Tidal Power

Wave and Tidal Power Technology Near Commercialization

Scotland, which is authorized to set its own energy policy separate from London’s Westminster government, has set a goal of generating 100% of the nation’s annual electricity needs through only renewable sources by 2020, and 100% of its entire power and transportation needs from non-carbon energy by 2030. This decision has created an all-of-the-above clean development strategy as well as a stronger commitment to energy self-reliance. By looking inward at what internal resources exist, Scotland is now home to the most-advanced wave and tidal energy development center in the world.

For decades, engineers have been trying to turn the immense potential of tidal energy into electricity. While ocean currents don’t reach the same speeds that wind can, the inherent energy potential by comparison is enormous. Seawater has more than 800 times the density of air, so for the same rotor swept area, water moving at 2.5 meters per second (m/sec)—roughly 5 knots—exerts the same amount of force as would be applied by wind blowing at nearly 100 m/sec (about 195 knots).

The Orkney Islands: A Storied Past and Present

Studies conducted by several commissions in the UK suggest that wave and tidal stream energy has the potential to meet as much as 20% of the nation’s total electricity demand, split roughly three quarters from wave and the rest from tidal. Additionally, the UK is estimated to be home to roughly 50% of Europe’s entire tidal energy resource.

According to an article in E&T—a magazine published by The Institution of Engineering and Technology—the UK has a potential energy resource of 29 TWh per year available in tidal currents, of which 11 TWh are in the Pentland Firth, the body of water separating the mainland from the legendary and beautiful Orkney Islands, far to the north of the nation. For the sake of comparison, all of the UK’s nuclear power plants generated about 64 TWh of electricity in 2015.

Orkney, who’s massive Scapa Flow harbor once sheltered different Pictish, Roman, and Viking fleets, eventually became the home port for the storied Hudson Bay Co. that helped develop much of Canada. In the 20th century, Scapa Flow became a major sea and air base for the British Royal Navy and was the site of several major battles in the Second World War including the surprise attack on the HMS Royal Oak, leading to almost 900 deaths. The wreck of the ship is now among several protected war graves and historical sites in the harbor itself.

While the past looms heavily over the islands, Orkney today is home to the European Marine Energy Centre (EMEC), which is continuing this maritime tradition by playing a key role in demonstrating the emerging value of wave and tidal power as a sustainable source of renewable energy. Founded in 2003, it is the only accredited test center for marine renewable energy that is suitable for testing a number of wave and tidal energy devices simultaneously. It offers developers of both types of converters the opportunity to test in open sea conditions, often in challenging environments (Figure 1). To date, EMEC has hosted 19 wave and tidal energy clients (with 30 different marine energy devices) originating from 10 countries.

1. Taxing trials.
This image shows the AR-1000 tidal turbine being deployed at the EMEC test site. Courtesy: Atlantis Resources Corp.

“There are some other test centers around the world working on wave or tidal, but certainly we think we have more going on here than anywhere else,” said EMEC’s Managing Director Neil Kermode in an exclusive interview with POWER.

Today several experimental units, operating in some of the harshest weather conditions in the world, are producing electricity to the national grid through the company’s infrastructure. All monies generated by the sale of electricity are fed back to the developers, increasing the funds for future industry investment.

Berthing a New Tidal and Wave Power Energy Industry

Since being established, the center has received around £36 million of funding from the Scottish government and a consortium of other pubic entities. However, it has been financially self-sufficient since 2011. Now, a decade and a half since opening, trials at EMEC have potentially yielded their first commercial-scale energy installation.

Scottish developer Atlantis Resources Corp. has been busy developing and deploying tidal energy units in the MeyGen cluster in the Pentland Firth. Phase 1A is scheduled to be operating autonomously at full 6-MW capacity by the end of September. From there, developers hope to scale up to over 100 MW and beyond in coming years.

“The deployment at MeyGen—since the technologies were initially tested at EMEC—is a bit like graduating, and going off and getting your first job,” said a proud Kermode. “We have proved out the alchemy that you can convert seawater into electricity. These tidal machines have started to harvest the inherent energy at a commercial scale,” he continued.

The Pentland Firth separating Orkney from the mainland has some of the strongest tides in the world, so the area is a natural test bed and proving ground for tidal wave power technology.

“Tidal energy is slightly more of a specialist technology,” Kermode admitted. “It is really useful only where you have the right conditions.”

Indeed, tidal may eventually become perfect for island communities that otherwise rely on a distributed grid, imagine archipelagos like Indonesia and the Philippines deploying these systems.

“These communities would be daft not to develop this resource, especially as it can easily be mated to new distributed grid technologies,” said Kermode.

But wave energy has a larger potential worldwide. “Think Chile or even California with their long west-facing coastlines: imagine the energy in the sea that could be brought on to the beaches,” he said.

