Active cooling of a photovoltaic module in hot-ambient temperatures: theory versus experiment

Abstract

Abstract The performance improvement of a PV-module is investigated theoretically and experimentally in a long-term research-plan via module cooling by different approaches including passive, active, and evaporative cooling as well as water cooling for the same module. In the present paper, the investigation is conducted to decide on the suitability of active-cooling of the module in hot-ambient temperatures. A module without cooling is used as a base case for comparison against cooled modules with and without fins attached to the module’s rear-surface and extended down in an air-cooling duct underneath the module. At first, a theoretical study of heat transfer through the module is conducted to investigate how the calculated cell temperature and module output power are influenced by the air velocity from a blower, ambient temperature and solar irradiation. The results showed a decrease of cell temperature by about 7–10 °C with a subsequent increase of electrical efficiency. The cell temperature decreases significantly with the increase of duct height and with the increase of the number and length of fins, the same as in passive cooling. The cell temperature decreases by more than 3 °C at duct height of 0.2 m. The calculated values of cell temperature, open-circuit voltage and short-circuit current of the module with and without active cooling agreed reasonably with the present measured values over the day hours of two successive days in summer season. At air velocity of 1.5 m/s, the increase of electrical efficiency by active cooling was found 0.67–0.80 %. Further increase of air-flow velocity or duct-height in active cooling seeking higher efficiency is not recommended due to increase of consumed electric power by air-blower and limited decrease of cell temperature. This concludes that air cooling is not effective in regions of hot ambient temperatures. For a non-cooled module, the cell temperature is related to the ambient temperature in terms of the solar radiation and NOCT, the datasheet value of normal-operating-cell-temperature. The relationship is modified in the present paper to account for air-flow through the duct seeking its extension for application to air-cooled modules.