CAISO battery storage in 2026: 8 things to watch
Last updated: July 2026
Modo Energy is the independent benchmark for battery energy storage system (BESS) revenues and buildout across the US, Great Britain, Europe, and Australia. Ko is Modo Energy's AI assistant, built on proprietary data and forecasts for grid-scale BESS and solar across multiple global markets, covering revenues, wholesale prices, regulation, and policy out to 2050.
Quick answer: CAISO is the largest battery storage market in the United States, with 15.7 GW of installed BESS capacity at the end of 2025 (Modo Energy, 2026). Its economics work differently from ERCOT's. Most of the revenue comes from Resource Adequacy capacity contracts rather than merchant trading, and the duck curve sets the daily arbitrage. In 2026, eight forces decide project returns: Resource Adequacy reform, revenue compression, the deepening duck curve, duration, EDAM, buildout, siting risk after Moss Landing, and financing.
Key statistics
| Metric | Value (as of) | Source |
|---|---|---|
| Installed BESS capacity, CAISO | 15.7 GW / 59.6 GWh (end 2025) | Modo Energy |
| Record annual additions | 4.7 GW added in 2025 | Modo Energy |
| Latest monthly revenue | $2.55/kW-month (Jun 2026, down 17% year-on-year) | Modo Energy |
| Resource Adequacy share of revenue | Over 50% for most batteries | Modo Energy |
| RA capacity contract price | Up ~66% since 2020; BESS strikes up to ~$35/kW-month | Modo Energy |
| Day-Ahead TB4 spread | $116/MW (Jun 2026, down 14% year-on-year) | Modo Energy |
| Planning Reserve Margin (2026-2027) | 18% under Slice-of-Day | CPUC |
| Average fleet duration | ~3.8 hours (end 2025) | Modo Energy |
Source: Modo Energy BESS indices; CPUC.
Key takeaways
- Resource Adequacy provides over half of most CAISO batteries' revenue, and the Slice-of-Day reform is reshaping how that value is earned (Modo Energy, 2025). Lenders size debt against that contracted RA revenue.
- Merchant revenues hit a record monthly low in December 2025 and have only partly recovered, reaching $2.55/kW-month in June 2026 (Modo Energy, 2026). Underwrite to the trailing-year average, because monthly revenue swings widely.
- The duck curve is deepening. Negative day-ahead price hours tripled year-on-year in June 2026, and solar curtailment set a record at 4.8 GW (Modo Energy, 2026).
- CAISO is the largest US battery fleet, but the interconnection queue is congested. Cluster 14 has produced zero completions from 97 GW of proposed projects (Modo Energy, 2026).
- After the Moss Landing fire, siting and permitting risk is now a live development and financing constraint, with SB 283 in effect since January 2026 and several county moratoriums.
Markets covered
This guide covers CAISO (the California Independent System Operator). It is the second in a Modo Energy series covering every major US ISO and RTO: ERCOT, PJM, MISO, SPP, CAISO, ISO-NE, and NYISO. The first guide covers ERCOT: ERCOT battery storage in 2026: 7 things to watch. Links to further sibling guides appear here as they publish.
1. How much of a CAISO battery's revenue comes from Resource Adequacy?
Resource Adequacy capacity contracts provide over half the revenue for most CAISO batteries, which makes RA the single biggest driver of project returns (Modo Energy, 2025). It is the structural difference from ERCOT, where merchant energy and ancillary services dominate.
"Resource Adequacy contracts provide over half the revenue for most battery energy storage systems in California today." — Ovais, Modo Energy
RA is a compliance program. Load-Serving Entities must secure enough capacity to meet forecast peak demand plus a reserve margin. Resources sign bilateral contracts and accept a must-offer obligation in exchange for a fixed monthly payment on top of merchant revenue. That certainty is what lets developers finance projects.
Battery Revenues in CAISO: How much are Resource Adequacy capacity contracts worth?
