Global direct and diffuse solar insolation analysis on horizontal and tilted surfaces at Colombo, Sri Lanka

Abstract

An analysis of global, direct and diffuse solar radiation on horizontal and tilted surfaces at Colombo was carried out to assess the solar resource potential on horizontal and tilted surfaces. The calculated monthly average global horizontal solar resource potential varied between 4.00 to 5.95 kWh/m2/day while 5.00 kWh/m2/day was the calculated annual average global horizontal solar resource potential at Colombo. Estimated annual average diffuse solar radiation component on horizontal surface was 1.82 kWh/m2/day and the direct solar radiation component was 3.18 kWh/m2/day which was about 63.6% of the global horizontal insolation at Colombo. Solar resource assessment was then carried out for tilt angles 15 , 17.5 , 22.5 , 30 , 40 and 6.9 for the tilted surfaces in due south orientation. The derived maximum solar resource potential was 1830 kWh/m2 per annum for the surface tilt angle of 6.9 which is equal to the local latitude. The solar resource potential was decreased with increased surface tilt angle. The percentage decrements compared to the global horizontal solar radiation were 0.7%, 1.4%, 3.0%, 6.8% and 14.3% for surface tilt angles of 15 , 17.5 , 22.5 , 30 , and 40 respectively. According to the results of the analysis, it is required to tilt the surface maximum of 30 towards the south and maximum of 25 towards the North during a year to maximize the solar resource potential on the tilted surface free to rotate about its East-West axis, placed at zero surface azimuth angle. 1918 kWh/m2 per annum was the estimated maximum possible solar resource potential on tilted surface which is 5.1% greater than that of horizontal surface. With the availability of Solar Radiation data, it may possible to assess the Solar Resource Potential of any other location of the country in future by using the same procedure.