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Time for tidal lagoons?


Gail Rajgor

While tidal stream technology is seen as closer to commercial viability, tidal lagoon (tidal barrage) projects arguably could make an even bigger impact on electricity supply networks in the nearer term, says Gail Rajgor.

The UK's decision to give the planning and development green light to the £1 billion 320MW Swansea Bay tidal lagoon project in June 2015 was hailed by Tidal Power Lagoon (TPL) chief executive Mark Shorrock as a potential "game-changer". For once, it was not necessarily an over-zealous use of the phrase.

As he noted, with a 120-year lifespan, the ability to produce predictable amounts of energy for 14 hours a day every day, the creating of a large local supply chain (and with it a significant volume of jobs), and by using what he describes as a "zero carbon energy infrastructure", this and the other, much larger, tidal barrage projects planned by TPL across five other sites in the UK could provide up to eight per cent of the UK's electricity supply alone. The next two proposed projects by TLP at Cardiff and Newport, for which planning applications are expected in 2017 and 2018 respectively, alone represent some 4000MW of lagoon power and £10 billion of capital investment.

However, just months after the Swansea Bay project was given the green light, it was put on hold for a year, reportedly in part because of negotiations with Department for Energy & Climate Change (DECC) over the contract for difference (the subsidy the Government will pay for each unit of renewable energy produced by the lagoon).

It is understood that DECC is also concerned about the strength of the private investment. In February 2016 - almost exactly eight months to the day the Swansea bay project was initially granted development consent by the Planning Inspectorate - the UK Government announced an independent review into "the feasibility and practicality" of tidal lagoon energy in the UK. In a statement, DECC said more work needs to be done to determine whether tidal lagoons present value for money. The review will commence this spring, while discussions about Swansea Bay Tidal Lagoon continue, it added.

Call for clarity

Energy Minister Lord Bourne acknowledged that tidal lagoons on the scale of Swansea Bay are an "exciting" prospect, but he expressed concern that it is "an untested technology". He said: "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. This review will help give us that clarity so we can determine what role tidal lagoons could have as part of our plans to provide secure, clean and affordable energy for families and businesses across the country."

The review will consider:

  • An assessment of whether, and in what circumstances, tidal lagoons could play a cost effective role as part of the UK energy mix;
     
  • The potential scale of opportunity in the UK and internationally, including supply chain opportunities;
     
  • A range of possible structures for financing tidal lagoons;
     
  • Different sizes of projects as the first of a kind;
     
  • Whether a competitive framework could be put in place for the delivery of tidal lagoon projects.

Those behind the Swansea Bay development appear quite optimistic. Indeed, Shorrock describes the review as a "huge step" from the Government and a "clear signal" that it sees the potential advantage of tidal lagoon power. Keith Clarke, Chair of Tidal Lagoon Swansea Bay Plc, agrees and insists the time has now come for tidal power. "We are confident that tidal lagoons are no longer a footnote in UK energy policy," he says. "We hope the review process will ensure we get to deliver, long term, home grown and cost effective electricity for many generations to come."

In parallel to the review, the Government has requested that Tidal Lagoon Power clarifies the financial and technical viability of Swansea Bay Tidal Lagoon as the pathfinder for the industry. Clarke says this signals the strength of its planned programme of lagoons. It should also help to secure investor confidence, he suggested.  

One such investor in the project is Sanjeev Gupta, executive chairman of the Liberty Group and global energy and commodities company SIMEC. As well as backing the Swansea project and others planned by TPL in the UK, Gupta wants to see tidal lagoons built in India. Indeed, as part of their agreement, a joint venture between SIMEC and TLP is being created to develop largescale tidal lagoons in India. The first feasibility studies will be conducted in the Gulf of Khambhat under the terms of a Memorandum of Understanding with the Government of Gujarat.

The case for tidal energy is "compelling" and "overwhelming", Gupta says. Although the first lagoon [at Swansea Bay] is expensive, over 120 years it is comparable to the new Hinkley Point power station, he notes. "If the Government is supporting Hinkley we believe it should support Swansea, because that then leads to the larger lagoons which are infinitely cheaper," he said in an interview with BBC Wales. "Ultimately, once it's properly analysed and looked at it's too compelling for anyone to ignore. I've invested in it because I'm convinced it's the way to go."

Competition time

Gupta is not the only one convinced. Another company to welcome the UK government's review is Ecotricity, with the company revealing that it now plans to go head-to-head with Tidal Lagoon Power in a bid to build the first tidal lagoon site in Britain. Indeed, the company believes it can do so for half the price currently proposed for Swansea Bay, although it will not reveal its plans until later this year.

