Efficiency increase of photovoltaic systems by means of evaporative cooling in a back-mounted chimney-like channel

Abstract

An increased cell temperature due to solar irradiance causes a decrease in conversion efficiency of a solar cell, i.e., a loss in electrical output. In this study, we present a cooling method for a cell temperature decrease by means of water droplet evaporation in a chimney-like channel attached to the back side of a photovoltaic module. The system design process starts with shadowgraph imaging of various atomizer nozzles. The optimal atomizer nozzle is then integrated into a laboratory test setup for parameter studies of the cooling performance and of the water usage. A cooling approach with two pin-jet nozzles positioned at the inlet and outlet of the cooling channel facing each other yields the best result in terms of water usage per efficiency increase. The efficiency of the solar cell is increased by 8.7% consuming 9.2 l of water per hour and square meter of the photovoltaic module. The evaporation rate limits the amount of moisture absorbed by the air in the channel to only 10% of the water needed for effective atomization. The excess water settles as a water film in the channel and on the back side of the photovoltaic module, causing an additional film cooling effect. A comparison of the optimized cooling system with results from the literature for continuous water spray cooling shows six times less water usage per percent efficiency increase. With the use of the chimney-like channel, deposits such as moss or calcium do not occur on the front side of the photovoltaic module. Moreover, the risk of stress cracks in the glass surface due to temperature gradients is avoided. The current data give a strong indication that ongoing optimization with custom designed atomizer nozzles will further reduce the water usage towards a profitable system operation.