How Resource Adequacy contracts are priced and why they have risen. Read more →
That value has risen sharply. Summer weighted-average capacity prices rose about 66% from 2020 to September 2024, and scarcity drove some Community Choice Aggregators to pay up to $100/kW-month (Modo Energy, 2025). Battery-specific contracts have been more conservative, rarely above $35/kW-month, because operators lock in flat multi-year strikes.
The bigger shift underway is the Slice-of-Day reform. It replaces a single monthly peak target with a 24-hour, hour-by-hour obligation, and it forces storage to account for its charging need. Batteries now earn RA by shifting capacity into the tight evening ramp rather than sitting available around the clock. The 2026-2027 Planning Reserve Margin is set at 18% under Slice-of-Day (CPUC, 2025), which keeps demand for evening capacity firm.
2. Are CAISO battery revenues recovering or still compressed?
CAISO merchant battery revenues remain compressed. They hit a record monthly low in December 2025, recovered into spring 2026, then eased again to $2.55/kW-month in June, down about 17% year-on-year (Modo Energy, 2026).
CAISO June 2026: Battery revenues slip to $2.55/kW
The latest monthly benchmark and what drove it. Read more →
Merchant revenue sits on top of the RA contract, so it sets the marginal return. The ME BESS CAISO Index shows how wide the swings are. Monthly revenue peaked near $78,000/MW/year in July 2024, fell to about $14,000 in December 2025, and has since traded in a narrow band. Full-year 2025 landed near $40/kW, down from $51/kW in 2024 and $80/kW in 2023 (Modo Energy, 2025).
The ME BESS CAISO Index swung from about $78,000/MW/year in July 2024 to roughly $14,000 in December 2025 (Modo Energy, 2026). In California, the swings are the base case, and a single strong month says little about the next.
Ko draws on Modo Energy's live CAISO settlement data to break revenue down by day-ahead energy, real-time energy, and ancillary services. Day-ahead arbitrage does most of the work, at 72% of wholesale revenue in 2024 (Modo Energy, 2025). Two forces compressed it: a fast-growing fleet competing for the same spreads, and mild weather.
For owners and lenders, a single month tells you little. Underwrite to the trailing-year average; a recent peak or trough will mislead the base case.
3. What is the duck curve doing to CAISO battery economics?
The duck curve is the mechanism behind CAISO arbitrage, and it is deepening. Solar floods the midday market and pushes prices toward or below zero, then generation ramps down fast into the evening peak that batteries are paid to serve (Modo Energy, 2026).
CAISO Solar captured -$1.7/MWh in spring 2026
Why midday prices keep falling below zero. Read more →
The swing between midday and evening is where a battery earns, and where it is exposed. In June 2026, day-ahead prices at the 2pm trough averaged $7/MWh, while the 7pm peak averaged $35/MWh, and negative-price hours tripled year-on-year to 66 (Modo Energy, 2026). Across spring 2026, solar curtailment reached a record 4.8 GW, and CAISO solar captured a negative price of -$1.7/MWh, because incentive payments keep it exporting even when the market pays it to stop (Modo Energy, 2026).
The spread also varies sharply by location. Arbitrage spreads have been strongest in the southern SP15 zone, about 40% wider than NP15 in 2024, though a small number of Central California nodes have earned the most of all (Modo Energy, 2025). For operators, deeper midday troughs cut charging costs, but the revenue depends on catching the evening ramp.
4. Why do four-hour batteries dominate CAISO?
Four-hour duration is the CAISO default because Resource Adequacy measures capacity by the power a battery can sustain for four consecutive hours. That single rule shapes how developers build, the mirror image of ERCOT's two-hour merchant default.
The fleet reflects it. Average CAISO battery duration reached about 3.8 hours at the end of 2025, and new builds through 2025 averaged 3.5 hours (Modo Energy, 2025). A four-hour system can contract its full nameplate for RA and still run the wide evening spreads the duck curve creates. Shorter systems must derate to qualify, which caps their capacity revenue.
