The Tehachapi Energy Storage Project (TSP) was a 8MW/32MWh lithium-ion battery-based grid energy storage system at the Monolith Substation of Southern California Edison (SCE) in Tehachapi, California, California, United States. It has the capacity to power between 1,600 and 2,400 homes for four hours. At the time of commissioning in 2014, it was the largest lithium-ion battery system operating in North America and one of the largest in the world. TSP is considered to be a modern-day energy storage pioneer with significant accomplishments that have proven the viability of utility-scale energy storage using lithium-ion technology. While originally envisioned as a research and development project, TSP operated as a distribution-level resource for SCE and for calendar year 2020, SCE reported that TSP operated in the wholesale energy market with revenue exceeding operating and maintenance costs. In 2021, SCE began the decommissioning of TSP, which was followed by formal decommissioning by state regulators in 2022. The physical dismantlement of TSP is expected to be completed by the end of 2022.
System
In May 2013, Southern California Edison awarded the TSP contract to a consortium led by LG Chem, the battery division of the South Korean industrial conglomerate LG Corporation. LG Chem supplied the battery systems while ABB supplied the inverters and LG CNS provided the engineering and construction support.
The TSP system was one of the first to demonstrate the assembly of a large quantity of lithium-ion batteries into a single system on the order of megawatts of power and tens of megawatt-hours of energy to provide electric grid support. The project uses electric vehicle-grade batteries and demonstrates the synergies between batteries for the automotive and electric grid sectors. During 2009 to 2014, more than 120 grid energy storage projects were commissioned, marking a significant turning point for grid batteries. The TSP system had a significant role in this as a large, utility-owned system providing multiple energy services using commercially available products.
The TSP system was designed and evaluated using an application-driven approach. Energy storage for the wind farms at Tehachapi Pass have been extensively studied before, including the impacts of energy storage at Monolith Substation. As Edison International, parent company of Southern California Edison (SCE), describes, there is a continued interest in energy storage from utilities, along with a view that there will be technical innovations to help with managing the grid in a more efficient and reliable manner.
The history of seismic activity in Kern County, including damage to substation structures, created some challenging system design requirements, such as having the populated battery racks designed and tested to meet IEEE 693-2005, Recommended Practice for Seismic Design of Substations recommendations. Since commissioning in 2014, the area has experienced not only seismic activity, but also flash floods and subsequent mudslides.
One key lesson learned is the importance of subscale testing by the electric utility prior to full system deployment so that the safety and operational controls and features could be fully evaluated. This was the first known use of a subscale system by an entity other than a manufacturer or integrator to facilitate full-scale testing, commissioning, and ongoing operations. The mini-system test plan included two phases: Performing safety testing on the expected behavior of the batteries and battery management system during interruptions to communication paths during system startup and operation and Performing system acceptance tests on the Mini-System to verify correct operation of the control algorithms, test modes, and system response prior to performing the same tests on the full system. The original mini-system provided engineers with support for full system startup and commissioning, but, with only one battery section and one inverter lineup, engineers were unable to test the multi-inverter lineup-battery section operation of the system in the laboratory, such as inter-section balancing controls, multi-inverter operation, and symmetrical and unsymmetrical operation of the inverter lineups. To more closely resemble the full system, the mini-system was expanded in December 2015 to include twice the number of each component, resulting in a system with two inverter controllers, inverter lineups, and battery sections.
The TSP system is constructed of 608,832 lithium-ion battery cells that are enclosed into 10,872 modules of 56 cells each and then stacked in 604 racks. A bi-directional inverter or power conversion system (PCS) provides the DC-to-AC conversion during battery discharging and AC-to-DC conversion for battery charging. The batteries are housed in a building. The TSP system can supply 32 megawatt-hours of energy, at a maximum rate of 8 megawatts. This is sufficient to power between 1,600 and 2,400 homes for four hours. The amount of energy stored at TSP is equivalent to that stored in more than 2,000 Chevrolet Volt hybrid electric vehicles.
Specifications for mini-system and full systemMini-System at Pomona, CA (Original)Mini-System at Pomona, CA (December 2015 Expansion)Full System at Tehachapi, CAFootprint77 square feet154 square feet6300-square-foot buildingPower30 kW60 kW8 MWEnergy116 kWh232 kWh32 MWhInverterOne mini-cabinetTwo mini-cabinetsTwo 40-foot containersSections124Banks1232Racks24604Modules367210,872Cells2,0164,032608,832
Deployment TSP is an example of commercially available large-scale energy storage for electric grid applications; and part of the increasing fleet of energy storage systems. The deployment of TSP has been part of the key foundation in developing energy storage in California and for increasing grid reliability overall. TSP is also providing improved integration and opportunities for better operation of renewable energy resources.
