As Labor leader Bill Shorten toured a solar farm in South Australia, the storm cloud hovering over the cost of his climate plan continued to brew.

Mr Shorten visited the SSE Solar Farm outside Adelaide on Wednesday with Labor’s energy spokesman Mark Butler.

The pair later met with British billionaire Sanjeev Gupta at his Whyalla steelworks. Mr Gupta says electric vehicles will be commonplace in Australia without the need for government subsidies.

Labor wants 50 per cent of all new car sales to be electric by 2030, as well as an increase of electric vehicle in the government fleet.

But it’s the ambitious 45 per cent emissions reduction target which has voters looking for the finer detail.

Mr Shorten says it’s impossible to cost the plan as businesses will be in control of how they reduce pollution.

Mr Butler says Labor has had “deep engagement with the business community” to develop the party’s policy.

Business groups have told Labor they want the safeguard mechanism – which was introduced by the Liberal government – to continue.

It puts a limit on how much carbon the nation’s top 250 polluters can emit, giving them the option of buying international offsets if they fail to meet the target.

And that’s where the big question arises, with Mr Shorten saying he hasn’t made assumptions on how many permits will be bought as it “will depend on price”.

Prime Minister Scott Morrison doesn’t think that answer is good enough.

“It’s very important for Australians to know what the cost is of a change of government,” he told reporters in Perth.

“You can’t tell other people to do the math.”

Mr Shorten earlier rejected an offer from Greens leader Richard Di Natale to work together on climate policies should he win government, instead of opting to take the hand of business.

“Sorry Richard, it’s not happening,” he told reporters in the Adelaide seat of Boothby, which the Liberals hold by 2.7 per cent.

If Labor wins government at the May 18 election Mr Shorten doesn’t expect the Senate to stand in the way of his party’s policies.

While in the South Australian capital he promised to unlock the renewable energy potential of the Spencer Gulf if he wins the election.

Mr Shorten has also been on the attack against the coalition’s preference deal with Clive Palmer, but Labor has put his party above the Liberals on their how-to-vote cards in 87 lower house seats, including putting it second in two Tasmanian seats.