Four turbines off the north coast of Scotland generated enough energy to power nearly 4,000 homes in 2019.

Sitting in a natural channel, they harness the energy of the changing currents and are helping build the case for tidal as the energy source of the future.

To date, very little research has been done into the impact tidal projects have on the surrounding marine environment.

Sitting off the north coast of Scotland, on the depths of the ocean floor, a gigantic feat of engineering has just achieved a significant milestone.

MeyGen, the world’s largest tidal array, has completed the longest ever run of uninterrupted generation by a multi-megawatt tidal turbine, powering almost 4,000 homes in 2019.

The four giant turbines have now exported 24.7 gigawatt hours (GWh) of predictable renewable power to the national grid. And this is just the first phase of a project that could eventually power 175,000 homes with more than 250 submerged turbines.

The array is off the mainland of Scotland, near the uninhabited island of Stroma, in a natural channel that speeds up the tidal flow of water between the North Sea and Atlantic Ocean.

Like giant underwater windmills, the turbine rotors are driven by the fast-moving currents, which in turn drive generators that then produce electricity. They are fixed to the sea bed and connected to the grid via an armoured cable.

Low-voltage supply from the turbines is converted onshore for export to the grid. Image: SIMEC Atlantis Energy

Awash with potential

Although tidal energy as a concept has been around for some time – the first project launched in 1966 – there has been renewed focus on its potential as an energy source. A 2016 estimate from the European Commission said wave and tidal power could account for 10% of the EU’s energy needs by 2050. And back in 2013, the UK estimated 20% of its power needs could be met by tidal.

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As a green energy source, it offers a number of advantages over other renewables. It is not reliant on the sun shining or the wind blowing. And as water is far more dense than air, smaller turbines can be used to generate equivalent amounts of electricity, and they can be placed much more closely together than on land.

Each turbine sits on a foundation weighing between 250 and 350 tonnes, coupled with 6 ballast blocks weighing 1,200 tonnes. Image: SIMEC Atlantis Energy

A power source still in its infancy

There are a number of large-scale projects in various stages across the world, including the Sihwa Lake power station in South Korea and the Jiangxia Pilot Tidal Power Plant in China. But compared to many other renewable energy sources, tidal is still in its comparative infancy.

There are also a number of questions that remain over the impact of tidal arrays and barrages on the marine environment. Initial research has looked at the impact the noise of the turbines might have on marine animals and how the flow of water might be affected, but more in-depth and up-to-date studies are needed.

OCED renewable primary energy supply by product, 1990-2018 Image: International Energy Agency