The debate over the fastest way to decarbonize the grid is intensifying, as experts debate a paper from last December claiming modular renewables could beat nuclear power.

The paper, from a Rocky Mountain Institute (RMI) team led by the institute’s chief scientist and co-founder Amory Lovins, criticized the work of more than a dozen authors who asserted that wind and solar could not scale up as quickly as nuclear in the race to cut carbon emissions.

But now the Lovins paper is facing criticism from experts who say the RMI analysis contains significant errors, including a factor-of-10 mistake in some results.

The Lovins team, which included RMI scientists Titiaan Palazzi, Ryan Laemel and Emily Goldfield, published its critique of previous deployment rate studies in the peer-reviewed Energy Research & Social Science.

“Contrary to a persistent myth based on erroneous methods, global data show that renewable electricity adds output and saves carbon faster than nuclear power does or ever has,” concluded the authors.

While admitting that an analysis of this topic “turns on complex details,” the authors contended that previous studies used misleading tactics to support the argument that nuclear can outpace non-hydro renewables.

Lovins et al. were most critical of a 2016 Science Policy Forum article by Junji Cao, Armond Cohen, James Hansen, Richard Lester, Per Peterson and Hongjie Xu, which called for China and U.S. to cooperate to develop nuclear power as a way of reducing carbon dioxide emissions.

Lovins delivered an initial critique of Cao et al.’s study in a letter to Science. The response to this review led the RMI team to delve deeper into the topic and publish its own paper, said Lovins.

In its paper, the RMI accused Cao et al. of cherry-picking data to support a nuclear-is-faster hypothesis.

For example, according to the RMI team, Cao et al. had tended to use per-capita rather than absolute build-out measures, conflating technologies with countries and making it hard to measure the full decarbonization impact of infrastructure additions.

“If you measure per-capita, then how fast the deployment moves depends on the population of the country in which it occurs,” Lovins told GTM. “This produces very strange results. It makes a very populous country like China look like it lags behind everybody else.”

Lovins said a review of the Cao et al. data on nuclear and renewables build-outs in a single country, China, actually confirmed RMI’s thesis, but noted that this finding had not been highlighted in the Science paper.

He claimed Cao et al. had chosen a per-capita measurement approach based on earlier work by The Breakthrough Institute (BTI), an ecomodernist think tank that espouses the use of nuclear energy to combat manmade climate change.

Lovins claimed the selection of countries chosen by Cao et al., along with other authors, was also based on BTI research. “I didn’t have any trouble finding a dozen authors who were making similar claims without looking into the numbers to see if they were right,” he commented.

“I don’t want to speculate on anybody’s motives, but clearly there was a failure in the peer-review process,” he said. “This is not really an argument about reputation, but about scientific soundness.”

The RMI paper’s scientific soundness is also being called into question, however. Staffan Qvist, an independent energy consultant, and the authors of Cao et al.’s paper have hit back against the claims in the Lovins article.

Qvist contends that it is Lovins, rather than Cao, who is guilty of cherry-picking, for example by choosing an arbitrary study period of 17 years that happens to coincide with a rapid growth rate for renewables and waning nuclear deployment.

Qvist also defends Cao et al.’s use of per-capita rather than absolute rates, pointing out that normalizations are essential when comparing different data sets, such as nuclear versus renewables build-outs in China (population 1.4 billion) and France (67 million).

But Qvist’s most damning indictment of the RMI paper is that it contains a mathematical glitch leading to a tenfold mistake in some of its results.

When presenting electricity production levels for a selection of countries, the RMI team forgot to divide a decade’s worth of generation by 10 to get an annual value, said Qvist. When GTM alerted the Lovins team to this, Palazzi, a senior associate at RMI, admitted the mistake.

“However,” he said, “this error does not influence any of the...paper's [chief] findings. It is still true that on a one-year, three-year or 10-year basis, modern renewables have grown faster than nuclear.”

For Qvist, though, the error is significant. "It is indicative of the quality of the entire effort and the familiarity and understanding of this data that this order-of-magnitude error was published and discussed in their paper,” he said.

The discussion illustrates the importance of choosing the right terms of reference in any scientific argument.

To the uninitiated, it remains unclear whether normalized or absolute quantities would make more sense in trying to judge whether one type of technology can expand more quickly than another.

And even when looking at normalized values, there might be better options than a per-capita measure. For example, said Lovins: “You need to track not only carbon, but also money."

“If you substitute a very [expensive] carbon-free resource instead of an inexpensive one, you will save less carbon per unit of expenditure. A lot of people have missed this point.”

Because nuclear costs around three times more than energy efficiency, shutting down reactors and diverting the money into energy-efficient programs would create a net carbon savings, he argued.

Regulators, he suggested, should consider auctions for carbon-free resources and allow the market to decide which options could operate most cost-effectively.

The strong rhetoric indicates that this debate is related to a deeper issue of allegiance to particular energy sectors.

The language employed by both Lovins and his detractors is reminiscent of the rhetoric used by Stanford University’s Mark Jacobson and critics led by Christopher Clack in the infamous debate about how to achieve an energy system that is 100 percent based on renewables.

As with the Jacobson-Clack feud, the dispute over pathways to decarbonization seems ultimately to reflect entrenched views on how to achieve a common goal. A central question seems to be whether nuclear power deserves a seat at the clean-energy table.

Traditional renewable energy champions, as exemplified by RMI, point to wind and solar power’s turbo-charged growth rates and eye-popping cost reductions as evidence that nuclear is becoming irrelevant.

To many, nuclear doesn’t look like an option worth backing. In many formerly promising markets, it is now seen as too costly. It still hasn’t really worked out what to do with its waste. And its biggest hope, the small modular reactor, is facing hurdles on the road to commercialization.

Against this, nuclear power advocates such as The Breakthrough Institute fear that the intermittency of solar and wind and low capacity factors will require unfeasibly large levels of overcapacity or storage to achieve a fully decarbonized energy system.

In contrast, they argue, nuclear energy has already proved it can power leading economies with a minimal footprint and, historically at least, reasonable costs.

“One of the things we provide to the grid is massive carbon abatement on a much larger scale than anybody else,” said Matthew Wald, senior communications advisor for the Washington, D.C.-based Nuclear Energy Institute.

In recent years, the nuclear industry has delivered around 800 million megawatt-hours of carbon-free energy a year in the U.S. alone, he noted. This compares to about 227 million megawatt-hours for wind and 35 million megawatt-hours for solar, he said.

“We have been pushing the idea that the best system is a mixed system,” said Wald. “We’ve got a global warming problem and we’re going to need all available tools, meaning all the solar and all the wind we can integrate and all the nuclear we can lay our hands on.”