oa Spatial distribution of air temperature and solar radiation in the Canarian photovoltaic greenhouse in arid climates

The distribution of solar radiation and air temperature in a greenhouse are two of the main factors influencing the growth and yield of plant [1]. For this reason, studying the spatial distribution of the internal air temperature and solar radiation is very important to provide useful information for knowing the effect of the shading of photovoltaic panels on the climate parameters inside the greenhouse. In addition, the distribution of the air temperature and solar radiation depends on various factors, such as changes in external climate, the presence of the plants, covering and photovoltaic panels, solar radiation intensity, ventilation methods, the thermo physical and optical properties of the covering material, and the shape and dimensions of greenhouse [2]. However, the solar radiation significantly affected photosynthesis, growth and yield of plants.

Our work consists of studying the influence of flexible photovoltaic panels on the climate of the Moroccan Canarian greenhouse. We have installed two identical greenhouses: one greenhouse without any system of shade and the second greenhouse with a photovoltaic panels that occupied 30% of their east-west roofs in checkerboard format (Fig.1).

The dimensions of each greenhouse were (15 m length, 11 m wide, and 5 m height) in the middle and gutter height of 4 m at a roof slope of 10°. The greenhouses cover material was a plastic polyethylene (PE) film with the thickness 200 μm and light transmittance of 75%.

The inside solar radiation was measured using CMP3 pyranometers (Kipp & Zonen), having a time response of 18 μs, a maximum error of ±1.5%, a sensitivity of 5-20 μV W^-1 m^-2. A working temperature range of -40 to +80°C and a wavelength range of 300 to 2 800 nm. The solar radiation sensors was placed of 3 m height above the ground level, one point of measurement in the control greenhouse and nine measurement points in the photovoltaic greenhouse. However, the air temperature was measured in three levels at the center of each greenhouse. Values of solar radiation and air temperature were measured at 5 s intervals, averaged at each 10 min and recorded in a data logger (CR3000).

The results of the spatial distribution of air temperature and solar radiation comparison in the two greenhouses show that a 30% occupation of the roof of a Canarian agricultural greenhouse with flexible photovoltaic panels does not have a significant effect on the internal air temperature and solar radiation, In addition, the analysis of results showed that the internal temperature inside the photovoltaic greenhouse was decreased by 3.24°C compared to the internal temperature of control greenhouse, while the solar radiation decreased by 55% under the photovoltaic greenhouse.