Duke Energy (NYSE:DUK) is expanding its exposure to solar power.

On Wednesday, the electric utility announced that it's adding to its nearly 100 megawatts of solar generating capacity by buying two Californian solar power projects from Germany's SolarWorld. The solar farms in question, designated Highlander Solar 1 and 2, target production of 21 MW of electricity when they go on line -- sufficient power to supply 4,000 homes with electricity. Duke Energy Renewables President Greg Wolf says that when combined into a single solar farm under Duke ownership, they will constitute "the company's largest commercial solar farm in the nation."

Duke says it has already lined up Edison International (NYSE:EIX) subsidiary Southern California Edison to buy the power generated by the farm under a 20-year-long power purchase agreement.

Financial terms were not disclosed.

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