In the same way that 10 or 20 years ago someone might challenge the viability of a single 5-MW or 10-MW wind turbine unit being floated offshore, today many are a bit skeptical of wave and tidal energy harnessing systems. “But we have seen these great leaps already. Development is not a function of time or money, but of repetition. Learning and repeating,” said Kermode.

A Variety of Sites with Assorted Conditions

EMEC’s Billia Croo test site (Figure 2), completed in 2003, is located on the western edge of the Orkney mainland in an area with some of the highest wave energy potential in Europe. Average significant wave height is from 2 m to 3 m, with the highest wave on record reaching 18 m. The site consists of five cabled test berths—in up to 70 m of water—located approximately 2 km offshore, as well as a near-shore berth for shallow water projects.

2. Stormy seas.
The EMEC grid-connected wave test site is ideally placed on the western edge of the Orkney mainland, at Billia Croo outside Stromness. Courtesy: Rob Ionides

EMEC’s tidal test site at the Fall of Warness, located to the west of the island of Eday, was chosen for its high-velocity marine currents, which reach almost 4 m/sec in spring tides. The facility offers seven test berths at depths ranging from 12 m to 50 m in an area 2 km across and approximately 4 km long.

Additional scale test sites provide a more flexible sea space for use by smaller-scale technologies, supply-chain companies, and equipment manufacturers. EMEC also works on a variety of projects to help facilitate the development of marine renewables, spanning environmental and wildlife studies, knowledge sharing projects, and infrastructure development.

In total, approximately 200 people are currently employed in Orkney in the marine renewables sector (out of a population of just over 20,000). Orkney itself has produced more than 100% of the community’s electricity needs now for several years.

“From hundreds of small wind energy systems and solar systems, including my own, all together approximately 1,000 structures on the islands have renewable energy systems out of roughly 10,000 structures across the islands. That is one of, if not the, highest uptakes of renewables in all of Scotland,” said Kermode.

A new project just launched at EMEC is geared at replacing the diesel fuel currently powering the island’s bus and ferry system with hydrogen derived from marine-produced electricity. “In the first pilot project, we will create roughly 200 kg of hydrogen a day. That could power several busses a day. A 2-MW facility will eventually power one ferry. There are nine ferries. So the project will eventually scale up, if successful, to the point where we are hopefully using electricity generated from water to get rid of carbon-based fuels,” said Kermode. This is, of course, part of the UK’s own goal of moving away from carbon-based transportation systems.

EMEC is targeting other areas with large wave and tidal resources that are not connected to a grid or have a less-than-ideal distributed energy system, examples being Indonesia, Chile, and the Philippines. For this purpose, EMEC and its partners “are developing power cables designed to hook directly into a beach head battery storage system that would store the intermittently generated energy from tidal or wave systems,” continued Kermode.

In turn, these new battery storage grid systems would take the mean of the system off the site and put it on the grid. “So the amalgam of the two technologies can help to make them both more efficient. That way the peak energy is stored. With battery technology coming on now, its no longer an issue of throwing the right-sized cable at it. We can store the energy and dispatch it out more regularly. For remote communities that are paying a lot for their electricity, often relying on diesel generators, this is a much better option,” said Kermode.

Wave and Tidal Projects

Over the years, more technologies have been tested at EMEC than anywhere else in the world. There are currently 13 European Union–funded research projects taking place in Orkney.

Pelamis Wave Power P2. In 2005, international energy generator E.ON set up a development team to investigate various wave and tidal technologies. As part of its first significant investment in wave power, the company purchased a second-generation Pelamis Wave Power P2 machine in 2009: the world’s first wave power machine to be purchased by a utility company.

Arriving in Orkney in July 2010 (see “UK Installs Hub to Test Wave Energy Projects” in the September 2010 issue of POWER), the 750-kW P2-001 machine was successfully installed at the Billia Croo wave test site that October. In May 2012, ScottishPower Renewables, part of wind energy developer Iberdrola, deployed P2-002 at EMEC’s wave test site on an adjacent berth to E.ON’s P2 device. The addition was part of a unique joint working arrangement between the two renewable energy developers to maximize learning from operating and maintaining the machines as a wave farm. After a three-year testing period, E.ON returned ownership of P2-001 to Pelamis Wave Power.

The 750-kW P2 comprises five connected sections, which flex and bend in the waves. This movement is harnessed by hydraulic rams at the joints, which in turn drive electrical generators located inside the device. The device is 180 m long and 4 m in diameter. It weighs approximately 1,350 tons.

Andritz Hydro Hammerfest. In December 2011, the Andritz Hydro Hammerfest (AHH) project successfully deployed its initial 1-MW precommercial tidal turbine at EMEC’s test site (Figure 3). The device delivered its first energy to the national grid in February 2012.