In 2014, TSP was one of the large-scale energy storage projects in the interconnection queue for the California Independent System Operator (CAISO) with planned benefits including firming renewable generation, frequency regulation, spin and non-spin replacement reserves, ramp management, and energy price arbitrage. The TSP system was tested using eight core tests performed by the grid operator or under market control. Some of the lessons learned included the challenges related to outage scheduling, challenges with interconnection agreements, benefits of component validation testing at the factories, and preparing detailed step-by-step test plans in advance. Both the utility and system provider gained important perspectives and insights during the design, construction, commissioning, and operating of the TSP system.
To evaluate the 13 operational uses, SCE defined eight tests to measure the ability of TSP to respond to the following system needs or signals: Provide steady state voltage regulation at the local Monolith 66 kV bus Provide steady state voltage regulation at the local Monolith 66 kV bus while performing any other tests Charge during periods of high wind and discharge during low wind under SCE system operator control Charge during off-peak periods and discharge during on-peak periods under SCE system operator control Charge and discharge seconds-to-minutes as needed to smooth intermittent generation in response to a real-time signal Respond to CAISO control signals to provide frequency response Respond to CAISO control signals to provide spin and non-spin reserves Follow a CAISO market signal for energy price. Tehachapi Operational Uses and TestsOperational UseTest12345678TransmissionVoltage Support1XXDecreased Losses2XDiminished Congestion3XIncreased System Reliability4XDeferred Transmission Investment5XXOptimized Renewable-Related Transmission6XXSystemSystem Capacity/Resource Adequacy7XXRenewable Integration (firming & shaping)8XOutput Shifting9XISO MarketFrequency Regulation10XSpin and Non-Spin Reserves11XDeliver Ramp Rate12XXEnergy Price Arbitrage13X
The final project report for the United States Department of Energy after system deployment concludes that TSP is a modern-day energy storage pioneer, achieving a number of significant accomplishments that have proven the viability of utility-scale energy storage using lithium-ion technology. These accomplishments include:
The largest lithium-ion battery energy storage system in North America in terms of energy capacity (32 MWh) at the time of commissioning in 2014 The first battery energy storage system in California specifically designed and operated as a dual-use asset, supporting utility transmission and distribution functions and operating in the competitive power market The first known use of a subscale or mini-system by an entity other than a manufacturer or integrator to facilitate full scale testing, commissioning, and ongoing operations The first battery energy storage system integrated with SCE’s systemwide Supervisory Control and Data Acquisition (SCADA) system providing high-level visibility and control to grid operators The first battery energy storage system to be operated by SCE and one of the first to be interconnected, certified, and operated in the CAISO market The first modern, large-scale, lithium-ion battery energy storage system installed in an SCE substation and connected to the regional transmission network Serving as the foundation for subsequent SCE energy storage procurements
Operation Since the start of market operations in 2016, TSP has been listed in the Monthly Electric Generator Inventory of the Energy Information Administration (EIA) as an electric generator. During that time period, the EIA began publishing more-detailed energy storage information in its Annual Electric Generator Report, including battery capacity, charge and discharge rates, storage technology types, reactive power ratings, storage enclosure types, and expected usage applications.
The operation of the TSP system has been described as a real-life example of grid-connected energy storage, and some of the initial testing included storing wind energy at night and delivering it during the day when customers need it. The California Independent System Operator (CAISO), a grid system operator, shares its operating experiences of TSP internationally with other grid operators as part of continued close collaborations. The ongoing operation of the TSP system continues to provide grid services in the energy market and lessons learned for grid energy-storage systems.
In its annual report to the California Public Utilities Commission (CPUC) for calendar year 2020, SCE reported that TSP continued to operate in the CAISO wholesale market and that market benefits exceeded operating and maintenance costs. In addition to market operations, SCE continued to collect operating data to evaluate the long-term operating characteristics of grid scale lithium-ion battery storage technology.
TSP was taken offline on May 17, 2021 and on August 23, 2021, SCE submitted a request to the CPUC for the decommissioning of TSP due to the cost of safety upgrades and cybersecurity concerns. On May 5, 2022, the CPUC formally decommissioned TSP, nine years after it came online. The physical dismantlement of TSP is expected to be completed by the end of 2022. All of the battery cells will be recycled and the inverter will be repurposed. TSP operated for more than four years beyond the original two-year demonstration period, which SCE considers to be significant due to the fact that TSP uses first-generation lithium-ion BESS products that are no longer in production. The additional operational period has provided lessons learned about long-term operations, maintenance, and repairs. Due to the system size, TSP will be one of the first and largest lithium-ion battery systems to undergo decommissioning. SCE describes that:
Analysis