Bill Gates helps power up green battery maker Aquion Energy

Bill Gates has become the latest investor to back an innovative new water-based battery technology, which promises to store power generated by intermittent renewable energy projects such as wind and solar farms.

Aquion Energy confirmed this week it has raised $35 million in a new funding round for its Aqueious Hybrid Ion batteries and energy storage systems, including an undisclosed sum from the billionaire Microsoft chairman.

The company claims that its batteries are an environmentally benign and cost-effective alternative to existing energy storage technologies that use salt water as an electrolyte rather than costly and hazardous chemicals.

The funding round was led by Bright Capital, while Gates participated as a new investor alongside Gentry Venture Partners. Kleiner Perkins Caufield & Byers, Foundation Capital and Advanced Technology Ventures also took part in the funding round as returning investors.

The $35 million will add to a $15 million loan facility that Aquion Energy closed last year and follows a $20 million funding round completed in 2011.

The money will be used to commercialize the battery technology with pre-production units expected to be delivered throughout 2013, leading to mass production from its Pennsylvania plant in early 2014.

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