California utility PG&E and BrightSource Energy have signed a deal that will expand the two companies’ solar power agreement.

This story from Fortune Magazine says the utility will buy 1,310 megawatts of carbon-free electricity to be generated by seven giant solar power plant projects – the world’s biggest solar deal to date. This latest deal comes after BrightSource made an agreement in February to provide 1,300 megawatts of power to Southern California Edison:

PG&E had previously signed a power purchase agreement with BrightSource in April 2008 for 500 megawatts with an option to buy another 400 megawatts. The new 1,310-megawatt deal will supply enough electricity to power about 530,000 homes in California.

Those are impressive numbers, but not an electron of electricity has been produced yet. BrightSource now faces the challenge of licensing, financing billions of dollars in construction costs and then building nearly a dozen large-scale solar power plants to meet a 2016 deadline for the Southern California Edison (EIX) contract and a 2017 completion date for PG&E (PCG). (The big wild card is whether transmission lines will be available to connect the power plants to the grid.) The first PG&E project is set to go online in 2012 with the first SoCal Edison solar farm to begin generating electricity the next year. Those first two power plants are part of a 400-megawatt complex BrightSource is planning for the Ivanpah Valley on the California-Nevada border.

The article goes on to say that the Oakland, California-based BrigtSource now holds more than 40 percent of the big solar contracts in the U.S.