Editor's note:Dennis Wamsted is an energy analyst at the Institute for Energy Economics and Financial Analysis (IEEFA).

The U.S. Department of Energy's (DOE) full-throated support for carbon capture and storage (CCS) technology rests on flimsy assumptions about the capabilities of projects that have not yet been built. It is time to set the record straight.

Four Corners Power Plant: Capture Target Far Exceeds Actual Emissions

Take the DOE's recent announcement as an example: the department will cover 50% of the cost of a front-end engineering design (FEED) study for a CCS retrofit of the two-unit coal-fired Four Corners Power Plant in northwestern New Mexico, with a total study budget of $13.1 million. In its project description, the DOE stated the goal is to install CCS equipment capable of capturing 10 million tonnes of carbon dioxide annually at this 1,540-megawatt plant.

According to U.S. Environmental Protection Agency (EPA) data, capturing 10 million tonnes of carbon dioxide annually is equivalent to taking about 2.4 million cars off the road. But here is the problem: Four Corners has exceeded 10 million tonnes of emissions in only one of the past eight years, and it is highly unlikely to reach that level again in the future.

First, to produce 10 million tonnes of carbon dioxide, the plant would need to maintain an annual capacity factor of 75%; over the past eight years, its average capacity factor has been only 58.4%. The goal of a federal CCS project should clearly not be to encourage the plant to emit more carbon dioxide than it currently does.

Second, the two units are old—a critical weakness for coal-fired plants. Studies have repeatedly shown that aging coal plants suffer from performance degradation and rising maintenance costs, and Four Corners is no exception. The two units have been operating for 54 and 55 years, respectively. Even if the FEED study takes 18 to 24 months and permitting and construction take another 3 to 4 years, both units will likely be around 60 years old when the CCS equipment comes online.

Third, the plant's electricity price is already relatively high. Adding expensive CCS equipment would only further increase generation costs, making it even harder to compete as wind and solar power are deployed at scale across the Southwest.

95% Capture Rate: A 'Bold Claim' Lacking Operational Verification

The DOE and project proponents also claim the facility will capture 95% of the plant's carbon dioxide emissions—a claim with almost no operational experience to back it up. IEEFA research shows that the only two operating coal-fired CCS projects in North America have never come close to that level. The claim also obscures the significant uncertainties associated with the massive scale-up of CCS at Four Corners compared to these two projects. 95% may be a goal worth pursuing, but presenting it as an established fact is hard to believe.

Unfortunately for the DOE, Four Corners is not an isolated case.

Sutter Power Plant: Historical Emissions Never Reached Target

In August, the DOE signed an agreement to provide $8.6 million in federal funding to study installing CCS equipment at the 530-megawatt Sutter combined-cycle gas plant in California. The plan also claims to capture 95% of emissions, or up to 1.75 million tonnes of carbon dioxide per year.

But there is a small problem: the plant has never emitted that much carbon dioxide since it began operations in 2001. Its 'best' year was 2002—its first full year of commercial operation—when it emitted 1.59 million tonnes. The plant faced severe economic difficulties in the mid-2010s, and its owner, Calpine, shut it down in 2016 and 2017. Although it has been restarted, its average capacity factor over the past three years has been only 45.3%, with average annual carbon dioxide emissions below 1 million tonnes.

So, let's set aside the claim of capturing 1.75 million tonnes per year and focus on the 95% capture rate. The problem here is equally tricky. Carbon capture equipment performs best under steady-state operation, and Sutter does not meet that condition. For example, over the past 18 months, the plant's capacity factor exceeded 60% five times and fell below 10% five times—far from steady-state operation.

Notably, Sutter has been operating for 23 years, making it middle-aged for a combined-cycle gas unit. Like coal plants, such units experience rising maintenance costs and declining performance as they age. Moreover, California is rapidly moving away from fossil fuels, with solar, wind, and battery storage quickly gaining market share, and emerging zero-emission geothermal technology showing near-term commercialization potential.

Technology Scale-Up and Operational Fit Remain Unknown

As with the Four Corners coal case, the DOE's optimistic promotional materials make no mention of the difficulties of building first-of-a-kind technology and integrating it with large power generation units. The only experience with CCS on a gas plant comes from tests conducted between 1991 and 2005 at a combined-cycle plant in Bellingham, Massachusetts, where only a portion of the flue gas was treated. The tests ran well, but left many questions unanswered: How will the process respond under real-world, non-steady-state operating conditions? Will capture efficiency hold up when the technology is scaled up? What will it cost?

There are many more such cases, but the conclusion is clear enough.

The DOE and other advocates portray CCS as a 'silver bullet' for solving carbon emission problems. It is not. There are serious questions about the cost and performance of capture projects, as well as the feasibility and safety of transportation and storage. IEEFA does not consider CCS to be the solution, but if advocates could discuss the issue more pragmatically, it would be a useful first step.