Stabilization of the temperature in a greenhouse using a Geothermal-Battery-Energy-Storage (GBES) system

•The capital costs are estimated with considering an electricity price of 0.07 USD/kWh.•A GBES was proposed to store solar energy in daytime and extract heat at night.•Temperature in a greenhouse was effectively stabilized using a GBES.•Greenhouse insulation is a useful measure to prevent heat loss.•The imbalance of heat storage and extraction causes soil temperature fluctuation.•An intermittent operation of GBES saves input energy significantly. Solar and geothermal energies have been widely used for heating greenhouses over the past decades. However, the solar energy was not available at night and the geothermal energy was often supplied at high capital costs. To improve the cost-effectiveness, we propose a novel Geothermal-Battery-Energy-Storage (GBES) system which uses solar heat storage with geothermal energy for heating a greenhouse. Three operating modes of the system were tested. In Mode A, the GBES-based greenhouse has a temperature of 3.7°C higher than a conventional greenhouse. By covering a double-layer membrane for the greenhouse, in Mode B, its temperature is even 6.6°C higher than that in Mode A, because the insulation of the system prevents heat loss effectively. When further heating the system in an intermittent manner, Mode C maintains the same energy efficiency as Mode B, but saving the input energy by 40%. Moreover, the Coefficient of Performance (COP) of the GBES system can reach up to 5.9, which is 1.6 times higher than a conventional geothermal greenhouse, and at a remarkably low capital and operating cost. The GBES system shows the promise in stabilizing the temperature of a greenhouse at a low cost.