3. Hammer time.
The Andritz Hydro Hammerfest HS1000 project is just one of many tested at EMEC. Courtesy: EMEC

The original HS1000 turbine was based on technology initially developed for the smaller HS300, which was installed in Norway as the first-ever tidal current turbine with a permanent connection to the public grid in 2004. Directly based on experiences from the testing period at EMEC, AHH is in the process of redeploying three commercial-scale 1.5-MW turbines as part of Phase 1A of the MeyGen project in the Pentland Firth.

According to Andritz, each unit has a horizontal-axis rotor equipped with a specially designed variable-speed pitching mechanism and a nacelle yawing system, allowing optimal harnessing of the tidal currents in both flood and ebb directions. Automatic control software governing a sensor-driven monitoring system adjusts the leading edge to capture optimum output from a given tidal stream environment.

Designed for the most taxing marine currents, which the Pentland Firth certainly has, the AHH units are able to handle flows up to and above 5 m/sec. The tidal turbines are deployed on the seabed up to 100 m below the surface and kept in position by gravity, pins, or pilings, depending on the seabed and tidal stream characteristics.

In July, Atlantis Resources Limited—owner and developer of the MeyGen site—provided an operations update for Phase 1A. It said two of the three AHH turbines had been successfully reinstalled and reconnected to the grid after upgrades and servicing. The third AHH turbine was due to be reinstalled during the next workable tide in August, together with an Atlantis developed AR1500 1.5-MW turbine. The company expected MeyGen Phase 1A would be operating autonomously at full 6-MW capacity as early as the end of September.

“We are delighted that we have conducted another successful installation campaign and that we will soon have the array operating autonomously, generating predictable revenue. Both turbines have already operated at or close to full power since redeployment,” said Tim Cornelius, CEO of Atlantis Resources.

The Andritz turbines, built in Ravensburg, Germany, are designed to withstand the constant pounding from tides and waves over a period of 50 years. The average power generation per turbine is expected to be 4.4-GWh per year, according to the company.

The Atlantis Resources unit is also designed to withstand the extreme environmental conditions expected in the Pentland Firth and at its other planned location in the Bay of Fundy in Canada. Designed by Lockheed Martin, the turbine unit also has parts that move independently and is designed for long-term use with minimum maintenance.

The next phase, 1B, is expected to generate a further 6 MW from four more 1.5-MW turbines. Phase 1B is in the final planning stage with all necessary consents and grid connections in place.

Another phase—involving perhaps 86 turbines generating close to 100 MW—could potentially evolve into a third phase producing up to 398 MW, depending on how the turbines interact with each other under the water. From small things, great things can one day come.

Penguin Wave Energy Converter. At the wave test site at Billia Croo, Finnish-developer Wello is testing a 1-MW Penguin wave energy converter (Figure 4). Installed by Green Marine in March 2017, this is the first of three Penguin’s to be deployed as part of a Horizon 2020 funded research and innovation project—Clean Energy from Ocean Waves (CEFOW).

4. Wave technology.
Green Marine installed the Wello Penguin at the EMEC wave test site at Billia Croo. Courtesy: Colin Keldie/CEFOW

SR2000 Tidal Turbine. Currently at EMEC’s Fall of Warness tidal test site, the Orkney-based Scotrenewables Tidal Power is testing its 2-MW 64-m-long SR2000 (Figure 5), which the company boasts is the world’s most powerful floating tidal turbine. In May 2017, the company announced that the SR2000 had generated more than 18 MWh during a continuous 24-hour testing period.

5. Floating tidal equipment.
The SR2000 is touted as the world’s most powerful tidal turbine. It is now being tested at EMEC’s Fall of Warness test site. Courtesy: Scotrenewables Tidal Power

Subsea Power Hub. At the scale test site at Scapa Flow, Aberdeen-based engineering firm EC-OG is testing its Subsea Power Hub. The company’s off-grid solution combines a tidal energy converter with a lithium-based energy storage system.

6. Power hub.
The Subsea Power Hub combines a tidal energy converter with energy storage. Courtesy: EC-OG

U.S. Wave and Tidal Potential

According to the U.S. Bureau of Ocean Energy Management, the Electric Power Research Institute (EPRI) has completed a recent analysis of the U.S. wave energy resource potential. EPRI estimated the total wave energy resource along the outer continental shelf to be 2,640 TWh/yr. That is an enormous potential, considering that just 1 TWh/yr of energy will supply about 93,850 average U.S. homes with power annually.

While an abundance of wave energy is available, it cannot be fully harnessed everywhere for a variety of reasons, such as environmental concerns in sensitive areas and other competing uses of the ocean, including for shipping, commercial fishing, and naval operations. Nonetheless, it was estimated that the total recoverable resource along the U.S. shelf edge was 1,170 TWh/yr, which is almost one third of the 4,000 TWh of electricity used in the U.S. each year.

Lee Buchsbaum (www.lmbphotography.com), a former editor and contributor to Coal Age, Mining, and EnergyBiz, has covered coal, energy and other industrial subjects for nearly 20 years and is a seasoned industrial photographer.

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