A Framework to Calculate Uncertainties for Lifetime Energy Yield Predictions of PV Systems

Today, lifetime energy yield predictions should include an assessment of the uncertainties of the predicted values as a precondition for financing large PV plants in order to properly quantify risk and return. However, the approach to perform the yield prediction with attendant uncertainty estimation is not standardized which makes it difficult to compare one investment and another. Often important sources of uncertainties are not even included in the overall uncertainty assessment. A method to calculate uncertainties and P-values for year by year and lifetime energy yield predictions of PV systems is presented. The focus is on the cumulative impact of the combination of uncertainties on delivered energy going into the project pro-forma and downside financial analysis, not on estimation of uncertainties for individual modelling steps.