USA: How do power grids beat the summer heat?

Union of Concerned Scientists

By Julie McNamara

In the searing heart of summer, when blazing days stack end on end and the air hangs heavy and still, the power grid gets put to the test as people turn to air conditioners to find reprieve.

Millions upon millions of air conditioners, cranking away on rooftops, in windows, behind buildings; block by block, business by business, home by home: together, these many machines can add up to a major increase in electricity demand.

In Texas, grid operators estimate that such sweltering summer days can result in a doubling of peak electricity use compared with during spring.

When summer rolls around, people start using a lot more electricity to try to stay comfortable. In Texas, grid operators show this surge in summer use and estimate nearly half can be attributed to the weather. Credit: ERCOT.

At the same time, many power plants and power grid components can themselves struggle in the face of sky-high heat, which means even more strain is placed on the grid right when it’s needed most.

The upshot is that while most of us are lying low to try to beat the heat, the power grid is in an all-out sprint to ensure that it keeps up. And that means grid operators pull out all the stops, from long-range planning to moment-of operations, targeting both supply and demand.

Some of these approaches, like keeping polluting power plants around to run just a few times a year, are costly and inefficient. But as cleaner resources come online and technologies on the grid evolve, new and exciting solutions are emerging that are not only cleaner but cheaper, too.

These advances couldn’t come at a more critical time as climate change increasingly points toward more dangerous high-heat conditions that threaten health and well-being, especially in the absenceof cooling, which elevates the importance of increased access to cooling itself, as well as ensuring the resilience and reliability of the enabling grid.


The foundation of reliable grid operations is planning: estimating how much electricity people will need and whether there are enough resources around for that need to be met—including during heat waves, and including during heat waves when unexpected incidents occur.

One check on this is the annual summer reliability assessment conducted by the nation’s top reliability cop, the National Electric Reliability Corporation (NERC), which evaluates just such questions for every region of the grid.

In its annual summer reliability assessment, NERC examines each region of the grid and assesses sufficiency of resources to meet potential summer needs. For the vast majority of regions in 2019, resources far outpace anticipated needs. Credit: NERC (2019).

This consideration of “resource adequacy” and “reserve margins” ends up shaping grid decisions large and small, which makes it critically important to get the underlying assumptions just right. Otherwise, for example, uneconomic power plants might be unnecessarily kept around, wasting consumer money and hindering the transition to clean electricity. Or, operators might not recognize that the timing and magnitude of peak demand can rapidly change in shape as installations of rooftop solar surge across the country, with abundant solar power easing afternoon grid stress and in turn pushing the peak later and lower in the day.

As ISO-New England illustrates, as more and more rooftop solar gets added to the system, the summer load profile can change, with peak demand not only dropping lower but also shifting later, too. Credit: ISO-NE.


But long-range planning is really just the start. Next up is making sure that all those power generating, power saving, and power transmitting resources can actually be used.

Power plants and supporting grid infrastructure routinely undergo maintenance, meaning sometimes they have to go offline. If fixes are quick, then outages during low-demand seasons like spring mean there’s still plenty of slack on the system to mitigate effects. For longer lasting outages, though, operators plan ahead to ensure that not too many outages are planned at once, and that enough resources remain available to make it through those hottest summer days.

Yet even when operators do the best planning they can, equipment still breaks and accidents still happen. And then, too, there’s the fact that summer heat can itself wreak havoc on the grid.

For example, virtually all coal and nuclear power plants require cool water to run; in the summer, as hot weather steadily drives up the temperatures of area waterways, that water can eventually get too hot to be of cooling use or can be limited by drought, meaning those massive generators have no choice but to curtail operations or even entirely shut off—right when we need their power the most.

High temperatures can also decrease the efficiency of transmission lines and increase the likelihood of a disruption on the system, which if not rapidly addressed can quickly cascade into far larger outage events, like the 2003 Northeast blackout which thrust over 50 million people into the dark. And now in California, in the face of climate change and the growing threat of wildfires, utilities are starting to pre-emptively shut off transmission lines in high-risk areas during high-risk days to minimize chances of sparking a new blaze.

