Welsh tidal lagoon project could open way for £15bn revolution in UK energy

Backers of an ambitious proposal to transform the UK’s power supply will learn in the next few weeks if they are to be given the go-ahead to build tidal lagoons to generate electricity. The green light could see a series of major lagoon projects costing more than £15bn being constructed around the coast of Britain.

A tidal lagoon generates electricity from the natural rise and fall of the tides. Rising water flows into dams many miles in length, driving turbines. It is then held back behind walls as the tide recedes before being released to drive the turbines again, generating thousands of megawatts of power.

A prototype is set for construction in Swansea Bay in the next few years – but only if it is given the go-ahead by a government review of tidal lagoon technology, chaired by the former energy minister Charles Hendry, which is scheduled to release its recommendation early next month.

Green energy experts believe Hendry will give approval, although it remains to be seen if tidal lagoon technology – which was backed strongly by the former chancellor George Osborne in the last Conservative manifesto – finds favour with Theresa May’s administration.

Mark Shorrock, chief executive of Tidal Power Lagoon, the backer of the Swansea Bay prototype lagoon, said the technology could be an important zero-carbon source of electricity generation for the UK. “In addition, the money to build tidal lagoons will come from British investors and the expertise and technology we develop could be sold around the world,” he said. Tidal lagoons could also provide much of the power needed to make up for the predicted shortfall in UK energy that will be caused by the phasing out of coal plants and ageing nuclear reactors over the next decade, he added.

How the Swansea Bay visitor centre might look.

Six major projects have been earmarked for construction: a prototype at Swansea Bay; and then full-size lagoons at Cardiff, Newport, Colwyn Bay, Bridgwater Bay and west Cumbria. “The crucial point about tidal lagoons is that their power generation is not subject to the vagaries of the weather. It is predictable. We know exactly when every high tide will be for years ahead. In addition, the lagoons will be built to last – for about 120 years,” Shorrock said.

The £1.3bn Swansea Bay prototype has been designed to generate 350 megawatts of power – enough to supply 150,000 homes with electricity – and could be in operation by 2019. About 11 square kilometres of the bay would be surrounded by a 9km wall. Cycle paths would be built on the walls and a sailing and canoeing centre would be set up inside the lagoon.

Tides would sweep water into the lagoon and drive an array of 16 turbines, generating electricity. Then, after high tide has passed, the stored water would be released to pour back out of the lagoon to drive the turbines in the opposite direction – and generate more electricity. Shorrock claims the lagoon would be able to produce power for about 14 hours a day.

Power of the sea

Swansea Bay electricity would cost around £89.90 per megawatt hour, he added, compared with the £92.50 per megawatt hour price predicted for electricity from the Hinkley Point C nuclear plant. “However, when we scale up operations with the Cardiff lagoon – which will have 10 times the generating capacity of Swansea – we will be able to produce power for £65 a megawatt hour,” he said.

The Cardiff lagoon would cost £9bn to construct and contain 65 square kilometres of water within a 20km wall. It would have a capacity of 3,000 megawatts of electricity – compared with the proposed 3,200 megawatts from Hinkley Point C.

A request for planning approval for the Cardiff lagoon is to be made by 2018 with the aim of establishing a manufacturing industry for lagoon components in the UK.

However, it is the speed of this follow-up that worries many green campaigners. Most back the idea of the Swansea Bay test project but some fear that construction of much larger follow-up schemes – starting in Cardiff Bay but going on to Colwyn and Bridgwater shortly after – could begin too soon to adopt any lessons that will be learned from construction of the prototype lagoon.

This point was stressed by Mark Robins, of the RSPB. “The Swansea tidal lagoon could prove to be very useful but we will have to monitor how the first prototype affects the movement of silt in the estuary, disrupts bird populations and impacts on fish stocks before we scale up. This is a completely new technology and it is going to be built in a very complicated natural site – the Severn estuary. We need to be very careful how we go.”

Mark Shorrock of Tidal Lagoon Power, which is proposing the Swansea Bay project. Photograph: Adrian Sherratt for the Observer

Richard Benwell, of the Wildfowl and Wetlands Trust, agreed. “We are cautiously welcoming,” he said. “However, we would want the scheme’s impact to be very carefully monitored before building started on the next-generation lagoon at Cardiff.”

However, there is strong pressure from the scheme’s backers to instigate a speedy follow-up of the Swansea lagoon. They want to establish a supply chain for generators, turbines and other components to kick-start tidal technology in the UK, establish a series of major lagoon generators and eventually become the world leader in the field.

Some worry about the environmental dangers. Others stress the advantages for local economies around Wales and Liverpool where tidal lagoons are likely to be clustered.

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