Coal Power Trends: Visualizing the Decline of America’s Dirtiest Fuel

, Senior energy analyst | August 26, 2019, 6:00 am EDT
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This post is a part of a series on Clean Energy Momentum

Coal fueled half of US electricity generation just a little over a decade ago, but its market share has been collapsing ever since. My colleague Emma Spellman, one of our 2019 UCS Schneider Sustainable Energy Fellows, took a closer look at the data and generated some great new perspectives on that downward trajectory. Here are her thoughts and visuals:

America’s dirtiest fuel is on the decline. The need to transition fossil fuels to renewable sources of energy is not new; in fact, it’s on its way. Policy, market development, and technological progress play pivotal roles in this transition.

Emma Spellman, UCS Schneider Sustainable Energy Fellow 2019

While these components continue to change and progress, it’s important to recognize how far we’ve come to help us keep the momentum going.

A graphic in a recent Guardian article skillfully illustrates these concepts in showing Britain’s quick transition away from coal. In the graphic, which shows the percentage of coal in their electricity mix each day over several years, coal-heavy days in 2012 give way to the first coal-free days by 2017, and a predominance of coal-free days this summer—including its first “coal-free fortnight.”

Indigo rising: transition in the Northeast and Great Plains

Inspired by the Guardian graphic, I set out to replicate this gradient approach for the US.

Unlike Britain, the US has multiple electrical grids, and those are separated into regions. Many are operated by regional transmission organizations (RTOs) or independent system operators (ISOs). And I found the right data for a couple of those—ISO-NE (New England) and SPP (the Southwest Power Pool, stretching from Oklahoma and parts of Texas and New Mexico to the Canadian border).

ISO-New England. New England states were early champions in clean energy policy and energy efficiency, and have been making a move away from coal for years. And when I graphed the ISO-NE data for generation in the region over the last dozen years, that transition showed quite clearly—in black and white and indigo.

In my graphic, each row corresponds to a year and each stripe within that row corresponds to a day. Pure black indicates the maximum during these years (in ISO-NE’s case, about 21% of that day’s generation coming from coal). Lower percentages are linearly scaled to some shade of gray. Indigo indicates days with zero coal generation within ISO-NE.

There is a clear gradient from 2008, with each year becoming lighter and lighter, and coal-free days beginning to pop up in 2012. In 2018, New England saw indigo for 108 days— 29.6% of the year, and over five times as many days as in 2013, just five years earlier.

Southwest Power Pool. SPP shows a different version of the transition away from coal. The speed of transition may not be on par with its northeastern counterpart, but the direction is right.

To start, it’s scaled to 77%, thus starting at a much larger ratio of coal to total generation for the maximum days. Unfortunately, there are also no indigo days. In fact, the minimum in the time frame observed is 24% (higher than ISO New England’s maximum).

However, there is still lightening as the years go by, which, for a historically coal-dependent region, is definitely promising. Days in which coal accounted for more than half of the region’s generation dropped to 55 in 2018 (15% of days) from 357 in 2014 (as in, virtually every day of the year). And coal’s average contribution over those years dropped to 42% from 60%.

Looking Forward

While these are two important case studies, I would love to continue to look at other regions as well. Unfortunately, some regions’ data wasn’t publicly available, some only went a couple years back, while others had varying formats between each year or even each month. However, the difficulties in data retrieval don’t negate the importance of the analysis.

While the transition to renewables from dirty sources of energy  is clearly not over, these graphics prove that we’re going in the right direction when it comes to coal, verifying past analyses by UCS and others.

Obviously, these graphics point towards the question: What’s taking coal’s place? We have to be aware of what fuel types we’re moving to as transitions like these happen.

Natural gas is an important example: While it burns more cleanly than coal, it is certainly not the standard we’re reaching for (and some regions’ ramped-up reliance brings challenges of its own).

Fortunately, our rapid increase in using renewable energy sources like wind and solar, plus energy efficiency, has been another way we’ve decreased our reliance on coal. Wind power’s portion in the Southwest Power Pool in spring, for example, more than quadrupled between 2011 and 2018, rising to 27% from 6%.

A decline in coal is notable and as the trend continues. We must keep our sights on policy and technology to allow for clean energy to fill the gaps.


Credit: Emma Spellman, Union of Concerned Scientists
Credit: Emma Spellman, Union of Concerned Scientists

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  • BEWARE: Demolishing coal-fired power stations will delay the transition to 100% renewable energy
    Why? Simply because without those power stations converted to burn renewable-energy biomass as back-up power the cost and the time taken for the transition to 100% renewable energy will be multiple times greater.

    Meanwhile, burning fossil-fuel natural gas as back-up power may keep the lights on but it will bind the world into a fossil-fuelled future for many more years.

    So we absolutely need biomass burning for the transition.

    Tree-huggers may foolishly rejoice that fewer trees will be felled if there are fewer biomass-burning power stations to burn them in?

