Edge of Innovation

Tidal lagoons: Generating renewable energy with invisible moon power

Something amazing could be happening down in Swansea. While solar arrays and offshore wind farms are all the rage in the chase for clean, renewable energy, tidal power stations could well prove to be more reliable and effective.

If the £1 billion, 320MW Tidal Lagoon Swansea Bay project gets the go-ahead, it will become the world’s first man-made, energy-generating lagoon, capable of providing electricity for over 155,000 homes. If the UK is going to hit its target of producing 15% of its energy from renewable sources by 2020, harnessing tidal surges could be vital.

There are two types of tidal power. Tidal Stream involves submerging turbines in fast-moving sea currents — SeaGen installed a groundbreaking 1.2MW tidal energy convertor in Strangford Lough, Northern Ireland, back in 2008. In this case, electricity is generated by water flowing over the turbine blades, which is then carried back to shore by cable.

Tidal Range is arguably more efficient. The term describes the difference between high and low tide. For example, the river Severn has the third highest tidal range in the world, with the water level rising and falling by as much as 15 metres (49 feet). Only Canada’s Ungava Bay (17 metres/56 feet) and Bay of Fundy (16.3 metres/53.5 feet) are higher.

Swansea Bay benefits from an average tidal range during spring tides of 8.5 metres (28 feet) and the Tidal Lagoon project proposes enclosing an area of it with a man-made sea wall.

As the project documentation explains: “As the tide comes in, the lagoon has structures called ‘sluice gates’ which are closed to stop water entering the lagoon, creating a water level difference between the inside of the lagoon and the sea. Once this difference is big enough the water is allowed to rush into the lagoon through the turbines which turns them and generates electricity.”

Turbine cross-section Tidal, Lagoon Swansea Bay
The bi-directional turbines at Swansea will be encased in a concrete turbine housing within the sea wall.

With bi-directional turbines, the process also works in reverse, generating electricity as the tides ebb and flow. The Tidal Lagoon Swansea Bay project is designed as a 320MW installation, capable of generating energy 14 hours every day. It should be the first of six, with larger lagoons planned for Cardiff, Newport, Colwyn Bay, Bridgwater and West Cumbria.

Should? There’s nothing wrong with the technology. Unfortunately, the £1 billion project has run into problems over pricing, with opponents warning that the project is too costly compared to other renewable energy sources. The Government has now announced an independent review into the feasibility and practicality of the tidal power in the UK.

“Tidal Lagoons on this scale are an exciting, but as yet an untested technology,” said Energy Minister Lord Bourne. “I want to better understand whether tidal lagoons can be cost effective, and what their impact on bills will be — both today and in the longer term.”

The future of ‘moon power’ hangs in the balance. — Dean Evans (@evansdp)

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