The possibility of adding solar panels to the roof is not possible for the Reva E2O or you can say its legally impossible to do so. The batteries of the car are made with some limitations and they cannot be used for multiple energy sources like sun and electricity easily. Also, the weight of solar panels and other equipment's need testing before using on any vehicle, making it a long and hectic procedure. The space in the electric car is still limited and installing some new equipment will end up the feasibility factor also.