"The Government has been agonising for a while about what level of support to give to the first tidal [lagoon] project in Britain. They’re clearly interested in the technology, which is a good thing, but they’ve been put off by the price tag of £168/MWh [over 35 years] proposed by Swansea Bay – that’s understandable," commented Ecotricity founder Dale Vince. “We’re confident that tidal power projects can be built around Britain at much closer to £90/MWh. That’s the same price the Government are paying to support nuclear energy, but without the risks or clean-up costs.”

Meantime, TLP's Shorrock says there is no reason not to proceed with the Swansea Bay negotiations. "We have made a value-for-money proposition to Government," he says, suggesting the review should not impact the finalisation of the company's commercial discussions with the Government. TLP is proposing a lower price per MWh to be paid for the electricity from Swansea Bay over a 90-year period instead of the original 35 years planned. 

"Recognising the extremely long asset life of a tidal lagoon enables the overall financing costs to be significantly reduced," Shorrock says. “We have proposed an equivalent CfD strike price for the 320MW Swansea Bay Tidal Lagoon below that of offshore wind. Our structure has a subsidy that reduces over time, meaning that for around half of the proposed 90-year contract, the lagoon pays money to Government.

“By linking Swansea Bay Tidal Lagoon to the successful delivery of a second, full-scale lagoon, this approach further reduces the required and proposed equivalent CfD strike price of Swansea Bay to under £100/MWh, comparable to the Hinkley C nuclear power station. Application of these bespoke support structures to the Cardiff Tidal Lagoon, a 2700MW capacity project, the equivalent CfD strike price requirement is £68.30/MWh."

Nonetheless, Ecotricity's Vince wants the UK government to open up the tidal energy market - including the Swansea Bay project - to competitive tenders. At the same time, companies involved in tidal stream projects hope the review into lagoons does not inadvertently lead to delays for them too. “The opportunity that tidal stream energy offers the UK must not be overshadowed by the hiatus surrounding Tidal Lagoons and Swansea Bay," says Peter Dixon, Executive Chairman of Kepler Energy. The company is working to bring forward plans for a tidal energy fence that will be located in the Bristol Channel. "Our tidal energy technology will use the very latest carbon composite technology, and can be deployed in shallower, lower velocity tidal waters around the UK coastline and also in overseas waters, in countries such as China, Korea, Japan and India. Subject to planning and financing, the Bristol Channel tidal fence, which is likely to be located in the Aberthaw to Minehead stretch of water, could be operational by 2025.” 

***

Turbine technology
 

The turbine selected for Tidal Lagoon Swansea bay is a state of the art Kaplan bulb turbine which will be manufactured by a consortium of one of the world’s leading turbine manufacturers -Andritz Hydro and global leaders in power electronics - GE-Power Conversion. Bulb turbines are commonly used in conventional run-of-river hydro projects which experience a low head range and varying flow conditions. The following are some useful facts about the Swansea turbines:

  • The size of a turbine is measured by the runner (propeller) diameter in the case of Swansea this will be 7.35m.
     
  • There are numerous reference projects around the world which use similar size bulb turbines including a similar scale tidal range project- Sihwa in South Korea which uses 7.6m bulb turbines.
     
  • Unlike run-of-river plants tidal lagoons generate power on both the ebb and flood tides and so the turbines have to work in reverse i.e. they are bi-directional.
     
  • Swansea, as with all conventional hydro power plants utilises the head difference between the upstream and downstream (inlet and tailwater) water levels to generate power.  The higher the head the greater the potential energy.  In the case of a tidal lagoon the head difference is created from the natural tidal variation (tidal range) and through manipulating the lagoon levels using the turbine wicket gates to prevent water from entering or leaving the lagoon until the optimum head difference is reached.
     
  • Bulb turbines are normally ‘double regulated’ this means flow and hence power can be adjusted mechanically in two ways: firstly by having variable pitch guide vanes called wicket gates (which can also completely stop the flow) and secondly by having a variable pitch propeller called a ‘Kaplan runner’. 
     
  • One of the pioneering aspects of the Swansea turbine is the use of variable speed (varspeed) regulation in the form of power electronics.  This gives very high efficiencies across the broad head range experienced by tidal range plants and also allows high efficiencies in reverse operation and pumping modes. 
     
  • The lower average rotational speed with varspeed technology also significantly reduces potential injury to fish compared to the conventional fixed speed turbines.  The addition of variable speed technology means the Swansea turbines are effectively triple regulated.

The turbines at Swansea are encased in the concrete turbine housing and will always be submerged with the exception of when they are de-watered for maintenance or cleaning purposes. The efficiencies and overall energy production or Guaranteed Minimum Annual Energy Production is one of a raft of contractual guarantees which link back to a contractual scale model test, this means we can guarantee with certainty the efficiency of the turbines and the annual energy we will export onto the grid. The Swansea turbines are best described as ‘state of the art conventional hydro’.
 

ABOUT THE AUTHOR
 

Gail Rajgor is a freelance journalist, editor and photographer.

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