A two-stage stochastic unit-commitment formulation for evaluating the impact of battery energy storage systems on reserve requirements

In this paper, a suitable problem formulation is proposed to evaluate the effect of battery energy storage systems (BESSs) in reducing the reserve requirements of the power system. The problem is formulated as a two-stage stochastic unit-commitment problem. In the first stage, the commitment decisions, the energy dispatch and the reserve capacity needs are determined, while the second stage includes decisions that correspond to the real-time operation. The proposed optimization formulation follows a probabilistic approach and estimates the day-ahead reserve requirements that minimize the expected cost based on the uncertainty of renewable energy sources (RESs) generation. Moreover, the upward and downward regulation required to keep balance in the system are integrated for each scenario. To validate the proposed methodology, the updated version of the IEEE RTS 24-bus system for electricity market and power system operation studies is considered. As input data for the simulation, hourly time series provided by the Hellenic Transmission System Operator (TSO) are used to obtain realistic profiles for the RESs generation. An overall reduction in operational cost close to 2% was observed. Moreover, a significant reduction of over 20% was observed in reserve requirements. The results, therefore, indicate that BESSs installation can reduce reserve requirements by mitigating the deviation between forecasted and actual RESs generation.