Not renewable but..
http://www.forbes.com/sites/christopherhelman/2014/07/02/dean-kamen-thinks-his-new-stirling-engine-could-power-the-world/?utm_campaign=techtwittersf&utm_source=twitter&utm_medium=social
@hippy started
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Not renewable but..
http://www.forbes.com/sites/christopherhelman/2014/07/02/dean-kamen-thinks-his-new-stirling-engine-could-power-the-world/?utm_campaign=techtwittersf&utm_source=twitter&utm_medium=social