tortoises have been moved from the site, but an estimated 100 remain, according to Associated Press.