An algorithm for calculating the shade created by greenhouse integrated photovoltaics

Energy, Ecology and Environment (2024) 9(3):272–300 https://doi.org/10.1007/s40974-023-00306-4 ORIGINAL ARTICLE An algorithm for calculating the shade created by greenhouse integrated photovoltaics Theodoros Petrakis1 · Vasileios Thomopoulos2 · Angeliki Kavga1 · Athanassios A. Argiriou3 Received: 4 July 2023 / Revised: 11 November 2023 / Accepted: 13 November 2023 / Published online: 30 December 2023 © The Author(s) 2023 Abstract Integration of photovoltaic modules into greenhouse roofs is a novel and intriguing method. The cost of products grown in greenhouses is particularly high because of their high energy consumption for heating and cooling, and at the same time the increase in demand for available land, increasing its cost and creating spatial issues, the integration of photovoltaics on the roof of greenhouses is a highly viable solution. Simultaneously, the use of solar radiation is critical to maintain optimal crop development, while also being a renewable energy source. However, photovoltaics reduce the incoming solar radiation in the greenhouse, due to their shade. Shading can be either beneficial for the crops or not, depending on the crop type, thus it is vital to find the shading caused by photovoltaics both temporally and spatially. In this study, a model calculating the shading in a greenhouse due to roof-integrated photovoltaics is developed, based on the Sun position, the geometry of both the greenhouse and of the roof-integrated photovoltaics and their position on the greenhouse roof. Calculating the coefficient of variation of radiation data, for the shaded and unshaded areas using the proposed algorithm, it was found the coefficient of variation for the shaded areas is lower than that for the unshaded areas for a least 76% of the time. Also, the radiation values under the shaded area are more uniform. The proposed model is a tool for PV designers, operators, and owners, in order to optimize the potential of their solar panel installations. Keywords Shading · Photovoltaics · Greenhouses · Agrivoltaics · Algorithm 1 Introduction Greenhouses are structures used for growing plants in controlled environments. They are commonly built with transparent materials like glass, polycarbonate, or plastic film to enable sunlight to enter and provide the essential energy B Angeliki Kavga Theodoros Petrakis Vasileios Thomopoulos Athanassios A. Argiriou 1 Department of Agriculture, University of Patras, 26504 Patras, Greece 2 Computer Engineering and Informatics Department, University of Patras, 26504 Patras, Greece 3 Laboratory of Atmospheric Physics, Department of Physics, University of Patras, 26504 Patras, Greece 123 required for plant growth (Kim et al 2022). However, this also means greenhouses can experience shading from nearby structures, trees, or even the greenhouse structure itself. As the main source of energy for greenhouses, solar radiation is essential. Utilizing natural heat sources like the Sun is crucial for greenhouse operations since heating costs make up a sizeable share (30 to 70%) of total production costs, especially during frigid winter months (Sun et al 2022). However, in regions such as Greece, where temperatures tend to rise significantly for extended periods, often spanning from May to October, the temperature inside the greenhouse can exceed 60◦ C, leading to severe issues for the crops. To address this problem, various methods have been developed to lower the temperature, including the deployment of nets and screens, which help create an appropriate microclimate inside the greenhouse, especially during the summer season (Kitta and Katsoulas 2020). The shadowing of the crop and the greenhouse area, in general, is utilized as a tool in most approaches used to cool a greenhouse in the summer. More specifically, in Ahemd et al (2016), it is stated that combining a shading and a cooling method of the greenhouse can create An algorithm for calculating the shade created... a temperature difference of 5–10 ◦ C between the indoors and outdoors, with respect to a greenhouse in which only a cooling system is applied. The reduction in temperature due to shading can in some cases lead to a reduction in ventilation requirements. Besides reducing the temperature, shading presents other important benefits for the crop. These benefits are related to the increase in the quality and quantity of production, the decrease of disease and pest activity, the better management of natural resources such as water, due to the lower evaporation under the shade, while at the same time, the reduced evaporation leads to the better assimilation of CO2 , due to the increased stomatal resistance (Angmo et al 2021). Aside from the conventional means of shading the greenhouse, one approach that is employed and is still of scientific interest is the integration of photovoltaics (PVs) into the greenhouse’s roof. Solar radiation, on the one hand, is the most crucial element for achieving a satisfactory production practice, since photosynthesis is a biological process that relies heavily on sunlight. On the other hand, an energy production system using solar radiation such as a photovoltaic system is essentially based on the intensity of the radiation incident on the system. The necessity for both cultivation and a photovoltaic system in sunlight adds value to greenhouses, which are installed in areas without, or with reduced existence of obstacles. Simultaneously, due to increased demand for accessible land, substantial difficulties are addressed, both spatially and economically. Hence, utilizing the same plot of land for both food and energy production emerges as an ideal solution (Hassanien and Li 2017; Yano and Cossu 2019). Semi-transparent photovoltaic (PV) panels can provide shade for crops without negatively affecting their biological requirements. More specifically, the necessary for plants’ photosynthesis (Liu and van Iersel 2021), requires solar radiation within the 400–700 nm range of the spectrum (Roxani et al 2023; Jin et al 2023). At the same time, as indicated in Dean et al (2014), exposure to a specific spectrum range, such as to UV-B, can have severe impacts on the plant’s DNA, adversely altering the plant’s structure and development. Finally, excessive solar radiation has a deleterious impact on transpiration and blooming, in addition to photosynthesis. The PV shading feature could offer numerous benefits for both the crops and the microclimate. These panels can be installed on the roof (Waller et al 2022) or the walls (Aira et al 2021) of the greenhouse, allowing most of the impacting sunlight to penetrate while simultaneously generating electricity. Moreover, researchers have conducted experiments to modify shading by rotating the photovoltaics on the greenhouse roof, considering how shading affects plants differently throughout various growing seasons (Moretti and Marucci 2019). 273 Numerous studies have investigated the effects o (...truncated)