The South Australian Government has accused Liberal leader Steven Marshall of misleading voters about the expected benefit his energy policy would deliver to households.

In a bout of robocalls on Tuesday night, Mr Marshall claimed his policy to fast-track a new interconnector and subsidise up to 40,000 household batteries would result in significant savings.

"Today I've announced our Liberal energy solution. A solution that will deliver cheaper and more reliable energy for our state while saving the average household over $300 a year," Mr Marshall's recording stated.

Sorry, this audio has expired Robocall from Steven Marshall to South Australian voters

The $300 figure was extrapolated by the Liberal Party from wholesale energy market modelling conducted by ACIL Allen Consulting.

It was derived by comparing current wholesale electricity costs of about $109 per megawatt hour with a projection of $47.87 in 2022 under the Liberals' policy position.

But the modelling also includes what it calls a "static projection", which shows that even without the Liberal policy, prices would fall to $63.13 per megawatt hour by 2022.

Today Mr Marshall conceded prices would fall significantly even if his policy was not put in place.

He admitted his party's measures, including a new interconnector, would deliver only a portion of the $300 saving.

"Well I think it's between $60 to $70 per household and that's an excellent saving," he said.

"It's a significant saving on where we have been under Labor. And I make the point, we should never have got ourselves into the point here in South Australia that we've been put in because of Labor's chaotic energy policy settings.

"Prices will come down on average, for the average household, by more than $300. That is a fact."

'Don't believe them', Energy Minister says

The ACIL Allen modelling shows only marginal difference in electricity prices between the static scenario and Liberal policy before 2022.

South Australian Liberal leader Steven Marshall announcing his party's state energy policy. ( ABC News: Martin Davies )

The modelling of the Liberal policy position also factors in policies already announced under Labor, including Tesla's 100-megawatt battery and Solar Reserve's 150-megawatt solar thermal plant due to begin operation in 2020.

Mr Marshall said unlike Labor, the Liberal Party had been transparent about the price impacts of its policy.

"We've subjected ourselves to an independent modelling company. We've published their results in full. We've got nothing to hide," he said.

But Energy Minister Tom Koutsantonis said the Opposition's promises were not believable.

"They promised when they privatised ETSA prices would go down, they went up. They promised when they abolished the carbon tax prices would go down, they went up," he said.

"Now they're telling you, 'trust us. In seven years' time you'll save $70'. Don't believe them. It's a lie."

Premier Jay Weatherill was scathing about Mr Marshall's recorded message and subsequent clarification, saying he had "torpedoed his own energy plan".

"Last night, Steven Marshall rang around, it seems, just about everybody in South Australia telling them that they would save $300," he said.

"Today he admitted it wouldn't even be $70 and it wouldn't even be until 2022 and it wouldn't even be until an interconnector was built, and we don't even know whether that interconnector will be built.

"This represents a gross misleading of the people of South Australia.

"Tonight, he should commission another robocall to go out and tell people what he told them the night before was false."

Mr Koutsantonis said the Liberals' projections were based on an interconnector to New South Wales being connected by 2021.

"Steven Marshall earlier this year was saying it takes six to seven years to build an interconnector. Now he's saying he can do it in three. It's simply impossible," the Energy Minister said.

In May this year, transmission company Electranet told a parliamentary committee an interconnector could be built in that timeframe, and would cost consumers in New South Wales and South Australia between $500 million and $700 million.