Europe’s heatwave is creating quadruple whammy for the grid

Western Europe is again sweltering under a heat dome, following weeks of extreme temperatures that broke June records in several countries and contributed to thousands of deaths.

The hotter it gets, the harder the grid has to work. For the electricity system, a heatwave creates a ‘quadruple whammy’: higher demand, reduced output from thermal and wind generators, unusual power flows with high solar output and transmission equipment having smaller safety margins.

This can push parts of the grid to its limits and expose problems that might have gone unnoticed for years. In the worst case scenario, this can cause a cascading blackout like what happened in the Northeast US in 2003. 

The first and most obvious problem is increased demand. During a heatwave, air conditioners run longer and cooling systems stay on to keep homes, hospitals and businesses safe. Refrigeration becomes critical as food and medicines must stay cold.

But, higher electricity demand is only one part of the four-part stress test. Extreme heat can also make power harder to produce and move.

At the same time that demand rises, some power stations may have to reduce their output.

Nuclear, coal and gas plants rely on water for cooling. When rivers, lakes or other water sources become too warm, plants may have to cut production to comply with environmental limits.

Damaging mismatch

That is already happening in Europe. Recent heatwaves have reduced nuclear output in France and Hungary as river temperatures rose. 

Exacerbating the situation, wind generation is also reduced under a heat dome as air stays relatively still.

This creates a damaging mismatch: the system can lose generation at exactly the moment consumers need more electricity.

Hot, sunny days can bring lots of solar power, which is a good thing. But the grid might not be able to handle the unusual power flows which are driven by high solar generation, which is often connected behind older and weaker lines.

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During a heatwave, power may need to travel farther or flow through parts of the grid that are not usually under as much pressure. Lines that were lightly used the day before can suddenly become critical bottlenecks.

Grid reliability amid Europe’s recent heatwaves isn’t solely about whether the continent has enough electricity generation capacity. It’s also about the system being able to move that electricity from where it’s available to where it’s needed.

Power reduction

The fourth blow, and perhaps the least understood, is that extreme heat can reduce how much electricity power lines can safely carry.

Grid equipment becomes hot when it operates and needs to be cooled down. Older equipment may already be operating close to its limits during a heatwave. 

When a line becomes too hot, it expands and sags. Grid operators must limit the amount of electricity flowing through it to prevent lines from overheating and causing equipment damage.

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In August 2003, people across parts of the northeastern and midwestern US and Ontario experienced a blackout that occurred when a transmission line sagged too close to the ground under hot weather and went out of service. This triggered a cascading failure that brought down the entire grid for days.

The transmission system may have less capacity available during a heatwave, at the same time that consumers are demanding more power, and while electricity is being rerouted across the network.

That is the quadruple whammy.

Transatlantic lesson

The pressure doesn’t always end after the hottest hours. PJM, the largest electricity market in the US, offers a useful example. 

An analysis by Gridraven found that across the most-constrained lines in PJM, congestion costs reached roughly $1 billion in May, including an unseasonal heatwave, and remained at $778 million in June when temperatures were less extreme.

Over the same period, dynamic line ratings (DLR) identified roughly 13% more capacity than PJM’s ambient-adjusted ratings. 

In extreme heat, grid stress is not limited to a few peak hours, and even small differences in available capacity can matter when a line is constrained again and again. The resulting cost is clearly visible in PJM.

While building more transmission is a central part of Europe’s long-term plan, operators still need a more accurate view of weather conditions and available transmission capacity in the short term to ensure safety and manage congestion in a cost-efficient manner.

The next heatwave will come. Europe needs a more intelligent grid to be better prepared when it does.

About the author: Before launching Gridraven, Georg Rute led digitalisation at Estonia's national grid, Elering, spearheading the digitalisation task force. Prior to that, he was the co-founder of Sympower, which now manages 1.5GW of grid flexibility.