Abstract
Shading in greenhouses is a simple and cheap method usually used to reduce the intensity of solar radiation and air temperature. Moreover, combining Photovoltaic (PV) panels and crops on the same cropland could alleviate the increasing competition for the agricultural land between food and energy production. In addition, the integration of PV with greenhouses could reduce, or partially replace the energy consumption for greenhouse crop production. Therefore, the aim of this study was to investigate the shading effect of semi-transparent mono-crystalline silicon double glazing photovoltaic panels (STPV), mounted on top of an agricultural greenhouse, which occupied 20% of the roof area, on the microclimate conditions and the growth of lettuce plants inside a greenhouse. Results showed that the combination of STPV and polyethylene cover decreased the solar radiation by 35% to 40% compared to the use of polyethylene cover only for clear days which was in the acceptable range of photosynthetically active radiation for lettuce plants. Moreover, STPV shading decreases the air temperature by 1°C-3°C and had no effect in the relative humidity under natural ventilation. Furthermore, there were no significant differences (p0.05) in the growth of lettuce plants between the shaded greenhouse by the STPV and the unshaded. Shading insignificantly increased the fresh weight, leaf area and the chlorophyll contents (p0.05). In conclusion, the integration of STPV modules can decrease the solar irradiation and the internal air temperatures as well as generate electric energy for environmental control systems without significant influence on the growth of lettuce plants. Meanwhile, it can decrease the water consumption by decreasing the evapotranspiration rate. Keywords: semi-transparent photovoltaics, greenhouse, shading, lettuce growth, microclimate, energy consumption DOI: 10.25165/j.ijabe.20171006.3407 Citation: Hassanien R H E, Li M. Influences of greenhouse-integrated semi-transparent photovoltaics on microclimate and lettuce growth. Int J Agric & Biol Eng, 2017; 10(6): 11–22.
Highlights
The protected cultivation in greenhouses has become the preferred system as a palliative way against global climate change
Results showed that the combination of Semi-transparent Photovoltaics (STPV) and polyethylene cover decreased the solar radiation by 35% to 40% compared to the use of polyethylene cover only for clear days which was in the acceptable range of photosynthetically active radiation for lettuce plants
In the last ten years there are a number of studies have been conducted by integrating PV modules on a certain areas of the agricultural greenhouses roofs to protect plants by decreasing the solar radiation, light intensity and air temperature inside the greenhouses as well as reduce, or partially replacing the energy consumption[5,6]
Summary
The protected cultivation in greenhouses has become the preferred system as a palliative way against global climate change. To provide the optimal air temperature, relative humidity, water, CO2 concentration and lighting inside greenhouses, the environmental control systems are required to achieve a high production while keeping the operational and energy cost at a minimum[1,2,3]. Heating and cooling systems are two major costs involved in greenhouses production. In the last ten years there are a number of studies have been conducted by integrating PV modules on a certain areas of the agricultural greenhouses roofs to protect plants by decreasing the solar radiation, light intensity and air temperature inside the greenhouses as well as reduce, or partially replacing the energy consumption[5,6]. Photovoltaic systems can decrease the greenhouse gas emissions as a highly attractive climate
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