Tehachapi Energy Storage Project

The TSP system was one of the first to demonstrate the assembly of a large quantity of lithium-ion batteries into a single operating 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.[10]

The TSP system was designed and evaluated using an application-driven approach.[11] Energy storage for the wind farms at Tehachapi Pass[12] have been extensively studied before, including the impacts of energy storage at Monolith Substation.[13] 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.[14]

The history of seismic activity in Kern County,[15] including damage to substation structures,[16] 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.[17][18] Since commissioning in 2014, the area has experienced not only seismic activity,[19] but also flash floods and subsequent mudslides.[20]

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.[1][21] 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.[21] The batteries are housed in a 6,300 square foot building.[22]

Inside the Tehachapi Energy Storage Project During Construction

Mini-System Used for Sub-Scale Testing and Evaluation

TSP is an example of commercially-available, large-scale energy storage for electric grid applications[24][25] and part of the increasing fleet of energy storage systems.[26] The deployment of TSP has been part of the key foundation in developing energy storage in California[27] and for increasing grid reliability overall.[28] TSP is also providing improved integration and opportunities for better operation of renewable energy resources.[29]

During 2009 to 2014, more than 120 grid energy storage projects were commissioned, marking a significant turning point for grid batteries.[30] The TSP system had a significant role in this as a large, utility-owned system providing multiple energy services using commercially available products.[30]

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.[21][31] 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.[7] Some of the additional 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.[23]

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/non-spin replacement reserves, ramp management, and energy price arbitrage.[32] The TSP system was tested using eight core tests performed by the grid operator or under market control.[33] Both the utility and system provider gained important perspectives and insights during the design, construction, commissioning, and operating of the TSP system.[34][7][17]

To evaluate the 13 operational uses, SCE defined the following eight tests that were designed to measure the ability of TSP to respond to the following system needs or signals: 1) Provide steady state voltage regulation at the local Monolith 66 kV bus 2) Provide steady state voltage regulation at the local Monolith 66 kV bus while performing any other tests 3) Charge during periods of high wind and discharge during low wind under SCE system operator control 4) Charge during off-peak periods and discharge during on-peak periods under SCE system operator control 5) Charge and discharge seconds-to-minutes as needed to smooth intermittent generation in response to a real-time signal 6) Respond to CAISO control signals to provide frequency response 7) Respond to CAISO control signals to provide spin/non-spin reserves 8) Follow a CAISO market signal for energy price.[7]

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.[7] These accomplishments included:[7]

• 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/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.

Since the start of market operations in 2016, TSP has been listed in the Monthly Electric Generator Inventory of the U.S. Energy Information Administration (EIA) as an electric generator.[35] During that same 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.[36]

The operation of the TSP system has been described as a real-life example of grid-connected energy storage[37] and some of the initial testing included storing wind energy at night and delivering it during the day when customers need it.[38] The California Independent System Operator (CAISO), a grid system operator, has shared its operating experiences of TSP internationally with other grid operators as part of continued close collaborations.[39] The ongoing operation of the TSP system continues to provide grid services in the energy matket and lessons learned for grid energy storage systems.[40][41]

One of the major benefits of the TSP system is the wide range of studies and analyses performed by multiple organizations to address various aspects of the energy market. Operational information has been used as part of developing incentives for distributed energy storage for California, New York, Hawaii, and several other states.[42] The Energy Management System (EMS) and EMS structure for TSP have been studied in order to develop and determine the technical, market, and regulatory requirements for energy storage systems.[43]

The University of California, Riverside has used TSP for the stochastic valuation of energy storage in wholesale power markets to determine optimal power dispatch sequences.[44] The findings from this study include: 1) System performance is heavily affected by roundtrip effiency and power-to-energy ratio, 2) The optimal power-to-energy ratio for wholesale power market is much higher than the nominal configuration of 1-to-4 typically used in existing energy storage projects, 3) The majority of revenues are from frequency regulation services.[45]

In a separate analysis, the University of California, Riverside used real market data from TSP in order to develop an optimal supply and demand bidding, scheduling, and deployment design framework based on the day-ahead and real-time market prices, location, size, efficiency, lifetime, and charge and discharge rates.[46] The topic of used and second-use batteries is also examined and analysis shows that by using one of the proposed bidding methods, TSP could still be profitable even after losing half of its energy capacity.[46]

Based on the studies described above, the University of California, Riverside performed another analysis for the scenarios where battery systems are investor-owned and independently-operated and participating in existing markets.[47] The study proposes a new optimization framework to coordinate the operation of large, price-maker, and geographically dispersed energy storage systems in a nodal transmission-constrained energy market.[47]

The Edison Electric Institute (EEI), which represents all investor-owned utilities in the United States, has described how TSP has capabilities to provide nearly instantaneous maximum capacity for renewables ramping, which minimizes needs for traditional backup generators.[48]

The European Commission performs an ongoing analysis of energy storage systems, including TSP, and has global collaborations with technical experts to exchange and to learn about operating details, challenges, and best practices.[49]

An official ribbon-cutting ceremony, site tour, and presentation of a certificate of recognition from the California State Senate were held on September, 24, 2014.[2][50][51] The ceremony speakers included Doug Kim (Director of Advanced Technology, Southern California Edison), Zack Scrivner (Supervisor, Kern County Board of Supervisors), Dr. Imre Gyuk (Energy Storage Program Manager, United States Department of Energy), Dr. Seokhwan Kwak (Vice President of Marketing, LG Chem), and Romeo Agbalog (Office of State Senator, Jean Fuller - 18th District).[51] Tours of the control room, battery room, and inverter enclosures were provided.[50][51]

Upon commissioning, TSP was selected to be a Finalist for the 2014 Innovation Award for Energy Storage North America (ESNA).[52][53] TSP is a member of the ESNA Hall of Fame.[54] In 2016, the California Energy Storage Alliance featured TSP in the leadoff position in a video with policymakers, utility executives, and energy storage pioneers entitled Gamechangers: How Energy Storage Transforms the Power System that describes how SCE pioneered the use of grid energy storage.[55]

The 2018 and 2019 Economic Round Table Reports from the Greater Antelope Valley Economic Alliance include TSP as a highlight in the Renewable Energy sections.[56][57] Kern County, CA describes TSP as a key feature in its renewable energy portfolio[58] for storing energy from solar power and wind power and improving grid flexibility and reliability.[59] Kern County continues to cultivate energy storage as providing economic development opportunities for 2020 and beyond.[60] In 2019, the U.S. Department of Energy featured TSP in Success Stories Spotlight: Solving Industry’s Energy Storage Challenges.[61]

• Electric grid
• Electrical substation
• List of energy storage projects
• Energy market

• Southern California Edison
• California Independent System Operator
• United States Department of Energy, Office of Electricity
• United State Energy Information Administration