Electric car pioneer Tesla unveiled a "home battery" last week which its founder Elon Musk said would help change the "entire energy infrastructure of the world". Environmentally-conscious German customers are targeted as potential buyers of the product.The Tesla Powerwall, unveiled on Thursday (30 April), can store power from solar panels, from the electricity grid at night when it is typically cheaper, and provide a secure backup in the case of a power outage.In theory the device, which typically would fit on the wall of a garage or inside a house, could make solar-powered homes completely independent of the traditional energy grid.