The integration of photovoltaic (PV) panels in greenhouses enables dual land use, combining crop production with electricity generation. However, PV installations can reduce both the intensity and uniformity of light at the canopy level, potentially affecting crop growth. This study employed computational fluid dynamics (CFD) simulations to evaluate the effects of different layouts of commercial-size thin PV modules—both opaque and semi-transparent—installed at gutter height in greenhouses on irradiance and, in particular, on its distribution within the greenhouse. Achieving a homogeneous distribution of light is critical for effective plant growth beneath photovoltaic systems. The influence of greenhouse size and roof shape on the intensity and uniformity of visible radiation was investigated as well. The results showed that during winter (21 December), irradiance in a mono-span tunnel greenhouse was 4–6% higher than in a multi-span large structure; in summer (21 June), this difference increased to 10–13%. Among the opaque PV layouts tested, the north–south (NS) straight-line arrangement provided the most uniform light distribution, outperforming the checkerboard and east–west (EW) layouts. The EW straight-line layout was the least effective regarding light uniformity. Roof shape (arched vs. pitched) had minimal impact on radiation distribution. Semi-transparent PV modules consistently resulted in 17% higher irradiance and more uniform light distribution than opaque ones. These findings can inform efficient PV deployment strategies in greenhouses to enhance both energy yield and crop productivity.

The integration of photovoltaic (PV) panels into greenhouse cultivation has garnered increasing attention in recent years, driven by the dual goals of expanding renewable energy use and improving land-use efficiency for both crop production and electricity generation. This study combines experimental and modeling approaches to evaluate how the greenhouse environment influences the temperature of large-scale organic photovoltaic modules (OPVMs) installed horizontally above a tomato crop canopy in a tunnel-shaped greenhouse. The impact of temperature on the performance characteristics of OPVMs is well recognized. Therefore, predicting their temperature in a greenhouse environment is very important. Results show a strong correlation between OPVM temperature, ambient air temperature, and solar irradiance, with peak temperatures occurring around midday. The study demonstrates that the Ross model—a steady-state method commonly used to predict silicon PV temperature—can be effectively applied to OPVMs. Additionally, a new energy balance-based model is introduced, showing comparable accuracy. It is shown that differences in radiometric properties of the OPVMs had a negligible effect on their thermal response. Additionally, this study examines the power conversion efficiency of the modules throughout the growing season and the impact of OPVMs on tomato yield.

Despite its potential benefits, dual land use for crop growth and electricity generation (agrivoltaics) is not widespread. This study investigates the effect of two types of organic photovoltaic (OPV) modules (red and blue), which differ by spectral characteristics, on greenhouse microclimate and crop performance. The characteristics of the OPV modules were first determined outside greenhouses. Then, experiments involving a tomato crop were done in three greenhouses. Two greenhouses had modules installed above the canopy, at gutter height, while the third served as a control without modules. Radiation transmittance values of the red and blue modules were 32.2 and 28.8%, respectively. The installation of OPV modules resulted in a similar reduction of irradiance at the canopy level, about 38%, in the two OPV greenhouses (OPVGs). Dust accumulation over 11 months of installation inside the greenhouses reduced radiation transmission of the red and blue modules by 2.6 & PLUSMN; 0.8% and 4.9 & PLUSMN; 1.8% (absolute values), respectively. The amount of solar radiation transferred to sensible and latent heat depended apparently on the modules' radiometric characteristics. The level of diffuse radiation in the global solar radiation affected the temperature of the modules. In the control greenhouse, the accumulated yield was higher than in the blue and red OPVGs by 15% and 9%, respectively. Yet, the ratio of accumulated yield to irradiance at the canopy level was higher in the OPVGs. There were no significant differences among the greenhouses concerning the acidity and sugar content of the tomatoes.& COPY; 2023 IAgrE. Published by Elsevier Ltd. All rights reserved.

This paper investigates the differences electrical behavior and lifetime of organic photovoltaic (OPV) modules installed inside, on the outside of a polytunnel type greenhouse roof and on a fixed frame next to the polytunnel with the aim of finding an installation location that would reduce degradation and therefore prolong the lifetime OPV modules in a greenhouse application. The modules had different degradation rates, influenced by three factors: exposure to harsh weather conditions, mechanical stresses on the modules caused by the movement of the greenhouse plastic sheeting they were fixed to, and dust accumulation on the modules. Efficiency values of modules declined to 32%, 47% and 47% and fill factor values reduced by 33%, 21% and 21% for modules on top of the polytunnel, inside the polytunnel and on frames adjacent to the polytunnel respectively during the measurement period. Installing OPV modules inside a tunnel can increase module lifetimes and consequently increase the overall lifecycle output of the modules. Not fixing the OPV module directly to the polyethylene cover, thereby avoiding the stresses on the module due the film movement, could improve OPV lifetimes further. (C) 2021 Elsevier Ltd. All rights reserved.

