Optimal Sizing of a Photovoltaic/Battery Energy Storage System to Supply Electric Substation Auxiliary Systems under Contingency

Electric substations (ESS) are important facilities that must operate even under contingency to guarantee the electrical system's performance. To achieve this goal, the Brazilian national electricity system operator establishes that alternating current (AC) auxiliary systems of ESS must have, at least, two power supplies, and in the case of failure of these sources, an emergency generator (EG) must at least supply energy to the essential loads. In order to improve the availability of auxiliary systems, a microgrid with other sources, such as photovoltaic (PV) systems and Battery Energy Storage Systems (BESS), can be an alternative. In this case, an economical optimization of the PV/BESS system must be addressed considering the costs associated with the installation and maintenance of equipment, and the gains from the credits generated by the photovoltaic system in the net metering scheme. In this paper, the size of the BESS system was determined to supply energy to the load of auxiliary systems of an ESS, as well as a PV system to achieve a null total cost. Furthermore, multi-objective optimization using the genetic algorithm technique was employed to optimize the size of the hybrid PV/BESS to minimize the investment cost and time when the demand was not met. Simulations under different scenarios of contingency were allowed to obtain the Pareto frontier for the optimal sizing of a PV/BESS system to supply energy to AC auxiliary systems in an ESS under contingency.

Automated summary

In order to ensure the performance of the electrical system, the Brazilian national electricity system operator requires at least two power supplies for the AC auxiliary systems of the Electric substations (ESS), and an emergency generator (EG) to supply energy to essential loads in case of failure of these sources. To improve the availability of auxiliary systems, a microgrid with photovoltaic systems and Battery Energy Storage Systems (BESS) can be considered. This study focuses on the economic optimization of the PV/BESS system, taking into account the costs of equipment installation and maintenance, as well as the gains from the credits generated by the photovoltaic system in the net metering scheme, aiming to achieve a null total cost.