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 6,300-square-foot (590 m2) 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.
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