Empiral Models for Estimation of Clearness Index in Nigeria

Abstract

Knowledge of clearness index is essential in the design and assessment of solar application systems. Clearness index is the ratio of global solar radiation and extraterrestial solar radiation. However, actual measurements of global solar radiation are generally made only at a few places because of the cost of the equipment required as well as the care, skill and cost needed for its maintenance and re-calibration. Therefore this study is aimed at development of Angstrom-Prescott based empirical regression models for estimation of clearness index values for Nigerian locations based on sunshine duration hour. Ten empirical regression equations (Linear, Quadratic, Compound, Growth, Logarithm, Cubic, S'Exponent, Inverse and Power) were investigated using daily sunshine duration hour data values of 24 ground stations obtained from Nigeria meteorological agency (NIMEF) Oshodi, and averaged monthly values extraterrestial solar radiation Ho obtained from NASA surface meteorology and Solar Energy SSE Satellites dataset from the same period 1983-1993.