Estimation of daily global solar radiation based on different whitening applications using temperature in Mediterranean type greenhouses

The study aimed to estimate the daily global solar radiation (Rs) in Mediterranean-type greenhouses. Five different temperature-based Rs estimation models developed for open-field conditions were calibrated and validated in Mediterranean-type greenhouses in Almeria, Spain and Antalya, Türkiye, between August 26, 2013, and January 1, 2023, and between October 1, 2018, and 1 January 2023, respectively. Whitening applications were categorized according to greenhouse light transmissivity and classified as follows: without whitening or light-whitening, medium-whitening, and severe-whitening. Additionally, the best-performing model were compared with greenhouse plastic light transmissivity method. The estimation performance of the models was evaluated using the statistical indicators of the p-value of the slope, determination coefficient (R2), Nash–Sutcliffe model efficiency coefficient (NSE), root mean square error (RMSE), mean absolute error (MAE), relative error (RE), and Willmott Index (d). Compared with the other models, the Bristow and Campbell model showed a slightly higher performance in all whitening applications. Although the light transmissivity coefficient method performed slightly better than the temperature-based Rs estimation model, there was no statistical difference in the performances of the estimation models. Temperature-based estimation models offer a highly viable alternative for individuals who rely on the light transmittance approach to estimate Rs in greenhouses. This method can prove particularly useful in areas where measuring Rs outside the greenhouse is not possible or where partial time measurements cannot be taken owing to equipment malfunctions. All calibrated models can be used to estimate solar radiation using temperature data from various Mediterranean countries with similar climates and greenhouse cultivation.