The received solar radiation include both direct and diffuse radiations. The direct radiation can generate greater electricity or heat than diffuse radiation. Peak density of direct radiation in Thailand is approximately 1,350- 1,400 kWh/m2 yr, covering 3% of the count area in Central region and trys southern part of Northeaster region (See figure 2) while 19.5% of the country's area has approximately 1,200 1300 kWh/m2-yr (See figure 3). Density of direct radiation in Thailand usually escalates from danuary and reaches the peak in April before descending to the bottom in December.