Plans to harness wave and tidal energy from the Pentland Firth and the sea around Orkney are to be unveiled.

The Crown Estate, which owns the seabed around the UK, is due to announce which companies have successfully bid to install devices.

First Minister Alex Salmond has called the far north the "Saudi Arabia" of marine power because of its potential to produce huge amounts of energy.

The first devices could be in place by 2020.

The Crown Estate is the organisation that grants seabed lease development rights for marine renewable energy projects.

It is to announce the successful companies and joint ventures for each site in the Pentland Firth and around Orkney.

It will also explain how this helps secure the UK's energy supply and benefits the UK economy.

'Too long'

Last October the Crown Estate said the timetable granting leases and the installation of devices remained on schedule.

It said legal paperwork opening the way for companies to harness wave and tidal power would be signed by the end of March this year.

The organisation has forecast that enough power for 500,000 homes could be generated by 2020.

But Thurso and Wick Trade Union Council said the process was taking too long.

The council is eager to see new sources of work created to compensate for those that will be shed during the decommissioning of the defunct Dounreay nuclear power complex near Thurso.

Earlier last year, the Crown Estate announced it had received 42 bids for the leases.

It said the level of interest exceeded initial expectations and more projects than originally planned were taken forward to the negotiation phase.

Commercial development

Last month, three Scottish companies won a multi-million pound funding boost to help prove the commercial viability of their marine power devices.

The money from the Department of Energy and Climate change, DECC, was awarded by The Carbon Trust.

Edinburgh-based Aquamarine Power was awarded £5.1m and raised the same again from its shareholders.

The funding will be used to develop the second generation of its Oyster wave device, which is the world's largest working hydro-electric wave energy converter.

It is currently producing electricity at the European Marine Energy Centre (Emec) in Orkney.