Tidal Energy Testing Facilities Replicate Conditions at Sea
With the right equipment, the oceans’ currents, tides, and waves can be converted into clean electric energy to supply power grids around the world. Tidal-wave technology harvests power from the rise and fall of the tides while wave systems harness the energy of surface waves. Many companies developing such technologies must test their systems at sea because few laboratories can realistically duplicate ocean conditions. And going to sea to test equipment prototypes can be a risky and expensive proposition.
But two test centers in the United Kingdom can provide the safe and controlled environment needed; they can simulate in hours or days conditions that would take years, most of the time waiting, at sea.
One test center is on one of the Orkney Islands, off the northern tip of Scotland. It celebrated its 10th anniversary last year, while the other recently began construction on the grounds of the University of Edinburgh.
The European Marine Energy Centre (EMEC), in Stromness, Orkney Islands, and the university’s were featured in “An Overview of the U.K. Marine Energy Sector.” The paper was published in the April 2013 issue of Proceedings of the IEEE. The article also covered the development of the country’s marine energy industry and detailed the government programs that support such research. The authors, based in the U.K.—John Lawrence, Jonathan Sedgwick, Henry Jeffrey, and Ian Bryden—are experts on marine renewable energy. Lawrence is a marine data specialist at the EMEC in Stromness. Sedgwick is a new-technologies consultant in energy demand at an engineering consulting company, E.ON New Build and Technology, in Nottingham, England. Jeffrey is a senior research fellow at the University of Edinburgh, and Bryden is a professor of renewal energy at the school.
Unlike with wind and solar power generation, the power from tides is more predictable and especially attractive to countries like the United Kingdom, which is entirely surrounded by water. The country’s Carbon Trust, a group of experts who advise government and industry on reducing carbon emissions and improving energy efficiency, estimates that between 15 to 20 percent of the U.K.’s present electricity demand could be met by marine energy. According to the article, it has invested nearly £180 million to support a range of marine energy activities, including the foundational research and development as well as the infrastructure to test the technologies.
The cost of producing energy from tides and waves can be higher than from other renewable sources because the equipment must be strong enough to withstand rough seas. The equipment includes tidal energy generators, which are large underwater turbines placed in areas where the tides are high; they produce electricity by capturing the kinetic motion of the tides’ ebb and flow. Wave energy converters rely on machines that flex and bend as waves pass over them.
Equipment developers need a place to try their prototypes in order to understand how best to install, operate, and maintain them under the harsh conditions of the sea. Realizing that no one organization could afford the cost of building a test site with its test berths for holding the equipment, underwater cables, connections to the national grid system, and other services, the U.K. spent £30 million to build the European Marine Energy Centre. The location was not chosen by accident. The Orkney Islands have some of the world’s harshest wave and tidal conditions. EMEC opened in 2003 and is still the world’s only full-scale open-sea test facility for wave and tidal energy converters.
It has 14 fully equipped berths that sit at depths of between 12 and 50 meters. These are connected to an onshore substation by 11 kilovolt sub-sea cables. The station, in turn, connects to the national grid. The cables also contain fiber optics, which allow developers to monitor and communicate with their devices. Specialist instrumentation and weather stations measure wave, tidal, and weather conditions to provide real-time ocean data. Two smaller-scale test sites, which are not connected to the grid, use specially designed buoys to dissipate the electricity generated.
According to the authors, since EMEC was established, more grid-connected marine energy converters have been deployed there than at any other site in in the world.
The University of Edinburgh has been at the forefront of marine energy research since 1974, developing many of the laboratory techniques and technologies currently used worldwide. Now under construction, the school’s All-Waters Combined Current and Wave Test Facility will test marine energy devices in any combination of current and wave environments, generated in any direction. A joint project of the university and the U.K. Engineering and Physical Sciences Research Council, which contributed £6 million to the construction, the center will be operated by an Edinburgh subsidiary, FloWave TT Ltd. Construction began last September, and the facility is expected to be up and running later this year. It should cost £9.5 million.
Unlike the European Marine Energy Centre, this testing facility is on land. It will use a 5-meter-deep tank that measures 30 meters in diameter; this will allow it to mimic the normal and extreme conditions of coastlines around Europe. The facility will be able to simulate combinations of waves of up to 28 meters (91.9 feet) high and currents of up to 12 knots. That makes it suitable for testing submersible devices, remotely operated vehicles, offshore wind installation and service vessels, and other marine tools. A rising tank floor and overhead crane will enable installation of individual devices, or arrays of wave or tidal current generators.
“It will be able to handle wave and current conditions simultaneously, with no directional restrictions to either,” wrote the authors. “No other facility in the world can achieve this.”