There is a data in Bulgaria from long-term surveys for the duration of sunshine process. The average sunshine period for Bulgaria is about 2100 hours per year. In some regions it can reach 2500 hours, which correspond to 1400 ÷ 1600 kWp/m2 per year on horizontal surface.
The sunshine duration is different for the different geographic areas. For town of Sandanski – 2510 h/year, Plovdiv – 2260 h/year, Sofia – 2020 h/ year.
The good photovoltaic solar energy resources of our country are obvious from the following maps of Bulgaria and Europe.