The results suggest the answer could vary a lot depending on the cost and mix of other energy sources on the decarbonized grid, like renewables, nuclear fission, or natural gas plants outfitted with carbon capture devices. In most scenarios, fusion appears likely to end up in a niche much like that held by good ol’ nuclear fission today, albeit without the same safety and waste headaches. Both are essentially gargantuan systems that use a lot of specialized equipment to extract energy from atoms so it can boil water and drive steam turbines, meaning high up-front costs. But while the electricity they provide may be more expensive than that from renewables like solar, that electricity is clean and reliable regardless of time of day or weather.

So, on those terms, can fusion compete? The point of the study wasn’t to estimate costs for an individual reactor. But the good news is that Schwartz was able to find at least one design that could produce energy for the right price: the Aries-AT, a relatively detailed model of a fusion power plant outlined by physicists at UC San Diego in the early 2000s. It’s just one point of comparison, Schwartz cautions, and other fusion plants may very well have different cost profiles, or fit into the grid differently depending on how they’re used. Plus, geography will matter. On the East Coast of the US, for example, where renewable energy resources are limited and transmission is constrained, the modeling suggested that fusion could be useful at higher price points than it is in the West. Overall, it’s fair to envision a future in which fusion becomes part of the US grid's “varied energy diet,” he says.

In an earlier analysis from 2021, Samuel Ward, a physicist then at the University of York, and his colleagues developed a warier outlook. They outline a number of scenarios that could sideline fusion, some of which may be good news for the world: that wind and solar can do much of the work of decarbonizing the grid by the time fusion comes around, for example, or that batteries get really good and really cheap. Even fission itself could become more spry with the development of so-called “small modular reactors,” which are designed to be cheaper to build. Plus, says Ward, now at Eindhoven University of Technology in the Netherlands, fusion cost projections involve materials and supply chains that in many cases do not yet exist. 

“Fundamentally, it comes down to big uncertainties,” he says. “It's a tricky feeling, especially when people have pushed this idea of a ‘holy grail’ or ‘limitless’ energy. They use these words, and I don't think it's done fusion any favors.”

Fusion companies—unsurprisingly—are keen to explain why their designs will not only crack the physics of fusion but also be uniquely economical. Proposed reactors can be broadly grouped into two categories: One, known as tokamaks, use powerful magnets to produce plasma. (Fusing atoms takes a lot of heat, pressure, or both.) The other uses an approach called inertial confinement that aims to crush and energize a target by striking it with a laser, as in NIF’s ignition experiment, or high-speed projectiles.