Improving hourly PV power plant performance analysis: Irradiance correction methodology

Modeling the energy generation of photovoltaic power plants with large DC/AC ratios can result in an over-prediction of energy due to the hourly averaging of measured irradiance data. This is caused, in part, by the over-estimate of convertible solar irradiance during times when inverters transition into or out of a mode of operation where they are clipping energy. During these transition hours, the excess solar irradiance at small time scales that cannot be converted into AC energy due to clipping will be incorporated into the hourly averaged irradiance resulting in an over-estimate of the solar resource and, consequently, AC energy as well. Preliminary findings suggest that this effect can be as large as 13% during peak irradiance hours and 0.2% to 0.3% annually.