Solar radiation inside greenhouses covered with semitransparent photovoltaic film: first experimental results

Abstract

The southern Italian regions are characterized by climatic conditions with high values of solar radiation and air temperature. This has allowed the spread of protected structures both as a defense against critical winter conditions both for growing off-season. The major energy source for these greenhouses is given by solar energy and artificial energy is used rarely. So the problem in the use of greenhouses in these areas, if anything, is opposite to that of the northern areas. In these places you must try to mitigate often the solar radiation inside the greenhouses with suitable measures or abandon for a few months the cultivation inside these structures. The solar radiation intercepted by passive means can be used for other purposes through the uptake and transformation by the photovoltaic panels whose use however is problematic due to complete opacity of the cells. New photosensitive materials partially transparent to solar radiation onto flexible media, allow to glimpse the possibility of using them to greenhouses cover, getting the dual effect of partially screen the greenhouse and use the surplus to generate electricity. The research was carried out to evaluate the possibility of using a flexible photovoltaic film realized by the University of Rome Tor Vergata (research group of ECOFLECS project coordinated by prof. Andrea Reale) for covering greenhouses. Two greenhouses in small scale were built: one covered with photovoltaic film and one covered with EVA film for test. In both greenhouses during the first research period it was grown a variety of dwarf tomato. The research was carried out comparing the solar radiation that enters into greenhouse in the summer (August 2012) and in winter conditions (December 2012) in both greenhouses. The result show that the average ratio between the daily global solar radiation under the photovoltaic film and outside radiation is about 37%, while between the radiation under EVA film and outside radiation is equal to approximately 63%. These result allow us to assert that during the hot season the use of photovoltaic film might be useful to mitigate the excesses of solar radiation into the greenhouse. During the cold season the use of this film not allows to achieve the minimum indoor climate conditions for the cultivation, however, it is possible to think to remove it in the periods of low solar radiation because it is a very flexible film.