Water has been used as a source of energy in the UK for thousands of years, but rarely on the scale planned by Tidal Lagoon Power (TLP). The Cheltenham-based company envisages building a network of tidal lagoons around the coast to take advantage of an abundant resource for generating renewable power, with the technology then being available for exporting to other parts of the world.
The company’s first lagoon is planned for Swansea Bay, where there is a large tidal range of 8.5-9m that could generate a net annual output of 400GWh – enough to power 107,000 homes. The company proposes to take a small proportion of the bay and build a wall of about 10.5km long, enclosing 11km² of water. Power is generated by water flowing from the sea into the lagoon through turbines; when the tide drops, the water collected inside the lagoon is allowed to flow back out again towards the sea. A couple of hours have to be given each way to allow for a head difference between the sea and the lagoon. Underground power cables will carry the energy from the lagoon to the national grid at Baglan, near Port Talbot.
The way the lagoon system is designed makes the levels of costs and materials lower than those involved in building a traditional breakwater or sea-wall. The Swansea Bay project will use sandy material dredged from a thin layer of the seabed within the lagoon, which is then hydraulically filled into long geotextile castings called Geotubes – an idea that has been around in marine construction for many years, but that has not been used on a large scale. The Geotubes are stacked and packed with sand, and covered with a layer of small rocks and then a layer of larger rocks to protect against degradation. The construction will take between 24 and 30 months to complete.
The company needed to try out the idea on an area of manageable size, says Ton Fijen, TLP technical director. “We wanted a relatively small area where there are large tides for our pilot project, to show people that the technology works and that it’s cost-effective, that it can provide a cheap source of power for many years to come.”
The Swansea Bay proposal uses existing technology: low-head bulb turbines that generate electricity when water flows past their blades, but set up in a different configuration from that used before now. TLP plans to use a bulb Kaplan-type turbine, and is optimising its design to use 16 turbines.
“The three turbine blades are 7m in diameter. They don’t need a lot of maintenance,” says Fijen. “There is a plant in La Rance, France, which uses the same principle to generate power – in the 1960s they built a wall across the estuary there with a number of smaller turbines, 5.5m in diameter. It is only now that they are requiring significant upgrading and repair. For 40-odd years they have been working with normal maintenance routines but without any major refurbishment.”
With hydropower, turbines usually feature in run-of-river schemes comprising a river with a dam – as the water runs out of the dam it drives a turbine and electricity is produced – where the flow is one way. But for its lagoon system, TLP is looking at using turbines in a reversible mode. “We are talking to manufacturers about producing a turbine that is efficient in both flow directions,” says Fijen.
“Previously we were looking at the Klockhman design, which tried to generate power by not changing the direction of flow – the ingoing and outgoing tides would produce flow from a turbine in one direction only – but you have losses in other respects because it requires such a complex construction. So we said: no, it’s much better just to optimise the turbine to work bi-directionally.”
The company is working with three turbine manufacturers: Alstom of France, Voith of Germany and Andritz of Switzerland. “All are busy developing the turbines, and we are getting proposals from them in the next couple of months,” says Fijen.
If demand takes off for the lagoon system, TLP will then be better placed to satisfy it. “We would like to be in a position where we use all three manufacturers, because if we have a whole programme of lagoons in place – we want to build six or seven lagoons in the UK alone – then the number of turbines we require is so substantial that we need more than one manufacturer. There is a limit to how many turbines they can produce in a year,” he says.
“Some of the lagoons that we are thinking about will have 100 turbines. We want to be able to build them in a reasonable period. What we plan to do at Swansea is up for grabs. We will have one turbine design, but have them produced by more than one manufacturer.”
To predict the energy levels to be produced by the lagoon, the company has been developing computer modelling suites with Liverpool University. Its model takes into account the characteristics of the lagoon and the tidal predictions over a long period, and calculates how much water will flow from the sea into the lagoon and vice versa. The model can calculate the flow delivery in cubic metres per second, how much will flow through the turbines, and what power will be generated per turbine and by the whole system.