    Don’t celebrate too soon – massive wild-fires will eventually consume most of the trees that tree-huggers want to hug and those trees will go up in smoke sooner or later.

    I am sorry but the harsh reality is that tree-hugging, massive wild-fires and burning fossil-fuel natural gas is not helping, but hindering the transition.

    So ignoramus politicians who offer to “cushion” the effect of demolishing critical power station infrastructure that we urgently need to save for the transition to 100% renewable energy should have effigies of themselves burned at the stake.

    My 100% Renewable energy blog

    • ucsjrogers

      Thanks for these thoughts, ScotSci. Biomass is a hot topic in these parts, as you may know. As for the wildfires: I think we agree that it’d be better to work toward a future where that type of unfettered combustion is less likely, with that transition away from heat-trapping emissions, from the power sector and beyond. – John

  • NEISO has quit coal through new combined cycle natural gas plants, imports from Quebec (direct and wheeled through NY). Also, imports of LNG play into NEISO’s picture.

    Not much resembling the UK, where biomass from the US & Canada are a multi-GW piece of the pie. The growth of wind in the UK, dwarfs the stagnant growth of wind in NEISO over the same period. The UK also has far more bi-directional flows (interconnections) with Europe to balance the decline in coal against wind variability. NEISO is a net importer of electricity.

    An important question to ask in NEISO (as is also the case in NY), is whether the decline in load (or TWh/yr is from EE or declining populations and flight of the snowbirds).

    The coal, no coal analysis is ok, but for NEISO it is no slam dunk it’s on the right path. Especially in comparison to SwPP, with its 20+ GW of wind, and enormous potential for solar with its transmission builds (none of which NEISO is doing)… SwPP is not only heading in the ‘right’ direction, it is leading the US right behind ERCOT in the ‘getting us to integrated REs quickly’ category.

    • Net importer of electricity on the order of 25+ TWh/yr with another 8 TWh/yr coming from Quebec with the completion of the Romaine project.

      Given NEISO won’t allow new transmission, those 8 TWH/yr will be wheeled through NY, where we have our own issues with getting new transmission built.

      Luckily for NEISO, we are adding capacity from St.Lawrence/Massena to Marcy/Edic to New Scotland (Albany). The wheeling pathway itself.

      • ucsjrogers

        Thanks for weighing in, Hans. Transmission is certainly an important piece of how our regional grids all hold together (so to speak), and something we pay a lot of attention to:

        And the job of decarbonizing the power sector will be a lot easier if we have strong connections between regions rich in one renewable energy resource or another — so that excess solar power in one area can supply another, and abundant wind power (land-based or offshore) can serve markets far beyond.

        – John

    • Why aren’t you warning about that unwise binding of the US grid into fossil-fuel natural gas burning for many more years because of the market economy’s stubborn insistence on demolishing coal-fired power stations instead of converting them to burn biomass fuel for back-up power, leaving the US with no option but to wed itself to natural gas back up power for the foreseeable future?

      • NEISO – New England Independent System Operator – the 6 New England states whom operate under an equivalent transmission network to the U.K.’s National Grid. Whom coincidentally owns a large chunk of both NEISO and NYISO (you can figure out that acronym right).

        ERCOT – Electric Reliability Council of Texas, although it shares Texas with SwPP – Southwest Power Pool, which is an ISO/RTO serving much of the Great Plains, as well as MISO – MidContinent ISO.

        For what it’s worth, there are tens of GW of multifuel steam boilers in the US that use biomass as a few source. Often they are BTM – behind the meter at paper or lumber mills. New England has some, the Southeast US has more, and California had agricultural biomass to power plants for air quality (which ironically, they allowed to close, not receiving RE credits like solar).

        So we’re not ignoring biomass applications for power gen, we have actually been using it all along.

        We should be honest though…. how much of the world’s commercial biomass production is the U.K. using? The resource isn’t infinite.

      • As far as warning about ‘binding’ to NG…. that ship long ago sailed.

        We have over 500 GW of NG plants, while we flare enough to power around 10 GW’s worth.

        As the inefficient Combustion Turbines barely run, they are not a large source of carbon emissions in the broader picture. As some 300 GW are high efficiency hybrid combined cycle, I worry about those not at all… their carbon emissions without corresponding electricity production is quite low (they ramp and sync fast).

        But what I do worry about, after the 270 GW of coal still operating, is the 70 GW of inefficient NG [or dual fuel – heavy oil] steam boilers we still have. NY has 12 GW alone (and its citizens wont allow combined cycle to be built) plus a GW of coal.

        Some of that 70 GW is multifuel -biomass/black liquor, coal and NG, in various mixtures.

      • ucsjrogers

        ScotSci/Hans, I’m with you both on the risks of natural gas overreliance; NG fuels half of ISO-NE’s generation, and that definitely has its downsides. That’s one reason why we’re so keen on offshore wind for the region, as a powerful new resource that can obviate the need for a lot of that gas. – John