The battle over the viability of 100 percent renewable energy will soon spill into a court of law.

Among clean energy advocates, there is disagreement about what kind of renewable energy target to shoot for -- 80 percent or 100 percent -- and what's the most expeditious way to get there. Stanford professor Mark Jacobson has long led the charge for a 100 percent plan, publishing road maps he says will reliably power the grid without any fossil fuel or nuclear energy.

This summer, 21 notable clean energy scholars led by grid researcher Chris Clack published a critique of Jacobson's work in the Proceedings of the National Academy of Sciences, the same prestigious journal that released Jacobson's study.

Now Jacobson is suing the publisher and the lead author for libel.

His lawsuit, filed September 29 in D.C. Superior Court, asserts that the National Academy of Sciences (NAS) inflicted "significant undue damage" by publishing statements in the critique that Jacobson said were false or misleading.

Clack declined to comment on specific questions due to the pending litigation, but said via email that he was disappointed that the suit had been filed.

"Our paper underwent very rigorous peer review, and two further extraordinary editorial reviews by the nation’s most prestigious academic journal, which considered Dr. Jacobson’s criticisms and found them to be without merit," Clack wrote. "It is unfortunate that Dr. Jacobson has now chosen to reargue his points in a court of law, rather than in the academic literature, where they belong."

Jacobson declined to comment other than to say that "the complaint has nothing to do with stifling scientific inquiry or opinions," and pointed to a paragraph that describes what he sees as "egregious false statements" published by NAS and Clack.

Error or assumption?

The conflict revolves around the accuracy of the critique. Clack and his co-authors pointed out what they saw as grave errors in Jacobson's work, which has become a model that policymakers and celebrities cite and emulate.

When the journal alerted Jacobson that the critique was moving through the editorial process, he responded with a critique of the critique.

Jacobson sent multiple messages to the journal on this topic, first with a list of "thirty false and five misleading statements in the Clack Article," and later with a line-by-line counter-rebuttal. The journal saw those comments and went ahead with the publication. Having failed to achieve satisfaction via the internal editorial process, Jacobson is turning to the courts to resolve the dispute.

Many of the factual disagreements hinge on highly technical points, but one stands out in a big way.

The Clack paper called out Jacobson's work for its use of hydropower, which backs up the proposed grid system by dispatching power when wind and solar can't cover demand.

Jacobson's supplementary details list an installed hydropower capacity of 87.5 gigawatts for 2050, essentially the same as it is today. But elsewhere, he includes a chart showing 1,300 gigawatts of hydropower dispatched, which is roughly 15 times the stated installed capacity.

Clack and company describe this discrepancy as a modeling error that undermines the whole system Jacobson proposes: If the key backup resource needs to deliver 15 times more power than it actually can, the grid balancing falls apart.

In his response, though, Jacobson describes this as an "intentional assumption." His idea is that the annual flow of water through U.S. hydropower facilities has to be held constant, but it is possible to increase the discharge rate by upgrading turbines at existing dams.

This explanation, and associated costs, do not appear in the original article or its supplement. But Jacobson says he explained his thinking to Clack, and Clack went ahead and published a critique of the hydro modeling anyway. Jacobson says that amounts to a false claim.

Let the legal battles begin

For practical observers, the salient point here is that the 100 percent renewables plan hinges on a massive upgrade project at hydropower facilities around the country, which raises serious logistical and ecological concerns.

There's a big difference between operating current hydro capacity and the "intentional assumption" scenario that involves storing up the water and releasing it in massive deluges at times of peak grid demand. Downstream communities, aquatic ecosystems and river navigation would all be impacted. It's unclear just how feasible this would be, and such discussion is not included in the original study.

The lawsuit isn't really concerned with this, though. It seeks to penalize the critical publication for not listening to Jacobson's responses to the critique.

As a result, Jacobson is asking the court to order a retraction of the article, plus damages from NAS and Clack on the order of $10 million each. The initial conference is set for December 29.

It's unclear how the courts will evaluate these claims, but the case clearly ups the stakes on the academic debate over the best path to decarbonization. The fight over 100 percent renewables, versus some other target, already elicits heated debate on Energy Twitter and other forums.

Now the stakes are no longer just academic or intellectual -- there's big money on the table.