Off Grid Electric, a San Francisco-based company that develops rooftop solar and battery systems in Africa, has raised $55 million as it expands into Ghana.

The Series D round was led by Helios Investment Partners and included GE Ventures, the venture capital subsidiary of General Electric Co., Off Grid said in a statement Thursday. The company's Ghana expansion is part of a partnership with Electricite de France SA.

Just as mobile phones bypassed landlines in developing countries, off-grid solar and battery systems are viewed a way to provide power to more than 600 million people in sub-Saharan Africa. The declining price of panels has allowed startups including Off Grid to offer consumers pay-as-you go leasing options that compete in price with traditional kerosene lamps and diesel generators.

"The fundamental economics drive this all," Xavier Helgesen, co-founder and chief executive officer of Off Grid, said in an interview. "I keep telling people that an electron from a solar panel is the cheapest electron you are going to find pretty much anywhere in the world."

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