California utility Pacific Gas and Electric Co and solar firm BrightSource Energy Inc. on Wednesday announced the expansion of a solar thermal plant deal that will eventually generate 1,310 megawatts of clean energy from a previous agreement of 900 megawatts.

The agreement consists of seven solar thermal projects that when completed, will generate a total of 3,666 gigawatts of power annually, the equivalent electricity consumption of 530,000 average homes in one year.

Solar thermal plants use the sun's heat to produce steam that powers a turbine which generates electricity. BrightSource's technology consists of a boiler that sits at the top of a tower where the energy of the sun is converted into steam.

Today's agreements reflect the technological milestones that the BrightSource Energy team has achieved over the past year, John Woolard, CEO of BrightSource Energy said in a statement Wednesday.

The deal advances PG&E efforts to meet California's renewable energy standard in which utilities are required to purchase at least 20 percent of their electricity from alternative energy sources by 2010.

The BrightSource and PG&E deal is an expansion of a previous contract they had for 900 MW.

The first 100 megawatt plant will be built in Ivanpah, Calif. starting in about six months. However the project has yet to gain approval from the California Energy Commission and the Bureau of Land Management.

Our key areas of focus will be on permitting, financing, and then constructing and operating these solar power plants. I have the utmost confidence in our experienced and time-tested team to make this happen, Woolard said.