Analysis of Calculation Methods for Energetic Measures in Systems with Electric Energy Storage

Self-Sufficiency (SS) and Self-Consumption (SC) are commonly used metrics to evaluate how much a Renewable Energy Source (RES) contributes to covering the demand within an energy system. There are many equations in the literature for these metrics that differ slightly. They consider efficiency losses stemming from system components differently. Most of the equations are designed for systems that are not capable of trading imported or generated energy, that is temporarily stored in an Electric Energy Storage (EES), back to the Energy Market (EM). This work analyses systems consisting of a RES, a central EES, an EM and a demand that needs to be covered. The constructed model heeds efficiency losses and allows trading of stored and imported energy. An effort was made to construct formal definitions for SS, SC and multiple other metrics for analysing such systems. These equations were used to compare formulas from different publications for SS and SC. The analysed samples confirm the notion that many of the equations are not extendible to systems capable of trading energy. Efficiency losses are often neglected completely, partially or are ambiguously defined which adds additional complexity to the comparison.