Since leaf temperature (LT) is not a trivial measurement, deep-neural networks (DNN) and machine learning (ML) models were evaluated in this study as tools for estimating foliage temperature. Two DNN methods were used. The first DNN used convolutional layers, while the second DNN was based on fully-connected layers and was trained by cross-validation techniques. The machine learning used the K-nearest neighbors (KNN) method for LT estimation. All models used the meteorological and microclimatic parameters (hereafter referred to as features) of the examined greenhouses to determine the average foliage temperature. The models were trained on 75% of the collected data and tested on the remaining 25%. RMS and absolute error were used to evaluate the performance of the different models compared to the LT values measured by a thermal camera. In addition, after finding the correlation of each feature to the leaf temperature, the models were trained based on the high-correlated features only. The machine learning model was superior to DNN when all available features were used and when only high-correlated features were used, resulting in errors of 0.7 °C and 0.8 °C, respectively.

Insect-proof screenhouses are commonly used to grow plants in warm climates. However, there is relatively little literature on their microclimate compared to greenhouses. This study presents computational fluid dynamics (CFD) results of airflow, temperature, and humidity ratio patterns in a screenhouse with a roof consisting of a large flat insect-proof screen and impermeable walls. First, vertical profiles of velocity, temperature, and humidity at the center of the screenhouse were obtained by 2D steady-state CFD simulations and validated by experimental results. Root mean square error (RMSE) values were used to measure the differences between the two. The lowest RMSE values among simulations with different turbulence models were 0.49 K, 1.26 g kg(-1), and 0.05 ms(-1) (with the RNG turbulence model) for temperature, humidity ratio, and air velocity, respectively. The main deviation of the CFD results from the experimental results was observed with the air velocity in the upper region of the screenhouse. Inflow and outflow in the leeward and windward parts of the flat roof were observed, respectively. This resulted in large-scale airflow within the screenhouse opposite the outside wind direction at the canopy level. The results suggested that the leeward section of the screenhouse is warmer than the windward one and has a lower humidity ratio. Large-scale rotating airflow formed in the center of the screenhouse, close to the roof, a large area with a humidity ratio similar to ambient conditions. (c) 2022 IAgrE. Published by Elsevier Ltd. All rights reserved.

Measured evapotranspiration (LE) of screenhouse banana plantations was utilized to derive and compare two types of machine-learning models: artificial neural network (ANN) and multiple linear regression (MLR). The measurements were conducted by eddy-covariance systems and meteorological sensors in two similar screenhouse banana plantations during two consecutive seasons, 2016 and 2017. Most of the study focused on the season of 2017, which includes a more extended data set (141 days) than 2016 (52 days). The results show that in most cases, the ANN model was superior to MLR. When trained and validated over the whole data set of 2017, the ANN and MLR models provided R2 of 0.92 and 0.89, RMSE of 37.5 and 45.1 W m−2 and MAE of 21 and 27.2 W m−2, respectively. Models could be derived using a training dataset as short as one month and still provide reliable estimations. Depending on the chosen calendar month for training, R2 of the ANN model varied in the range 0.81–0.89, while for the MLR model, it ranged 0.73–0.88. When trained using a data set as short as one week, there was some deterioration in model performance; the corresponding ranges of R2 for the ANN and MLR models were 0.37–0.89 and 0.37–0.71, respectively. As expected for a screenhouse decoupled environment, solar radiation (Rg) was the variable that most influenced LE; using Rg as the sole input variable, the ANN model resulted in R2, RMSE and MAE of 0.88 and 47 W m−2 and 25.6 W m−2, respectively, values that are not much worse than using all input variables (solar radiation, air temperature, air relative humidity and wind speed). Using Rg alone as the input to the MLR model only slightly deteriorated R2 (=0.88); however, RMSE (=124 W m−2) and MAE (=75.7 W m−2) were significantly larger compared to a model based on all input variables. To examine model performance in different seasons, models were trained using the data set of 2017 and validated in 2016, and vice versa. Results showed that training on the data of 2017 and validation in 2016 provided superior results than the opposite, presumably since the 2017 measurement season was longer and weather conditions were more diverse than in the 2016 data set. It is concluded that the ANN and MLR models are reasonable options for estimating evapotranspiration in a banana screenhouse.

