While there are still a number of critics of Elon Musk’s $2.6-billion move to merge electric car and battery maker Tesla with the struggling SolarCity, the serial entrepreneur’s vision for the merged entity seems compelling. SolarCity’s rooftop solar panels will produce enough electricity to store in Tesla Powerwall home batteries for night-time use, while the Telsa electric car will be charged in the garage overnight. At least in theory, that sounds very much like solar synergy in the making.