The total rated power of battery energy storage across the US could be as high as 140 GW by 2030. CAISO and ERCOT have led the way and are set to deliver the bulk of this forecast.
But how much of this capacity is commercially operational today? What are the biggest battery sites in CAISO in 2024? And which batteries are coming into the picture in 2025?
How much battery energy storage will be operational in CAISO by the end of 2024?
CAISO plans to bring 1.5 GW of battery energy storage online in Q4 2024, marking the largest single-quarter increase to date. This will bring total operational power capacity to 12 GW, as buildout rapidly increases from 470 MW just four years ago.
We’ve measured operational battery energy storage systems by nameplate capacity, as listed on CAISO’s Master Control Area Generating Capability List.
The Master List provides details for resources that are actively operating in CAISO’s markets and are part of the California ISO Balancing Area Authority (CISO BAA). It excludes batteries participating in CAISO markets that are not under the CISO BAA. Those sites would be in neighboring Balancing Areas comprising the Western Energy Imbalance Market.
The battery energy storage systems measured here include standalone, co-located, and hybrid resources.
Both co-located and hybrid batteries are physically located alongside other generation technologies, sharing a point of interconnection to the grid. However, they differ in how they engage with the power market.
The system operator regards co-located batteries as separate market entities with their own resource IDs. This makes it possible to measure their operational capacity.
Hybrid resources, however, are managed as a single entity with one resource ID. The Master List does not isolate the capacity provided by each technology type. Here we have used data from the EIA to split hybrid sites and obtain the power that batteries contribute independently.
What will the biggest battery energy storage sites in CAISO be by the end of 2024?
Half of the projected 12 GW for 2024 will come from 17 sites with a rated power of 200 MW and over, and the five largest sites by rated power will contribute a quarter of total capacity.
This includes California’s largest site to date, Edwards & Sanborn—a 1,066 MW/3,287 MWh battery system accompanying an 875 MWdc solar farm in Kern County. The Master List registers it as 13 individual resources, combining co-located and hybrid units.
Following this are Moss Landing (700 MW/3,000 MWh), Nova Power Bank (620 MW/2,480 MWh), Desert Sunlight (420 MW/1,840 MWh), and Desert Peak (400 MW/1,600 MWh) — all four-hour duration systems.
In fact, most batteries in California have durations of four hours. This makes them eligible to earn revenue through California’s Resource Adequacy contracts. Developers establish these contracts with Load Serving Entities as long-term bilaterally traded agreements to ensure sufficient capacity is available in the system to meet future requirements. Participating resources must prove they can sustain a steady output for four consecutive hours. This forms a significant source of steady revenue to support the case for financing BESS assets.
Where has CAISO built its batteries?
CAISO is divided into three congestion regions. The first two lie North and South of a constrained segment of the transmission system known as Path 15. These are regarded as NP15 and SP15.
The third zone, ZP26, covers an additional constrained region between Path 15 and Path 26 on the transmission system but forms a smaller portion of CAISO’s area.
The first batteries in California were built in SP15, and today the zone accounts for 75% of CAISO's total BESS capacity.
This is partly due to the solar capacity that dominates the southern region. Intermittent generation increases price volatility during the day, improving battery arbitrage revenues. It also provides opportunities to raise the utilization of these renewable generators as part of co-located and hybrid sites.
What batteries are coming online in 2025?
Looking at the battery landscape in CAISO over the next 12 months, we expect an increase of at least another 5.6 GW in rated power.
49 batteries across 39 sites are engaged in the New Resource Implementation process to begin operating in 2025. This includes batteries that are active and undergoing testing to see if they can synchronize with the grid. Once a battery achieves this stage, its Commercial Operation Date (COD) is assumed to be fairly accurate.
The largest of these is a portion of the Atlas Complex, a 3,200 MW solar farm in Arizona that will have 1,920 MW of battery energy storage online when fully operationalized.
With these resources coming online, BESS power capacity across CAISO will reach 17.6 GW by the end of 2025.
However, total capacity could be even greater than this. The pipeline is most representative six months in advance, meaning the capacity expected to come online in Q3 and Q4 will likely increase.
Readers can download all of the data behind the charts in the article from the workbook below.