Southern California Edison on Thursday received approval from state regulators to proceed with one of the largest wind power contracts in the nation.

The California Public Utilities Commission approved the contract between Southern California Edison, a unit of Rosemead-based Edison International, and Alta Windpower Development, a subsidiary of Allco Financial Group Inc. of Australia.

The 20-year contract, signed in late 2006 calls for Alta Windpower to start delivering 250 megawatts a year of energy from its wind farm in the Tehachapi Mountains in 2010. The amount of power increases over following six years until it reaches 1,500 megawatts a year. A megawatt can power about 700 single family homes.

Edison and the state’s other investor-owned utilities are required to have 20 percent of their power come from renewable sources by the end of 2010. At full capacity, the Alta Windpower contract would cover about half of that amount.

“This contract represents a substantial step toward meeting our renewable power and long-term greenhouse gas reduction goals,” said Michael Peevey, president of the Public Utilities Commission.

In March, Edison announced it was spending $1.8 billion to build more transmission capacity to bring energy from the Alta Windpower wind farms to Edison’s existing grid starting in 2013.