Agricultural greenhouses have been identified as a niche application for organic photovoltaic (OPV) integration, leveraging key performance characteristics of OPV technology, including semi-transparency, light weight, and mechanical flexibility. For optimal electrical design and performance assessment of greenhouse-integrated OPV systems, knowledge of the solar irradiance incident on OPV module surfaces is essential. Many greenhouse designs feature roof curvature. For flexible OPV modules deployed on curved greenhouse roofs, this results in a non-homogenous distribution of solar radiation across the module surfaces, which affects electrical output. Conventional modeling methods for estimating solar irradiance on a PV surface assume planarity, and therefore they are insufficient to evaluate OPV (and other flexible PV) installations on curved greenhouse structures. In this study, practical methods to estimate incident solar irradiance on curved surfaces were developed and then applied in an outdoor performance evaluation of large-area, roll-to-roll printed OPV arrays (3.4 m2 active area) installed on a gothic-arch greenhouse roof in Tucson, Arizona between October–February. The outdoor performance of six OPV arrays was assessed using the curved-surface modeling tools primarily considering the effect of irradiance on electrical behavior. The OPV arrays had an overall power conversion efficiency (PCE) of 1.82%, with lower PCE in the afternoon periods compared to morning and midday periods. The OPV arrays experienced an average 32.6% loss in normalized PCE over the course of the measurement period. Based on these results, we conclude that the higher performing OPV devices that are more robust in outdoor conditions coupled with accurate performance monitoring strategies are needed to prove the case for agrivoltaic OPV greenhouses.

A study related to the application of organic photovoltaic (OPV) modules in greenhouses is presented. It considers the impact of nonhomogeneous shading by semitransparent OPV modules, placed on the cover of a greenhouse tunnel housing a tomato crop, on energy partitioning and the spatial variability of radiation, air temperature and vapour pressure deficit (VPD) within the tunnel. Experiments were conducted in two similar tunnels covered by a diffuse polyethylene sheet. Flexible semitransparent strips of OPV modules were placed on 37% of the roof area of one tunnel, creating an approximately 23% nonhomogeneous shading, while the other tunnel, homogeneously shaded by a 25% black shading net, served as a control greenhouse. The results show that on cloudy days (high diffuse radiation), spatial variability of radiation in the OPV tunnel was smaller than on sunny days (low diffuse radiation). Conversely, variability in air temperature and VPD did not change much with the change in diffuse radiation. Except when diffuse radiation was high, no significant difference in the energy partitioning between nonhomogeneous shading by OPVs and homogeneous shading was observed. Most of the net radiation in the tunnels was converted into latent heat. With a high solar elevation angle, the spatial variability of radiation within the tunnel was higher than with a low solar elevation angle. Additional experiments are needed to determine the best arrangement of semitransparent OPV modules on the roof, without resulting in any significant increase in spatial variability. Agronomic aspects of plant growth under the OPV modules are briefly presented.

Recognizing the growing interest in the application of organic photovoltaics (OPVs) with greenhouse crop production systems, in this study we used flexible, roll-to-roll printed, semi-transparent OPV arrays as a roof shade for a greenhouse hydroponic tomato production system during a spring and summer production season in the arid southwestern U.S. The wavelength-selective OPV arrays were installed in a contiguous area on a section of the greenhouse roof, decreasing the transmittance of all solar radiation wavelengths and photosynthetically active radiation (PAR) wavelengths (400–700 nm) to the OPV-shaded area by approximately 40% and 37%, respectively. Microclimate conditions and tomato crop growth and yield parameters were measured in both the OPV-shaded (‘OPV’) and non-OPV-shaded (‘Control’) sections of the greenhouse. The OPV shade stabilized the canopy temperature during midday periods with the highest solar radiation intensities, performing the function of a conventional shading method. Although delayed fruit development and ripening in the OPV section resulted in lower total yields compared to the Control section (24.6 kg m−2 and 27.7 kg m−2, respectively), after the fourth (of 10 total) harvests, the average weekly yield, fruit number, and fruit mass were not significantly different between the treatment (OPV-shaded) and control group. Light use efficiency (LUE), defined as the ratio of total fruit yield to accumulated PAR received by the plant canopy, was nearly twice as high as the Control section, with 21.4 g of fruit per mole of PAR for plants in the OPV-covered section compared to 10.1 g in the Control section. Overall, this study demonstrated that the use of semi-transparent OPVs as a seasonal shade element for greenhouse production in a high-light region is feasible. However, a higher transmission of PAR and greater OPV device efficiency and durability could make OPV shades more economically viable, providing a desirable solution for co-located greenhouse crop production and renewable energy generation in hot and high-light intensity regions.

