I don't buy it that solar input would ever be greater than losses from evaporation. Here is why. It takes one BTU to raise the temperature of one pound of water one degree F, BUT for each pound of water that evaporates the remaining water will loose roughly 970 BTU's! That is a very big difference. Look at it another way, to raise the temperature of a pool that has 30,000 gallons by one degree requires roughly 250,000 BTU's of energy. That same energy is lost for each 31 gallons of water that evaporate from that 30,000 gallons pool.