Ultra-low energy reverse osmosis with thermal energy recovery from photovoltaic panel cooling and TFC RO membrane modification

The electrical efficiency of solar photovoltaic (PV) panel decreases with increase in its temperature, and therefore transfer of heat from the panel is very important. The capitalization of the transferred heat for useful purpose is of prime importance since the conventional solar PV panel has the conversion efficiency of only 5-17%, and therefore the larger part of incident solar radiation remain unutilized. The present paper addresses the temperature control of solar PV panel by direct contact heat exchange with flowing feed water to reverse osmosis (RO) from top of the panel, thus recovering energy together with improving the performance of PV panel. The RO at higher temperature resulted in the improvement in the flow performance of the membrane. Further, the modification in membrane morphology by controlled sodium hypochlorite treatment improved the flow performance by increasing hydrophilicity of the membrane as evident by decline in contact angle from 48.05 degrees to 26.22 degrees. Thus, a two-pronged technique of controlling the PV panel temperature by heat transfer and tuning the membrane morphology toward more hydrophilicity helped in significant improvement in RO permeate flow and better electrical performance of PV panel. As a result, the overall energy consumption of RO has been reduced by about 40%. This novel approach opens up the avenues for significantly reducing the overall energy consumption for brackish water RO systems.