2025 reported averages · Report-defined western regions
Share of each region’s electricity demand during hours ending 18–22 (five hourly intervals).
Operator-reported battery schedules, not a guarantee of supply on every evening. Percentages use different regional demand totals.
Batteries already supply a meaningful part of evening electricity demand in parts of the western grid. The California group has the largest reported share in this comparison, followed by the Desert Southwest. These are shares of the electricity each region needs, not rankings of battery size or total electricity delivered.
That distinction matters: installing a battery and using it to meet demand are different measures. This comparison captures batteries’ reported role during the evening window, when California ISO says net demand is highest. It does not show where their charging electricity came from.
More Detail, Sources and Data
What the Percentages Measure
California ISO’s Department of Market Monitoring reports these four averages together on pages 3 and 16 of its 2025 Special Report on Battery Storage. Each value expresses reported battery supply as a share of the load, or electricity demand, of that report-defined region during hours ending 18 through 22 in 2025. The source discusses the figures in its five-minute-market battery-schedules section. These are published operator aggregates, not a new Vastkind calculation from raw meter readings.
The window contains five hourly intervals, not four hours from 18:00 to 22:00. The share passage does not specify a clock timezone or its precise averaging weights, so we retain the source’s hour-ending labels rather than translate them into local-clock times.
| Report Region | Share |
|---|---|
| California | 15% |
| Desert Southwest | 11% |
| Intermountain West | 3% |
| Pacific Northwest | 1% |
Comparable Shares, Different Regional Totals
All bars start at zero and use the same 0–20% scale. Vastkind transcribed the published whole-percentage values, checked both source passages and drew this comparison. No additional precision is inferred. The shares cannot be summed into a western-grid total or averaged without the underlying regional demand totals.
A larger share does not necessarily mean more electricity delivered in absolute terms. The comparison does not establish lower bills, avoided emissions, policy effects or reliable supply on every evening. The report discusses hybrid resources separately; the share passage does not establish complete coverage of every hybrid battery.
The Report’s Four Regional Groups
These are the report’s balancing-area groups on page 9, not a new Vastkind grouping of entire states. A balancing area is a part of the power system managed to keep electricity supply and demand in balance.
- California: California ISO; Balancing Authority of Northern California; Los Angeles Department of Water and Power; Turlock Irrigation District.
- Desert Southwest: Arizona Public Service; El Paso Electric; NV Energy; Public Service Company of New Mexico; Salt River Project; Tucson Electric; WAPA-Desert Southwest.
- Intermountain West: Avista Corporation; Idaho Power Company; NorthWestern Energy; PacifiCorp East.
- Pacific Northwest: Avangrid Power; Bonneville Power Administration; PacifiCorp West; Portland General Electric; Powerex; Puget Sound Energy; Seattle City Light; Tacoma Power.
Source, Dates and Reuse
California ISO, Department of Market Monitoring, 2025 Special Report on Battery Storage, pages 3 and 16 (values), page 9 (regions). The document is dated October 28, 2026; its official posting notice is dated October 30. The measurements describe 2025, not today’s grid.
Original factual comparison by Vastkind. Source: California Independent System Operator; copyright and other proprietary rights remain with their respective owners. Reuse follows CAISO’s public-information terms; no Creative Commons or public-domain status is claimed. No CAISO artwork or logo is copied.