For the model to be accurate, input from the turbine producers is essential, says Fijen. “We rely on information from the manufacturers about how their turbines operate, what flow regime they have, what hydro losses they incur and how efficient they are, which we use for calculations.”
The amount of power to be produced can be estimated with more accuracy than for other alternative energy sources, he adds. “The energy produced is predictable. With solar power and wind power, you can’t predict when you’re going to be producing. The nice thing about tidal power is that you know exactly when you are going to be producing, what tides will be happening at what stage, and at what time. In the Severn Estuary, you can predict the power and tidal stage a year, 10 years, 20 years in advance.”
Although the Swansea Bay project is taking great strides forward, there are still hurdles to overcome, says Fijen. “The project brings lots of challenges: how to build the lagoon cost-effectively, how to build it quickly and reliably. Then there are challenges about the turbines – they have rarely been used in a bi-directional mode – challenges that from an environmental and social perspective the project is acceptable for the local inhabitants, that it is a project that they can use.”
First, the company has to convince its funders. “The major challenge is trying to come up with a project that is fundable. The funders would like to see that you can prove the viability of the project and that you have a return of about 8%. We are reasonably confident that we can make that work. Funders are worried and excited about the fact this is a world first. But they realise this is a process that is repeatable.”
The environmental aspect is also complex. The scheme is classed as a Nationally Significant Infrastructure Project – a label applied automatically to any project more than 100MW – so it has to go through a strict environmental and planning approval process. “It has been a long process, with consultations with feedback to the authorities and preparing specialist studies that are now to be compiled in a final set of documents for submission, but that has taken the better part of a year-and-a-half to complete and adhere to,” says Fijen.
“A project of this nature has a big impact on the area where it is based: for example, what interchanges have to be upgraded, how the cable will run from the works to the sub-station – where will it run, over whose land, whose permission we will need.”
The response has been positive overall, he says. “The feedback is that they see the benefit of a project such as this. There is always going to be some environmental impact, but in general the feedback has been supportive – that the big tides in the Severn Estuary are a resource we should be exploiting. They see the negative aspects are relatively minor and that Swansea can get an asset it can use – a facility that allows safe use of the bay for water sports, recreation, walking and cycling around the bund wall.”
Expressions of concern focus on the impact the scheme could have on fish and the aesthetics of the area, he says. “We have studied the mortality rates of fish in great detail using experts to give us feedback on how to minimise that, but there will always be a small percentage of mortality. We think that is acceptable, and hope the authorities agree.”
The company is hoping to submit its environmental and planning applications by mid-January this year, and expects there to be a 12- to 15-month approval process. If the project is approved, it hopes construction will start around March or April 2015.
Meanwhile, TLP is already investigating other potential sites, says Fijen. “In the next 10-15 years we could build five or six of these lagoons around the UK: two or three in the Severn Estuary, one in North Wales, one near Liverpool. Tides are predictable, but they generate only for 12-14 hours each day. But if you have a system of lagoons around the country, tides do not happen at the same time at each location. Together, you may be able to generate for a whole 24-hour period in a predictable method.”
The company’s prospects of achieving its ambitions were boosted in early December with news that the Crown Estate, which manages property owned by the Crown, has launched an industry engagement process to understand interest in future tidal-range and lagoon projects. “It is recognising a feature that could be important in providing power from an environmentally friendly perspective, and it is taking this type of technology seriously,” says Fijen.
Turbines in reversible mode: how the lagoon system works
Lagoon lowdown: TLP’s Swansea Bay project
- Tidal Lagoon Power’s development team has been working on the £650 million project since early 2011.
- The company has studied 14 different lagoon designs and turbine configurations over the past two years. As part of this work, a hydrodynamic model was developed using recent and historic data to depict the flow of water into Swansea Bay.
- Other companies involved in the project are Atkins Global, Costain, KGal, Van Oord, Titan Environmental Surveys, ABP Marine Environmental Research, Intertek and LDA Design.
- If the lagoon is completed on time – by 2017 – it would equate to about 1,850 full-time jobs across the region for the three-year construction period.
- An additional 60 long-term operational jobs, and up to 90 additional jobs linked to visitor spending, would be created.