Can We Trust Our Power Plants to Keep Us Cool During Dangerous Heat?

Originally published by Union of Concerned Scientists, The Equation.
By John Rogers, Energy Campaign Analytic Lead

In the face of this week’s astonishing temperatures, reliable electricity and the air conditioning it powers have often been the only thing keeping dangerous, even deadly heat at bay. But how do different types of power plants actually stand up to the soaring temperatures?

The wave after wave of punishing — even “unprecedented” — heat that has been hitting various parts of the country has serious implications for so many aspects of our lives: work, play, health, community, economy.

The electricity we depend on every day and night becomes even more crucial when temperatures soar. Many of us depend on power to keep us cool(er), via air conditioners or fans, at home or in public facilities where we seek refuge from the heat. The latest heat wave has been hitting my home as I pen this post, making me more appreciative than ever of the electricity powering the ceiling fan overhead, and the air conditioner I’ll be lucky to be able to count on tonight.

It takes a lot going right to keep the lights on (and the fans and ACs running) during heat waves. Getting the power to those cooling devices generally requires a string of connect-the-dots that gets the energy where we need it: from power plants, down transmission lines, through substations and transformers, across distribution lines, and to our homes, businesses, and communities.

But how we actually make the electricity in the first place is worthy of a lot of attention for a whole host of reasons — not least because of how different options stand up to higher temperatures.

So how does heat hurt power generation? Here are three important ways.

1. Many power plants need water (not just hydro ones)

This fact that hydroelectric plants need water is obvious, and hydro power’s water woes have been getting a lot of attention lately. A multi-year drought in the West has left reservoirs at historically low levels and seriously cut hydro generation potential. In California, hydro supplies are down 40% vs. last year, according to BloombergNEF, and Sacramento’s utility expects hydro to be only 7% of the supply mix, instead of 20%.

But hydro plants are far from the only power sources needing abundant water. Almost every power plant that uses a heat source — burning coal or gas, for example, or fomenting a nuclear reaction — to make steam to drive electricity-producing turbines uses water to cool that steam as a key part of the power production process.

That roster of cooling-water-dependent power plants in this country includes the ones responsible for more than three-quarters of our electricity: every nuclear plant, virtually every coal plant, and most of the gas plants.

All of those power plants become less efficient with higher water temperatures, as they have to use more water to get the same cooling effect. And they can get into real trouble when cooling water isn’t plentiful enough or is too hot, sometimes having to dial back or shut down. And sometimes that happens right when we need their power the most — in the middle of heat waves.

Even ocean-cooled power plants get into trouble because of their water habits (or their age).

2. Air temperature also affects power plants

When it comes to temperature, it isn’t just water that matters for many power plants: Air temperature does too. Gas plants, for example, like colder temperatures (up to a point), and perform worse in summer than in winter. That stems in part from the decrease in air density with the increase in temperatures that gives the moving air less oomph to drive the turbine blades in gas combustion turbines. Gas turbines that are rated at 60 oF might generate at 15% less than their nominal output when ambient temperatures reach 100 oC.

How a gas plant’s output (green line) changes with temperature (Source: GE)

Steam-based power plants that eschew the cooling water approach and use air instead (“dry cooling”) also face temperature-based drops in output. Warmer air can’t get provide the same cooling, and the lower density of the air is another hit.

3. Heat and drought can hit renewables too

Renewable energy facilities aren’t necessarily immune from these effects. Some renewable energy sources also use steam, including geothermal, biomass, and concentrating solar, and can get into trouble if the water sources they depend on dry up or overheat. Or, if those renewable plants depend on dry cooling, they too can be affected by high air temperatures.

Even sun-loving solar electric/PV modules lose output as their temperatures climb. The type on my home’s roof, for example, lose 0.29% of their power output for each oC (meaning 1% for every 6 oF) above the temperature at which modules are rated (25 oC, or 77 oF). Mine are still churning out loads of kilowatt-hours right now, but are even happier when it’s sunny and cooler.

How temperature affects a solar PV module’s power output (current times voltage): Current goes up, but voltage goes down more (Source: Seaward Group USA )

The higher-temps-equals-lower-density issue affects wind energy production too, which is one reason wind farms generate more in spring and fall. (California is an exception in that respect, with wind production in July, August, and September being above its annual average.)

Bonus: Wildfires and sea jellies

While air and water temperatures and water availability are the main factors affecting power plant production during heat waves, there are actually lots of other ways heat can trip up electricity generators. Higher seawater temperatures can lead to “jellyfish blooms,” for example, which can in turn mean more sea jellies clogging up water intakes for power plants cooling with ocean water. Higher temperatures and related drought can mean more wildfires, and smoke-filled skies and soot-blanketed panels can mean less solar production (as in California in 2020).

The way forward (hint: not through fossil fuels)

What do these heat-related impacts on our ability to generate power have in common? Climate change is making all of them worse: higher temperaturesmore extreme heat, deeper and longer droughts, increased ocean temperatures, more wildfires,… Heat waves themselves are now “hotter, larger, longer and more frequent” because of global warming.

Climate change hits much more than just the generation side of the power sector, as transmission and distribution lines sag and short out, transformers overheat, and wildfires take out crucial connectors, all while electricity demand soars. Blackouts, and worse, follow. And as extreme event after extreme event show, some people and communities get hit even harder at times like these.

All that means that any solutions to the heat-related problems that ail power generators need to take into account not just how they suffer from climate change, but how they contribute to it.

Take hybrid cooling systems for power plants, which offer the option of wet or dry cooling. They might address some of power-plant water dependencies (though if the heat is affecting both the air and the water…). But if the power plants they’re hooked up to are burning coal or gas, the “solution” can make things worse.

So what about the renewables side of things? While building or expanding reservoirs for hydro doesn’t seem likely, some other renewable energy technologies do have options.

  • For wind, turbine manufacturers offer hot-weather packages (and cold-weather ones, Texas…) that can make sure the innards (electronics, etc.) aren’t slowing things down when the heat is on, and allow the turbines to maximize output from whatever wind is available.
  • For solar, the output from higher efficiency PV cells drops less with each degree; they also convert more of the incoming solar radiation into electricity, leaving less behind as heat.
  • While rooftops get hit by the heat too, rooftop PV can help avoid some of the heat-related issues with other parts of the grid, including transmission lines, distribution lines, and transformers.
  • Diversification can help: A recent Sacramento Bee editorial pointed out the benefits of harnessing California’s huge offshore wind potential, since the weather out there might help us address our problems closer to home.

It’s worth a quick thought for another clean energy source: energy efficiency. The more we can do with the kilowatt-hours we have, and the more our buildings are equipped to withstand extreme temperatures, the better off we’ll be at times like these.

Overall, what we’re experiencing now should just be more fuel for the (carbon-free) fires of our commitment to the transition to clean energy. As the author of an MIT study of climate change impacts on solar panels put it,

The results in no way mean that it doesn’t make sense to put up more solar panels — quite the opposite… Decarbonizing electricity is probably the first thing we should do to put a lid on global warming. —Dr. Ian Marius Peters, MIT

Dangerous heat keeps coming, and all power options are not created equal. The more our electricity planning takes into account both of those factors, the better.


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