A Viking past and 'green' future

Up Helly Aa on Shetland, but the Vikings also had ties with the firth

Feared by sailors for centuries, the fast-flowing tides of the Pentland Firth could make it a powerhouse in terms of "green" energy.

Influential government advisory body, the Sustainable Development Commission (SDC), highlighted its potential in a report released last week.

Here, the BBC Scotland website takes a look at some of the facts, figures and history of the firth.

LENGTH AND BREADTH

The firth stretches for about 17 miles (27km), while the gap between the mainland and Orkney is between six miles (9km) and eight miles (12km).

The histories of the coastlines along the channel are littered with shipwrecks.

FAST-FLOWING

The tide flows through from the Atlantic to the North Sea and back twice a day.

The currents are estimated to reach speeds of up to 12 knots.

VIKING MYTH

The firth is mentioned in the Norse Sagas and said to be the site of a great battle.

The Vikings had a strong influence on place names on the northern mainland and on Orkney.

TIDAL STREAM

Tidal stream technology could be deployed on the firth.

This uses the energy contained in fast-flowing tidal currents generally found in constrained channels.

POWER POTENTIAL

According to the Sustainable Development Commission, 5% of the UK's electricity could be generated using tidal stream.

Almost 60% of that power could be sourced around the Pentland Firth.