Sistema de mejora de la eficiencia de paneles solares fotovoltaicos mediante refrigeración geotérmica

Abstract

Photovoltaic solar energy has become one of the safest and most economical sources of energy available. Despite this, the efficiency values of commercial solar panels rarely exceed 20%, and this number is further reduced due to overheating. Overheating of solar cells under normal operating conditions considerably reduces their efficiency. In this thesis, a novel cooling system for photovoltaic solar panels, based on low enthalpy geothermal cooling, is designed, theoretically described, and experimentally validated. The proposed system dissipates the excess heat generated in the solar cells inside a panel during its normal operation by means of a single-phase closed circuit refrigeration system that uses the underground as a heat sink. A prototype of the technology has been designed and manufactured, aimed at photovoltaic generation plants with a single-axis sun tracking mechanism, to increase the maturity of the technology and verify the technical and economic feasibility of the proposed system. Said prototype was tested under relevant operational circumstances and different environmental conditions in Alcalá de Henares, Madrid, Spain. In this location, the underground temperature is stable and equal to 16±2 °C at relatively low depths throughout the year. Additionally, the heat exchange with the subsoil is improved thanks to the presence of an aquifer, located at a depth of approximately 4 m below the surface in the test area. It has been proven that, thanks to the proposed cooling system, it is possible to significantly reduce the temperature of the solar panels by up to 20º C in the tested conditions, using a coolant flow of 1.84 l/min per each square meter of solar panel. This temperature reduction results in a significant improvement in the net efficiency of the system. Compared to a standard uncooled solar panel, operating under the same conditions, a maximum net efficiency improvement during the summer season of up to 13.4% has been measured, with daily average net efficiency improvements of up to 9.4%. An average annual increase of the net power generated by the system around 5.9% has been experimentally determined, in good agreement with the theoretical calculations, which demonstrates the technical feasibility of the proposed concept. The correlation between the efficiency improvement and the environmental conditions, refrigeration flow, and performance and energy consumption of the refrigeration system pump has also been determined. Finally, other potential benefits of the technology have been observed, such as the reduction of the temperature range reached by the solar panels throughout the year and the reduction of the thermal gradient between the front and rear surfaces of the panels.