MORE than £31 million in public cash has been written off in just two years amid a series of failed investments in renewable energy companies.

Scottish Enterprise, the public body tasked with boosting economic development, will see no return on its £15.2m investment in Aquamarine Ltd which went bust last year after failing to make wave power commercially viable.

The loss emerged in the quango’s annual accounts for 2015-16, which were laid before parliament yesterday.

It comes just one year after Scottish Enterprise admitted it had lost the £16.3m it pumped into Pelamis, another tidal energy firm. The biggest write-off in the agency’s 25-year history, it was described at the time as “exceptional”.

Now the second huge loss in as many years has prompted fresh questions over the SNP Government’s energy strategy and sparked doubts over its claim that Scotland can become “the Saudi Arabia of tidal power”.

Scottish Conservative MSP Alex Johnstone said there was a “definitely a place” for wave energy.

“However, these two major losses serve as a warning about renewable energy,” he said. “The SNP is utterly obsessed with it, and that’s to the determinant of more dependable sources. Perhaps if it had a more rounded approach, the taxpayer wouldn’t have had to write off such significant sums in these instances.”

Aquamarine Ltd had previously been hailed as a “Scottish success story” by then First Minister Alex Salmond, who had personally announced public cash injections into the firm.

In 2008, Mr Salmond launched with great fanfare the £10m Saltire Prize, an ambitious international contest designed to make Scotland a world leader in wave and tidal power development.

But while both Aquamarine and Pelamis were once seen as among the key contenders to clinch the prize, it emerged last year that it would go unclaimed as no company was in a position to meet the requirements set out eight years ago.

Despite the setbacks, the Scottish Government has continued to invest in renewable energy, with development body Wave Energy Scotland being allocated a £13m annual budget last year to administer funds to potential projects.

Aquamarine Ltd, despite being handed a £580,000 grant from the EU in September last year to improve its wave energy converter, called in administrators the following month. It stopped trading in November last year after attempts to find a buyer proved unsuccessful. The firm had more than 50 employees as recently as 2014.

Bosses blamed the economic climate and accepted the “financial as well as technical challenge in bringing an entirely new form of energy generation to commercialisation”.

A spokeswoman for Scottish Enterprise said: “The team at Aquamarine Power Ltd had made great strides in the development of wave technology where they were successful in securing £66m of private sector investment to aid its development.

“The investment in Aquamarine was subject to regular reviews in line with our normal governance process.

“However it is important to acknowledge that the development of any new technology industry is high risk, even more so when its deployment is in a harsh environment.”