Thermal energy assessment of a small scale photovoltaic, hydrogen and geothermal stand-alone system for greenhouse heating

This experimental study shows the results of an analysis of the performance of a stand-alone renewable energy system for greenhouse heating on a winter day. The systems consist of photovoltaic panels connected to an electrolyzer which during daylight hours produce hydrogen by electrolysis and then store it in a pressure tank. During the night, thanks to a fuel cell, the hydrogen is converted into electricity in order to feed a ground source geothermal heat pump to heat a tunnel greenhouse. The procedure for estimating hourly solar radiation, hydrogen production and consumption for short-term energy storage on a partly cloudy day is also given. The solar energy usability concept, the capacity of energy storage systems and the thermal energy load govern the effective energy management of the system. This performance analysis is necessary to determine the actual total efficiency of integrated photovoltaic, geothermal and hydrogen renewable energy systems and their contribution to the load. The overall system efficiency obtained, starting from the amount of solar energy available during daylight hours until it is used as thermal energy at night, was 11%.