Wholesale prices - which are one component of what households and businesses pay for power - were lowest last month in South Australia at $72 per megawatt-hour. The state sourced 55 per cent of electricity from renewables and 58 per cent when rooftop solar was added, Hugh Saddler, an analyst with The Australia Institute, said.

Victoria's price of $79 per MW-hour was next lowest among mainland states. Renewable projects are surging in that state, with their share of supply jumping by a half in three years from 12.3 per cent to 18.9 per cent.

NSW had the most expensive wholesale power last month at $82 per MW-hour. Clean energy - including hydro running hard - reached only 14 per cent of supply in the state. NSW sources 12 per cent of its power from Victoria or Queensland, the report found.

Coal debate

Dr Saddler said since the end of April, new wind farms had lifted capacity by 14 per cent while new solar farms had almost doubled capacity, though from a much smaller base.

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"There's no sign of any slowdown of new projects coming on line," he said, noting these would include the 928 MW of new capacity announced last week by the Andrews government as part of its Victorian Renewable Energy Target.

Over the next two years new renewables would increase capacity by almost a 10th, or the equivalent of twice the size of AGL's ailing Liddell coal-fired power plant, the report estimates.

Despite the surge in renewables, the Morrison government continued to discuss the prospect of new coal-fired power stations, a stance at odds with market trends.

"The future is about coal - but about when the coal-fired power stations close," Dr Saddler, who is also an honorary professor at the Australian National University, said.

The rise of renewables meant emissions from the electricity sector continued to retreat, with wind and solar nudging out black coal-fired power. Still, rising fossil fuel use in the transport sector meant total energy combustion emissions "are basically flat", he said.

'Bodyblow'

In a separate blow to coal-fired power, Japan's Marubeni Corporation, one of world's largest developers of coal plants, was reported to be withdrawing from new projects.

Japan's Nikkei said Marubeni would also halve the ownership of plants it already held by 2030 and accelerate its shift to renewable energy.

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Tim Buckley, an analyst with anti-fossil fuel group the Institute for Energy Economics and Financial Analysis, said the news that Marubeni was shifting its global weight behind renewables was "a bodyblow to the global coal industry and a profoundly important endorsement of the aims of the Paris Climate Agreement".

"It is inevitable that other global coal plant developers like POSCO of South Korea, Siemens of Germany and GE of America will be forced to evaluate their own position in light of Marubeni’s decision," he said.