A 100ft underwater turbine destined to form part of a major tidal energy project has been installed in the sea around Orkney.
The one megawatt (MW) device, which can power the annual electricity needs of 500 homes, will now undergo a series of tests to check its performance and reliability.
The turbine will eventually be used in the world's largest tidal stream energy development, in the Sound of Islay in the west of Scotland.
Those behind the project said the installation of the device at Orkney signalled a "major step forward for the global marine renewable energy industry".
The HS1000 tidal turbine has been developed by the company Hammerfest Strom and was installed at the European Marine Energy Centre in Orkney.
It will now enter a test period in preparation for larger-scale production.
It is the same machine that will be used by ScottishPower Renewables (SPR) as part of the world's first tidal turbine array in Islay. The £40 million project, aimed at harnessing the power of the sea to generate enough electricity for more than 5,000 homes, received planning consent from the Scottish Government in March.
Officials hope the Orkney tests will help them to finalise the timetable for the Islay project, with machines being installed as early as possible between 2013 and 2015.
SPR chief executive Keith Anderson said: "We are delighted that the HS1000 turbine has been successfully installed in Orkney, and Hammerfest engineers deserve huge credit for carrying out this difficult operation in very testing weather conditions. We look forward to monitoring its progress when fully operational next year.
"This is a major milestone in the development of tidal power technology in Scotland, and for the tidal power industry across the world. We anticipate using this turbine as part of our project in Islay, which will be the first of its kind in the world, and remains the only consented tidal array project in Scotland. Beyond this, we have ambitions to use this turbine as part of even larger-scale projects in the Pentland Firth, which we are currently investigating."
Managing director of Hammerfest Strom Stein Atle Andersen said: "The device was installed in one of Europe's most challenging waters, during the roughest time of the year, which shows the extreme conditions the technology and the team is capable of handling."
WWF Scotland director Richard Dixon, said: "This announcement is another positive step forward for the marine renewable industry in Scotland. There is a massive amount of power in our seas and Scotland is well placed to lead in developing the technologies to turn this potential into clean, green electricity.
"Alongside energy-saving measures, wave and tidal energy have a critical role to play in meeting the Government commitment to decarbonise our power supply by 2030.
"Given the huge renewable energy potential around our coast, and the strong skills in offshore engineering, marine energy offers a fantastic opportunity for Scotland.
"With careful planning, we can harness wave and tidal energy to help cut our climate emissions while safeguarding the nation's tremendous marine environment."
First Minister Alex Salmond said the project was a "fitting end" to an exceptional year for renewable energy in Scotland.
He said: "This year projects were switched on representing £750 million of investment in renewables, and a staggering £46 billion of investment is in the pipeline.
"We have seen momentous progress towards our goal of generating the equivalent of 100% of Scotland's electricity needs from renewables and more from other sources by 2020, with enough renewable energy capacity installed to more than meet our interim target of 31%.
"The testing of the HS1000 tidal turbine is another exciting and significant development, and is a tribute to the engineers involved. I look forward to hearing the outcome of the tests."