A Proposal for Evaluating the Clearness Index Based on Extra Terrestrial Radiations at a Given Site

Forecasting of intermittent power produced due to renewable energy resources is highly desirable to accurately determine its future values to be utilized for various purposes like scheduling, contingency solutions by the grid operators. Among the renewable resources, solar energy is the most widely used that has grown leaps and bounds over the past due to technology advancements and it is anticipated that it is going to dominate the future as well. This power is often used independently or integrated into the grid. Such integration of solar generation is demanding the reliable forecast of the same. Clearness index determination is very important for accurately forecasting the solar power. This paper presents a methodology to determine the clearness index values which is of paramount importance to handle the forecasting issue to provide better forecast of the Photovoltaic (PV) power. This method includes finding out the clearness index by estimating the Extra-terrestrial Radiations at a given location and using the Global Solar radiation past data available at a given site. This methodology has been implemented successfully for district Rajouri of Jammu & Kashmir state and clearness index values have been estimated for the same. Moreover the correlation between Extra-terrestrial radiation and the Global solar radiation from the past data for the chosen site was found around 0.95 which is quite high.