Potential energy cost and footprint reduction in Mediterranean greenhouses by means of renewable energy use

Greenhouses are intensive agricultural systems and require optimum combination of solar lighting, heating, cooling and ventilation. Various methods are suggested for the control of internal space factors of greenhouses but require significant amount of energy. Photovoltaics integrated in the greenhouse roof could be used to supply a part of this energy with no significant effect on greenhouse crop yield. Accordingly, aim of this work is to present the potential reduction of the cost of energy needed for greenhouse heating and cooling in southern European and Mediterranean regions, by implementing renewable energy sources. Furthermore, the potential carbon footprint reduction resulting when using renewables compared to conventional energy sources is also studied. Thus, the integration of a PV system on the greenhouse roof for electricity production was studied and the effects on energy needs and greenhouse environmental impact were considered. Two case studies were considered for a 1 ha tomato greenhouse in central Greece: (a) covering a small percentage of the greenhouse roof (0.65%) by a PV system of about 10 kWp and (b) covering about 6.5% of the greenhouse roof by a PV system of 100 kWp. It was found that a PV system covering only 6.5% of the roof surface could be enough to completely cover the electricity needs for the auxiliary processes of a greenhouse. The estimated PV electricity production could reduce the life cycle impact of a greenhouse by 5-10%.