Struggling to stay cool? So is the generator powering your aircon

If you think you've got problems staying cool during the heatwaves that have gripped the northern hemisphere this summer, consider the fate of power generators.

Every time you switch on a fan or air conditioner, it adds a little bit of demand to the grid. When everyone does it at the same time, say when arriving home at the end of the day to a sweltering house, the effect can be enormous. Making matters worse, this shift often happens toward sunset, just as generation from solar panels is tapering off.

In California, conventional power plants at present have to increase their output by nearly half in the three hours heading into the evening peak. Delhi, where air conditioners and fans at times account for half of electricity consumption, saw its highest-ever grid demand last month amid a record-breaking heat wave.

All of this is an immensely water-intensive process. Thermal generators — those powered by the heat from burning fossil fuels, biomass or waste, or from nuclear fission — work by piping liquids through a furnace, causing them to expand. That drives turbines and produces electricity, before the liquids are cooled in heat exchangers and return for another trip through the furnace.

Thermal power plants accounted for about 41% of water withdrawals in the US in 2015, more than three times what the entire household sector used and greater than all the irrigated agriculture in the country. All of those problems intensify as the temperature rises and rivers dry up.

For the simplest power plants that draw cooling water directly from rivers and the ocean, heat waves can cause shutdowns. Temperatures around discharge stations are closely monitored to prevent wildlife deaths, algal blooms and other problems, and when they get too high — either because the diluting river water itself is warmer, or because there's less of it as a result of drought — the discharges have to stop, blacking out the generator in turn.

More sophisticated systems use cooling towers — those vast, concave concrete structures associated with large nuclear and coal plants — as giant heat exchangers, a more efficient use of water. The problem is that they depend on low air temperatures to operate most effectively. During a heat wave, generators find it harder to cool down and need to reduce their output to avoid overheating.

That's what we're seeing happening right now. The heat wave is already hurting the efficiency of Europe's power plants, with gas and nuclear generators reducing their planned output, according to Lane Clark & Peacock LLP, adding to upward pressure on electricity prices. French atomic plants are relying on waivers to discharge hotter-than-usual water into the rivers.

These issues are significant. Climate change has already increased the amount of time thermal plants experience outages by 0.75 to 1 percentage points, according to a study last year. With each additional degree Celsius of warming, the effects of such unplanned shutdowns alone would be enough to require an extra 40 to 60 power plants worldwide, assuming a typical 450-megawatt unit.

There are few neat solutions to these problems. Reducing fossil-fired power will take the edge off the warming that's causing heat waves to intensify, but in the best-case scenarios, the world has decades of summer power crises in front of it. Renewable power suffers less in the heat, but during extreme events wind speeds often drop, while the efficiency of solar panels and battery storage goes down, too. Power systems that experience more profound peaks as a result of 2022-style heat waves will find it harder to give up the switch-on, switch-off dispatchable power that only fossil fuels can currently provide at sufficient scale. Hypothetical peaking generators based on burning green hydrogen would face the same cooling problems as current gas, coal and nuclear plants.

The worst problems will be experienced in emerging economies such as China and India, who spent billions over the past two decades building thermal power plants that won't be well-suited to managing future summer peaks. In 2016 alone, cooling water shortages in the middle of a drought caused Indian power plants to lose about 14 terawatt-hours of generation, enough to power Sri Lanka for a year.

Fossil power sold itself to such countries on the basis that for all its long-term effects on the global climate, in the short term it would be the only way to provide reliable electricity when it's most needed. This heat wave is showing that even that promise won't hold up.

David Fickling is a Bloomberg Opinion columnist covering commodities, as well as industrial and consumer companies. He has been a reporter for Bloomberg News, Dow Jones, the Wall Street Journal, the Financial Times and the Guardian.

Disclaimer: This article first appeared on Bloomberg, and is published by special syndication arrangement