What is a tidal lagoon? Independent review endorses Swansea Bay

The UK is one step closer to building the world’s first tidal lagoon.

A pioneering £1.3bn wave power project in Wales has this month been endorsed by a former UK energy minister after a year-long review.  

If plans are followed through a 9.5km-long sea wall would be built in Swansea Bay housing 16 large turbines. This tidal barrier could then generate up to 320 megawatts of energy – powering the equivalent of 155,000 homes.

Once in operation Swansea Bay is expected to produce energy for the next 120 years.

A sound-bite of a 30p charge per household for the next three decades has been written into former MP Charles Hendry’s report, but cost analysis and subsidy payments have been left out of his findings.

A tidal lagoon has never been built before anywhere in the world. France has long-standing barrages, constructed post-war, which harness the potential energy in a similar way, but specific geographical  features are required to generate power. Swansea Bay will see a wall, with turbines fitted inside, running round the water like a giant horseshoe.

By keeping the turbine gates shut for a few hours at a time, a difference of height on either sides of the wall develops. As the tide begins to ebb or flow the sluices can be opened at the right time allowing for maximum water velocity to crank the turbines.

There are other approaches to harnessing the power of the sea, for example ‘tidal stream’. This uses the kinetic energy of waves passing through turbines rather than artificially creating a potential difference to generate electricity.

Tidal stream can be thought of like wind power turbines, but under water.

The Hendry report advocates the UK as a player in all future marine energy technologies with Swansea Bay seen as a pilot project.

But this doesn’t mean the development is in the green.

Most recently a study of the lagoon’s effects on Atlantic salmon and sea trout numbers, published in December 2016 by Natural Resource Wales (NRW), outlined concerns that populations could fall by more than 20% each if current plans go ahead.

NRW is responsible for determining the lagoon’s marine planning application but is yet to make its decision on the bay. In a statement to the press it said it was working closely with other experts to ensure its decision is rigorous and fair.

Other worries revolve around the technology form itself. Earlier this month the Energy Technologies Institute attacked the cost of wave energy, citing expenses up to ten times more than other low-carbon alternatives.

And should the country invest in wave power, the research body advocates tidal stream rather than lagoons, contrary to the conclusions of the Hendry Report.

So far six areas have been eyed up around the UK as potential lagoon sites.

Should all the lagoon projects be built, developers believe they could provide up to 12% of all the UK’s electricity needs.

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