each of multiple solar cell arrays has a face oriented differently relative to the direction from which solar radiation is incident on a motor vehicle and a characteristic voltage / current output correlated with the intensity of incident solar radiation for converting the incident solar radiation into electricity . a processor processes data related to the voltage / current output from each array as the array is converting solar radiation into electricity for selectively connecting the arrays in configurations correlated with the intensity of incident solar radiation . the arrays provide supplemental electricity to keep the vehicle battery charged preventing certain small loads from draining the battery while the vehicle is parked with its engine off . the arrays can be advantageously mounted in outside rearview mirror assemblies .