A technician demonstrates a utility-scale battery that can store the energy produced by solar panels on the roofs of houses as part of Nice Grids, a smart solar district demonstration project, in Carros, southeastern France, June 12, 2015. On the French Riviera, Europe's biggest electricity network operator is trying out the smart grids of the future but its project of linking solar panels to batteries is not yet ready for commercial roll-out. In the village of Carros north of Nice, ERDF - a unit of state-owned utility EDF - has connected a range of batteries to solar panels in households and companies and huge utility-size batteries to its local power distribution network. Picture taken June 12, 2015. REUTERS/Eric Gaillard