This paper presents the electrical performance of organic photovoltaic modules (OPVs) on top of a polyethylene covered greenhouse high tunnel in a Mediterranean climate. Modules from a previous study were kept on the tunnel and monitored together with new modules with improved connectors installed on the greenhouse roof and on frames adjacent to the greenhouse. Measured module power conversion efficiencies ranged from 1% to 3%. The typical combined output of the modules across the tunnel roof were 105Wh on a sunny day and 81Wh on a cloudy day. Module burn-in period was about 15 days, losing around 36% of its initial efficiency. Ts80 lifetimes ranged from 7 days to 94 days. Tunnel integration was shown to accelerate module degradation.

Airflow patterns and turbulence characteristics inside a naturally ventilated screenhouse with tomato plants were experimentally investigated using 3D sonic anemometers simultaneously measuring air velocities at six horizontal positions in the space between the screened roof and the top of the canopy. The screenhouse had a flat roof and was ventilated through the roof only. Testing was carried out during about 3 weeks of crop development, under variable external conditions. The mean horizontal air velocity component above the canopy was generally lower than 0.20 U-oh (where U-oh is the mean horizontal external wind speed) and mostly in a direction opposite to the external wind. At low external windspeed, the airflow direction was not necessarily opposite to the wind direction. The vertical air velocity component was generally lower than 0.07 U-oh. The root mean square of the air velocity components, the turbulence intensity and the turbulence kinetic energy were much larger during the day than at night mainly due to the higher daytime effect of buoyancy and to a lesser extent due to the higher external wind speed. Spectral energy slopes of the velocity components were close to -5/3 during the day when wind speed was high. However, at night, when wind speed was low, the spectral energy slope of the velocity vector increased significantly. The integral length scales of turbulent eddies were greater in the horizontal than the vertical direction which is not surprising given the volume under consideration is bounded by the top of the canopy, the roof and the sidewalls. (C) 2019 IAgrE. Published by Elsevier Ltd. All rights reserved.

This study presents a detailed analysis of the outdoor behaviour of organic photovoltaic (OPV) panels on a polytunnel type greenhouse roof in a Mediterranean climate, looking at the effects of environmental variables and panel orientations on the electrical behaviour and degradation of the panels, thus providing crucial outdoor testing results of greenhouse integrated OPVs in this climatic region. The OPV panel placed at the polytunnel ridge of the roof yielded highest outputs, efficiencies and fill factors during the measurement period. However, the use of panels on the East and West sides of the greenhouse roof, could reduce midday output peaks and therefore provide a more balanced power supply throughout the day. The diurnal variation in OPV behaviour was influenced by simultaneous effects of changing irradiance and temperature. It was found that although output was higher, the OPVs showed dips in fill factor and efficiency at times with high incident irradiance. This was assumed to be due to a reversible degradation phenomenon under high direct irradiance conditions, which led to higher performance during morning hours compared to the afternoon and was followed by a recovery overnight and to some extent in shaded conditions.

The use of flexible and semi-transparent organic photovoltaic (OPV) modules as shading elements in a greenhouse tunnel with a tomato crop is presented. Experiments were performed in two similar greenhouse tunnels, covered by diffuse polyethylene sheet, during two summer growing seasons. In 2018, one tunnel was shaded using OPV modules (covering 37% of the roof area and resulting in 23% shading) and the second tunnel served as a control. In 2019, a 25% black shading screen was added to the control tunnel. The microclimate, yield, and physiological parameters were examined in the two tunnels. Results show that at noon (11:00 to 13:00), there was no significant difference in the mean seasonal (June-September 2018, May-August 2019) air temperature and humidity between the tunnels. In 2018, the tunnels differed in terms of the spatial radiation transmittance and leaf temperature. The average radiation level along the OPV tunnel centreline was much lower, and the radiation distribution was less homogeneous than in the control. In 2019, with similar shading percentages in the tunnels, similar average radiation levels were observed. The leaf temperature in the OPV was lower than in the control in 2018 and varied from higher to lower in 2019. The leaf area index (LAI), cumulative yield, and average fruit mass were higher in the OPV than in the control in 2018, and similar in 2019. The average value of the maximum power output of three OPV modules increased roughly linearly with irradiance. (C) 2020 IAgrE. Published by Elsevier Ltd. All rights reserved.

