A Photovoltaic Greenhouse with Passive Variation in Shading by Fixed Horizontal PV Panels

Simona Moretti,Alvaro Marucci

doi:10.3390/en12173269

Abstract

The traditional shading systems that greenhouses use cause some of the solar radiation that is reflected or absorbed to be lost and, therefore, not used by the plants under cultivation. An interesting solution to these problems is to position photovoltaic (PV) panels on the roofs of greenhouses. All of the photovoltaic greenhouses that have been realized in Mediterranean areas are characterized by a fixed position of the PV panels and excessive shading, especially in autumn and winter. The purpose of this study is to describe a prototype of a photovoltaic greenhouse with both fixed and horizontal PV panels that exploit the natural variation in the elevation angle of the sun’s rays during the year to allow for “passive” variation in shading. The considerable variation in the elevation angle of the sun’s rays (from 24.4° to 71.1°) results in a high variation in shading (from 39.4% to 72.6%), with the highest values in the summer months and the lowest values in the winter months. This trend is favorable for meeting the photosynthetically active radiation (PAR) needs of greenhouse plants. If the plants under cultivation require more solar energy, it is necessary to increase the distance between the panels. We implement a specific mathematical relationship to define the precise distance to be assigned to the photovoltaic panels on the roof pitch.

Highlights

Climate changes in recent decades have been causing adverse weather conditions to occur more frequently
We implement a specific mathematical relationship to define the precise distance to be assigned to the photovoltaic panels on the roof pitch
By applying Formula (6), we found that to reach the maximum solar radiation threshold required by the plants listed in Table 2, the distance between the panels on the roof pitch of the studied prototype greenhouse should be increased by 15 cm, from 27 cm to 42 cm

Summary

Introduction

Climate changes in recent decades have been causing adverse weather conditions to occur more frequently. Crops in the open field are subject to strong tensions that can cause deficits in agricultural production and undermine the satisfaction of growing demand All this requires the cultivation of a substantial number of crops in a protected environment. The parameters that characterize the microclimate inside the greenhouse can be kept under control thanks to specific cooling and heating systems; it is not possible to do the same with open-field crops [3]. In this way, greenhouse cultivation can be functional [4] and predictable [5]. In winter or during the night, the temperatures are reduced and not favorable to growth; heating systems are needed [7]

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Conclusion