The return to sea power

Renewable energy is generated from the earth’s natural resources such as the sun; water and wind using technologies that ensure energy stores are naturally replenished. By James Clark

Renewable energy is becoming an important issue in today’s world. In addition to the threat of climate change and ever increasing fossil fuel costs, there have been significant developments in renewable energy, which include efficiency as well as reduced prices for consumers. All of this has added to the demand for alternative energy and accelerated the transition towards cleaner and more sustainable methods of electrical power. One area we are expanding on in the UK right now is tidal power.

A tidal lagoon is a U shaped breakwater built out to sea containing hydro turbines. Water fills up and empties with the tides, generating electricity four times a day, everyday. Due to the incredible tides on the West Coast of Britain, by keeping the turbine gates shut for just three hours, there is already a 14ft height difference in water between the inside and the outside of the lagoon. Power is then generated as the water rushes through 200ft long draft tubes, rotating the 23ft diameter hydro turbines.

Although tidal energy is new in our lifetime, tidal lagoons are a modern interpretation of a very old, simple and natural idea. UK millers were harnessing the power of our tides almost 1000 years ago. The UK’s first tide mill was recorded in Nendrum Monastery, Northern Ireland in 619 AD, while another tide mill located in Dover was recorded in the Doomsday book in 1086 AD. By the 18th century there were over 700 tide mills operating along the Atlantic coastline of Europe and the US, with 200 operating in the UK, of which 140 were in London. The last working mill located in Woodbridge closed in 1957.

Why choose a tidal lagoon?
A tidal lagoon is a power station that generates electricity from the natural rise and fall of the tides. Tidal lagoons work in a similar way to tidal barrages by capturing a large volume of water behind a man-made structure, which is then released to drive turbines and generate electricity. Unlike a barrage, where the structure spans an entire river estuary in a straight line, a tidal lagoon encloses an area of coastline with a high tidal range behind a breakwater, with a footprint carefully designed for the local environment. As the tide comes in the turbine wicket gates, which are used to control flow through the turbine holds the water back. This creates a difference in water level height between the inside of the lagoon and the sea. Once the difference between water levels is optimised, the wicket gates are opened and water rushes into the lagoon through the bulb turbines mounted inside concrete turbine housings in a section of the breakwater wall. As the water turns the turbines, electricity is generated. The water in the lagoon then returns to closely match the same level as the sea outside. This process also happens in reverse as the turbines operate in both directions, meaning electricity can be generated from both the incoming and the outgoing tides. The tide can be held within the lagoon for approximately 2.5 hours as the sea outside goes out and the head builds.

As the tides rise and fall naturally, with no requirement for fuel, tidal power is truly renewable and, unlike other forms of renewable energy, is entirely predictable. As there are always two high and two low tides every day, tidal lagoons will generate electricity over four periods a day, every day of the year. As the tide is held for 2.5 hours four times a day, power can be generated for up to 14 in every 24 hours The height and time of the tides can be predicted years in advance to a high degree of accuracy, allowing the precise operation of the lagoon on each tidal cycle well in advance.

In 2011, Tidal Lagoon Power was formed to develop, construct and operate tidal lagoon power plants in the UK and at selected international locations. To date, the number of potential UK tidal lagoon locations identified from an engineering, power generation and commercial viability perspective stands in double figures and could equate to over 25GW of installed capacity. In the UK Tidal Lagoon Power is currently developing a UK fleet of six tidal lagoons in Swansea Bay, Cardiff, Colwyn Bay, Newport, West Cumbria and Bridgewater Bay, to meet up to eight per cent of the UK’s electricity demand, or power for around 30 per cent of UK homes, as well as progressing a number of potential projects overseas. The Swansea Bay Tidal Lagoon is set to be the world’s first tidal power plant.

The Swansea Bay Tidal Lagoon will cost the bill payer no more than the amount he pays for nuclear power, at a cost of around 30 pence a year per household. The project was awarded a development consent order in 2015 and is primed for construction. It will comprise 16 hydro turbines and a six-mile breakwater wall, generating electricity for 155,000 homes for the next 120 years. To date, approximately £35 million has been spent on project development. With the exception of a commercial loan from the Welsh Government this has been financed privately. It is hoped that work will begin on the lagoon in 2018 and it’s expected to take four years to complete.

Supported by UK Government commissioned review
Plans for the tidal lagoon in Swansea Bay have recently been backed up by a Government review headed up by the former UK energy minister Charles Hendry. In the course of the review he visited Swansea, Cardiff, Newport, Liverpool, Bristol and Sheffield to speak to people directly involved with and affected by the proposals. He concluded that tidal power would make a strong contribution and bring considerable economic opportunity to the UK. The UK Government still needs to agree on a deal.

The case for tidal lagoon infrastructure
On a final note British-made turbine technology and engineering expertise will create and sustain thousands of skilled jobs in the UK steel and manufacturing supply chain, according to the October 2016 ‘Ours to Own’ report. This is encouraging news as it was reported back in 2016 that the UK steel industry was in crisis. For years UK companies have been shifting manufacturing to other countries, but as worldwide costs increase UK businesses have started to invest back in Britain.

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