Long term variations of solar radiation

Abstract

The variability of solar irradiance is the most important issue that determines the reliability of solar power generation in short-term time scales. For long time scales the energy produced by solar irradiation has to be predicted with high certainty. However, environmental parameters such as global temperature, precipitations, cloud cover have changed drastically during last century. Therefore, the overall performance of photovoltaic (PV) solar panels would have been affected by these changes. In present work the effect of cloudiness on the availability of solar energy is analyzed for 18 sites. For the analysis measured daily sunshine duration data was used (Lithuanian Hydrometeorological Service, European climate assessment dataset). For the statistical analysis Pearson correlation and Mann-Kendall trend test was applied. It was established that for most examined sites the amount of solar irradiation is increasing. It was shown that the increase for some sites is significant and reaches 8-11 % over 30 year. Obtained results have shown that it is important to account solar insolation changes for the future solar applications such as photovoltaic electricity generation.