While running, there is no additional "waste" heat: Without solar panels, 100% of the sun rays heats the earth; with solar panels, 20% is converted to electricity, and then converted to heat again.
Not quiet 100%×(1-albedo) heats the earth. So solar panels have a lower albedo then some surfaces so it just might heat the earth more but the CO2 not emitted reduces the isolation (green house effect) of earth and can therefore lead to a net reduction in temp.