Why is a tech billionaire trying to buy Australia’s dirtiest energy company AGL?

It is, by any measure, an extraordinary intervention in Australia's rapidly evolving electricity market. A consortium worth hundreds of billions of dollars on Saturday lodged a formal offer to buy AGL Energy - the country's biggest greenhouse gas emitter - for just short of 5% above the closing share price on Friday.

The headline name behind the bid is Mike Cannon-Brookes, the 42-year-old co-founder of software company Atlassian, green solutions investor, climate action advocate and one of Australia's richest people. But in reality, Cannon-Brookes' company Grok Ventures is the smaller player in the consortium, which is led by Brookfield, a Canadian investment giant with $688bn worth of assets under management last year. Including AGL's debt, the bid was just short of A$8bn.

According to the main players, a significant part of the motivation is to close and replace the company's coal-fired power plants and prevent a controversial demerger that would hive off those coal plants from AGL into a new entity called Accel Energy.

The consortium says it has up to $20bn to spend on building and contracting at least 8 gigawatts of renewable energy and energy storage to replace about 7GW of existing power plants. AGL's Bayswater and Loy Yang A coal plants, currently scheduled to shut by 2033 and 2045, would be gone by 2030. The company would reach net zero emissions by 2035 and suddenly be playing its part in limiting global heating to 1.5C, in line with scientific advice.

The proposal is much bigger than just the coal power plants. It would involve Brookfield and Grok Ventures acquiring all of AGL's generation assets and its retail business. Cannon-Brookes stresses it isn't a philanthropic investment.

He says he is confident backing renewable energy over ailing old coal power plants can keep electricity prices down, create 10,000 construction and 600 ongoing jobs and wipe out about 40m tonnes of carbon dioxide a year - more than 8% of Australia's annual emissions footprint - while turning a profit.

Analysts and some within AGL see access to the company's 4.5 million customers across the country as a key motivation for any would-be suitor.