A Method For Estimating Solar Radiation From Air Temperature Data In Samaru, Northern Guinea Savanna Of Nigeria

A major limitation to the application of weather data in engineering designs and agricultural engineering is the lack of solar radiation data, while temperature and rainfall data are relatively available. Four empirical model methods (Bristow-Campbell (BC model), Campbell- Donatelli (CD model), Donatelli- Bellocchi (DB model) and Donatelli-Campbell-Bristow-Bellocchi (Modular DCBB)) were tested by comparing their estimated global radiation values with measured solar radiation data obtained for several years from the meteorological station at Samaru, northern Nigeria with the aim of determining which model estimate correlates more with measured values. The CD model had the best slope of the regression estimated vs measured of 0.87 with the DB and BC models having a slope of 0.65. The CD model also had the lowest RMSE of 2.7 while the DB model had the highest value of 4.5. From the coefficient of residual mass (CRM), BC, CD, and DB models overestimates the global solar radiation while the DCBB model gave underestimated values. The CD model which accounts for situations in which the night air temperature cooling is less than the corresponding clear day and also accounts for the date by using the average air temperature proved to be a reasonably accurate method for estimating global solar radiation for Samaru. Keywords : Solar radiation, air temperature, model, northern Nigeria Global Journal of Engineering Research Vol. 7 (1) 2008: pp. 21-28