Synergising PV plants and BESS for firm generation and power reserve services using opportunity costs

Reliably dispatching power and maintaining sufficient system reserves becomes increasingly complex as the integration of Photovoltaic (PV) plants grows. This paper investigates this problem by combining PV plants and Battery Energy Storage Systems (BESS) for an optimised provision of firm generation and power reserve. A piecewise linear model for PV systems is firstly developed and integrated with a BESS model to enable plant-level Firm Renewable Energy Time Shift (FRETS). An improved security constrained economic dispatch model is then tailored to study power networks including several PV + BESS stations. Generation and reserves are co-optimised based on dispatch merit and opportunity costs related to providing power reserve instead of power supply. We evaluate the proposed approach using the IEEE 9-bus and RTS 24-bus test systems integrating one and five PV + BESS stations, respectively. For this, we conducted multi-period, 1-hour look-ahead simulations under varying conditions of demand and solar irradiance. By setting all generation plants to provide reserves between 3% and 8% respect to dispatched power, reserve costs accounted for only 3% and 6% of generation costs for both test systems, respectively, with the PV + BESS stations contributing to firm generation and power reserve services simultaneously.