Effect of integrating photovoltaic panels with greenhouses for energy production on greenhouse microclimate, and cucumber growth and production in the greenhouse

The growing scarcity of fossil fuel resources, the imperative to reduce greenhouse gas emissions, and the urgent need to address global climate change all call for implementing sustainable technologies to advance climate-smart agriculture for food security and energy production. One significant challenge facing PV greenhouses is to efficiently generate energy and grow crops on the same plot of land while minimizing the shadow cast over the plants by the photovoltaic (PV) panels. Therefore, this study was conducted through a project "Climate-smart Agriculture for Enhancing the Sustainability of Greenhouses Under Climate Change" funded by the Science, Technology & Innovation Funding Authority (STDF). This study investigates how the shading of photovoltaic panels and their distribution above the greenhouse roof covered with white net saran affects the growth and yield of cucumber plants in a greenhouse environment. Moreover, to study the effect of these PV panels on microclimate parameters in the greenhouse such as shading distribution, solar radiation distribution, light intensity, and air temperature under the PV panels, as well as estimate the generated energy. This study used two photovoltaic panel types to cover the east-oriented greenhouse roof for energy production. The first was solid photovoltaic panels which are used on a commercial scale. The second was the semi-transparent photovoltaic panel that resulted from cooperation between this project and Jet Solar company for solar energy and produced a prototype as the first product in Egypt to cover greenhouses for energy production. The semi-transparent PV panel contains two transparent regions and three vertical strips from a polycrystalline silicon solar cell. The transparent region is 55% of the total area of the semi-transparent PV panel. The photovoltaic panels were installed on the eastern side of the greenhouse roof at a tilted angle of 30°to provided sufficient electrical energy and distributed in 3 systems, which are solid photovoltaic panels in a row pattern, solid photovoltaic panels in a checkerboard pattern, and semi-transparent photovoltaic panels in a row pattern. The percentage of the covered area with these photovoltaic panels was about 30% of the roof area of the greenhouse. Differences were observed in the percentage of shading, size of the shaded area, distribution of solar radiation, and light intensity during the day associated with sunrise and sunset in different PV treatments where the shading was reached a maximum of 40% of the experimental area at midday in solid photovoltaic panels in a row pattern and a checkerboard pattern that the shading density was intense while, the shading in semi-transparent PV panels in a row pattern reaches 20% of the experimental area, and the intensity of shading was light. The results indicated that the integration of semi-transparent PV panels in the greenhouse roof led to decreased light intensity, solar radiation, and temperature conditions in the greenhouse to a lesser extent than integrating solid PV panels due to the semi-transparent PV panel containing a transparent region that reaches 55% of the area of this photovoltaic panel. This resulted in the enhancement of cucumber plant characteristics such as plant height, number of internodes, internodes length, fruit length, fruit weight, number of fruits, and yield compared with the use of the solid photovoltaic panels in a row pattern or a checkerboard pattern. the results revealed that the estimated electric energy of 18 semi-transparent panels was 323.08 kW/year which indicated that these semi-transparent panels are suitable for greenhouses in high-irradiation regions where electricity production may be high which covers all the ventilation and cooling systems and irrigation control. Therefore, this study accentuates that the integration of semi-transparent photovoltaic panels in a row pattern above the greenhouse roof is the new shading method that involves shading, avoids the loss of solar radiation, achieves a more homogeneous light distribution from photovoltaic panels, and energy production to control the greenhouse microclimate to confront and adapted with climate change without any damage to the plants for ensure the food production.