CAISO battery storage in 2026: 8 things to watch
CAISO battery storage in 2026: 8 things to watch
The California Independent System Operator (CAISO) is the largest battery energy storage market in the United States. Its benchmarked battery energy storage system (BESS) fleet reached 16.2 GW on 13 August 2026, after a record 4.7 GW year in 2025 (Modo Energy, 2026). Resource Adequacy contracts provide over half the revenue for most CAISO batteries, which earned $2.55/kW-month in June 2026 (Modo Energy, 2026).
This guide is the second in Modo Energy's US ISO and RTO series.
Key statistics
| Metric | Value (as of) | Source |
|---|---|---|
| Installed BESS capacity, benchmark basis (separately metered resources) | 16.2 GW (13 Aug 2026) | Modo Energy |
| Installed BESS capacity, all sites (including shared-meter hybrids) | 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 (2025 analysis) | Modo Energy |
| RA capacity contract price | Up ~66%, 2020 to Sep 2024; 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
- Slice-of-Day reform is changing how Resource Adequacy value is earned, and lenders size debt against that contracted revenue (Modo Energy, 2025).
- Merchant revenue hit a record monthly low in December 2025 and has only partly recovered (Modo Energy, 2026).
- Negative day-ahead price hours tripled year-on-year to 66 in June 2026, and spring 2026 solar curtailment averaged a record 4.8 GW (Modo Energy, 2026).
- As of the January 2026 queue data, Cluster 14 had produced zero completions from 97 GW of proposed projects (Modo Energy, 2026).
- Siting risk is now a financing constraint. SB 283 has applied since January 2026.
1. Resource Adequacy provides over half the revenue for most CAISO batteries
For most CAISO batteries, Resource Adequacy capacity contracts provide over half of total revenue. In ERCOT, by contrast, merchant energy and ancillary services carry the return, which makes RA the structural difference between the two markets.
"Resource Adequacy contracts provide over half the revenue for most battery energy storage systems in California today."
Ovais Kashif, Market Analyst, Modo Energy
RA is a compliance program. Load-Serving Entities must secure capacity to cover forecast peak demand plus a reserve margin, and resources sign bilateral contracts with a must-offer obligation for a fixed monthly payment. That certainty is what lets developers finance projects.
Summer weighted-average capacity prices rose about 66% between 2020 and September 2024, which is where Modo Energy's published RA price series ends. Scarcity drove some Community Choice Aggregators to pay up to $100/kW-month (Modo Energy, 2025). Battery contracts stay more conservative, rarely above $35/kW-month, because operators lock in flat multi-year strikes.
Slice-of-Day reform is the bigger shift. It replaces a single monthly peak target with a 24-hour obligation, and makes storage account for its charging need. Batteries now earn RA by shifting capacity into the tight evening ramp. The 2026-2027 Planning Reserve Margin is 18% (CPUC, 2025), which keeps evening capacity demand firm.
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 →
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 to $2.55/kW-month in June, down about 17% year-on-year (Modo Energy, 2026).
Merchant revenue sits on top of the RA contract, so it sets the marginal return. 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 split revenue between 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 chasing the same spreads, and mild weather.
Underwrite to the trailing-year average. A single peak or trough will mislead the base case.
CAISO June 2026: Battery revenues slip to $2.55/kW
The latest monthly benchmark and what drove it. Read more →
What are CAISO batteries earning right now?
The ME BESS CAISO index is the independent benchmark behind the revenue figures in this article, and it attributes performance to the days, services, and strategies that drove it.
Explore the Benchmarks →3. What is the duck curve doing to CAISO battery economics?
The duck curve is deepening, and it is compressing the spread batteries trade. Midday solar pushes prices toward or below zero, then generation ramps down fast into the evening peak batteries are paid to serve (Modo Energy, 2026).
The swing between midday and evening is where a battery earns. In June 2026, day-ahead prices at the 2pm trough averaged $7/MWh while the 7pm peak averaged $35/MWh, against $16.55/MWh and $52/MWh a year earlier. Daily TB4 spreads narrowed from $135/MW to $116/MW, and negative-price hours tripled to 66 (Modo Energy, 2026).
Across spring 2026, solar curtailment averaged a record 4.8 GW, and CAISO solar captured a negative price of -$1.7/MWh (Modo Energy, 2026).
The spread varies by location, and that gap is narrowing. SP15 arbitrage spreads ran about 40% wider than NP15 in 2024 (Modo Energy, 2025). The SP15 premium over NP15 then fell from $36/MW in June 2025 to $20/MW in June 2026 (Modo Energy, 2026).
Deeper midday troughs cut charging costs, but revenue still depends on catching the evening ramp.
CAISO Solar captured -$1.7/MWh in spring 2026
Why midday prices keep falling below zero. Read more →
4. Four-hour duration dominates CAISO, and the average battery now runs 3.8 hours
Four-hour duration is the CAISO default because Resource Adequacy measures capacity over four consecutive hours. That single rule shapes how developers build.
The fleet reflects it. Average CAISO battery duration reached about 3.8 hours at the end of 2025, and new builds 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. Shorter systems must derate to qualify, which caps their capacity revenue.
Duration also decides how much of the evening ramp a battery captures. In Q2 2026, every two-hour project Modo Energy tracked sat in ERCOT. Every financed project outside Texas was sized to four hours (Modo Energy, 2026). For owners weighing build spec, four-hour remains the California standard.
