Wasted Water World

Tidal Potential Waiting to be Tapped

By Helen Campbell

Few can have missed the urgent drive for a lower carbon future and the push to develop forms of renewable energy to help enable it. One of the lesser-used forms of renewable energy is tidal power, which converts the energy obtained from tidal variations into electricity.

The lunar cycle and the laws of gravity mean the standout benefits of tidal energy are its predictability and reliability, especially when compared with the more widely known and developed forms of renewable energy – wind and solar. Although 70 percent of the Earth’s surface is water, with the vast bulk of that oceanic, tidal power certainly does not work everywhere. Nevertheless, there is good potential for the technology in specific circumstances and, if it takes off, the tidal energy sector could provide lucrative new business for project cargo carriers.

Just a tide is not enough. The key to tidal power is the differential between flood tide and ebb tide – the difference must be a minimum of 4.5 meters, preferably at least 7 meters to facilitate a sufficient head of water for the turbines and commercially economic operation. Other constraints are the comparably lower capacity of tidal energy developments – averaging between 20 percent to 35 percent – and that tides flow twice a day only at times that do not necessarily chime with peak demand.

Areas with large numbers of small remote islands often provide the right conditions for tidal flows and depth variations appropriate for tidal power developments. Around the UK, suitable locations include off the north of Scotland; globally, the right conditions are to be found in the English Channel towards France; around the numerous islands that make up countries such as the Philippines and Indonesia; and offshore parts of Canada, in particular the Bay of Fundy, situated between Nova Scotia and New Brunswick, and which boasts the biggest tides in the world. Most of Africa, other than the island of Madagascar, is not seen to hold good tide potential.

Battery storage is also important, to counter the fact that the tides, while reliable, flow only twice a day. However, tidal power could feasibly be harnessed on both sides of an island, with one side feeding the local network for a period of time, to be taken over later by the other array, taking account of the different tidal timings on each side of the island and better balancing out power supply and distribution during a 24-hour period.

Fast-flowing rivers also provide good tidal power potential, as does adding them downstream of huge hydropower plants – this approach can provide a valuable second opportunity to harness power after huge volumes of water have already been released in freefall from a dam.

Stream Opportunities

The two main forms of tidal power technology are tidal barrage and tidal stream. Barrage installations see tidal waters filling an estuary via sluices which are opened to allow the tide to flow into the basin. When the sluice is closed, the sea level drops and the flow of elevated water in the basin drives turbines to generate electricity.

Barrage is expensive – one UK development, the Swansea Tidal Lagoon, was thrown into doubt when the UK government withdrew its backing, although developers are now trying to raise the funding themselves. The bulk of the hardware for tidal barrage is concrete, with a handful of large bespoke turbines required per development.
Much more likely to provide project cargo opportunities in the medium term is tidal stream. This harnesses the kinetic energy of moving water through devices installed on the seabed, and which are very similar to onshore wind turbines, albeit a lot more squat. A significant advantage of water over air is water’s far-superior density.

“The turbines we are developing at the moment are around 18 meters in diameter including the blades, so a lot smaller than wind turbines,” said Cameron Smith, director of project development at Simec Atlantis, a leading developer of tidal stream technology. “The reason for that is that water is 700 times denser than air, so you can use a much smaller blade to extract the same amount of energy as you would do from a wind turbine.”

Simec Atlantis’ largest development, and indeed the largest approved tidal stream development in Europe, is MeyGen, just off the very tip of John O‘Groats in the far north of Scotland. Situated between the tip of the mainland and the island of Stroma, one of the Orkney Islands and whose name means “Island in the Tide” in Gaelic, MeyGen is in the perfect tidal conditions to harness power.

The project is in two phases, with 6 megawatts of the 86-megawatt first phase already installed and feeding the national grid via four turbines of 1.5 megawatts each. The full first-phase capacity will require a further 50 1-megawatt turbines and will be able to supply 2,600 homes. While the project has grid capacity for 252 megawatts, the site could accommodate enough turbines to provide up to 398 megawatts of power.

Question of Scale

“Tidal stream is no longer research and development – it works,” Smith said. “The challenge is to make it cost effective. We could just add one, two or three turbines. What we really want to do is build 50, because that means we can get huge economies of scale. We can increase the size of the blades, we can use bigger vessels, we can keep the vessels for a reasonable amount of time, and we can cut down on vessel mobilizations. That would all make a huge difference to our levelized cost of electricity.” Levelized cost of electricity is the net present value of the unit-cost of electricity over the lifetime of a generating asset.

Simec Atlantis recently signed a joint venture with the regional authorities in Normandy, Northern France, to build a large-scale tidal stream development between the Channel Islands and the French mainland.

Construction is expected to begin in 2021 and turbines will be fitted out in either Cherbourg or Le Havre. Simec Atlantis is also looking at the Philippines, China, Indonesia and Japan.

“We are certainly being asked to go to these countries and to look at putting in demonstration projects in these areas where there are strong tidal currents between the islands, and there are a number of other companies doing the same,” Smith said.

