Fusion Energy: 5 Problems to Solve Before It Powers the Grid

Fusion energy has never looked closer. In 2025, research reactors in China and France held plasma for 18 and then 22 minutes, and a US laser facility produced net energy from fusion several times. Yet no fusion plant has ever sent electricity to the grid.

The International Energy Agency's State of Energy Innovation 2026 report sets out what still has to happen first. These are the five problems fusion must solve before it can power the grid, and why each one matters.

Fusion's Biggest Problems at a Glance

1. Reaching Reliable Energy Gain

The first test is simple to state and hard to meet: a reactor must release far more energy than it takes to run. The report points to a gain of 10, known as Q=10, as the level at which a reactor could be part of a power plant that produces more electricity than it consumes.

Most experiments today fuse two deuterium atoms, a simpler step before the deuterium-tritium fuel expected to reach that level. No facility has yet produced more heat than the energy put into the whole system.

Reaching the target once is not enough. A power plant must be able to start, ramp up and ramp down reliably over many days, and the report notes that today's leading designs may not be the first to get there.

2. Breeding Tritium Fuel Inside the Reactor

Commercial fusion is expected to run on deuterium and tritium. Tritium is radioactive, decays with a half-life of 12 years and is not found in nature in useful amounts, so a power plant will have to make its own.

The plan is to breed it from lithium in a "blanket" that surrounds the reaction. Designs using solid ceramics, liquid metals and molten salts are being explored, but all are at an early stage in their materials, coolants and ways of extracting the tritium.

The lithium needed is modest. A 1 gigawatt plant would use less than 5 tonnes of natural lithium a year, although it relies on lithium-6, a form that makes up less than 10% of natural supply and is hard to separate.

3. Materials That Last for Years

Inside a fusion reactor, the walls face extreme heat and a constant stream of high-energy neutrons. Tungsten, beryllium and graphite are used in experiments today, but they wear out too quickly for a commercial plant.

New options include tungsten alloys, flowing layers of liquid lithium or tin, and silicon carbide composites that can withstand more than 1,500°C. Each still has engineering problems to solve before it can be used at scale.

This matters for cost as much as for safety. Fusion plants will be expensive to build, so they need to run for decades without major repairs, and the report says much of the research on neutron damage is still inconclusive.

4. Getting the Heat Out to Drive a Turbine

A fusion reactor makes heat, and that heat has to be carried away to drive a turbine without disturbing the reaction. The first plants may borrow systems designed for nuclear fission, letting the heat cool before it is used.

Efficient commercial plants will need a system built for fusion's higher temperatures and harsher conditions. Liquid metals, molten salts and helium are being studied to carry heat away from the reactor, with supercritical carbon dioxide as a possible fluid for the turbine side.

So far most of this work is theoretical. The next step, according to the report, is to test these options in real experiments.

5. Building Smaller Reactors Faster

Even if the physics works, fusion has to be affordable. If today's tokamak and stellarator designs were simply scaled up to hundreds of megawatts, the materials alone would cost too much to compete over the long term.

Size is a big part of the challenge. The 192 lasers at the US National Ignition Facility fill a building of 16,000 square metres, while newer tokamaks such as ITER and SPARC are designed to be about four times smaller per megawatt than the Joint European Torus, which closed in 2023.

Many early demonstration projects are not designed for repeatable construction. Once each design proves it can produce heat at scale, the focus will need to shift to factory-style manufacturing, and some developers, such as Commonwealth Fusion Systems with its manufacturable superconducting magnets, have already started.

Why Fusion Is Still Worth the Effort

Governments have spent around USD 100 billion on fusion research since the mid-1970s. Private money is now joining in, with more than 80 fusion start-ups today, up from 20 a decade ago, raising USD 10 billion since 2020.

The appeal is clear. A working fusion plant could supply steady power that helps keep grids stable, with no CO2 emissions and minimal long-lived radioactive waste.

In 2025, Google and Microsoft became the first companies to sign contracts for power from future fusion plants. Large public projects such as ITER, built in France by an international partnership, continue to test the science at scale.

The Problems Must Be Solved Together

What makes fusion hard is that none of these problems can be solved alone. A reactor that reaches high energy gain is of little use if its walls wear out in months or if it cannot make its own fuel.

That is why the report argues that funding should be spread across all the key gaps rather than one approach. Fusion teams compete for money, but they gain the most when they share what they learn.