Five hours decide the bill.
For a Class A facility in Ontario, Global Adjustment is not allocated on how much electricity it uses over a year. It is allocated on how much it was drawing during five specific hours—and those five hours are known only after they have passed.
Published IESO data. Facility-specific analysis. No guaranteed outcomes.
A share of five hours, not a share of the year.
Ontario's Industrial Conservation Initiative (ICI) allows eligible large consumers to be billed as Class A. Instead of paying Global Adjustment on volume, a Class A facility pays a share of the province's total Global Adjustment cost, and that share is set by a single number: its Peak Demand Factor.
- the base period runs May 1 to April 30;
- the five hours of highest Ontario demand within it are identified by the IESO;
- a facility's demand during those five hours, divided by system-wide consumption across the same five hours, gives its Peak Demand Factor; and
- that factor sets the facility's share of provincial Global Adjustment costs for the following adjustment period, July 1 to June 30.
The consequence is that a facility's Global Adjustment cost for an entire year is determined by its metered demand across five hours. Reducing consumption at any other time does not change the allocation.
The five hours now setting Class A charges.
These are the five highest hours of Ontario demand in the May 1, 2025 – April 30, 2026 base period, as published by the Independent Electricity System Operator (IESO). The Peak Demand Factor they produce applies from July 1, 2026 through June 30, 2027—so for facilities billed as Class A, these hours are setting charges now.
All five arrived on summer weekdays, in the late afternoon or early evening, between mid-June and mid-August. That pattern has held for years, which is what makes the exposure worth modelling—but the hours themselves are confirmed only in hindsight.
Fifth place was decided by 148 MW.
Only the top five hours count. The sixth-highest hour of the 2025–26 base period came within 148 megawatts of the fifth—about six-tenths of one per cent—and contributed nothing to any facility's Peak Demand Factor.
This is why curtailment decisions are difficult in practice. A facility that responds to every likely peak spends operating flexibility on hours that may not count; one that responds to too few can miss an hour that does. The economics depend on how accurately the facility can identify the hours that matter, and on what responding actually costs it.
The exposure is measurable before it is managed.
Every Class A facility already has a Peak Demand Factor and a Global Adjustment cost attached to it. Both are visible in its interval data and its bills. That establishes the size of the exposure—what it currently costs, and how much of it is theoretically addressable—before any equipment is contemplated.
What the data shows
Interval demand during past peak hours, the resulting Peak Demand Factor, and the Global Adjustment charge it produced.
What constrains a response
Process requirements, minimum loads, notice periods, and the operating flexibility genuinely available on a summer afternoon.
What storage could change
How much grid demand a system of a given size and duration could displace during those hours—and what it would cost to install and operate.
Global Adjustment is one of several value sources MPSS evaluates, and it is assessed alongside the others rather than in isolation. Capacity committed to peak response cannot simultaneously be credited to resilience or to a market obligation.
Global Adjustment, briefly.
What is Global Adjustment?
Global Adjustment covers the difference between the market price of electricity and the regulated or contracted rates paid to Ontario generators, along with the cost of conservation programs. For large industrial consumers it is frequently the largest single component of the electricity bill.
What is a Peak Demand Factor?
A Class A facility's Peak Demand Factor (PDF) is its share of Ontario demand during the five highest peak hours of the base period. The IESO applies that percentage to total provincial Global Adjustment costs to determine what the facility pays each month of the following adjustment period.
Which five hours are currently being used?
The five peak hours of the May 1, 2025 – April 30, 2026 base period, shown on this page, set the Peak Demand Factor applied from July 1, 2026 through June 30, 2027.
Are the peak hours predictable?
Only partially. They have consistently fallen on summer weekday afternoons and early evenings, and in the most recent base period all five landed within a 49-day window. But the exact hours are only confirmed after the fact, and a facility acting on a forecast is responding to a prediction rather than a certainty.
Can a battery reduce Global Adjustment costs?
It may. The result depends on the facility's Class A status, baseline Peak Demand Factor, operating profile, battery availability, charging strategy and actual performance during the five peak hours. MPSS measures the opportunity against the facility's own data and shows a range where appropriate rather than a single figure.