Quantifying power and energy fluctuations of photovoltaic systems

Abstract

The high share of power generation based on fluctuating renewable energy sources, especially wind and solar, has increased the levels of variability and uncertainty in power systems. The aim of this study is to develop a method for quantifying the variability of photovoltaic (PV) systems. The developed method investigates the power measurements of a PV system and quantifies its power and energy fluctuations in three steps. The first includes a classification of days into three classes according to the variability and power output of the PV system. The second consists of computing the empirical cumulative distribution functions of PV power ramps for the given classes. The third calculates the PV daily energy fluctuations based on predicted PV power output. This method of PV variability quantification was then applied to seven rooftop PV systems in different locations that feature different installed capacities, years of installation, orientations and solar cell types. The testing of this method indicates that it can be used to quantify the power and energy fluctuations of different PV systems, independent of their locations and technical characteristics. The proposed method was developed as part of a general approach for quantifying the flexibility potential of buildings and city districts with PV systems.