Modeling of photovoltaic cell temperature losses: A review and a practice case in South Spain

To determine temperature losses in a photovoltaic (PV) installation, the operating temperature of the cells in the PV panels must be known. This temperature cannot be directly measured because the cells are not accessible from the outside, as they are inside the panels, with other layers of material surrounding them. Therefore, the parameter to which direct access exists by means of measuring is the temperature of the outer surfaces of the modules. However, the cell junction temperatures are typically 1-3 degrees C higher than the temperature measured on the module's rear surface, depending on the module construction. Some methods exist for determining the cell temperature, including measuring the open-circuit voltage of the panels, but because this is difficult to do with an on-site PV installation, normally this temperature is determined by using models. Numerous models appear in the literature for determining the cell temperature, so in this paper, a recompilation of twenty models is taken into account for determining the temperature and miscellaneous losses of a PV installation located in South Spain in a year's time. These models have different relations between the value of the cell temperature and some environmental parameters, considering or not the value of the wind speed and the form in which the panels are installed. A maximum difference in annual temperature losses found using the twenty models was 90.4 h/year. This non-negligible quantity indicates the importance of an appropriate choice of model and the correct conditions for applying it to make a precise estimation of the capture temperature losses. Moreover, it would be interesting to reach an agreement on the best procedure for determining this type of losses, especially for correctly performing comparisons of these losses in different PV plants in operation, which can reach very significant values in locations with high temperature registers.