IESO Reliability Outlook: New Energy Storage to Keep Ontario System Prepared for Summer 2026
June 19, 2026
Ontario’s electricity system is prepared for summer 2026 with adequate supply – bolstered by more than 1,000 MW of new capacity added to the grid since last summer – to meet demand, according to the IESO’s latest 18-month Reliability Outlook.
Ontario demand is forecast to grow this year by a slower 0.5 per cent owing to ongoing geopolitical developments that are slowing economic growth globally. Under extreme weather conditions, the IESO is forecasting peak demand could still reach close to 26,000 MW, and the growing role of energy storage and demand-side management in the Ontario system will help meet this demand. At present, battery storage accounts for more than three times the capacity that was available last summer. The new capacity these projects represent will help offset newly reduced import assumptions (from 2,000 MW to 1,800 MW) resulting from tightening grid conditions in neighbouring jurisdictions.
Electricity demand is expected to rebound in 2027. Against this backdrop, the IESO continues to refine its operating plans in anticipation of a sequence of nuclear outages over the next year, including the shutdown of the “B” units at Pickering Nuclear Generating Station, starting in October 2026 and a scheduled vacuum building outage at Darlington Nuclear Generating Station in April 2027.
For demand-side management, there are now more than 320,000 residential and small business consumers participating in the Save on Energy Peak Perks demand response program capable of providing more than 200 MW of demand reduction, and this summer marks the introduction of Peak Performance, a similar program designed for commercial and institutional facilities. For other large consumers, the Industrial Conservation Initiative will continue to offer the opportunity to reduce exposure to global adjustment costs while helping the system reduce peak demand periods.
For this quarter’s 18-month outlook, read the IESO’s Seasonal Update here and see the Reliability Outlook data tables here.