New York City Skyline

How coronavirus exposed the importance of marginal emissions

 September 24, 2020 

Roughly nine months into the global coronavirus pandemic, much has been written about the temporary—and potentially lasting—emissions reductions that have come along with stay-at-home orders and a deep economic recession. DNV GL’s recently released Energy Transitions Outlook 2020 forecasts 75 gigatons of avoided CO2 emissions through 2050, mostly thanks to a big slump in energy demand that resets the trajectory of annual global emissions.

But a closer look at power grids and how they responded to falling demand shows that there’s more to the story—with implications for how we think about more-effective ways for slashing the emissions associated with our energy use.

WattTime analyst Christy Lewis focused her spotlight on the greater New York City metropolitan area of downstate New York, one of the early hotspots for COVID-19 in the United States. The New York City metro area—currently hosting its annual Climate Week—was hit hard and went into aggressive lockdown. What happened next in that region of the NYISO power grid was revealing.

Let’s zoom in to late March and early April 2020. Although just six months ago on the calendar, in ‘coronavirus time,’ that feels like it was eons ago. For context, the week spanning the March-April transition was also precisely when public interest in Netflix’s Tiger King peaked, which feels like it happened last century, so there’s that. 

By March, the pandemic had already been sweeping around the world, with global financial markets starting to tumble. On March 20, California became the first U.S. state to order its residents into stay-at-home lockdown. New York State followed two days later, on March 22. The story of life—and the economy—under lockdown is probably all-too-familiar to you already. But what transpired on New York’s power grid?

Answer: something curious.

Coronavirus emissions graph in New York City

For most of March, the rolling 7-day average of daily electricity demand and daily grid emissions tracked essentially in parallel. A ~7% drop in average daily load was accompanied by a similar ~7% drop in average daily grid emissions. Then the two curves diverged sharply. The next 7% decline in average daily load came along with a whopping 45% drop in average daily emissions. So what happened?

The answer lies in marginal generators and marginal emissions rates, and what they contributed to overall daily emissions.

New York is a state with bold decarbonization targets: 100% carbon-free electricity by 2040 and a net-zero-carbon economy by 2050. But it’s not there yet. While upstate New York has made great strides with zero-emissions generation (mostly modern renewables such as wind and solar), downstate New York remains heavily dependent on fossil-fueled generation, which accounted for 69% of energy generation in 2019.

Yet as electricity demand rises or falls (mostly the latter, in this era of coronavirus), not all generators respond to that fluctuating demand like a swelling or receding of the tides in New York Harbor. Specific generators—the ones that are sitting ‘on the margin’ of demand—turn on or off, or ramp up or down, to maintain the supply-demand balance.

What we saw happening in those weeks of March and April was the byproduct of a simple fact of grid dispatch order: as electricity demand continued falling through late March and then into April, the marginal generators that were turning off were by and large the polluting, fossil-fueled ones. Even though demand declined gradually, New York’s downstate grid got a lot cleaner in the process. Data from WattTime’s analysis confirms as much: Throughout the first month of New York’s stay-at-home order, carbon-free generation remained a stalwart, supplying 7,500 to 8,500+ megawatts (MW) of capacity each day. Meanwhile, fossil-fueled generation plummeted, from supplying 5,500 MW of daily generating capacity at the start of lockdown to just 3,500 MW by mid-April.

So with economies around the country and around the world trying to rebound (or at least wanting to), what do we do with this insight? As energy demand climbs alongside economic activity, are we destined to see carbon emissions rise, too? Not necessarily.

In the same way that New York’s electricity demand and associated grid emissions decoupled in late March and early April thanks to the influence of marginal generators, so too do real-time grid emissions fluctuate all the time, not just during pandemic-induced global economic recessions. Every time you flick a light switch, plug in an electric vehicle to charge, schedule the battery from a residential solar+storage system in California to discharge… a marginal generator responds. And whether that marginal generator is surplus renewable energy or a polluting peaker plant can have a big influence on the emissions your energy use causes. Such fluctuations are most pronounced in grid regions amidst their fossil-to-renewable energy transition, where there’s a mix of clean and dirty generation.

Solutions like WattTime’s Automated Emissions Reduction (AER) technology harness this insight and convert it into a software signal that allows smart devices—thermostats, EVs, batteries, heat pumps, etc.—to sync their demand with moments of clean energy and avoid moments of dirty energy. Adopted at scale, it makes the kind of huge emissions reductions that downstate New York saw earlier this year achievable anytime, anywhere. 

We didn't need a global pandemic to find new examples of the deeper, faster emissions reductions right in front of us, but, well, here we are. Let's do something about it.

Image: Emiliano Bar | Unsplash

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