The tide is turning for energy generation from the oceans

By Mike Snowden, UK Programme Officer
With the right support, tidal energy could flourish in the coming years.

The ebb and flow of the tides is a constant feature in the lives of those who live by the coasts and estuaries of the UK but, whilst we are now used to the idea of harnessing the power of the sun and the wind in this country, the tides have remained elusive.

It’s estimated that the UK could be providing as much as a third of our electricity demand from tidal resources, with key areas of potential in the south west and north west of England and west Scotland.

The UK is well positioned to take advantage of tidal power, with its high tidal range and the shallowing of the continental shelf that increases tidal flow rates. Tidal power is known to represent a significant, predictable potential energy source, with four reliable tides per day, but progress in harnessing it has been slower than with the sun and the wind.

And despite the UK being well positioned with a wealth of tidal resource, the possible sites are still far more limited than for other renewable technologies.

There are two main types of tidal power to harness: rise and stream. Tidal rise takes advantage of rising water levels at high tide, trapping the water in a lagoon or reservoir before releasing the water when tides have lowered, directing the water through turbines to create electricity.

This technology can be utilised at estuaries when tidal barrages are built across the estuary mouth, or with tidal lagoons which effectively create artificial lakes connected to the sea.

Tidal stream relies on placing turbines in underwater currents that flow in certain locations, with the areas around headlands containing the most potential power. These turbines are far heavier than normal wind turbines and their deployment is more difficult, due to the need to build on the seabed.

Tidal lagoons offer an additional feature – if there is sufficient surplus power available on the national grid, say from wind power, then as high tide is reached, the turbines can be used to pump extra water into the lagoon for a short time.

This extra water is pumped up a height of just a few centimetres, but when it is released after the tide has receded, it falls several metres, generating much more energy than was used to pump it.

Tidal technologies have been used to an extent elsewhere; the famous Rance tidal power station in France was built in 1966 and the Sihwa tidal power station in South Korea in 2011, but generally the industry has been seen as too expensive and has obvious geographical restrictions.

Last week saw the publishing of Charles Hendry’s report on the feasibility of tidal lagoons around the UK, recommending the building of the Swansea Bay Tidal Lagoon as a pathfinder for a new industry.

The Swansea project could be built and generating by the early 2020s and will be monitored by a proposed new ‘Tidal Power Authority’ before a new competitive tender process would be launched to usher in a series of projects, making the most of the cost savings and learnings from the Swansea project.

Another recent development is the delivery of tidal stream power from the MeyGen project in Scotland to the national grid. The 6MW underwater turbine has been generating electricity for the grid since November 2016 and MeyGen has recently secured £17.6 million in funding to construct the next stage of the project, due to start generating in 2018.

This will then lead the way to around 400MW of installation on the site by the early 2020s, supported by a seabed lease from the Crown Estate, which owns almost all the UK’s seabed and is strongly supportive of tidal power.

Although there are lots of positive signs for these projects and the industries they represent, there are issues with deploying the technologies. For example, the grid infrastructure in places like Western Scotland is poor and may need upgrading to handle new generation.

To tackle this problem, organisations like Smarter Grid Solutions, longlisted for the 2017 Ashden Awards, provide Active Network Management to ensure that the local grid can handle the output of the Shetland Array of five tidal stream turbines installed there.

There are also wildlife concerns for tidal stream projects due to the noise of the turbines underwater and the effect this could have upon marine life, as well as the issues surrounding the changes to tidal flat ecosystems with the construction of barrages and lagoons.

The benefits of tidal energy are clear: renewable energy, reliably generating year-round and with an embedded cost of carbon lower than solar PV and only slightly higher than nuclear and offshore wind, considering the energy used in construction and maintenance.

Despite a relative lack of support from the government over the past decade, tidal technology has improved and come down in cost and we look forward to seeing this industry flourish in the coming years.

Photo: RebeccaLouiseJones - Own work, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=46356071