(Reuters) – Companies looking to harness the process that powers the sun and stars to generate electricity expect to spend about $7 billion by the time their first nuclear fusion plants come online, a survey published on Wednesday said.

Fusion occurs when the nuclei of two light atoms such as hydrogen, heated to extreme temperatures, fuse into one heavier nucleus releasing vast amounts of energy.

Looking to master the fusion process using lasers or magnets, private companies and government labs spent $500 million on their supply chains last year, according to the Fusion Industry Association (FIA) survey.

That spending is set to explode to $7 billion by the time fusion companies develop their first power plant and potentially trillions of dollars in a mature fusion industry, estimated to be sometime between 2035 and 2050, the survey of about two dozen developers said.

Much of the supply chain expense is expected to go to high grade steel and concrete and superconducting wire to build plants where fuels will be heated to more than 100 million Celsius in special chambers. Money will also go to super magnets, lasers, and power supplies.

Andrew Holland, the head of FIA, said there is little concern about geopolitical supply risk in the supply chain as no critical parts or materials face global supply shortfalls or come only from unstable countries.

“The biggest challenge honestly is just scale,” Holland said. “We want to make sure the supply chain companies are aware that fusion is coming so they can make the investments to scale up.”

While there is a global lack of tritium, a fuel that many companies plan to use to fire fusion plants, Holland said that is not a concern because the companies plan to breed tritium in the fusion plants with the use of lithium.

A fusion plant would only need the amount of lithium found in about four electric vehicles, he estimated.