Renewable energy sources and greenhouse industry: trends and perspectives

The use of renewable energy sources to feed greenhouse equipment can increase the environmental sustainability of greenhouse industry, and can guarantee stable energy costs for farmers. Based on the experiments carried out over the recent years at the University of Bari, the paper presents the suitable solutions concerning the applications of renewable energy sources to supply greenhouse heating and cooling systems. Solar thermal systems, photovoltaic solar cells and wind turbines were analyzed among the renewable energy sources. Solar thermal systems produce hot water and have a high energy exchange ratio with relatively low installation price. Solar thermal systems can be integrated in the existing greenhouse heating systems, which use warm water and are fed by fossil fuels, such as diesel fuel or gas. Photovoltaic systems are applicable during warm periods to feed greenhouse cooling systems which use electricity, i.e. forced ventilation, fog and pad evaporative systems. During cold periods electricity generated by photovoltaic modules could be applied to supply innovative heating systems based on ground-source heat pumps and pond water heat pumps. The main drawback of photovoltaic systems concerns the high costs related to the poor efficiency of the solar cells. The performance of photovoltaic systems can be improved by means of photovoltaic concentrators which use less expansive lens or mirrors as receiving surface in place of solar cells. The use of the wind energy appears cost-effective using large size high performance wind turbines in power plants with a size of several MW, but the technical management of large wind turbines doesn’t seem suitable for greenhouse farmers.