Tidal energy is a less well-known form of renewable power generation, sitting at the fringes of the spotlight currently being shone on the likes of solar panels and offshore wind farms. But the natural power resources hidden in the movement of the tides could potentially play an important role in our future green energy mix, especially given that, unlike wind or sunlight, the tides are as predictable as time itself, yielding a regular and unfailing source of power.
The most high-profile modern project utilising tidal power generation was the proposed 10-mile barrage across the Severn Estuary between Lavernock Point in Wales and Sand Point in Somerset. This massive project aimed to provide the same amount of electricity as three nuclear power stations, reaching 8.6GW during peak water flow times. It was claimed that the Severn Barrage, which would easily have been the UK's largest civil engineering project since the construction of the Channel Tunnel, would be able to provide for around 5%-6% of the country's electricity needs.
Why was the Severn Barrage scrapped?
The high hopes for the colossal project were crushed on 18 October, when the UK's Department of Energy and Climate Change (DECC) announced that the plug was being pulled in favour of pursuing other renewable options, as well as plans for new nuclear power generation. The announcement came after the Severn Tidal Power feasibility study reported that the project was comparatively high cost and high risk.
Chris Huhne, the UK Government's Secretary of State for Energy and Climate Change, framed the cancellation as primarily a measure to safeguard taxpayers' money. "The study clearly shows that there is no strategic case at this time for public funding of a scheme to generate energy in the Severn estuary. Other low carbon options represent a better deal for taxpayers and consumers," he said in a statement.
Indeed, from a pure cost perspective, the Severn Barrage always had the potential to become a white elephant.
The sheer scale of the project, along with the vagueness of cost estimates (original estimates spanned a mind-boggling range of £2bn to £20bn, with the recent Severn study predicting that costs could even rise to £30bn), the DECC clearly decided that the upfront cost was disproportionate to the long-term (still largely unproven) benefits, especially during a period of fiscal austerity and massive funding cuts to frontline services.
Beyond problems of financing, the Severn Barrage scheme was controversial from the start due to the undeniable environmental impact that the project would have had on local eco-systems.
Wildlife campaigners criticised the proposed barrage because it would have effectively halved the tidal range of the river, wreaking havoc on the salt marsh and mud flat feeding grounds of some 85,000 birds. As RSPB conservation Dr Mark Avery told edie.net in an interview back in 2006: "This is one of the most important sites in the UK for wild birds and the chances of them surviving if [the Severn Barrage] went ahead are fairly slim. There wouldn't be enough room left for all the birds and there wouldn't be enough food for those that remained."
After the scheme's abandonment, the World Wide Fund for Nature (WWF) released a statement welcoming the news (while urging for the government to continuing looking for new alternative energy solutions), emphasising the estuary's importance to humans as well as wildlife. "To many people, the Severn Estuary is part of their way of life. It is also home to an array of wildlife and habitats, which are recognised as internationally important under EU law and which people rely on for their livelihoods. The largest tidal power scheme could…reduce bird populations by up to 30 species, reduce numbers of protected fish and eradicate local populations of twaite shad and Atlantic salmon."
Indeed, another criticism of the project came from local shipping and fishing businesses, which would have had to navigate locks and face the loss of fishing grounds.
The future for tidal energy
The unpopularity and eventual scrapping of the Severn Barrage hardly spells the end for the tidal power industry, however. Barrage schemes are not the only method of converting tidal energy into electricity.
A number of manufacturers are developing the concept of tidal stream technology, which takes the basic principle of the wind turbine and submerges it beneath the waves to harness tidal movement instead. Engineers are in the process of working out the best ways to make tidal stream projects environmentally and commercially sustainable.
Abbie Badcock, the director of tidal analysts Tidal Today, points out that one promising demonstration project, SeaGen, is already online in Northern Ireland. "We have seen the operation of the Strangford Lough project [SeaGen], which is by Marine Current Turbines, who are the longest-standing of the tidal developers," she says.
"That's been operating continually for three months. They've had some restrictions; they've been the pioneers who have been through all the trials and tribulations and doing copious amounts of environmental assessments and overcoming a lot of the engineering challenges."
SeaGen is an important project in that it is a proof-of-concept for tidal stream technology as a method of generating power without as much of the disruption that was inherent to the Severn Barrage project. Underwater tidal stream turbines can also be scaled based on the suitability of different locations.
For large areas with high resilience, arrays of turbines can be set up to effectively form an underwater wind farm. Smaller eco-systems can generate power in a more local manner. "For example," Badcock says, "with very small devices outputting kilowatts rather than megawatts, you could look at having installations in rivers. In the United States, a lot of the river areas have been allocated for that and they've put in federal licenses and permits to the federal organisations over there. And that [power] could be disseminated to the local community so you could see a direct benefit."
The success achieved by Marine Current Turbines will be indispensable for the company as it moves forward with more substantial demonstration projects off the coast of Anglesey in Wales and in Scottish waters. But it is one of a group of manufacturers developing tidal stream projects, including Atlantis Resources Corporation, Voith Hydro Ocean Energies and Tidal Generation Ltd (co-owned by Rolls-Royce).
For these companies, Badcock explains, the challenge now is to develop these projects over the coming years from small demonstrations into full production. "In the next four years, they'll be getting those sites up and running and fully functional. By 2016, they're looking to get the beginning part of the projects at the site starting to come online so that by 2020, we'll have several hundred devices in the water. In contrast with the wind turbine industry, we are going to see a rapid ramping up to a production stage from a site and project development stage."
This evolution from demonstration to production will likely be the main topic of discussion at the 4th International Tidal Energy Summit that Tidal Today is holding in London at the end of November.
Badcock is quick to mention that although tidal stream technology brings many benefits, it is too early to rule out tidal barrages (or indeed tidal lagoons, another method proposed), as they might be appropriate given the right geographical and economic conditions.
Even DECC's Severn study that sealed the fate of the barrage acknowledged that "a Severn tidal project should not be ruled out as a longer term option if market conditions change". Other circumstances might see barrages implemented with minimal ecological disruption.
If UK Prime Minister David Cameron wants to fulfil his desire to make his stay in Parliament the "greenest government ever", he and his energy secretary will have to examine all options open to them.
It is unknown if the small voice of the tidal industry will be heard over the competing din of nuclear, CCS, wind and solar technologies, but companies are currently working very hard to convince governments that their technology is worth the investment.