The constancy and predictability of tidal cycles and seawater currents are attracting increasing attention from engineers, governments and others who understand the sea’s potential for sustainable electricity generation – and Wales hopes to become a world leader.
The Bristol Channel has the second-largest tidal amplitude in the world, and there are strong currents between Wales’s mainland and islands. The devolved nation’s ambitions received a leg-up last June, when the UK government approved a £1 billion tidal lagoon in Swansea Bay to generate electricity on both the ebb and flow tides. There are environmental hurdles to overcome before the 9.5km lagoon wall can be built, but its promoter envisages similar lagoons around Britain’s coast. Meanwhile, other projects in Welsh waters are taking a “small is beautiful” approach, which would sidestep some of the environmental issues.
Wales is a long-term recipient of European Union structural aid, and its 2014-20 European Regional Development Fund (ERDF) programme includes
€100 million for marine renewables. The grant aid will need match-funding from other sources. The main aim is to provide two demonstration zones, one off Anglesey for tidal-stream technologies and one for wave power off Pembrokeshire.
Jane Hutt, the Welsh government’s finance minister, explains: “By providing the generic environmental impact assessments, having the Crown Estate long-term leases in place and connection to grid, these zones will vastly reduce the time, costs and risks to developers in the sector, so accelerating the evolution of the industry.” Interest in the demonstration zones has come from North America and Scotland, among other places.
Both areas are well connected to the national grid, thanks to established power stations at Wylfa (nuclear) and Pembroke (oil-fired initially, now combined-cycle gas turbine). However, William Graham, who chairs the Welsh Assembly’s enterprise and business committee, has warned that reactive provision of grid connections is a barrier to marine renewables’ development. He says a proactive approach is needed because of the rapidly emerging nature of the industry and “the number of companies considering Anglesey as a base”.
Giving the go-ahead
The Crown Estate has consented use of the Anglesey zone from late 2018. The zone will be led by Menter Môn, a local company established to deliver EU aid programmes. The Pembrokeshire zone, due to follow shortly afterwards, is led by Cornwall-based Wave Hub, a UK government-owned company promoting wave, tidal and offshore wind development. Menter Môn and Wave Hub will decide which developers can use the zones.
Swedish company Minesto recently established a UK office on Anglesey and in early October had six vacancies there. Its plan to install the first commercial tidal kite generators in the Holyhead Deep – outside the future demonstration zone – is supported by €13 million from the ERDF and €3.5 million from KIC InnoEnergy, a company promoting innovation in sustainable energy as an offshoot of the European Institute of Innovation and Technology.
Minesto’s Deep Green device was inspired by the relatively strong forces that a wind-borne kite exerts on the arms of the person holding the cord. Each Deep Green turbine will be encased in a nacelle (streamlined casing) and attached to a wing structure, shaped to induce hydrodynamic lift when the equipment is tethered to the seabed in a steady current. The wing and turbine will be steered in an incessant figure-of-eight loop through the water, and it is this movement that will generate electricity.
Consequently, Deep Green is expected to function efficiently in relatively slow currents – speeds of 1.2 to 2.5m/s are quoted. A quarter-size prototype has been tested in the sedate environment of Strangford Lough in Northern Ireland. Suitable conditions for deployment occur not only in areas of tidal movement but also in ocean currents, which Minesto says are almost constant.
Anders Jansson, Minesto’s chief executive, also says the company has “seen a potential in deep rivers and water transportation channels”.
Minesto aims to install three devices near Holyhead with a combined capacity of 1.5MW in 2017. All being well, later additions would increase output to 20MW.
Why in Wales, rather than closer to Minesto’s headquarters?
“Quite ironically, we don’t have tidal currents in Sweden, but along the Welsh coast we see a fantastic resource of slow-moving currents, a strong political will and availability on the grid,” replies Jansson.
Deep Green units weigh seven tonnes each and can be transported by small boats, rather than requiring specialist vessels. This attribute, and Deep Green’s flexibility to operate in arrays of any number, will make the technology attractive worldwide, including in developing countries, Jansson predicts.
ERDF funding of €2.7 million has been awarded to Marine Power Systems of Swansea for manufacture and testing of WaveSub. This technology is the brainchild of engineers Dr Gareth Stockman and Dr Graham Foster, former postgraduates at the city’s university. They aim to deploy a quarter-size prototype in the Milford Haven Waterway Enterprise Zone next year, and hope to begin testing a full-size unit in 2018.