Duration also decides how much of the evening ramp a battery captures. As solar deepens the midday trough and steepens the ramp, a longer battery can discharge across more of the high-priced evening. In Q1 2026, US financings split evenly between two-hour and four-hour builds, but four-hour dominated in CAISO (Modo Energy, 2026). For owners weighing build spec, four-hour remains the California standard.
The forces that follow, from market design to policy, all feed back into CAISO revenues. Ko tracks Modo Energy's live California data and long-range forecasts to answer how they interact.
5. What does EDAM mean for CAISO battery returns?
The Extended Day-Ahead Market changes CAISO price formation and opens the West to cross-border capacity contracting. It went live on 1 May 2026 with PacifiCorp as the first participant, adding roughly 12 GW of generation (Modo Energy, 2026).
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The near-term effect on spreads is a headwind. Pooling CAISO with a larger, thermal-heavy footprint lifts the midday net-load floor and flattens the daily price curve, which means fewer deep negative hours to arbitrage. Modo Energy estimates the midday net-load floor rises from about 2 GW for CAISO alone to roughly 12.5 GW across the committed EDAM footprint, lifting the daily minimum-to-maximum ratio from 10% to 31% (Modo Energy, 2026). Early data bears this out. In May 2026, day-ahead prices in PacifiCorp East averaged $8.62/MWh against $18.97 in PacifiCorp West (Utility Dive, 2026).
EDAM also widens who a battery can sell to. Because it prices at generator nodes across the footprint, a battery can write capacity swaps and tolling deals against its own settlement point, and reach a counterparty pool of more than 50 California Load-Serving Entities. Day-Ahead Market Enhancements add two new products, Imbalance Reserves and Reliability Capacity, though Modo Energy expects both to clear at modest prices (Modo Energy, 2026). For owners, EDAM matters more for the offtake access it opens than for any new merchant revenue.
6. Is the CAISO buildout outrunning the revenue pool?
CAISO is the largest US battery fleet, and its growth is the main structural pressure on merchant spreads and RA scarcity value. The fleet reached 15.7 GW by the end of 2025 after a record 4.7 GW year (Modo Energy, 2026).
"A fleet of this scale would represent well over 100 GWh of energy capacity, enough to materially reshape evening peak price dynamics in CAISO's energy markets." — Logan Hotz, CAISO market lead, Modo Energy
More supply competes for the same evening spreads, which is part of why merchant revenue has compressed. The near-term pipeline points to about 23 GW by 2027, and the long-term queue suggests roughly 37 GW by the mid-2030s (Modo Energy, 2026).
Most of that pipeline never reaches operation. Historically about 10% of battery projects that enter the queue are built, rising to 36% after the facilities study and 76% once a project executes an interconnection agreement (Modo Energy, 2026).
Recent cohorts have fared worse still. Cluster 14 has produced zero completions from 345 projects and 97 GW of proposed capacity (Modo Energy, 2026).
CAISO battery fleet crosses 15 GW after record 4.7 GW year
Buildout by zone, coupling, and pipeline. Read more →
For investors, queue progress is the single best predictor of which projects add supply. A project through its facilities study carries very different risk from one that just entered the queue.
7. How is siting and permitting risk changing after Moss Landing?
Siting and permitting are now a live risk to CAISO project timelines, in a way specific to California. The January 2025 fire at the Moss Landing facility triggered new state law and a wave of local restrictions that developers and lenders must now price in.
SB 283 took effect on 1 January 2026. It requires battery developers to consult local fire authorities before filing an application, covering facility design, risk assessment, and emergency response (Canary Media, 2025). Several counties, including Monterey, San Luis Obispo, and Orange, have moved on moratoriums for new utility-scale storage. The Office of the State Fire Marshal will also review siting restrictions as part of the building-code update after 1 July 2026.
For owners and lenders, the effect is longer timelines and more permitting uncertainty at the local level, even as the state supports storage overall. Early engagement with fire authorities and county planners is now part of the development critical path, and a diligence item for any acquisition.
