Apple is to invest $848 million in a solar project that will power its planned new headquarters in California.

The technology firm’s CEO Tim Cook said in February that it has signed a deal with First Solar, which is building the 280 MW California Flats solar farm in Monterey County, California. Apple will receive electricity from 130 MW of the solar farm under a 25-year power purchase agreement (PPA).

The PPA is thought to be the largest of its kind between a clean energy provider and a commercial end user, said First Solar. "Apple’s commitment was instrumental in making this project possible and will significantly increase the supply of solar power in California," said Joe Kishkill, Chief Commercial Officer of First Solar.

Construction of the California Flats solar farm is expected to start in mid-2015 and will be completed by the end of 2016. The facility’s remaining 150 MW of output will be sold to Pacific Gas & Electric under a separate long term PPA.

Apple already uses renewable energy to help power its data centres. It recently announced plans to invest over $2 billion over ten years to convert a failed sapphire glass plant in Arizona into a data centre powered mostly by solar energy.