Market design and policy feed back into CAISO revenues too. Ko tracks Modo Energy's live California data and long-range forecasts.
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).
The near-term effect on spreads is a headwind. Pooling CAISO with a larger, thermal-heavy footprint flattens the daily price curve. 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. That lifts the daily minimum-to-maximum ratio from 10% to 31% (Modo Energy, 2026).
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. Pricing at generator nodes lets a battery write capacity swaps and tolling deals against its own settlement point, reaching more than 50 California Load-Serving Entities (Modo Energy, 2026). For owners, EDAM matters more for offtake access than for new merchant revenue.
WECC: What the launch of EDAM means for renewable investments
The two new products and the contracting shift. Read more →
6. The fleet passed 16 GW in 2026, and the queue points to 37 GW by the mid-2030s
CAISO is the largest US battery fleet, and its growth is the main structural pressure on merchant spreads. Counting every site, the fleet reached 15.7 GW at the end of 2025 after a record 4.7 GW year (Modo Energy, 2026).
Modo Energy's benchmark, which covers separately metered resources only, passed 16.2 GW in August 2026 (Modo Energy, 2026). The near-term pipeline points to about 23 GW by 2027, and the long-term queue to roughly 37 GW by the mid-2030s (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 revenue has compressed.
Most of that pipeline never reaches operation. About 10% of projects entering the queue are built. That rises to 36% after the facilities study, and 76% once a project executes an interconnection agreement (Modo Energy, 2026).
Recent cohorts have fared worse still. On the January 2026 queue data, Cluster 14 had produced zero completions from 345 projects and 97 GW of proposed capacity (Modo Energy, 2026). For investors, queue progress is the best predictor of which projects add supply.
CAISO battery fleet crosses 15 GW after record 4.7 GW year
Buildout by zone, coupling, and pipeline. Read more →
7. How is siting and permitting risk changing after Moss Landing?
Siting and permitting are now a live risk to CAISO project timelines. The January 2025 Moss Landing fire triggered new state law and a wave of local restrictions.
SB 283 took effect on 1 January 2026. It requires developers to meet the local fire authority at least 30 days before filing an application, and requires an inspection before operations begin (California SB 283).
Since 1 July 2026 the Office of the State Fire Marshal has also been directed to consider BESS siting restrictions in the next building-code update.
Local restrictions followed, and several were time-limited. Orange County imposed an emergency moratorium on new battery approvals in January 2025, then extended it while drafting permanent zoning standards (Energy-Storage.news, 2025).
For owners and lenders, that means longer timelines and more local permitting uncertainty. Early engagement with fire authorities and county planners is now on the critical path.
8. Who is financing CAISO batteries, and what does OBBBA change?
Resource Adequacy offtake is what makes a CAISO project bankable, and US banks returned to the lender base in Q2 2026. The One Big Beautiful Bill Act (OBBBA) leaves standalone storage a longer tax-credit runway than solar or wind, while tightening where project costs may be sourced.
CAISO led US battery deal activity in Q2 2026 with four transactions and 1.3 GW. The largest was IPX Power's Darden complex in Fresno County. That $4.95 billion solar-plus-storage financing pairs 1.15 GW of solar with 4.6 GWh of batteries, and drew 19 banks (Modo Energy, 2026).
TransGrid Energy's Atlas VIII in Arizona, inside CAISO's balancing area, raised $656 million of debt in 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.
US banks came back in Q2 2026, after three quarters with no US-headquartered lender in the top five. Wells Fargo, J.P. Morgan, Truist, KeyBanc, and CoBank all joined syndicates (Modo Energy, 2026). Deal size flipped too. Established markets averaged 274 MW per transaction against 372 MW in emerging ISOs. That reverses the Q1 pattern.
The tax change cuts two ways. Storage starting construction before 2034 keeps the full 30% investment tax credit, where solar and wind faced a 4 July 2026 deadline (ICS Tax, 2025).
But foreign-entity rules require a rising share of project costs from approved sources, at 55% in 2026 rising to 75% by 2030 (Novogradac, 2026). The runway is real; supply-chain sourcing is now a financing gate.
U.S. BESS Capital Markets Report - Q2 2026
Deal flow, lenders, and structures by market. Read more →
Frequently asked questions
How much battery storage capacity does CAISO have in 2026?
Modo Energy's CAISO benchmark reached 16.2 GW on 13 August 2026 (Modo Energy, 2026). Counting every site, including co-located batteries that share a meter, CAISO held 15.7 GW and 59.6 GWh at the end of 2025 after a record 4.7 GW year (Modo Energy, 2026). It is the largest battery energy storage market in the United States.
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 when it qualifies capacity.
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 over four consecutive hours. Four-hour systems can contract their full nameplate for RA, so four-hour is the California build standard. Average fleet duration was around 3.8 hours at the end of 2025 (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 13 markets, including all seven US ISOs and RTOs. It covers wholesale prices, market design, regulation, and policy out to 2050.
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 that data and on forecasts to 2050.
Explore live CAISO BESS data and forecasts to 2050 with free Terminal access.
Last updated: 18 August 2026
About the author
Neil Weaver is a Power Market Analyst at Modo Energy. Since 2021 he has covered battery storage and power markets across the US, GB, Europe, and Australia. He writes and presents The Energy Academy: Great Britain (YouTube). Find Neil on LinkedIn.
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