Why Heat Waves Raise the Risk of Blackouts

When a heat wave strikes, millions of people rush to turn on their air conditioners and fans to stay cool. But all that extra electricity use puts a huge strain on power grids — the networks that deliver electricity to homes, schools, and hospitals. In late June, a heat wave in France knocked out power for nearly 70,000 households after a transformer broke down in the extreme heat. For about 24 hours, people in parts of Brittany had no fans or air conditioning while temperatures climbed close to 40 degrees Celsius (104 degrees Fahrenheit).

Around the same time, the United States was dealing with its own dangerous heat wave, right before its 250th birthday celebrations. Federal officials issued blackout warnings and allowed grid operators to tell large electricity users — like data centers — to switch to backup generators. This helped keep power running to homes and emergency services like hospitals. It was a sign of just how much pressure the heat was putting on the country's power supply.

Heat-related blackouts are already on the rise in the United States. According to the nonprofit Climate Central, power outages during hot seasons rose about 60% over the past decade compared to the 2000s. Losing power during a heat wave is especially dangerous for young children, elderly people, and those with serious health conditions. Scientists say the problem is likely to get worse as climate change makes heat waves longer, more frequent, and more intense.

So why exactly does heat cause so many problems for power grids? The first reason is simple: when it's hot, everyone wants to use electricity at the same time. Air conditioners, fans, and cooling systems all draw power, causing demand to spike — especially in the evening when the sun starts to set but the air is still warm. At that same time, solar panels produce less electricity because the sun is lower in the sky, making the gap between supply and demand even harder to close.

Heat also damages the physical equipment that carries electricity. Power lines expand when they get hot and begin to sag toward the ground. If a sagging line touches a tree or another object, it can cause a short circuit or spark an outage. 'The grid operator has to reduce the amount of power that flows down these wires in the very hottest temperatures to make sure everything remains safe,' said Iain Staffell, a professor of sustainable energy at Imperial College London.

Power plants themselves also struggle in extreme heat. Coal, gas, and nuclear plants all use water from nearby rivers to cool their equipment. When rivers get too warm, those cooling systems become less effective, and plants sometimes have to cut back on how much electricity they produce. In Europe's June heat wave, several nuclear plants in France and Switzerland had to reduce output or shut down temporarily because river water was too hot.

Renewable energy sources face challenges in the heat too. Hydropower plants produce less electricity when water levels in rivers and reservoirs are low due to drought. Solar panels actually become slightly less efficient when they overheat, and wind speeds often drop during heat waves, meaning wind turbines spin more slowly. When all these factors happen at once, grid operators may need to buy expensive backup electricity — often from fossil fuels — to keep the lights on.

Experts say there are ways to make energy systems more resistant to heat. Small upgrades — like adding cooling fans to transformers or putting shades over power lines — can make a real difference. Battery storage is another promising fix: batteries can store cheap solar energy produced at midday and release it during the evening hours when demand is still high but the sun has set. Nuclear plants could also be built with backup cooling systems that don't rely solely on rivers.

Making the grid smarter and more flexible is also key to solving the problem. Dynamic pricing — where electricity costs more during peak hours and less during quiet times — can encourage people to run dishwashers or charge electric cars at night. Countries also need to invest in connecting their electricity grids to neighboring nations, so power can flow where it's needed most. In Europe, there is a backlog of about 1,700 gigawatts worth of renewable energy projects waiting to connect to the grid. Both Europe and the United States face the same challenge: building the right system fast enough to keep up with a warming world.