benefits of a PV powered solar controller comes at a cost in reduced system performance in the range of 1-10%. This is due to heat losses at times when the panel may be hotter than the water store but there is insufficient sunlight to power the pump. This happens mainly on hot days when hot water is likely to be in excess so the potential reduction is less significant than it would be at times when the store was cooler. References Further reading Martin C, Watson M (2002). "Further Testing of Solar Water Heating Systems" (PDF). United Kingdom Department of Trade and Industry. Retrieved on 2007-08-04. External links The Solar Trade Association Solar Installation Heating, ventilation, and air conditioning Solar thermal energy Photovoltaics