Investigating waves and currents in the Pentland Firth and their effect on marine energy generation
By Clare MacDowell, PhD student at the Environmental Research Institute, North Highland College UHI
The Pentland Firth is well known for being rich in marine energy as the wave and tidal systems from the Atlantic Ocean are channelled through its islands and headlands to the North Sea.
It is estimated that Scotland contains 25 per cent of Europe’s tidal stream energy and 10 per cent of its wave energy potential, and a considerable part of this resource lies within the Pentland Firth.
In 2010, the Pentland Firth and Orkney Waters region became the first place in the UK to be made available for commercial development of marine energy and in 2012 it was designated a Marine Energy Park by the then Department for Energy and Climate Change.
The most well-known project is the SIMEC Atlantis Energy MeyGen development which currently has four 1.5MW tidal stream turbines deployed in the Inner Sound between the Caithness mainland and the island of Stroma and which, by July this year, had generated more than 20,000MWh of electricity for export to the national grid.
A further four sites have been made available for tidal energy development and six for wave energy development. The European Marine Energy Centre, a dedicated test centre in Orkney, has several sites available for full-scale device testing and has worked with many different developers.
One of the big advantages of tidal stream power over other renewable energy sources is that it is, to some extent, predictable as tides are so reliant on the regular moon and sun cycles. However, different atmospheric and weather conditions can also affect tidal behaviour and therefore have a direct effect on the amount and consistency of tidal energy generated.
Similarly, the wave climate not only changes constantly with the weather, but is also influenced by the changing tidal currents and this in turn affects wave energy generation.
With this in mind, the Environmental Research Institute at North Highland College UHI in Thurso, together with the Marine Scotland Laboratory in Aberdeen, has conducted a study collecting wave and current data from the Pentland Firth.
The work has involved deploying an acoustic doppler current profiler and an acoustic wave and current profiler on the seabed approximately one kilometre north of Dunnet Head at the western entrance to the Pentland Firth from February to May 2018.
New technology in the form of an X-band radar was located on the cliffs overlooking this area to monitor waves and currents over a six-kilometre radius. Waves with a maximum height of up to 11 metres and current velocities of nearly 3m/s were recorded and the presence of previously unknown eddies and localised bathymetric effects were detected.
Our work so far has involved investigating how varying waves recorded in the Pentland Firth can affect current velocities and directions, as well as looking at how varying currents affect the wave height, period, direction and energy spectra of the waves, for waves travelling both with and against the tide.
The next stage of the project is to consider how these effects may influence marine energy generation and to develop better predictions of energy yields under forecast conditions.