Sizing of energy storage systems for ramp rate control of photovoltaic strings

Abstract

In this article, a comprehensive study on the sizing of energy storage systems (ESS) for ramp rate (RR) control of photovoltaic (PV) strings is presented. The effects of RR limit and inverter sizing, including their combined effect, on the sizing of the ESS are herein studied systematically for the first time. The study is based on 38 days of current–voltage curve measurements of a PV string of 23 PV modules. The results show that the daily irradiance profile has a crucial effect on the ESS power and energy requirements. It was found that an ESS power rating of 60% of the PV string nominal power is adequate to smooth almost all detected PV power ramps even with strict RR limits. With a typical DC/AC power ratio of 1.5, about 1.0 h of energy storage capacity is needed at the nominal power of the PV string to smooth all PV power ramps. The results illustrate that the set RR limit and the inverter sizing are important factors for sizing the ESS for PV RR control. Moreover, the results indicate that the needed ESS power capacity can be considerably reduced by smoothing the fastest upward power ramps by power curtailment.