In warm and mild winter climates insect-proof screenhouses are often used to grow plants. These screenhouses are usually much cheaper than fully climate-controlled greenhouses and enable growers achieving reasonable yield, at good quality. The insect-proof screenhouse structures are often built with different roof shapes for various reasons. An experiment was done to determine the light distribution above the canopy in screenhouses with two different roof shapes: flat and zigzag. The roofs of the screenhouses were made of a '50 mesh' screen. The light intensity was measured simultaneously in the two screenhouses, at their mid-length, across nearly two spans (14 m). The data was collected in the morning, midday and afternoon. Results show that light distribution in the transverse direction is more homogenous in the flat screenhouse than in the zigzag one. However, average light intensity across nearly two spans was very similar in the two houses. Light intensity in the screenhouses was about 55, 60 and 52% of ambient values in the morning, midday and afternoon respectively. Although the screen in the screenhouse with the flat roof was installed two years earlier than in the screenhouse with the zigzag roof only slight effect of degradation in light transmittance of the screen material was observed in that house.

The present study examines the radiometric and thermal properties of an organic photovoltaic (OPV) semitransparent flexible module. Transmissivity of the module was measured under outdoor conditions in the wavelength range of 390 to 1100 nm using a transmittance measuring box. Measurements were done at four different angles of sun incidence: 0, 21, 41 and 46 degrees. Simultaneous, to the transmittance measurements, the open circuit voltage and close circuit current of the module were recorded, to allow power and efficiency calculations of the OPV modules as function of the tilt angle. Supplementary laboratory measurements of transmissivity, reflectivity and absorptivity as function of wavelength, were done with a spectroradiometer equipped with an integrating sphere for wavelengths between 390 to 1100 nm. The overall heat transfer coefficient (U value) of the module was determined during several winter nights, using a standard hot box. The OPV module examined in this study had about 20% transmissivity, 15% reflectivity and 65% absorptance in the photosynthetically active radiation (PAR) range (400-700 nm). The boundary efficiency of electricity generation (product of V-oc and I-sc) of the module was about 2% and the overall heat transfer coefficient about 6.0 (W m(-2) K-1).

This study examines the feasibility of using semi-transparent, flexible organic photovoltaic (OPV) modules as greenhouse shading material. By using such modules, it may be possible to utilise existing greenhouse-based agricultural areas for electricity production. Using OPV modules to shade greenhouses and reduce excess solar energy may result in reduced heat load on the crop on the one hand, and use of renewable energy on the other. We examined the radiometric and thermal properties of an OPV module. Module transmissivity was measured under outdoor conditions at four different angles of radiation incidence: 0, 21, 41 and 46 degrees. Simultaneously, the open-circuit voltage, and short-circuit current of the module were recorded for power and efficiency calculations. Supplementary laboratory measurements of transmissivity, reflectivity and absorptivity were performed with a spectroradiometer. To further characterise the OPV module, its overall heat-transfer coefficient (U value) was determined. The examined module had about 20% transmissivity, 15% reflectivity and 65% absorptance in the photosynthetically active radiation (PAR) range. The mean daily power conversion efficiency of the module was about 0.8% and the overall heat transfer coefficient U, was about 6.0 Wm(-2) K-1. The temperature of a module placed on the polyethylene cover of a greenhouse high tunnel was about 50-55 degrees C at midday. Thermal images of the module revealed non-uniform heat distribution, with temperature differences between regions reaching up to 7.5 degrees C. OPV modules appear to be suitable for greenhouse shading and electricity generation but currently they are too expensive and their life duration is relatively short. (C) 2019 IAgrE. Published by Elsevier Ltd. All rights reserved.

The use of nets and screens to cover orchards has greatly expanded during the last decade, since the nets protect the trees from excessive radiation, strong winds, hail and insects. Furthermore, recent studies have shown that, in certain orchards, the nets can significantly reduce the water consumption of trees. The nets are usually stretched above the trees and are fixed to the supporting poles by cables that run all around the net circumference. In this study, experiments were done to determine the forces acting on a horizontal shade net that covered an orchard (232×100 m(2)) in which peach trees were grown. A net section of 40×6 m(2), at an upwind edge of the net-house, was used to measure the forces. Sixty load cells that were evenly distributed on the section circumference were used to attach the net to the net-house cables. Results show that the force acting on the net at the point where the load cell is attached to the net is a second-order polynomial of wind speed. The forces acting on the net were stronger at the points where the net was attached to a cable at the outer edge of the net-house. At points where the net was attached to inner cables of the net-house, the forces were smaller. Extrapolating the second-order polynomial, it was shown that, at a wind speed of 150 km h(-1), the largest force acting at the point where the load cell was attached to the net could be 50 kg.