Updated October 2, 2026 Q2 Set an Energy Record, Not a Power-Capacity Record U.S. battery installations reached 5.4 GW and a record 18.9 GWh in the second quarter of 2026, according to the September 22 U.S. Energy Storage Monitor release from the American Clean Power Association and Wood Mackenzie. Energy capacity rose 17% from a year earlier, while power capacity fell 7%. The two numbers tell different stories: developers added fewer gigawatts of instantaneous output but more hours of stored energy. Average system duration increased from 2.8 hours to 3.5 hours year over year. That makes the new fleet more useful for sustained evening demand and resource adequacy, rather than only short bursts of output. Duration is not a substitute for dependable charging supply, interconnection capacity, or an operating contract, but it changes what services each installed megawatt can deliver. 18.9 GWh Q2 installed energy capacity 3.5 hours Average installed system duration 207 GW Forecast cumulative capacity by 2031 Utility Storage Grew Longer as Residential Demand Split Utility-scale projects supplied 4.7 GW and 17.6 GWh of Q2 installations. Their power-capacity additions fell 8% year over year. ACP and Wood Mackenzie linked longer durations partly to a long-duration California project and utility-contracted storage in Texas. A growing energy total therefore should not be read as uniform acceleration in every market. Residential installations reached 676 MW, up 3% from a year earlier but down 15% from Q1. The report still forecast a 4% contraction in the residential market for 2026, citing tax-credit elimination, consumer hesitancy, and the transition to third-party ownership. California, Texas, Puerto Rico, Arizona, and Illinois supplied 88% of residential capacity installed during Q2. The community, commercial, and industrial segment added 48 MW. The 2031 Forecast Now Stands at 207 GW and 715 GWh The September outlook puts cumulative U.S. storage at 207 GW and 715 GWh by 2031, superseding the approximately 200 GW and 655 GWh forecast discussed in this article's July update. These are forecasts of the installed base, not capacity already operating. The report expects utility-scale storage to grow about 8% annually on average over the next five years, while warning that trade restrictions and supply bottlenecks could produce near-term stagnation in 2026 and 2027. Data-center demand is one reason for the higher outlook. Batteries can support capacity delivery and relieve some grid-connection constraints, but they do not generate electricity. Project economics still depend on charging energy, dispatch rights, availability guarantees, and the number of hours a customer needs support. Retooling idle EV battery factories may improve domestic cell supply; announced factory capacity is not the same as qualified cells shipped to a project. How to Compare This With the Original 70 GWh Outlook The original article followed SEIA's annual outlook. This update uses ACP and Wood Mackenzie's Q2 deployment results. Their series should remain separately labeled rather than combining one provider's quarterly total with another's annual target to claim a precise completion percentage. Reporting periods, coverage, and revisions can differ. The defensible takeaway is narrower: the latest Monitor shows a record for stored energy and a shift toward longer systems, not a guarantee that every earlier annual forecast will be met. For developers, the next checkpoints are actual commissioning dates, tested discharge duration, contracted revenue, and cell-delivery schedules. For readers comparing markets, GW measures power and GWh measures energy. Confusing them hides the most important change in the Q2 data. Primary source: ACP and Wood Mackenzie, U.S. Energy Storage Monitor release, September 22, 2026 . Historical reporting below is retained for context; the October update above is the current quarterly readout. The earlier SEIA-focused reporting below tracks the original 70 GWh forecast; the October update above provides the newer ACP/Wood Mackenzie results. First-quarter deployments reached 9.7 GWh, a record start that puts 2026 ahead of last year's pace even before the construction-heavy summer and fall periods. The February forecast still matters, but the May update changes the readout. Texas remains the growth engine, utility-scale projects are carrying the market, and the sector now has enough early-year data to judge whether 35 GW / 70 GWh is ambition or a real buildout trajectory. AI-generated image Battery rack modules inside a modern utility-scale BESS facility. Credit: AI-generated / CurrentCells Historical update - July 8, 2026 Q1 Confirmed the Storage Boom Is Ahead of Schedule SEIA's newest quarterly readout gives the February outlook its first real test. The U.S. installed 9.7 GWh of battery storage in the first quarter of 2026, up 32% from the same period last year. That is still well below the average quarterly pace needed to reach 70 GWh, but storage deployments are usually back-loaded. The key point is that the market did not stumble out of January's slow global start. Utility-scale systems continue to do the heavy lifting. Texas, Arizona, and California remain the states to watch, with ERCOT's merchant price signals pulling new batteries into the queue and Western load growth keeping Arizona near the top of the project list. EIA's 2026 capacity tracker still points to roughly 24 GW of new utility-scale battery additions nationally, with Texas accounting for more than half of planned power capacity. 9.7 GWh Q1 2026 U.S. additions 32% Year-over-year Q1 growth 24 GW EIA projected 2026 utility additions 53% Texas share of planned 2026 utility GW What the May data changes The 70 GWh forecast now looks less like a trade-group aspiration and more like a plausible base case if interconnection and equipment delivery hold. Q1 supplied 13.9% of the annual energy target. That would be weak for a flat installation calendar, but storage is not flat. Developers tend to bring large projects online late in the year, after winter construction slowdowns and ahead of summer reliability needs. The bigger constraint is no longer demand. It is execution: transformers, grid studies, interconnection agreements, battery-container delivery slots, and tariff risk on imported LFP cells. 2025 in Review: 28GW Installed Across the Country Before looking ahead, it helps to understand the base that 2026 is building on. According to SEIA's data, the U.S. installed more than 28GW (57GWh) of battery storage capacity during 2025. The utility-scale segment drove most of that activity, accounting for nearly 16GW/50GWh. Behind-the-meter (BTM) installations made up the remaining 12GW/8GWh, holding steady at roughly 13% of total market share. Three states dominated the utility-scale picture. California led with 59,815MWh of cumulative additions, followed by Texas at 26,271MWh and Arizona at 19,334MWh. Together, those three states accounted for 74% of all utility-scale storage installed last year. Nevada came in a distant fourth at 6,331MWh, highlighting just how concentrated the market remains geographically. AI-generated image California, Texas, and Arizona account for nearly three-quarters of U.S. utility-scale battery storage deployments. Credit: AI-generated / CurrentCells The BTM market saw a particular bump in the residential segment. SEIA attributes part of that growth to the expiration of the 25D residential tax credit at the end of 2025, which triggered a rush of installations as homeowners scrambled to lock in incentives before they disappeared. Commercial and industrial BTM storage also contributed, though the residential surge was the headline story for that segment. SEIA's Energy Storage Market Outlook: Key 2025 Figures Total installed: 28GW / 57GWh (29% year-over-year growth) Utility-scale: 16GW / 50GWh Behind-the-meter: 12GW / 8GWh (13% market share) Top states: California (59,815MWh), Texas (26