Average Monthly Solar Radiations at Various Places of North East India

The amount of solar energy reaching the Earth's atmosphere and surface is dependent on geographic location (latitude and longitude of the place), orientation, seasonal variations, time of a day and atmospheric conditions. Information on the availability of solar radiation is needed in many applications dealing with the harnessing of solar energy. In India, the Meteorological Department measures sunshine duration, global radiation, and diffuse radiation at some selected place. Locations where no measurements exist, monthly average or hourly average solar radiation can be estimated by using empirical correlation developed from the measured data of nearby locations having similar climatological conditions. In this paper, direct incident solar radiation, global horizontal solar radiation and diffuse radiation incidence have been calculated for different places of north-east India, viz. Guwahati, Shillong, Sibsagar and Silchar. The monthly average direct normal irradiance and global horizontal irradiance provided by National Renewable Energy Laboratory based on the hourly estimates of radiation over seven years (2002-2008) revealed that daily average of solar radiation in and around Assam is in the range of 3-6 kWh/m²/ day. By employing the method proposed by Sukhatme, the daily average of global and horizontal diffuse solar radiation have been calculated for Jodhpur, New Delhi and Vishakhapatnam apart from the above mentioned locations of North-East India. The measured values available for Jodhpur, New Delhi, Vishakhapatnam, and Shillong with the Meteorological Department are comparable with our calculated results. Thus our results can be considered as useful results for rapid mechanism for initial design of solar power generation system in these locations. Also method of calculations can be extended for remote and inaccessible regions also.