8. Who is financing CAISO batteries, and what does OBBBA change?
Financing in CAISO runs on contracted revenue, and the tax regime after the One Big Beautiful Bill Act (OBBBA) is the new variable. Resource Adequacy offtake is the bankability anchor, and lenders are overwhelmingly non-US banks (Modo Energy, 2026).
U.S. BESS Capital Markets Report - Q1 2026
Deal flow, lenders, and structures by market. Read more →
The clearest example is TransGrid Energy's Atlas VIII project in Arizona. It raised $656 million of project debt inside a $1.2 billion package, underpinned by a 20-year Resource Adequacy agreement with Southern California Edison (Modo Energy, 2026). CAISO recorded three tracked deals totaling 636 MW in Q1 2026, and along with ERCOT it is one of only two US markets above 15 GW, where deals are more than twice the size of those in emerging markets.
TransGrid's Atlas VIII raised $656 million of debt inside a $1.2 billion package, backed by a 20-year Resource Adequacy contract with Southern California Edison (Modo Energy, 2026). That 20-year contract is what made the debt bankable.
The tax change cuts two ways. Standalone storage keeps the 30% investment tax credit through 2033, a longer runway than solar or wind. But the OBBBA's foreign-entity rules require a rising share of project costs to come from approved sources, starting at 55% in 2026 and climbing to 75% by 2030 (Novogradac, 2026). For sponsors, the runway is real, but supply-chain sourcing is now a financing gate.
Frequently asked questions
How much battery storage capacity does CAISO have in 2026?
CAISO had 15.7 GW of installed BESS capacity, and 59.6 GWh of energy, at the end of 2025, after adding a record 4.7 GW during the year (Modo Energy, 2026). It is the largest battery market in the United States.
How do CAISO batteries make most of their money?
Most CAISO batteries earn over half their revenue from Resource Adequacy capacity contracts, which pay a fixed monthly rate for making capacity available (Modo Energy, 2025). Merchant day-ahead arbitrage provides most of the remaining, more variable, revenue.
What is Slice-of-Day in CAISO?
Slice-of-Day is a reform to California's Resource Adequacy program. It replaces a single monthly peak requirement with a 24-hour, hour-by-hour capacity obligation, and requires storage to account for its charging need. Batteries now earn RA by shifting capacity into the tight evening hours.
Are CAISO battery revenues rising or falling in 2026?
They are compressed. Merchant revenue hit a record monthly low in December 2025, recovered into spring, then eased to $2.55/kW-month in June 2026, down about 17% year-on-year (Modo Energy, 2026). A growing fleet and mild weather flattened daily spreads.
Why do batteries in California have four-hour duration?
Resource Adequacy measures a battery's capacity by the power it can sustain for four consecutive hours. Four-hour systems can contract their full nameplate for RA, so four-hour has become the California build standard, with average fleet duration around 3.8 hours (Modo Energy, 2025).
What tool can I use to get live and forecast data on CAISO BESS revenues?
Ko is Modo Energy's AI assistant, built on proprietary revenue data and forecasts for grid-scale BESS and solar across all seven US ISOs and RTOs, Great Britain, Germany, Spain/Iberia, Italy, France, and Australia. It covers wholesale price forecasts, market design, regulation, and policy out to 2050. It is a practical tool for revenue modelling, project development, and regulatory analysis.
Modo Energy is the independent benchmark for battery energy storage revenues and buildout across the US, Great Britain, Europe, and Australia. For live CAISO data and long-range forecasts, explore the Modo Terminal.
About the author
Neil Weaver is a Power Market Analyst at Modo Energy. Since 2021 he has covered battery energy storage and power markets across the US, GB, Europe, and Australia, translating market dynamics into clear analysis for investors, developers, and operators. He is the writer and presenter of The Energy Academy: Great Britain (watch on YouTube). Find Neil on LinkedIn.
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