Engineering leaders said the increased cost of generating 100% of Scotland’s electricity from wind, wave and tidal power by 2020 -- as championed by the First Minister -- could leave many struggling with their fuel bills.
The pledge would also push up oil and gas prices, the Institution of Mechanical Engineers (IMechE) warned, while a reduction in nuclear power would mean importing energy from coal and gas-fired plants in other parts of the UK.
It comes after The Herald revealed on Wednesday that leading financial organisation Citigroup had warned the target could add almost £900 to the average fuel bill.
There is also continuing controversy over the environmental impact of a £3 billion coal-fired power station at Hunterston. A public inquiry moved a step closer yesterday after North Ayrshire Council planners recommended the rejection of the project, with councillors due to take a final vote next week.
Citigroup also told clients, which include major energy companies, to rethink investing in Scotland because of uncertainty over independence and the potential impact on renewables.
It even warned companies such as ScottishPower owner Iberdrola that their assets could be left “stranded” following independence.
The Scottish Government denounced the latest criticism, saying it “does not properly represent our position”. A spokesman also said energy companies’ prices were to blame for increasing levels of fuel poverty.
Holyrood ministers have described the 100% plan as ambitious but realistic, and insist it will create jobs and investment.
The IMechE report warns that the target is based on inherent contradictions, idealistic solutions and inaccurate trends.
Far from allowing Scotland to export electricity, as Scottish ministers have claimed, the policy would turn it into a net importer, due to a parallel scaling-back of nuclear power.
Energy would have to be imported from England and Northern Ireland to keep the lights on, and attempting to meet the target so quickly would also cost billions and raise oil and gas prices, the report warned.
The group said that a more manageable target would have a less dramatic impact on energy prices.
It also claimed there was no “credible” plan to achieve the target in a country that lacked the skills and manufacturing base to do so.
The institution also said the plans contradicted a Scottish Government pledge to eradicate fuel poverty -- when households spend more than 10% of their income on energy bills -- by 2016.
Meanwhile, a ComRes poll for IMechE found 70% of the Scottish public, already hit by rising energy bills, were not prepared to pay more for renewable energy.
In addition, 63% said the Scottish Government should not close nuclear power plants if it meant importing energy to replace them.
Dr Colin Brown, director of engineering at IMechE, said: “The Scottish Government is absolutely right to exploit the country’s huge potential for renewable energy, but we have serious concerns that the over-ambitious 2020 target will push up prices and, combined with the Government’s distaste for nuclear power, turn Scotland from a net exporter to a net importer of energy.
“Without any clear, workable and engineering-based plan of action, it is doubtful whether these targets are achievable at all.”
A Scottish Government spokesman last night said more than a quarter of Scotland’s electricity needs already came from renewables, and projects under way were set to provide almost 60%.
“Scotland is already a net exporter of electricity to the rest of the UK -- and has been for a decade -- and meeting our targets will mean Scotland continues to attract investment, create new jobs and export clean energy to the rest of the UK and Europe,” he added.
Labour’s Shadow Energy Minister Tom Greatrex said: “The report makes clear that it will cost billions to reach the SNP’s renewables targets. This will increase already rocketing energy bills for Scottish consumers and push more and more people into fuel poverty.”
l Labour MP John Robertson has written to Energy Secretary Chris Huhne asking him to clarify why he suggested energy firms were “anti-competitive” just days after appearing to blame consumers for high prices.
The LibDem minister caused anger last month when he told customers they should switch suppliers more often to bring down their bills.