Mr Rattenbury has pitched the compromise after the Energy Security Board unveiled the draft design for the contentious scheme on Monday.

The position puts the ACT Greens leader at odds with his federal colleagues, who are adamantly opposed to any scheme which supports fossil fuels.

The expert board has made the controversial decision to recommend coal and gas be eligible under the mechanism, which would see generators being paid to help maintain reliability in the grid during the mammoth task of transitioning to net zero.

The mechanism could be up and running in 2025, according to the board.

Federal Energy Minister Chris Bowen has signalled that states and territories would be left to decide whether to support coal and gas, but has stressed their position must fit with the Albanese government's national climate goals.

The Canberra Times understands the ACT government wants more clarity on how an "opt-in" system would work given how interconnected the national energy market is.

A chorus of critics, including Mr Rattenbury, have previously argued the capacity mechanism shouldn't be used to support fossil fuels because it could prolong the life of ageing power plants.

Former federal energy minister Angus Taylor had advocated that approach, prompting critics to label the scheme "Coalkeeper".

The board's consultation paper stated the mechanism wasn't designed to extend the lifespan of coal-fired power stations.

However, it argued the scheme shouldn't just favour new technologies, such as renewables and storage.

Part of the argument was that limiting payments to new forms of generation would hand them a competitive advantage, which could make existing generators unviable and increase the risk of a "disorderly" transition to net zero.

At the height of the revolt against Mr Taylor's plan last September, Mr Rattenbury urged his fellow energy ministers to support his push to restrict the capacity mechanism to zero emissions technologies.

The proposal was knocked back, but ministers did agree to embed emissions reduction in the guiding principles for the scheme's design.

Following the release of the draft design on Monday, Mr Rattenbury maintained that the "best outcome" would be if only zero emissions technologies were eligible for payments.

However, if fossil fuels were to be included, the ACT Greens leader said a system should be established in which renewables were prioritised and received higher payments.

"I believe this would offer a better long-term outcome for the community as it would progress the energy system towards the zero emissions future we need, rather than propping up existing coal and gas generation," he said.

The energy board's paper lays bare the scale of the task of transitioning the electricity grid to meet demand in the coming decades.

It predicts electricity demand could at least double by 2050.

Huge volumes of wind and solar, backed up by storage, dispatchable hydro and gas-fired generation, will be needed to compensate for the exit of coal by 2043.

"Coordinating exit and entry of supply, including the mix of resources to ensure an orderly transition, is an enormously complex task," the board's chair, Anne Collyer said.

Mr Bowen and his state and territory counterparts earlier this month agreed to push ahead "at pace" with the development of the capacity mechanism.

The new minister declared at the time he wanted the mechanism to favour new technologies, but would leave the design work to the expert board.

The ministers will have the final say on the model.

Consultation on the paper is open until July 25, with a final design expected to be presented to ministers next February.

Opposition climate change and energy spokesman Ted O'Brien claimed the board had rejected Mr Bowen's preferred option by recommending the inclusion of coal and gas.

"Instead of trying to create a new climate war that pits technologies against each other, Labor needs to recognise that the answer lies in a balance of technologies," he said.

Meanwhile, Mr Bowen said the east coast had weathered the worst of the immediate energy crisis, avoiding the blackouts and load shedding which threatened to hit households last week.

But he said governments and regulators remained "vigilant" to the prospect of future disruptions, as he again blamed the Coalition and his predecessor Mr Taylor for contributing to the perfect storm of factors which have engulfed the energy market in recent weeks.