Energy Demand of Supplementary Lighting in Agricultural Greenhouses: Solar Energy Utilization

Light is a critical parameter for plant growth such that providing enough light for the plant can ensure better quality and higher yield in greenhouses. In many areas, in the cold seasons of the year, not enough natural light reaches the plant. Thus, to compensate for the natural light deficit, artificial light is used. Since the use of artificial light leads to energy consumption, effective parameters in the energy consumption of the lighting system such as available natural light, greenhouse shape, and the on-off plan of the lighting system should be considered. In this paper, available natural light is estimated based on greenhouse structure in five cities of Iran. Then, the natural light deficit was investigated. Finally, to achieve clean cultivation, the utilization of photovoltaic panels is investigated to compensate for the electrical energy needed for supplementary lighting. The results show that although Iran is recognized as a region with high solar energy potential, natural light is not enough for optimum tomato lighting demand. Using supplementary lighting in greenhouses could compensate for the lack of natural light in proportion to the capacity of the lighting system. In 73.22 % to 91.32 % of days in the period of September to April, the natural light is not sufficient for optimum lighting. Therefore, 98  to 377  electricity is needed to supply power for supplementary lighting system. Accordingly, the photovoltaic area and its associated with costs to compensate electrical energy consumption for the supplementary lighting is estimated to be 0.47  to 2.58  per m2 of greenhouse area, which is equal to $ 171.08 to $ 939.12 per m2 of greenhouse area, respectively.