espite a role on a Gillard government panel to help cut the impact of the carbon tax on companies exposed to foreign competition, former Caltex chairman Dick Warburton is no fan of carbon controls.

Rather, Warburton has made public his doubts that rising carbon dioxide levels are linked to climate change, a view at odds with the vast majority of climate scientists.

As recently as July, the renewable energy target, or RET, had bipartisan backing. Coalition Senator Simon Birmingham told a clean-energy summit in Brisbane that an Abbott government would retain the current settings, which now require large-scale electricity generators to source 41,000 gigawatt-hours of power from renewable sources by 2020.

''At every possible point, they tried to assure the community that there was a bipartisan consensus around the RET, and therefore the growth of renewables,'' Labor climate change spokesman Mark Butler says. ''What's clear now is that it was just an utter falsehood.''

Uncertainty about ongoing support for the scheme, set up in 2001 by the Howard government, chilled an initial investment surge. A five-fold increase in the clean energy goal - to at least 20 per cent of electricity by 2020 - triggered another boom, particularly for wind farms in South Australia which now account for about a quarter of the state's supply.

Growth prospects are dimming, however. Major fossil fuel-based suppliers, particularly Origin Energy and Energy Australia, have stepped up calls for a cut in the RET, arguing the energy sector is already over-supplied as demand wilts.

Alcoa's decision this week to shut its aluminium smelter near Geelong lopped another 350 megawatts off demand. By comparison, the capacity of Australia's largest wind farm, at Macarthur in Victoria, is 420 megawatts.

With the carbon tax likely to be axed when the new Senate sits in July, Prime Minster Tony Abbott appears to have made the RET his next focus, regularly stressing ''the upward pressure'' it places on power prices.

The Warburton-led panel - merely an advisory body, the government emphasises - will examine the RET's costs and benefits. A review of the RET in 2012 by the Climate Change Authority recommended few changes, other than to stop reviewing it every other year to avoid regular bouts of uncertainty.

The authority's review - which Warburton says he has not read - will itself be revisited later this year in the unlikely event the authority, which was set up by the Gillard government, dodges Abbott's axe.

NSW's Independent Pricing and Regulatory Tribunal estimates the RET will cost $40 per household in the 2014 fiscal year. Other states put the tab lower, and falling.

The 2 per cent impost is dwarfed by the almost 50 per cent of a typical power bill going on poles and wires and about 25 per cent on electricity generation, while the carbon price is responsible for about 8 per cent, IPART data shows.

The benefits of renewables are less obvious.

Analysts say wholesale power prices are forced lower by near-free wind and hydro power, at least nullifying the 2 per cent cost.

Other benefits include lower carbon emissions - 20 million tonnes averted between 2001 and 2012 alone, more jobs in rural regions and security against rising fuel costs, such as soaring gas prices.

''The only people who unambiguously benefit from a reduction in the RET are the incumbent [fossil-fuel] generators,'' said an industry analyst who requested anonymity.

NSW's government is selling its Macquarie Generation power plants - which burn 11 million tonnes of coal a year - and would be keen that there be less competition.

''Every week, they're worth less,'' Pitt & Sherry principal consultant Hugh Saddler said.