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 CarrosBy Geert De Clercq NICE, France (Reuters) – A major pilot project by Europe’s largest power network operator to integrate power from rooftop solar panels into the grid has shown that battery storage of renewable energy is not yet economically viable in Europe. The conclusion is a sobering one for proponents of sun and wind energy because as more of it comes on tap, better storage will be needed to keep the power produced when it is sunny and windy so it can be used at other times. The 30 million euro “Nice Grid” pilot is one of the biggest in a European Union-backed “Grid4EU” scheme in which France’s EDF, Italy’s Enel, Spain’s Iberdrola Czech Republic’s CEZ, Sweden’s Vattenfall and Germany’s RWE are testing the power grids of tomorrow.