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As the U.K. went into nationwide lockdown this spring, the words “unprecedented” were trotted out to explain everything from pubs being closed to national clap-alongs for health care workers.

But for the National Grid, the country’s electricity operator, “unprecedented” meant blowing through one record after another, often years ahead of schedule: max solar capacity in the energy system, lowest-ever carbon intensity—just this Sunday—and longest stretch without coal.

That record was still in place on Tuesday, with the country’s system now on its 46th consecutive coal-free day—over 1,000 hours—and counting. As of midday Tuesday, the country’s grid was 53% carbon-free, with the remainder comprising supplies of gas, biomass, and a small proportion of energy imports.

This sudden shift to a dramatically lower-carbon energy system isn’t an unexpected development inside National Grid—the goal is to completely decarbonize the country’s electricity system by 2025. But the lockdown has produced a kind of testing ground that will outlive the pandemic, giving a taste of how a mix of new energy sources will impact National Grid’s operations in the coming years. This will give rise to new challenges: periods of ultralow demand, negative pricing, and how to manage the delicate balance of an energy system dependent on the fluctuations of wind and sun.

The lockdown drop

When the U.K. went into lockdown in late March, the impact on energy consumption was immediate: Demand dropped about 20% across the system, according to the National Grid.

While domestic demand increased sharply as people stayed home and ran TVs and washing machines all day, that increase was offset by the much sharper decline in industrial consumption. But other than that drop, the patterns of demand didn’t look as different as you might expect: People used more energy in the mornings as they got ready for the day (they just tended to get up a bit later, as commuting was taken out of the equation), and again in the evenings as they cooked and watched TV.

But rather than making the electricity system easier to manage, a drop in demand at that scale makes it harder, says Kayte O’Neill, head of markets at National Grid. A demand drop requires fine brushwork, to ease the system’s voltage down in tandem and keep the entire system in balance, while managing the imports and exports of energy to neighboring Ireland and mainland Europe. Not keeping the system perfectly aligned means risking blackouts.

National Grid turned to programs it had been considering as part of the long-term strategy to decarbonize the whole grid: arranging for one of the U.K.’s nuclear stations to turn down its output, and entering discussions to turn up or down supply by the kinds of smaller renewable producers—mini solar farms or systems installed in industrial parks, for example—that otherwise wouldn’t be significant enough to have an impact on the larger grid.

“What this lower-demand period has done has accelerated those changes,” O’Neill says. Work that was expected to be rolled out over years was suddenly done in as little as five to 10 days, she says.

In this low-demand world, coal is a natural casualty. While a “typical, high-demand” day would draw on the full range of energy sources, O’Neill says, sources of demand are drawn into the grid in order of cost—and coal is the most expensive. With less demand and record supplies of solar power, in particular—a sunny spring has helped—coal is simply too expensive and not necessary, says O’Neill. That’s part of a longer-term trend: in 2019, coal fell to just 2% of electricity generation overall in the U.K., according to the International Energy Agency (IEA), while renewables provided 40%.

That hit to coal demand has been a feature of lockdowns around the world, according to the IEA. Coal demand is expected to drop 8% this year. With demand falling, renewables—which are more highly represented in energy grids, because they are easier to decarbonize than, say, airplanes—have come to make up a larger part of the total energy pie. That’s good for emissions, but it comes with its own operational challenges, largely in making sure that there are always reliable backups (frequently in the form of hydropower or nuclear) to underpin stable supply, the way coal has in the past.

Managing the careful process of keeping the energy system in balance has also required other, creative measures—how to make sure that enough control room engineers would remain healthy in order to run the grid itself. That required planning, with some workers during the lockdown living at work—in pods—and not seeing their families for weeks at a time.

That drop in demand has also produced bizarre market distortions, in some cases: In the U.K. as well as other European countries, power markets have become so oversupplied that prices have repeatedly dipped into negative territory in recent months—effectively requiring utilities to pay consumers to use energy. This kind of energy-dumping phenomenon will continue to be a problem until efficient energy storage technologies can be developed and deployed.

How to reopen the grid

Even after Boris Johnson announced slight easing measures to the country’s lockdown earlier this month, energy demand remained low, says O’Neill. While people can now spend longer outside, nonessential shops—for example—won’t be opened until mid-June, the government has said.

But a return to “normal” energy demand isn’t the concern.

“As demand goes up, if anything the system becomes easier to manage,” O’Neill says, adding that National Grid was still waiting to see whether potential long-term shifts caused by COVID-19—less commuting, more working from home, for example—would markedly shift the country’s electricity consumption patterns.

Either way, the National Grid has been preparing for a “l(fā)ow-demand summer”; keeping in place the measures it has used throughout the lockdowns. New precedents have also been set.

The pandemic showed that every sector of the U.K. is capable of working together in closer cooperation, O’Neill says—and that it may be possible for major decarbonization milestones to be hit far sooner than expected.