Capacity Value of Additional Generation: Probability Theory and Sampling Uncertainty

The concept of capacity value is widely used to quantify the contribution of additional generation (most notably renewables) within generation adequacy assessments. This paper surveys the existing probability theory of assessment of the capacity value of additional generation, and discusses the available statistical estimation methods for risk measures which depend on the joint distribution of demand and available additional capacity (with particular reference to wind). Preliminary results are presented on assessment of sampling uncertainty in hindcast LOLE and capacity value calculations, using bootstrap resampling. These results indicate strongly that, if the hindcast calculation is dominated by extremes of demand minus wind, there is very large sampling uncertainty in the results due to very limited historic experience of high demands coincident with poor wind resource. For meaningful calculations, some form of statistical smoothing will therefore be required in distribution estimation.