Deep Green: The turbine is held below the wing, which is shaped to induce lift when the device is tethered in a current
Installation costs pegged
They are keeping technical details under wraps for now, but in essence the WaveSub device finds and maintains its optimum operating position in the water column to maximise output. No piling is required. No specialist vessels will be needed to transport and deploy the units, each of which is likely to be up to 40m long and rated at 1.5MW.
“Through solving the fundamental challenges facing wave-energy developers, significant savings can be made, ultimately leading to a low levelised cost of energy,” says Stockman, the managing director of Marine Power Systems. “Large vessels alone, to transport and install devices, can cost tens of thousands of pounds per day.”
The WaveSub units can undergo routine maintenance such as de-fouling in situ, and are designed to be detachable, for return to more sheltered areas. A commercial WaveSub farm array would include one or two additional units that could be interchanged for ongoing maintenance. Where possible, Marine Power Systems uses commercially available components instead of bespoke parts to help de-risk development.
Export potential
Marine Power Systems predicts that, thanks to the relative ease of transport, it would be possible to export several WaveSub farms from one manufacturing and maintenance base in each region of the world. WaveSub has been developed with a one-size-fits-all philosophy, to minimise the variations required for deployment in different locations, which in turn reduces the amount of preliminary surveying required.
Pembrokeshire is also the planned host area for the first full-scale DeltaStream devices. The original prototype was tested in Milford Haven in 2001. The concept was conceived by marine engineer Richard Ayre while he worked on wave monitoring equipment in Pembrokeshire, and has been taken forward to production by the firm Tidal Energy of Cardiff.
One of the key aims is to avoid the high cost and environmental disturbance of driving piles into the seabed for devices which must be robust enough to withstand strong tidal and climatic forces. Each DeltaStream module consists of a triangular base frame with ‘rock feet’ beneath each corner to secure the structure to the seabed. Towers at each corner of the triangle support a turbine and nacelle, along with devices to adjust the turbine’s orientation to maximise efficiency.
Tidal Energy has consent from the Crown Estate to test DeltaStream in Ramsey Sound for up to seven years. The test module would run for 12 months initially, feeding power into the local distribution network. Results would inform the planned deployment of an array of up to nine DeltaStream modules, with a combined output of 10MW, off St David’s Head. The test module’s planned deployment last November was delayed by bad weather, and this summer Tidal Energy said that it faced new financial hurdles as a result of the delay.
The ERDF programme in Wales isn’t confined to development projects. It also aims to provide an additional 20MW of permanent installed capacity in the wave and tidal sector.
Academics from Swansea University emphasised the importance of taking a wide view of the sector when they gave evidence to a Welsh Assembly committee in October. Device developers are the pinnacle of a large supply chain, they said. “Securing the sector in the long term will depend on securing the added-value elements of the business.
“This involves investing in R&D, whole-system design and advanced manufacturing, together with high-level skills and training. This needs to be undertaken across a range of disciplines: mechanical, electrical and civil engineering, logistics, manufacturing, materials, offshore operations and infrastructure.”
The devices that are set to be tested or permanently installed in Wales illustrate how contrasting concepts are being developed to harvest energy from different areas of the world’s seas. Stockman of Marine Power Systems sees these approaches as complementary, rather than competing against each other, because marine kinetic energy is available in such contrasting circumstances.
“When you try to compare technologies that aim to capture energy from the near-shore, mid-shore and offshore, in some respects you might as well compare solar energy with wind energy,” he says.
Did you know? - Minesto’s Deep Green
- When flying a kite you feel a strong force in the rope and notice that the kite flies faster than the wind is blowing. Minesto used this concept in its Deep Green device. It attaches a turbine to the ‘kite’ and puts it in the ocean, where it reaches a speed 10 times higher than the water current. The speed has a cubic relationship to the power.
- Ten times higher speed gives 1,000 times more power. The kite is steered in a figure-of-eight shaped trajectory by a rudder. A quarter-scale prototype of the device is being tested in Strangford Lough in Northern Ireland. Deep Green is a simple and robust device, and weighs a lot less than many competing designs.
- The Deep Green tidal current device has minimal visual impact as it is submerged at least 15m below the water surface