Photovoltaic cogeneration. Experimental analysis of different modules.

Commercial photovoltaic modules have nowadays an efficiency around 12%-14%. It means that the most relevant part of solar radiation is lost. Such a remark gets more importance if the active surface is located in an urban environment, where the availability of surfaces exposed to the sun is scarce if compared to the buildings thermal loads. PhotoVoltaic / Thermal cogeneration (PV/T) aims to utilise the same area both for producing electricity and heat. The main problem of this technology is that solar cells are sensitive to temperatures and their efficiency lowers when temperature increases. Therefore heat cannot be collected at high temperatures. Nonetheless if a moderate temperature of heat collection is selected, it can be beneficial for electricity production as it can be lower than the equilibrium temperature reached under insolation by a bare panel. Against some problems that have to be faced (good thermal behaviour of the module studying the best thermal exchange between the solar cells and the channelled plate below, selection of the best working temperature according to the need of the plant served by the solar modules, selection of the best fluid to remove heat), PV/T technology seems to offer very interesting prospects, also considering recent economic incentives on renewable energies issued in Italy. The paper reports on an extended survey on electrical and thermal efficiency of some PV/T prototypes, carried on at the experimental testing rig built up in Vicenza, to understand working limits varying some parameters (solar radiation, water flow, inlet water temperature) and improve the efficiency.