Carbon-neutral coal ‘doesn’t make sense,’ scientists say

Source: Chelsea Harvey, E&E News reporter • Posted: Monday, September 10, 2018

Amid the Trump administration’s focus on reviving the coal industry, some experts are discussing creative strategies that could reduce emissions from existing power plants.

Outfitting plants with carbon capture technology, or offsetting their emissions with carbon-sequestering plants, are some ideas in the mix.

But when it comes to coal, making the industry truly carbon neutral is probably impossible, new research suggests. An analysis published today in the journal Scientific Reports suggests that the technological steps required to render U.S. coal plants climate neutral are almost certainly out of reach.

Canceling out their emissions, with the help of carbon-sequestering switchgrass plants, would require nearly two-thirds of all the arable land in the country. Even if the entire U.S. coal fleet were outfitted with carbon capture and storage technology, the emissions it fails to capture would still require about 20 percent of nation’s usable land, the study found.

Making up for the emissions associated with solar farms, on the other hand — accounting for the carbon footprint required to manufacture and install them — would require five times less land than the best coal scenario.

The takeaway, according to co-author Joshua Pearce of Michigan Tech, is that pouring resources into climate-neutral coal “doesn’t really make sense.” If the goal is carbon-neutral energy, focusing on alternative sources like solar is a better strategy, he said.

The research is especially relevant now, as the Trump administration has just unveiled its proposed replacement for the Clean Power Plan, an Obama-era climate rule aimed at reducing greenhouse gas emissions from power plants. The Trump administration’s alternative eliminates a federal cap on power plant emissions, leaving it up to the states instead.

As experts have noted, the proposal is unlikely to save the coal industry in the long run — coal’s overall decline is projected to continue, even with the new rule in place (Climatewire, Aug. 21). Even so, the uncertainties raised by the absence of a federal limit, coupled with the administration’s long-standing emphasis on reviving coal, might reignite discussions about the strategies that could be used to make coal plants less carbon-intensive.

As the new study notes, carbon emissions from various sources — power plants, transportation and so on — can theoretically be canceled out by planting forests or other types of vegetation that suck carbon back out of the atmosphere. This is the idea behind carbon offsets programs, which allow companies to invest in forests or other carbon sequestration projects in exchange for emissions they produce.

So some experts have raised the idea that emissions produced by coal plants or other power sources could be offset with carbon-guzzling “biosequestration” plantations, rendering them carbon neutral.

Carbon capture and storage technology is another option that many experts have raised for reducing the emissions from coal-fired plants and other fossil fuel power stations. But while CCS technology can be highly efficient at its best, capable of capturing more than 80 percent of the emissions produced by an individual plant, it doesn’t address the substantial carbon footprint associated with other steps in the supply chain — like the emissions produced when extracting and transporting coal for use as fuel.

So when accounting for all the upstream and downstream emissions built into the process, even CCS-equipped coal plants would require some biosequestration to render them completely climate neutral. The same is true for alternative energy sources, like solar, which also have an indirect carbon footprint associated with manufacturing, installation and other steps in the process.

But just how much biosequestration would be needed to completely offset all their emissions, and how much land it would require, has remained an open question until now.

“If you scrub out the pollutants and you sequester the carbon, you could have a carbon-neutral, completely environmentally friendly coal-fired electricity system,” said Pearce. “We said, ‘OK, there’s a lot of people working on this, millions of dollars have been invested in CCS — let’s find out if it makes sense.'”

Pearce, along with lead author James Gunnar Groesbeck of the Technical University of València, explored three major scenarios: coal with no CCS; coal with CCS in which the captured carbon is stored underground; and CCS in which the captured carbon is used in the extraction of oil, a process known as “enhanced oil recovery.”

They accounted for all the emissions from the beginning to the end of the process — the extraction, transportation and burning of the coal, and even the emissions produced by the oil extracted down the road by enhanced oil recovery.

Then they calculated the amount of biosequestration required to offset all of these emissions in each scenario, assuming plantations composed of switchgrass — a fast-growing crop that can be used in biofuels. They then compared these scenarios with the biosequestration that would be required for comparable carbon-neutral solar farms.

They found that climate-neutral coal would require vastly more land resources for biosequestration, even when outfitted with CCS.

A 1-gigawatt coal plant with no CCS would require a land area larger than Rhode Island to render it carbon neutral. If the researchers assume plantations with less efficient kinds of vegetation, it could boost the land requirement to the size of Maryland — about 10 times bigger.

Overall, they found that carbon-neutral coal plants with no CCS required about 13 times more land than their solar counterparts, while plants outfitted with CCS require about five times more land.

Theoretically, there are other forms of carbon sequestration besides the use of vegetation. Some experts are researching the use of special machines that could suck carbon dioxide directly out of the air. But it’s a technology that remains unproven at large scales. For now, biosequestration remains the dominant option when it comes to drawing carbon back out of the atmosphere.

And if that remains the only option, carbon neutral coal may simply be an unreasonable goal, the researchers suggest. The sheer amount of land it would require, even under the best of circumstances, makes its success unlikely.

If the goal is carbon-neutral energy, solar is the more feasible solution, according to this analysis.

“We ran the numbers, and it would have been nice if someone had done this earlier,” Pearce told E&E News. “It could have driven policy in a more pragmatic direction.”