Which all means operators need to keep a watchful eye on the grid, managing resources to be prepared for contingencies to occur, and relying on weather forecasters to help them anticipate exactly when such conditions might arise in order to proactively plan for how these situations can be overcome.

Markets and management

And when a heat wave does finally arrive? After all the planning, and the operations, and the forecasts—how does the grid actually manage that overwhelming dystopian symphony of compressors cycling on and off, on and off, day after day after day?

With good offense and good defense.

First, there’s the usual starting lineup of least-cost, most efficient, and often cleanest resources, ready and reporting for action (minus those lost to outages, planned or otherwise). These are the ones that are typically relied on all throughout the year.

Then, as hot days continue and the demand for power grows, the grid is increasingly forced to call on its back bench: the more expensive and less efficient “peaker plants,” some of which run only a handful of times a year.

Peaker plants often take the form of combustion turbines, and can be sited right in the heart of communities—which means on some of the worst air quality days of the year, these polluters are roaring to life, exacerbating exposures to already unhealthy air.

Unsurprisingly, inefficient plants running just a few times a year end up being quite expensive, too. In regions with energy markets, this is when prices on the grid start to spike.

Prolonged hot weather can send real-time electricity prices surging, as seen in this chart of a 2013 heatwave in New York. Credit: EIA.

This way of running the power system is ripe for disruption, and indeed recently, new technologies have started to edge in. In particular, peaker plants are beginning to be replaced by combined solar-plus-storage projects. These projects couple solar power plants with battery energy storage, resulting in clean, reliable, and rapidly dispatchable resources, useful not just in those peak moments, but in fact the whole year round.

But during heat waves, it’s not just power plants coming in to save the day—it’s everyday people, too. That’s because a huge part of responding to peak demand is actually lowering power demand itself during those very highest hours.

Some of these actions are systematic: utilities can permanently preclude the need for that last peaker plant by incentivizing people and businesses to use less electricity during those highest hours of the day, not just during heat waves, but every day. They can guide that response through time-varying electricity rates, which are high during high-demand hours and lower during the rest, to encourage shifting of flexible electricity use, like running a dishwasher or drying laundry, away from periods of grid stress.

Other demand-side interventions are more specific to major peak events. For example, in exchange for handsome compensation, electricity customers can agree to be called on a few times a year to ease their electricity consumption, much of which can be done automatically, like raising thermostats several degrees, or stopping industrial operations, or flipping off every other bank of lights in a big box store, all to avoid bringing the costliest final power plants online.

Yet even after all of that, sometimes, it’s still just not enough. Despite all the planning, all the power plants, all the demand response—still, more power is needed than the grid is able to give. That means first, looking to neighboring regions to see if they might have some electricity to spare and sell. Especially when weather varies across regions, sharing of resources can be an effective and efficient solution.

But sometimes, especially when wide swaths of the country are enduring a heat wave at once, it’s still just not enough. And that means turning to the extreme last resort of “load shedding,” the forgiving term assigned to cutting power to some consumers to keep the lights on for the rest. Because if not, and the grid gets overloaded, it can quickly become lights off not just for some but for all.

Looking ahead

To get through a heat wave, grid operators employ a highly dynamic approach informed by careful planning, toggling switches and turning dials to modulate supply and demand. And it turns out, this dynamic method of operations is in fact where the grid of the future is headed, as more variable renewable resources like wind and solar come online and technologies support far more flexibility and coordination in when and how electricity is consumed.

Indeed, grid management of heat waves can teach us a lot about how to get the most out of the resources we want, and how to limit our use of the ones we don’t.

It also elevates the critical importance of paying attention to these challenges, and proactively planning for an increasingly flexible, resilient, and reliable grid as we face the growing strain and stress of climate impacts in the years to come. Because during a heat wave, reliable access to electricity isn’t only a matter of comfort—it’s a significant matter of health and safety, too. Which makes it all the more important to ensure that grid operators aren’t just prepared for heat waves this summer, but are also looking out for worsening conditions to come.

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