The Biden administration has announced a breakthrough on nuclear fusion, fueling hopes of further progress toward clean energy.

Nuclear fusion — the process in which atoms are fused together to create energy — has long been studied as a potential power source.

But various hurdles have prevented the reaction from being a viable option for clean energy, and a commercial effort is still likely decades away.

Here’s what you should know about the Energy Department’s announcement:

1. It’s the first time a net energy gain has come from fusion

The crux of Tuesday’s news is that scientists at the Lawrence Livermore National Laboratory in California were able to produce more energy via fusion than they put in. They put in 2.05 megajoules of energy and got out 3.15 megajoules. 

This is the first time scientists in a lab were able to create a net energy output through fusion, demonstrating that it is possible to do so.

“It’s the first time it has ever been done in a laboratory anywhere in the world. Simply put, this is one of the most impressive scientific feats of the 21st century,” Energy Secretary Jennifer Granholm told reporters at a press conference. 

While the technology isn’t ready to be commercialized yet, the successful experiment raises the prospects of larger-scale deployment of fusion energy.  

Previously, the lab came relatively close to breaking even when it generated 70 percent of the energy it put into a fusion reaction last year.

2. It’s seen as another potential source of carbon-free energy

If fusion can become a large-scale power source, it will provide another way of generating carbon-free energy as the world looks to transition away from planet-warming fossil fuels. 

U.S. officials have said they hope to broadly have an entirely clean electric grid by 2035 and commercially viable fusion power within a decade.

Like wind, solar and traditional nuclear energy — where an atom is split apart instead of fused together — nuclear fusion doesn’t emit any planet-warming gasses or air pollution. 

“This milestone moves us one significant step closer to the possibility of zero-carbon, abundant fusion energy powering our society,” Granholm said. 

“We can use it to produce clean electricity, transportation fuels, power heavy industry [and] so much more,” she added. “It would be like adding a power drill to our toolbox in building this clean energy economy.”

Unlike traditional nuclear energy, called fission, fusion doesn’t generate radioactive waste that requires long-term storage. And unlike traditional hydropower dams, it doesn’t require finding — and flooding — a new reservoir.

The main place that fusion power would be useful if plugged into the current American grid would be as what is called “base load” power: a stable constant amount of electricity that current grids rely on.

In the U.S., about 19 percent of electricity comes from nuclear power, while 60 percent comes from fossil fuels such as coal, natural gas and petroleum, and the rest is from renewables, according to the U.S. Energy Information Administration.

Carolyn Kuranz, associate professor of nuclear engineering and radiological sciences at the University of Michigan, told The Hill on Monday that nuclear fusion does create byproducts that have small amounts of radioactive material, but she said the material can stay on the power plant site and be used to fuel future fusion reaction instead of needing to go elsewhere.

Paul Dabbar, who was the Energy Department’s under secretary for science during the Trump administration, also pointed to some advantages that fusion could have over wind and solar in an interview with The Hill this week. 

“It needs to be windy, it needs to be sunny, it takes a lot of land,” he said of the other energy sources, though he noted that battery technology could be used to improve on the intermittency issue.

However, fusion comes with its own drawbacks. A future fusion industry built around large, expensive individual plants would be dependent on an expanded, high-capacity electric grid to move power across the region or country — something that feels almost as far away at this point as commercial fusion power. 

3. Breakthrough positions US as leader in global quest for fusion 

The successful net power-producing experiment is a clear mark of success for America’s burgeoning public and private investment into fusion energy — particularly as the European Union, China and South Korea build out their own programs.

In January, China’s Experimental Advanced Superconducting Tokamak (EAST) sustained a record 17-minute fusion reaction, Smithsonian reported.

And the International Thermonuclear Experimental Reactor (ITER) in southern France will be the largest fusion facility in the world when it begins experiments in 2025, according to a statement.

In March, the Energy Department released a decadelong roadmap to bring commercial fusion to electricity markets.

That initiative touted the $2.5 billion that the private sector poured into fusion last year — about 3.5 times what the government spends directly.

An April White House summit also promoted the fact that two-thirds of private fusion companies and suppliers are based in the U.S. — and that American companies are the main recipients of international fusion funding.

But while it is tempting to think of fusion in terms of a “race” between countries, the drive for fusion power is highly international and collaborative.

U.S. companies built the central solenoid magnet for the ITER tokamak — necessary to create the magnetic fields that power and control the superheated plasma during a fusion reaction, according to the U.S. government.

And the Energy Department in November announced nearly $50 million for fusion research — of which part will go to support U.S. researchers at ITER and EAST, as The Hill reported.

4. Fusion still years off from becoming a mainstream energy source

The development was a major step toward fusion energy, but you’re not likely to be using this type of energy to turn on your lights anytime soon. 

Granholm told reporters the administration hopes to see commercial fusion within a decade. 

“The president has a decadal vision to get to a commercial fusion reactor within, obviously, 10 years, so we’ve got to get to work,” she told reporters. 

Kim Budil, director of the Lawrence Livermore National Laboratory, where the breakthrough occurred, said it could be even longer, taking “decades” before the technology is commercialized. 

“There are very significant hurdles” in both science and technology, Budil said. 

Dabbar told The Hill this week that he thinks the first commercial demonstration fusion reactors could crop up between 2030 and 2035 and that large-scale deployment could come a few years after that. 

“It takes a long time for energy systems to go from testing to full-scale deployment,” he said. 

5. It has military implications

The applications of this discovery — like the experiment itself — go well beyond peacetime.

While the ultimate implications of this test are a milestone on the road to clean energy, the “more immediate” implications were military, said Marvin Adams, deputy administrator of the National Nuclear Security Administration.

So are the program’s roots: The National Ignition Facility at the Lawrence Livermore National Laboratory uses extremely powerful lasers to “ignite” hydrogen and cause a self-sustaining explosion — a system developed in part to test advanced nuclear weapons without having to detonate an entire bomb. 

“You start with a little spark, and then the spark gets bigger and bigger and bigger, and then the burn propagates through,” physicist Riccardo Betti of University of Rochester told public radio station WBUR.

This is a tiny-scale version of the same process used to kick off a hydrogen or “thermonuclear” bomb — which uses fusion power to release 1,000 times as much energy as the bomb dropped on Hiroshima in 1945, Time reported.

Fusion reactors don’t contain nearly enough fuel to produce that kind of explosion — and a thermonuclear bomb requires a separate atomic explosion to trigger ignition, according to the International Atomic Energy Agency.

But U.S. officials hinted at military applications. Fusion is “an essential process in modern nuclear weapons” and a milestone like this one was a strong argument for American military power, Adams noted.

The successful test demonstrates America’s “world-leading expertise in weapons-relevant technologies” while continuing “to show our allies that we know what we’re doing,” Adams said.