Distribution of Solar Radiation on Greenhouse Convex Rooftop

Joseph Appelbaum,Avi Aronescu

doi:10.3390/su12177197

Abstract

Photovoltaic greenhouses became popular in many countries for growing crops and, at the same time, generating electricity mainly for own usage to control the air temperature inside the greenhouse. Solar radiation is essential for their photosynthesis process for crop growing, however, high levels of solar radiation may adversely affect the crop quality. Therefore, a balance between the need for sufficient solar radiation for plant grows and the need for electricity is important to maintain. Many greenhouses are built with curved rooftops of convex shapes and flat-plate photovoltaic (PV) modules are deployed on the rooftops. The present study proposes using flexible PV modules adhering to the curvature of the roof. The incident solar radiation on a curved surface is not uniformly distributed along the surface, therefore the density of the solar irradiation attains higher levels at regions where the PV modules may be deployed to generate greater amounts of electric power. The present study determines the density variation of the solar irradiation, in Wh/m2, (direct beam, diffuse and global) along the curvature of the convex surface of the greenhouse, and proposes the location of the PV modules to be deployed on the roof to obtain desired levels of solar radiation needed for designing the PV systems. North-south and east-west greenhouse orientations are considered.

Highlights

The popularity of the cultivation of vegetables and fruits in greenhouses is recently growing worldwide
A photovoltaic (PV) greenhouse may be considered an example of Building Integrated Photovoltaic (BIPV) system in the sense that BIPV simultaneously provides both shading for reducing cooling loads and for electric power generation
Solar radiation is essential for the photosynthesis process for crop growing, on the other hand, PV modules may cast shadows inside the greenhouse blocking light to the crops

Summary

Introduction

The popularity of the cultivation of vegetables and fruits in greenhouses is recently growing worldwide. The purpose of BIPV on rooftops is to fully utilize the roof area for electric power generation, whereas integrating a PV module on the roof of a greenhouse is to generate sufficient electricity mainly for environmental control of the inside air temperature. One has to seek a balance between the need for sufficient light for plant growth and the need for electricity for controlling the environment inside the greenhouse. For this reason, research on photovoltaic greenhouses concentrates on the percentage of shading by the PV modules on the roof that is compatible with each type of crop. The influence of whitening a greenhouse roof on the microclimate and yield of tomato crops was analyzed in [11]

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