MUMBAI (BLOOMBERG) - Indian tycoon Mukesh Ambani unveiled an ambitious push into clean energy involving 750 billion rupees (S$13.6 billion) of investment over three years, marking a new pivot for one of the world's biggest fossil-fuel billionaires.

Reliance Industries, which gets 60 per cent of revenue from oil refining and petrochemicals, plans to spend 600 billion rupees on four "giga factories" to make solar modules, hydrogen and fuel cells as well as build a battery grid to store electricity.

An additional 150 billion rupees will be invested in value chain and other partnerships, Asia's richest man told shareholders on Thursday (June 24).

The move towards green by Reliance, which reported an annual revenue of US$63 billion (S$85 billion), offers a glimpse of the new order awaiting some of the world's major fossil-fuel producers. Companies such as ExxonMobil and TotalEnergies have been under pressure to pare their carbon footprint, as governments, investors and consumers join to fight climate change and global warming.

Speaking at a virtual annual meeting, Mr Ambani gave scant details of how he would execute the plan. He was ranked No. 4 among global fossil-fuel billionaires by Bloomberg Green last year.

Shares of the company fell 1.9 per cent as of 9.37am in Mumbai on Friday, extending declines following their biggest loss in more than two months the previous day.

"Reliance is branching out into completely new businesses," said energy analyst Horace Chan at Bloomberg Intelligence. "That raises concerns whether the investments could generate acceptable returns and payback period, given the time to acquire technology know-how and seek strategic partners."

Mr Ambani is not entirely turning his back on oil and petrochemicals. On Thursday, he said a plan to bring Saudi Arabian Oil Co as an investor in the energy division - announced two years ago - would be finalised this year. He also said that Aramco chairman Yasir Al-Rumayyan would join the board of Reliance.

Aggressive targets

The proposed green transformation aligns with the priorities of Prime Minister Narendra Modi's government, which has been debating aggressive climate targets that would cut net greenhouse gas emissions to zero by mid-century, a decade before China.

Though fellow tycoon Gautam Adani, who built a coal-centred conglomerate of mines, ports and power plants, is also expanding his presence in wind and solar energy, Mr Ambani's plans are more ambitious in scope.

"The world is entering a new energy era, which is going to be highly disruptive," said Mr Ambani, 64. "The age of fossil fuels, which powered economic growth globally for nearly three centuries, cannot continue much longer. The huge quantities of carbon it has emitted into the environment have endangered life on Earth."

One of Reliance's "giga factories" will make solar modules, enabling 100 gigawatts of solar energy by 2030, including on rooftop installations in villages across the country; the second involves grid batteries to store electricity, for which Reliance will collaborate with global leaders; and, the third will build and install electrolysers for separating green hydrogen from water.

"Is this doable from a standing start in nine years? It's a stretch, it's not impossible," said Mr Tim Buckley, director of energy finance studies at the Institute for Energy Economics and Financial Analysis. "There's an element of wanting to align with the Indian government and profit in the process. Don't forget they've seen Adani make a lot of money in this. It's not altruism."

The fourth factory would be for fuel cells, which use oxygen from the air and hydrogen to generate electricity -- a technology that is being promoted by carmakers including Hyundai but famously dismissed as "mind-bogglingly stupid" by Tesla's Mr Elon Musk.

Adani plans

The Adani-led group is also raising its game in clean energy goals. Adani Green Energy agreed last month to buy SoftBank Group's US$3.5 billion renewable power business in India, in a bid to achieve its goal of having 25 gigawatts of renewable power capacity by 2025.

The green focus has led to a share rally with Adani Green jumping more than 580 per cent and Adani Total Gas - a joint venture with TotalEnergies - by 670 per cent since the beginning of last year.

Reliance last year set itself a target of becoming a net-zero carbon company by 2035 - a timeline shorter than the self-imposed 2050 cut-off of many of its global peers including BP and Royal Dutch Shell. Mr Ambani's group bought its first cargo of carbon-neutral crude oil in February and said it was looking for more of such partnerships.

India's government plans to expand its renewable energy capacity nearly fivefold to 450 gigawatts by 2030, as the nation aims to reduce its dependence on coal.