As coal's future in Australia's energy mix continues to dominate political debate in Canberra, returns lodged by so-called "third party campaigners" to the Australian Electoral Commission show a little-known group called ACA Low Emissions Technologies Limited was one of the top five spenders of 52 third parties.

The company, which had not previously lodged a return, was only outspent by GetUp, the Australian Education Union, the ACTU and the Business Council of Australia but massively outspent renewable energy advocates the Solar Council, which spent $36,000, and Greenpeace, which spent $53,000.

ACA Low Emissions Technologies takes its name from the former Australian Coal Association which merged with the Minerals Council of Australia in 2013.

The company is funded by the Minerals Council's COAL21 initiative, which has raised more than $300 million since 2003 through a levy on coal producers to support research and development into so-called high-intensity, low-emission coal and the elusive technology of carbon capture and storage.

State and federal governments have spent $436 million since 2004 trying to make clean coal technology a commercial reality.

"Third party campaigners" are people or organisations, other than registered political parties, candidates and government agencies, who incur political expenditure. Groups that spend more than $13,000 must lodge a return.

According to its AEC return, ACA Low Emissions paid for polling of voting intentions and funded broadcast advertisements as well as printed and published materials.

A Minerals Council spokesman confirmed most of the $2.43 million was spent on the "little black rock - Coal. It's an amazing thing" campaign, which was heavily lampooned on social media and described in some quarters as the "PR fail of 2016".

The campaign claimed carbon capture and storage, which is not in use at any commercial power stations in Australia, is "proven" and "can now reduce CO2 emissions by up to 90 per cent".

Prime Minister Malcolm Turnbull used his headland National Press Club speech last month to commit the Coalition to the objective of "reliable base load power with state-of-the-art, clean coal-fired technology".

Mr Turnbull has changed his opinion significantly since a 2010 "zero carbon Australia" convention where he advocated solar thermal as a "more proven technology than clean coal".

"You do start to get something of a sinking feeling as you contemplate the fact that the hope of the side [clean coal] has not yet stepped onto the field to play his first game, it's a real challenge," he said at the time.

Jeremy Buckingham, energy and resources spokesman for the NSW Greens, said clean coal was being used as "an excuse for inaction on climate change and coal".

"The coal industry has been pushing its deceptive clean coal message to the electorate by politicians when they know the technology or economics do not stack up," he said.

"Renewable energy technology has advanced to the point where investment should be directed into clean energy, not so-called clean coal."

Greg Evans, a Minerals Council director and chief executive of ACA Low Emissions, said the little black rock campaign was "100 per cent factual".

"The Little Black Rock campaign was not political," he said.

"ACALET is a non-partisan organisation which supports research and development of low-emission coal technologies including communicating the benefits of coal usage."

Australia's chief scientist Alan Finkel, who is conducting the national energy security review for Mr Turnbull, has backed  "truly clean coal" coupled with carbon capture storage as part of the future mix with renewables but does not support government subsidies to build cleaner coal-fired electricity plants.

This week an executive at Japan's largest supplier of high-tech coal-fired power plants said they would probably cost more than thought in Australia – up to $4.6 billion – and would still emit relatively large quantities of carbon.