An MIT-trained renewable energy entrepreneur believes Fortescue's plan to use renewable energy to make hydrogen will not be as cost-effective as using wind and solar.

The warning from Rewiring Australia founder Dr Saul Griffith comes as fellow billionaires squabble over what is the right renewable path for Australian energy.

Dr Griffith says Forrest’s plan to use solar power to create hydrogen from water and use it to fuel cars and steel making isn't feasible.

"The fundamental challenge is, green hydrogen has to start with electricity, and hydrogen is just a battery ... so you need three of four amounts of electrical energy for every one unit of hydrogen, so no matter how you look at it, it will be three of four times more expensive than just using the electricity directly," he told Liam Bartlett on 6PR Mornings.

See omnystudio.com/listener for privacy information.