Models for daily global solar radiation for the Caribbean island of Trinidad

Abstract

In this study, calibration and validation data sets from 2001 to 2005 and 2006 to 2010, respectively, were used to develop various Angström-Prescott models: A five-year model and five-year dry and wet seasonal models to calculate monthly average daily global solar radiation on a horizontal surface and twelve monthly models to estimate average daily global solar radiation on a horizontal surface. Also, ten yearly models were developed for each year in the period 2001–2010. The regression coefficients (a,b) for the five-year, dry season, and wet season models were found to be (0.21, 0.38), (0.21, 0.38), and (0.27, 0.28), respectively. For the twelve monthly models, a and b varied over the ranges 0.19–0.37 and 0.14–0.42, respectively. For the ten yearly models, a and b varied over the ranges 0.15–0.31 and 0.22–0.48, respectively. The regression coefficients of the twelve monthly models yielded a linear relationship between b and a over a one-year time scale. Similarly, the ten yearly models also yielded a linear relationship between b and a over a ten-year time scale. For all the models, measured and calculated daily global solar radiation were compared by calculating the mean bias error, mean percentage error, root mean square error, correlation coefficient, Nash-Sutcliffe efficiency, and p-values based on t-statistics. Good agreement was found between the measured and calculated values and hence these models can be used in Trinidad. The single five-year model was found to be adequate in modelling the dry and wet seasons. Using the full data set, 2001–2010, the average daily global solar radiation, average total global solar radiation, average daily number of sunshine hours, and average total number of sunshine hours were determined to be 16.93± 0.73 MJ m−2 day−1, 2.56±0.11 GJ m−2, 8.49±0.44 h day−1, and 1282±67 h, respectively, for the dry season; 15.52±0.81 MJ m−2 day−1, 3.32±0.17 GJ m−2, 7.03±0.38 h day−1, and 1504±81 h, respectively, for the wet season; and 16.08±0.71 MJ m−2 day−1, 5.87±0.26 GJ m−2, 7.65±0.24 h day−1, and 2792±83 h, respectively, for the whole year.