Evaluation of solar energy resources by establishing empirical models for diffuse solar radiation on tilted surface and analysis for optimum tilt angle for a prospective location in southern region of Sindh, Pakistan

Diffuse solar radiation data is very important and is required for solar energy system implementations. The main purpose of the present study is to evaluate solar energy resources by establishing diffuse solar radiation models and obtaining optimum tilt angle fora prospective location is southern region of Sindh, Pakistan. Due to the unavailability of measured diffuse solar radiation data, nine new models, based on available data from local agency and values obtain from existing models, to predict diffuse solar radiation on tilted surface has been established. The best model was chosen based on test results from statistical indicators. The optimum tilt angle for monthly, seasonally, half-yearly and yearly adjustment was determined. The optimum tilt angle varies from 0°in May, June and July to 49°in December. The yearly optimum tilt angle was found as 23°, which is close to latitude of investigated location (25°07′N). The monthly average total, beam and diffuse solar radiations were calculated for optimum and vertical tilted surfaces and were compared with those obtain for horizontal surfaces. The half-yearly adjustment of optimum tilt angle is recommended for the investigated location because very small difference in annual solar energy gains in comparison with monthly or seasonal adjustment. The total annual energy for completer year and for four seasons of the year was calculated and found that maximum total annual energy is obtained at optimum tilt angle.