Last December, researchers at California’s National Ignition Facility achieved what many in the fusion industry have called its “Wright brothers” moment. Using a laser, they zapped a golden vessel with a microseconds-long pulse of energy and received a dividend in return: About 50 percent more energy than they put in. That feat is called ignition, and it’s a triumph that’s been awaited since the 1970s. The perpetually 30-years-out technology of fusion power suddenly looks closer.
Well, not all that much closer. The ignition experiment still consumed energy overall, because the laser burned a lot more power than it delivered to its target. And there’s still plenty to figure out about how to harness fusion energy for electricity. But the result has prompted a revival of long-established predictions that fusion will solve all humanity’s energy needs. Startups working on fusion have reported a surge of interest from investors this year. The US government has announced a record $1.4 billion in funding for research, the beginning of a 10-year drive toward practical fusion. The potential payoff is big: Figure out the science, the wisdom goes, and fusion will unlock “unlimited clean energy.”
In many ways, that’s accurate. Just look up there, at that burning ball in the sky. It’s got 5 billion years left in the tank. Various national programs, a big international effort called ITER, and at least 40 private companies are trying to ignite simulacra of that process here on Earth. The goal is to smush atoms together—typically two hydrogen atoms, forming helium—and in the process lose a little bit of mass which, because e=mc2, means releasing energy, too. So you can argue that fusion energy is as limitless as there are hydrogen atoms in the universe.
When you put it that way, wind farms and solar panels can also look limitless, fed by an infinite stream of pressure waves and photons. In reality, of course, they are constrained by practical concerns. Permits. Financing. The construction and supply chains that produce turbine blades and photovoltaic films. The restrictions of a complicated grid that demands power at the wrong times, or doesn’t have wires in the right places.
Which is why, as the physics progresses, some are now beginning to explore the likely practical and economic limits on fusion. The early conclusion is that fusion energy ain’t going to be cheap—certainly not the cheapest source of electricity over the coming decades as more solar and wind come online. But fusion may still find its place, because the grid needs energy in different forms and at different times.
“I was wondering how the heck could fusion ever compete economically with the amazing gains in renewable energy,“ says Jacob Schwartz, a physicist at the Princeton Plasma Physics Laboratory. It was a question that inspired a pivot from working on the superheated details of fusion engineering to energy grid economics. In a paper published this month in the journal Joule, Schwartz and his colleagues tapped a sophisticated model of the US grid between 2036 and 2050 to study the conditions under which it would be economical to build 100 gigawatts worth of fusion plants, enough to power approximately 75 million homes. Basically, how cheap would fusion have to be to build it?
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.
“It’s not a question I get very often,” says Michl Binderbauer, CEO of TAE Technologies, when asked about the economics of his company’s design. People are more likely to query how he plans to get plasma in his reactor heated to 1 billion degrees Celsius, up from the 75 million the company has demonstrated so far. But the questions are intertwined, he says.
That extreme temperature is required because TAE uses boron as fuel, alongside hydrogen, which Binderbauer thinks will ultimately simplify the fusion reactor and result in a power plant that’s cheaper to build. He puts the costs somewhere between fission and renewables—roughly where the Princeton modelers say it needs to be. He points out that while fusion plants will be expensive to build, the fuel will be extremely cheap. Plus, a lower risk of accidents and less high-level radioactive waste should mean a reprieve from expensive regulations that have driven up costs for fission plants.
Bob Mumgaard, the CEO of Commonwealth Fusion Systems, an MIT spinoff, says he was happy to see the Princeton modeling, because he thinks their tokamak can smash those cost requirements. That claim principally rests in a superpowerful magnet the company hopes will allow it to operate tokamaks—and hence power plants—at smaller scale, saving money. CFS is building a scaled-down prototype of its fusion design in Massachusetts that will include most of the components required of a working plant. “You can actually go and see it and touch it and look at the machines,” he says.
Nicholas Hawker, CEO of First Light Fusion, an inertial fusion company, published his own economic analysis for fusion power in 2020 and was surprised to find that the biggest drivers of cost were not in the fusion chamber and its unusual materials, but in the capacitors and turbines any power plant needs.
Still, Hawker expects a slower ramp-up than some of his colleagues. “The first plants are going to break all the time,” he says, and the industry will require significant government support—just like the solar industry has over the past two decades. That’s why he thinks it’s a good thing that lots of governments and companies are trying out different approaches: It increases the chance that some technologies will survive.
Schwartz agrees. “It would be weird if the universe only permits one form of fusion energy to exist,” he says. That diversity is important, he says, because otherwise the industry risks figuring out the science only to back itself into an uneconomical corner. Both nuclear fission and solar panels went through similar periods of experimentation earlier in their technological trajectories. Over time, both converged on single designs—photovoltaics and massive pressurized water reactors seen around the world—that were built all over the globe.
For fusion, however, first things first: the science. It might not work anytime soon. Perhaps it will take another 30 years. But Ward, in spite of his caution about the limits of fusion on the grid, still thinks the research is already paying for itself, generating new advances in basic science and in the creation of new materials. “I still think it’s totally worth it,” he says.
Updated 4-11-2023, 1:10 pm EDT: A previous version of this article incorrectly referred to TAE’s reactor design as a tokamak.