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In this study, it is aimed to calibrate and test the Hargreaves model solar radiation (Rs) estimation equation in accordance with the Mediterranean - Southeastern Anatolian transitional zone conditions. The calibration equation was created by using the long-term average (1938 - 2020) daily values of the maximum, minimum, average air temperature (Tmax, Tmin, T), Rs and extraterrestrial radiation (Ra) data of Kahramanmaraş province. The Ra values were estimated depending on the geographical location and the time. Calibration coefficients (a, b) were determined as 0.0984 and 0.3695, respectively, using the Microsoft Excel program "solver" add-on. Long-term average daily Rs values varied between 4.99 - 32.56 MJ/m² day, and the Rs values estimated by the calibration equation varied between 7.33 - 33.25 MJ/m² day. The rate of explaining the change in the measured values with the estimated values was determined as 97.34% (R²= 0.9734). The mean absolute percentage error (MAPE) and root mean square error (RMSE), taken into account as an expression of the deviation between the measured and estimated Rs values, were determined as 8.71% and 1.54 MJ/m² day, respectively. The calibration equation was tested with the daily average Tmax, Tmin, T and Rs data measured at Kahramanmaraş Sütçü İmam University (KSU) in 2021. Temperature and radiation sensors operated by a Programmable Logic Controller (PLC) were used to measure these data. Measured and estimated Rs values varied between 10.40 - 29.13 MJ/m² day and 13.80 - 31.16 MJ/m² day, respectively. The rate of explaining the change in the measured values with the estimated values was determined as 86.71% (R²= 0.8671). MAPE and RMSE were obtained as 10.57% and 2.57 MJ/m² day, respectively. It has been concluded that using the Hargreaves model calibration equation suitable to the local conditions, solar radiation estimations with high accuracy can be made. [ABSTRACT FROM AUTHOR]

In this study, it is aimed to develop empirical models that can be used in estimation of daily average solar radiation (RS) based on some meteorological and geographical parameters. Seven estimation models were developed by nonlinear regression analysis method using various combinations of air temperature (T), relative humidity (RH), extraterrestrial radiation (Ra), saturated (es) and actual vapour pressure (ea) parameters. The models were created using the long-term average daily meteorological data of Kahramanmaraş province (1938 - 2020). The models were tested both these long-term average data and daily meteorological data measured at Kahramanmaraş Sütçü İmam University (KSU) in 2019 and 2020. Long-term average daily actual RS data varied between 4.99 - 32.56 MJ m-2 day-1. The estimated solar radiation values (RS) with the highest correlation (r = 0.99) with actual RS data were obtained with the RS_7 model, in which the parameters es, ea, T, RH and Ra were used together. The RS values obtained using this model varied between 6.45 to 33.99 MJ m-2 day-1. For the RS_7, which showed the best performance among the seven models, mean absolute percentage error (MAPE) and root mean square error (RMSE) were determined as 4.17% and 0.69 MJ m-2 day-1, respectively. The daily RS values measured in KSU varied between 7.75 - 33.48 MJ m-2 day-1 and 10.51 - 30.23 MJ m-2 day-1 for 2019 and 2020. The RS values closest to the measured RS values were estimated with the RS_7 model. The estimated RS values by this model varied between 11.74 - 33.93 MJ m-2 day-1 and 13.93 - 31.57 MJ m-2 day-1 for 2019 and 2020, respectively. MAPE values were determined as 11.33% and 7.54%, respectively. It is concluded that this model can be used to estimates daily average solar radiation and will be an excellent alternative since it is compatible with the Kahramanmaraş conditions. [ABSTRACT FROM AUTHOR]