The government launched its Positive Energy campaign ahead of last November's Glasgow climate summit, using television, radio and social media advertisements to promote the suite of "low-emissions technologies" it is relying on to reach its net zero target.

Energy department officials confirmed at Monday's Senate estimates hearings another $17.9 million would be spent to keep the campaign running until early April.

That would take the campaign's total cost to about $31 million.

The timing means the taxpayer-funded advertisements would run up until just prior to when the federal election campaign is likely to start.

Labor's climate and energy spokesman Chris Bowen accused the Morrison government of using taxpayer funds as its own "campaign slush fund".

"This time [it's] more than $30 million on pre-election greenwash to advertise the success of renewables policies they tried to abolish," Mr Bowen said.

Labor's Jenny McAllister honed in on the cost of the advertising campaign during Monday's hearing, comparing it to the amount spent on independent modelling for the Coalition's net zero target.

The government paid consultants McKinsey about $6 million to produce the modelling, which Senator McAllister noted was about one-fifth of the sum spent on the advertising blitz.

"So [the spending has a] ratio of 5:1 advertising and spin, to policy?" Senator McAllister asked officials.

Energy and industry department secretary David Fredericks responded by saying he was "very comfortable" the contracts for the modelling and advertising represented value for money.

ACT senator Zed Seselja, who was representing Energy Minister Angus Taylor at the hearing, was asked by Senator McAllister if he thought the advertising spend was a good use of public money.

Senator Seselja was quick to remind the Labor senator when her party was in government it spent $37 million selling the "mining tax".

"What we are doing on emissions reduction is very important. We're proud of it. It is important to get the messages out there."

A spokesman for Mr Taylor pointed out that Labor had letterboxed households across Australia with material explaining its controversial carbon tax.

Then Prime Minister Julia Gillard and Treasurer Wayne Swan defended the advertising spending at the time, saying it was important to provide people with accurate information about the policy.

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