Author:

Abstract

Solar photovoltaic systems are used in rooftops of buildings, especially to supply excess electricity to the grid. Analysis of the data from a site in Sri Lanka shows that, while the variation of the energy supplied during a given month is somewhat constant, large variations may occur from day to day, even within a given week. Further, dependent on the month, fluctuations from instant to instant could follow a typical sunny day sinusoid or on the other extreme fluctuate heavily. Since good statistics are not routinely available, many studies on solar electricity dispatch do not take these variations into account. Thus, supply authorities have to plan generation schedules without a knowledge of the likelihood of such variations. This paper analyses the power output of a 4.16 kWp domestic solar rooftop system, to allow the findings of fluctuations of solar energy output patterns to be used in system studies. The study shows that for a fixed rooftop installation, the maximum daily solar energy production can decrease to around 83% in months where the solar panel direction is adversely affected by the declination angle. It also shows that 80% of the maximum daily energy available in a given month can be assured 50% of the time in the worst-case scenario, while a day can produce just 3% of the maximum energy. It is also found that in the best month, near capacity production can be assured 90% of the time, where the sky is clear and the panel is ideally oriented.

Keywords: Photovoltaic systems, Rooftop solar, Solar power generation, Solar intermittency, Fluctuation statistics