Optimal hybrid backup systems for substation auxiliary services during outages through stochastic programming

Auxiliary services are fundamental to ensure the uninterrupted operation, control, and surveillance of critical infrastructure. Traditional dependency on diesel generators as backup power sources during service disruptions is increasingly challenged by their non-renewable nature, operational costs, and environmental impacts. Addressing these concerns, this paper introduces a novel stochastic programming method for the optimal design of a hybrid backup system (HBS), integrating photovoltaic (PV) panels, battery storage, and bidirectional inverters, specifically tailored for substation auxiliary services (SAS). The proposed model represents the uncertainties associated with solar irradiance and power outages (occurrence and duration) through a scenario-based analysis, ensuring a required level of robustness. The proposed model is applied to a case study and a sensitivity analysis of the most important parameters was executed. It was identified that the optimal investment corresponds to an HBS formed by 6 batteries and 22 PV panels (18 kWh/8.58 kWp), providing a robustness level of 99.526 %, which reduces the unavailable hours of the SAS by 61 %. The findings underscore the pivotal contribution of battery systems to support SAS under outages, facilitating the attainment of requisite reliability thresholds. Nonetheless, achieving higher levels of robustness is intrinsically linked to increased financial investment in the backup system infrastructure.