FMG executive chairman Andrew Forrest said it was clear some research analysts did not see the value in FFI and its 120 projects but it would become clearer over time.
"It does amaze me how forgiving iron ore analysts are when you've got massive deposits and guaranteed markets and the technology to get it into market, even though you're not in production, you've proven the resource, you've proven the market," he said.
"If you can imagine that times 120 - that's how I see it.
"I haven't ever tried to value the company, but I've had expressions of interest made to me by fund managers or by big infrastructure managers. They've talked around $20 billion.
"That was the kind of overture given to me to try and entice us to list FFI, which I don't think is in Fortescue's best interests.
"The two together are the greatest opportunity of being that world leader, that world example that a heavy industry can actually materially reduce operating costs and materially improve its margins by going green, by not smoking billions of dollars of cash each year in fossil fuel."
Morgans analyst Adrian Prendergast noted management were still unable to give more details on FFI, despite spending substantial capital.
"A 'bajillion' is a huge, unspecified number, which feels a lot like FMG's FFI business at the moment," he said.
Forrest said the company's aim was to "commercially destroy global warming" and said it wasn't a choice.
Forrest noted FMG had plenty of naysayers when it emerged 19 years ago as a "David amongst the Pilbara goliaths".
FFI already has 1100 employees and capital and operating expenditure for the 2023 financial year is expected to be $600-700 million.
The company is not yet producing any green hydrogen but maintained its target of 15 million tonnes by 2030.
FFI CEO Mark Hutchinson said the first green hydrogen produced would likely come from Australia but the Biden Administration's Inflation Reduction Act made the US a good option.
"On the call, FMG claimed that it is humble and frugal in its approach to FFI, a claim that seems at odds with: a) calling itself a leader in the space before developing any projects, b) its global branding efforts and high-profile appointments, and c) the billions being sunk cumulatively into R&D and other pre-development work," Prendergast said.
"We are hoping that FMG will be able to turn this view around when it provides some detail on planned FFI projects later in 2022. But in the meantime, we still have nothing to analyse outside of the capital FMG is spending."
While much of the focus was on FFI, Forrest said the company would continue to look for other metals opportunities, such as the Belinga iron ore project in Gabon, and stressed that FMG had "massive" iron ore and minerals growth ahead of it.
Earlier this month, FMG and its partner, Africa Transformation and Industrialization Fund, signed an exploration convention over Belinga.
Forrest said Belinga was comparable to the massive Simandou project over the border in Guinea, where Rio Tinto, Vale and others had "barbecued" billions of dollars.
"We earned our position [at Belinga] not through billions of dollars of capital, but through the strength and credibility of our reputation," he said.
According to Forrest, the Gabon government invited FMG to be a part of the project due to its green goals.
"It is simply the scale of Simandou, yet a peaceful, responsible government, not a military junta," he said.
"So I just wanted to say, don't take your eye off iron ore, but yes, the energy business will give us massive leverage to the world going green and we're seeing it right now."
Morgans retained a hold rating and $A17.20 price target for FMG.
FMG shares closed at $18.89 on Monday, giving it a market capitalisation of $58.2 billion.