Energy Use Efficiency and Carbon Footprint of Greenhouse Hydroponic Cultivation Using Public Grid and PVs as Energy Providers

Abstract

As the greenhouse cultivation industry considers new ways to reduce energy demand and increase sustainable production, the global energy crisis constitutes a major issue. In this paper, two different energy sources for heating and cooling the root zone area of baby leafy vegetables grown in hydroponic tanks by resistors and chillers, respectively, were compared in order to fully cover power demand. The energy needs in the first case were met by the public electricity grid, while in the second case, the energy needs were covered by a photovoltaic system. The greenhouse was equipped with photovoltaic panels, an inverter, a charge controller and a storage system. The target-value of the root zone temperature was 22 °C. Data on solar radiation, root zone temperature, air temperature and humidity from the indoor and outdoor space of the greenhouse were recorded, and the energy production and carbon footprint for different seasons of the year were evaluated along with the crop yield. The results showed that the energy provided by solar panels was able to cover 58.0%, 83.3% and 9.6% of the energy for heating or cooling the root zone area during the spring, summer and winter periods, respectively. Regarding the carbon footprint of the energy used between the two systems, the system with the PV had a substantially lower value, which was calculated at 1.6 kg CO2-eq kg−1, compared to 49.9 kg CO2-eq kg−1 for the system with PPG for the whole year.