Feasibility study of a combi-pv panel for greenhouse energy supply and water recovery by nightly radiation towards the sky

In southern European areas, characterized by high irradiation, the use of water for both evaporative cooling systems and hydroponic fertigation, represents a serious drawback for crop cultivation under cover. Water recovery systems seem to be an attractive solution, especially when they are integrated in the greenhouse construction. In this research, a feasibility study of applying a water recovery system driven by a combi-PV panel, in a semi-closed greenhouse was carried out. The prototype combi-PV panel was made by coupling an amorphous silicon panel with a sump stacked on the rear PV panel surface and filled with saline water. The system is driven by a cold-heat sink which is the PV panel itself. During night, the combi-PV panel exploits the radiative cooling of a ‘gray’ surface towards clear sky, chilling the water in the sump. In opposition, during day-time, the water in the sump is heated at a temperature higher than the environment. Thus, the water vapour will be condensing on the rear panel surface during night, being the warm air circulation facilitated by bouyancy effect. The evaluation of the system is in progress in order to assess the real amount of energy irradiated and consequently the water-drips to be collected on a proper surface inside the sump. The condensed water can be mixed with saline water to reduce the salinity and be used for fertigation.