Residential Energy Storage Study

Residential Battery Energy Storage Systems (BESSs) have become a popular solution marketed by the storage industry for electric grid1 resilience, mostly due to recent grid interruptions originating from fires and high wind events from Public Safety Power Shutoffs (PSPS). Utility program incentives have supported widespread customer adoption by reducing the cost of purchase and installation.  The BESS project is the next research phase following SCE’s Retail Automated Transactive Energy System (RATES) program, which studied an experimental subscription transactive tariff (completed 2020).2 In this project, four residential BESS systems were installed, three of which had existing solar Photovoltaic (PV) arrays. Incentives and marketing have accelerated the growth of residential battery storage systems.  The research objective was to demonstrate monitoring and automated control of four Behind-the-Meter (BTM) residential BESS systems, to provide real-time grid congestion support and demonstrate price responsiveness. These installations were located at three homes in the Moorpark, Thousand Oaks, and Westlake Village areas. In addition, “Site E” was in the Smart Energy Experience (SEE) Exhibit at SCE’s Irwindale Energy Education Center (EEC).  The project investigated and assessed how new, enabling Demand Response (DR) technologies could be provided by residential BESS in a way that enables SCE to leverage the asset value to customers and the electric grid.   This project also studied how customer resources could be deployed to automatically respond to grid needs while minimizing customer costs during peak pricing via Time-of-Use (TOU) schedules, which serve as an indicator of grid congestion.  Barriers of implementation were investigated to employ current BESS designs in a manner that provides the greatest value and resilience to the grid and the customer (co-optimization). The program balanced the benefits (cost savings and power backup capacity) while also relieving grid congestion.  It also investigated the integrated value of customer-owned BESS resources for Energy Efficiency (EE), DR, and other services that provide comprehensive value. BESS provides grid benefits, but also increases the complexity of controlling these systems. The project attempted to take BESS control to the next level by employing autonomous management through the manufacturer’s proprietary encrypted cloud-based Application Programming Interface (API). This interface was first designed for aggregators to leverage control of a virtually unlimited number of systems and develop specialized software to execute control commands, typically in a batch process.  A major goal was to study how SCE might share API control of the BESS. This innovative project proved more complex than anticipated, as described the Results and Discussion section of this report. The intent was to align BESS with grid pricing signals (proxy for grid congestion) and for autonomous real-time response, thus expanding the value of API control via pricing signals. The project encountered certain challenges, some of which were resolved, and others that will be the subject of future research. Implementation problems included delayed equipment supply, equipment reliability issues identified during installation and attempted operation, permit inspector and installer training gaps, and changes to equipment design and firmware not documented or communicated by the manufacturer.  On a positive note, the TOU-D-Prime rate tariff was found to help maximize customer savings for BESS, whether or not it was paired with PV generation.