Targets have been set to harness renewable energy

The tests were suspended when a leak was found in one the bouyancy tanks.

The structure has now been taken out of the water and a replacement tank is being sent to the islands.

Engineers from Robert Gordon University in Aberdeen now plan to relaunch the tidal turbine in two weeks' time.

The �180,000 prototype was designed by engineers at the university.

It forms part of Scottish Executive plans to provide 40% of power from renewable sources by 2020.

Codenamed Sea Snail, the 40-tonne tidal generator sits on the seabed and turns tidal movement into useable energy.

'Unique system'

It is capable of generating enough power to light 70 houses.

"Uniquely, the Sea Snail can take a turbine down to any depth on the sea floor and back on command," said developer Alan Owen, of RGU's faculty of design and technology.

"This ease of installation and maintenance offers interesting potential for smaller, single-turbine sites."

If the sea trials prove a success off Orkney, plans will get under way to develop a bigger tidal turbine which could generate enough energy to power 500 homes.