Surface measured solar radiation data and solar energy resource assessment of Pakistan: A review

Over the past decade, Pakistan has been facing a shortage of between 3000 MW and 6000 MW in the supply and demand of electricity, leading to several hours of power cut. Sixty-three percent of current electricity generation is based on fossil fuels, leading to cost vulnerability, whereas only one percent is based on renewable resources (non-hydroelectric). The geographical location and climatic conditions of the country offer a high solar energy potential, which signifies the need for solar resource assessment for the planning of solar energy projects. The article provides an overview of the solar resource assessment based on surface measured data and satellite data carried out by researchers. Various researchers have developed solar energy potential maps for the country based on solar insolation data measured by Pakistan Meteorological Department (PMD). The data measured by PMD reported in the previous literature have been compared with the long-term data from the World Radiation Data Centre (WRDC), and both data show good agreement. The approximate annual mean daily global horizontal insolation for the whole country, based on surface measured data by WRDC, is 5.30 kW h/m2 (19.0 MJ/m2 or 221 W/m2). The government of Pakistan sought to exploit the solar and wind energy potential during the last decade with the help of international agencies. Based on satellite data, the solar resource assessment was done by National Renewable Energy Laboratory, USA (NREL) in 2007, and the Energy Sector Management Assistance Program (ESMAP) of the World Bank in 2015. The solar atlas prepared by NREL was not validated by the surface measured data, whereas the solar atlas prepared under ESMAP is to be validated in 2017. A comparison of NREL estimated data and WRDC data shows that NREL's atlas overestimates solar insolation up to 25% in some regions. The annual mean daily solar global horizontal insolation estimated under ESMAP is 5.67 kW h/m2.