Summer Heat Drives Record Electricity Demand in Ontario and the U.S. Northeast

The peak electricity demand season is off to an intense start across Ontario and the Northeastern United States, with both regions already experiencing record-breaking loads in the early weeks of summer. These surges reflect not only extreme weather patterns but also deeper structural shifts in energy use.

According to the Independent Electricity System Operator (IESO), Ontario’s highest provincial demand for the current Industrial Conservation Initiative (ICI) base year, 2025-2026, has already surpassed 24,700 megawatts (MW) on two separate occasions: June 23 and June 24, 2025. This represents a clear increase from the previous year’s peak of 23,852 MW, recorded on June 19, 2024, during the first major heatwave of that summer.

The story is similar in the PJM Interconnection region, which coordinates the movement of electricity across 13 U.S. states and the District of Columbia. PJM's summer peak last year reached 152,307 MW on July 16, 2024. This year, however, demand has already climbed beyond 160,000 MW, with the highest load recorded on June 23, 2025. This marks a significant increase in just one year and highlights the growing challenges faced by grid operators as demand continues to push higher.

The primary driver behind these record peaks has been extreme heat and humidity. Across the region, average temperatures during these peak periods were between 1°C and 3°C higher than during comparable periods last year. High humidity compounds the problem by increasing the load on air conditioning systems, a major contributor to electricity consumption during summer months.

However, weather is not the sole factor at play. The gradual but steady electrification of the economy, which spans electric vehicles (EVs), industrial equipment, and building heating systems, is adding sustained upward pressure on electricity demand. Although the growth rate of EV adoption has moderated, the cumulative impact is still significant. As electrification expands, the frequency and magnitude of peak demand events are likely to increase, including during the winter months, which historically have seen lower demand levels in Ontario.

Looking Ahead: What to Expect and How to Prepare

Both Ontario and PJM are entering an era where new peak records may be set annually, driven by a combination of climate extremes and evolving energy consumption patterns. This trend raises several considerations for businesses, policymakers, and utilities:

1. Demand Management: Businesses participating in programs like Ontario’s ICI can manage exposure to peak pricing by closely monitoring weather forecasts and peak day predictions, particularly during periods of extreme temperatures.
2. Grid Reliability: Utilities will need to invest in transmission upgrades, energy storage, and demand response solutions to maintain system stability during increasingly volatile peak periods.
3. Energy Efficiency: Energy users can mitigate costs by investing in energy efficiency upgrades, from HVAC improvements to more efficient industrial processes, which also help reduce strain on the grid during critical periods.
4. Winter Preparedness: The historical pattern of winter as a “low-demand” season is shifting. As heating electrifies, winter peak management will become just as critical as summer.

The rising frequency of extreme weather events coupled with long-term electrification trends underscores the need for forward-looking energy planning at every level, from households to governments. Staying ahead of these changes will require not only operational vigilance but also strategic investments in infrastructure and innovation.

A Global Challenge: Heatwaves and Rising Demand Beyond North America

What is happening in Ontario and the U.S. Northeast is not an isolated phenomenon. Extreme heat is driving electricity demand to new heights around the world, placing unprecedented strain on grids and exposing vulnerabilities in power systems that were not designed for such conditions.

According to a recent report from Ember, Europe faced similar challenges this summer during a heatwave spanning late June to early July 2025. Temperatures across Germany and Spain averaged over 35°C, with some regions exceeding 40°C. France and Poland also saw national temperature averages climb above historical norms. These conditions pushed electricity demand up by as much as 14% on peak days and sent average electricity prices soaring to double their usual levels.

The impact of heatwaves goes beyond higher demand and pricing, it raises concerns about energy security, grid stability, and economic disruption. As Pawel Czyzak, Europe Programme Director at Ember, points out, heatwaves will only grow more frequent and severe. This reality underscores the need for integrated solutions such as battery storage, stronger interconnections between regions, greater demand flexibility, and dynamic tariffs. Notably, while heatwaves bring soaring temperatures, they also bring abundant sunshine, creating an opportunity to store excess solar generation and use it to offset evening demand spikes caused by air conditioning.

These challenges and opportunities are not unique to Europe. North America, Asia, and other regions will face similar pressures as climate patterns continue to shift. The path forward will require coordinated grid planning, technology deployment, and policy innovation to ensure electricity systems can meet future demands reliably and affordably.

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