Is tidal power reaching the crest of a wave?

Is tidal power reaching the crest of a wave?

After 10 years of marine energy research and development in Orkney are we on the cusp of a major breakthrough? Nick Terry reports

The test sites off the rugged coastline of Orkney are in some of the roughest sea conditions in the world. Here the tidal rush forcing itself through the gap between the North Sea and the Atlantic creates a fantastic surge of natural forces. But, with the European Marine Energy Centre in Kirkwall now ten years old, how near is Scotland to harnessing this massive form of power on a large-scale commercial basis?

The Scottish Government believes the commercialisation is now getting closer by the day. In February 2014, almost £5 million of funding was announced by Energy Minister Fergus Ewing during the RenewableUK Wave and Tidal Conference and Exhibition in Belfast for two initiatives.

Mr Ewing said five marine energy innovation projects are to benefit from a £2.8 million share of the Marine Renewables Commercialisation Fund (MRCF), while tidal power company Atlantis Resources Corporation is to receive a £2 million investment from the £103 million Renewable Energy Investment Fund to help establish a global engineering hub in Edinburgh. All great news for those who have been pioneers of this energy.

The Atlantis hub, which will become the company’s global centre of excellence is expected to create around 20 jobs once operational. The MRCF grant funding is critical to facilitating the success of the first wave and tidal arrays in Scotland, while reducing the cost and risk of the technology.

The funding will help build Scotland’s marine energy industry, bringing important socio-economic benefits to remote and coastal areas of Scotland.

Initiatives benefiting from the funding include work for construction firm McLauglin & Harvey, along with SeaRoc and Nautricity, to fund the foundation system which will be used for Nautricity’s 500 kilowatt turbine off the Mull of Kintyre; while the European Marine Energy Centre in Orkney will design and build a seabed monitoring pod.

There is also work for Green Theme to develop a cable-mounted device called ‘CableFish’
that includes a camera and GPS to helps with cable installation in fast flowing conditions, while marine data experts Partrac, along with partners, are to carry out surveys at two Scottish sites to understand turbulence in tidal flows.

With the elements buffeting these massive structures, engineering company Tension Technology International and partners are to design a novel mooring system that can be used for wave and tidal arrays.

“Scotland is at the forefront of developing offshore and low carbon energy generation technology with some of the world’s greatest wind, wave and tidal resources heavily concentrated in the waters around our country,” said Mr Ewing.

The Scottish Government is committed to the development of a successful marine-renewable energy industry in Scotland as part of achieving the European Union 2020 target: 20% of EU’s energy consumption from renewable sources by 2020. A stated target is meeting 100% of Scotland’s electricity demand from renewable sources by 2020. That’s only six years away.

Scottish Power Renewables, Aquamarine Power, Pelamis Wave Power and MeyGen are all attempting to produce large-scale electricity using the power of the sea.

Several companies are well advanced, including MeyGen’s tidal energy project in the Pentland Firth that will initially consist of six tidal turbines, Pelamis’ wave power device
at Farr Point will use the motion of waves to generate electricity, Aquamarine’s Oyster wave energy converter is to be deployed off the Isle of Lewis and Scottish Power Renewables hopes to create a tidal energy project off the north coast of Caithness

Meanwhile Rolls-Royce have a 500 kW tidal stream plant, a type of tidal turbine that is operational at a test facility, 40 meters deep off the coast of Scotland. And supply chains are set to benefit too in terms of equipment transportation, offshore site preparation, device positioning and connection. The largest items of expenditure including the structure, mechanical plant (hydraulics and turbines), electrical plant (generators and switch gear), vessels, foundations and moorings are still being designed and tested.

How does it work?

Tidal stream generators
TSGs make use of the kinetic energy of moving water to power turbines, in a similar way to wind turbines that use moving air. This method has the lower cost and lower ecological impact compared to tidal barrages.

Tidal barrage
Tidal barrages make use of the potential energy in the difference in height (or head) between high and low tides. Barrages are essentially dams across the full width of a tidal estuary, and suffer from very high civil infrastructure costs, a worldwide shortage of viable sites and environmental issues.

Dynamic tidal power (DTP)
Dynamic tidal power it is a theoretical generation technology that would exploit an interaction between potential and kinetic energies in tidal flows. It proposes that very long dams (for example: 30–50 km length) be built from coasts straight out into the sea or ocean, without enclosing an area. Tidal phase differences are introduced by the dam, leading to a significant water level differential (at least 2–3 meters) in shallow coastal seas featuring strong coast-parallel oscillating tidal currents. Each dam would generate power at a scale of 6-15 GW.

Wave Energy
Waves are formed by winds blowing over the surface of the sea. The size of the waves generated will depend upon the wind speed, its duration, the distance of water over which it blows (the fetch), bathymetry of the seafloor (which can focus or disperse the energy of the waves) and currents. The resultant movement of water carries kinetic energy which can be harnessed by wave energy devices.

Tidal Energy
Tidal streams are created by the constantly changing gravitational pull of the Moon and Sun on the world’s oceans. Tidal stream technologies capture the kinetic energy of the currents flowing in and out of the tidal areas. Since the relative positions of the Sun and Moon can be predicted with complete accuracy, so can the resultant tide. It is this predictability that makes tidal energy such a valuable resource.