Australians will be denied cheaper electricity unless swift action is taken on a national energy policy, the Turnbull government has been advised.

The Energy Security Board published its final design on Wednesday along with a letter from chairwoman Kerry Schott warning of the risk to household bills and business competition if it doesn’t get across the line.

“Any delay, or worse a failure to reach agreement, will simply prolong the current investment uncertainty and deny customers more affordable energy,” Ms Schott said in a letter to ministers before their August 10 meeting with federal Energy Minister Josh Frydenberg.

Modelling published in the latest design reveals Australia’s current renewable energy generation will grow from 18 per cent to 36 per cent over the next 11 years.

Reliance on coal is forecast to fall from 75 per cent to 70 per cent over the same period, without any closures.

Federal Resources Minister Matt Canavan is making last ditch attempts to reassure fidgety Nationals colleagues the Turnbull government’s signature energy policy will lower power prices.

Senator Canavan told ABC radio on Wednesday the framework would bring down power prices, saying his belief wasn’t based on faith alone, but on modelling which showed the policy would slash bills by more than $100.

The design forecasts bills will fall by up to $550 a year, with $150 of that as a direct result of the policy.

Former Nationals leader Barnaby Joyce is the junior coalition partner’s latest member to threaten to withdraw support for the National Energy Guarantee if electricity bills don’t come down.

Mr Joyce signalled he would oppose the government’s energy policy if it included making farmers reduce their stocks to cut carbon emissions.

“If we go down that path then forget it, I’m out. See you later. Goodbye, because that’s just nut-case stuff,” Mr Joyce told Sky News.

Senator Canavan said “absolutely nothing” would be required of farmers as the sector was not included by the National Energy Guarantee.

Labor fears a 26 per cent emissions reduction target for the electricity sector legislated as part of the guarantee would see the same target across the board.

A report by the Australia Institute last week revealed if that was the case the agricultural sector would have to reduce by 8 million beef cattle, 2.9 million sheep and thousands of pigs and dairy cows to meet the target.

Meanwhile, Senator Canavan has dispatched Queensland colleague George Christensen to Japan bearing letters calling for investment in coal-fired power stations.

“They’re all keen as mustard to invest in clean coal technologies in Australia,” the minister said.

Senator Canavan has not ruled out offering international proponents public money to attract more investment in coal.

By Karen Sweeney and Daniel McCulloch