While one of the installed MeyGen turbines is Simec Atlantis’ own, some of them were made in Germany and Austria by Andritz Hammerfest Hydro before being moved by train and transferred to a vessel. The considerations for transporting components for tidal turbine projects are fairly similar to those associated with wind developments, although retrieving a damaged blade from the seabed and replacing it is a lot more complex and expensive than replacing a blade on an onshore wind turbine.

Floating Tidal Options

“Second generation” tidal stream power, with turbines hosted by a hull moored to the seabed, could bring costs down. But while floating solutions utilize greater numbers of turbines, the turbines are significantly smaller than in a fixed development. Leading players in floating tidal include Sustainable Marine Energy, developing projects in Canada, and Orbital Marine Power (formerly Scotrenewables).

“Our turbines weigh in the region of 1,500 kilos with a blade diameter of 6 meters,” said David Stoddart-Scott, strategic projects manager at Sustainable Marine Energy. “They fit into containers while our hulls go onto flat-racks and are shipped that way, so the opportunities for [project] carriers there are currently limited. Our future preference, depending on global prices, is to build our structures as close to our installation sites as possible. In Canada though, that’s probably not going to happen, because their cost for building structural steel is more expensive than in Scotland, and obviously Scotland is more expensive than Southeast Asia.

“Our next platform is going to be slightly larger and will be slightly more difficult to fit onto flat-racks, so there will be opportunities for stuff to be shipped around. At the same time, the next five to 10 years will see our machines get bigger and bigger.”

Tim Wood, founder and director of engineering, procurement and construction services provider DWR Offshore, said about 10 percent of the company’s business is generated by the tidal power sector.

“We have noticed a bit of a drop- off in tidal, for reasons of a lack of support governmentally,” Wood said. “For shippers, there is potential there. In fact, that potential is there almost as a result of there not being so much support to develop physical tidal projects here [in the UK]. There has been quite a lot of support from various governmental schemes such as the Welsh European Funding Office (WEPO) and Scottish Renewables too, for companies to come up with designs for tidal, so there is a lot of innovation going on here and there are a few companies who are technically well advanced.”

Anticipated Global Growth

That innovation in the UK, coupled with the lack of governmental support, plus the expected impacts of Britain’s exit from the European Union on investment, may well mean greater global opportunities for project cargo shippers as the tidal sector starts to grow.

“Certainly, schemes like WEPO and the Cornish equivalent, the Marine Challenge Fund, are aimed at making European money available to develop regions of economic deprivation,” Wood said. “Part of the deal for companies to get hold of this money is that they set up a base in the areas where they are operating, and look to local manufacturers, at least for the prototyping.

“In terms of the shipping side of things, all of those companies are now looking abroad – where they’ve been previously demonstrating their units in Scotland, now you see those companies going to Canada, to the Philippines, and locations like Portugal and France. I am skeptical about whether they will carry on manufacturing in the UK. Brexit will have a huge impact on that, as will the final destination of the units.”

The technical complexity of tidal units will certainly play a significant role in the determination of manufacturing locations.

“Some of the units are extremely technically complex, but there are definitely parts of them which are not,” Wood added. “The big uncertainty with tidal, and how it does differ from wind, is that the variation in the types of device is absolutely huge. I would anticipate the more complex elements would be built somewhere in Europe with good fabrication, while the easier steel work would be built in the target markets, such as in Southeast Asia.”

Design Considerations

Tidal turbines generally weigh in the region of 50-100 tonnes apiece. Units can measure up to 20 meters high or more, with the blades to be factored into the width, adding in the region of 10-18 meters depending on design. Unsurprisingly, what developers need to make tidal work commercially is economies of scale. So, if tidal does take off, individual units are only likely to grow bigger in size and to increase vastly in number per array.

Whatever the number, and wherever tidal components are moved from and to, they will need careful handling. “The most delicate parts of these units are the parts where the blades fit into the turbine, just like the top of a windmill tower,” DWR’s Wood said. “The very top of it, the nacelle, houses all of the rotating equipment and all of the energy generation equipment, so that is the bit that needs to be taken very good care of.”

Again, it is the variation in design for tidal that will be the key to project cargo business-growth opportunities. Some companies’ designs do fit into a container, but the packaging necessary to protect tidal turbine units means that many other designs are simply too big once the packaging is taken into account, and they cannot be containerized.

“The guys who are good at transporting wind turbines will be good at moving tidal,” Simec Atlantis’ Smith noted. “We’re looking for people who are careful, and people who are good. These are high-value and quite complex pieces of machinery that can take up to two years to manufacture and, once they’re in water, they cost a lot of money. Each 1.5-2 megwatt would be insured to the ballpark of around £5 million to £10 million, and what’s important to us is that they arrive in the exact same manner and condition they were taken out in.”

While tidal timetables are wholly predictable years in advance anywhere around the globe, the timetable for tidal power revolution is less certain. Project carriers that have been busy moving wind turbines over the past decade look well placed to take advantage of tidal power sector growth, should the surge ever come.  

Helen Campbell is a freelance journalist based in London who has specialized in energy, environment, sustainability and technology for more than 20 years.

Image credit:  SIMEC ATLANTIS