A new poll shows four out of five Australians don’t know or incorrectly define “clean hydrogen”, as a report casts doubt on the official emissions reduction estimate for a $500 million project.

The survey, run by independent think tank The Australia Institute, found just over a fifth (22 per cent) of Australians know the government-backed definition of “clean hydrogen”.

It defines clean hydrogen as hydrogen made using renewable energy or fossil fuels with carbon capture and storage technology (CCS).

However, 42 per cent of the 1007 respondents from across the country incorrectly thought it was limited to renewable-generated hydrogen.

Three in ten did not know or were unsure what the term “clean hydrogen” referred to, while seven per cent erroneously said it was hydrogen made exclusively with fossil fuels.

The Australia Institute’s climate and energy program director Richie Merzian said clean hydrogen was a marketing term rather than a climate solution.

“It is designed to sell dirty high-polluting hydrogen made using gas and coal as ‘clean’,” Mr Merzian said in a statement on Thursday.

“The Australia Institute polling shows that the term is succeeding in sowing confusion.”

It comes as the Canberra-based think tank scrutinises an emissions reduction estimate for the Victorian Hydrogen Energy Supply Chain (HESC) project.

CSIRO scientists have been working with energy and shipping leaders on the $500 million project, which has a long-term target of producing 225,000 tonnes of liquefied hydrogen each year using brown coal from Victoria’s Latrobe Valley coupled with carbon capture and storage.

Energy Minister Angus Taylor has previously said HESC estimates it will reduce carbon emissions by 1.8 million tonnes a year, or the equivalent of taking 350,000 petrol cars off the road.

An email between HESC and the Department of Industry, Science, Energy and Resources, triggered by an inquiry from a journalist and obtained by The Australia Institute under Freedom of Information laws, outlines how the figure was calculated.

“HESC responded that they had compared the emissions from the HESC project using a CSIRO emissions factor for coal gasification for CCS, with emissions from hydrogen using SRM (steam reforming methane),” the report said.

“Put simply, HESC subtracted the amount of emissions from hydrogen produced by coal gasification with CCS under a theoretical best case (as CCS for coal gasification does not exist) from the amount of emissions that would be created by fossil gas hydrogen from SMR without CCS.”

The discussion paper claims the FOI document shows the estimate is based on a “flawed comparison and are therefore untrue”.

It is “entirely possible”, the report argues, that HESC will go ahead without carbon capture and storage and remain a coal gasification hydrogen export project, in part because of the “expensive, complicated and rarely successful” history of CCS projects.