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More predictable than the sun or wind as an energy source, the tides hold great promise for renewable energy. As long as the earth turns and the sun and moon exert their pull on the oceans, the regular, reliable force of tidal currents offers huge potential for power generation.
Arcadis, a global infrastructure design and consulting firm, is part of a consortium working to develop an innovative tidal power technology as a dependable and renewable source of energy. Developing tidal power grows out of Arcadis’ extensive global experience in hydraulic engineering, water systems and flood protection in the US, the Netherlands and around the world.
The consortium has received $2.5 million in funding from the Dutch government and $2.5 million from the Chinese government for tidal power feasibility studies so far. The group is currently assessing the viability of building a tidal power facility off China’s east coast that would produce the equivalent of six large coal or gas power stations and provide energy for more than 10 million homes.
Called Dynamic Tidal Power, or DTP, this new method of power generation harnesses the energy in oscillating tidal waves that run parallel along the coasts of continental shelves and contain powerful hydraulic currents, such as are found in China, Korea and the UK. The concept calls for a very long dam to be built perpendicular to the coast in a way that captures the hydraulic force of these currents in turbines built into the dam.
Origins of a new idea
The DTP idea emerged from casual conversations and back-of-the-envelope schematics in which some colleagues and I asked what would happen if a long dam like the Netherlands’ Delta Protection Project could capture the energy of passing tides. Soon, a small group of Dutch hydraulic engineering experts started getting more serious about exploring new ways to use tidal power.
This idea differs from other means of generating power from tidal forces in some significant ways. Existing tidal power programmes depend either on the forces of more extreme tides in a natural or artificial tidal basin, or free turbines mounted in a natural tidal stream.
Dynamic Tidal Power, on the other hand, depends on the forces of tides that flow parallel to the coast across a very long (over 28 km) dam built out perpendicularly to the coast, ending in the sea without closing off a tidal basin. The dam blocks the tides’ horizontal acceleration, creating a force or head. This head can be converted into power using a long series of conventional bi-directional low-head turbines installed in the dam.
The dam may also have a perpendicular barrier at the far end, forming a large T or Y shape. The dam changes the long-wave dynamics of the tide in such a way that the head difference created across the dam is much more than the kinetic energy height of the natural tidal stream. Although the head is relatively small (1-3 metres), the discharge (m3/s) is enormous, leading to high installed power rates.
My colleague and fellow Dutch coastal engineer Kees Hulsbergen and I invented and patented the concept in 1997. According to the team’s research models and feasibility studies, a typical single dam will deliver on the order of 5 GW of installed capacity.
As an example, verified by pump manufacturer Nijhuis Pompen and by Chinese experts using numerical flow model analysis and scale model tests, a turbine area of 50 m2 and a typical tidal water level difference of 2.5 metres will create a substantial flow of 210 m3/s through each turbine.
In this example, each turbine produces 3.6 MW of power. Since the dams in these studies can typically accommodate 1500 turbine units, the result is total installed power per dam of more than 5 GW. With a capacity factor (or load factor) of 30 per cent, and an availability percentage of 90 per cent, this leads to an estimated annual energy production of 12 billion kWh (12 TWh or 43 PJ) per year.
If two dams are installed at the right distance from one another (about 125 miles or 200 km apart) and feed into the same grid, they complement one another, with one dam at full output when the other is not generating power. In this way twin dams can be used for virtually continuous power generation. Because tides are predictable and regular, this technology makes it easier for utilities to manage power generated by the system.
In contrast to existing technologies that close off tidal areas with strong tidal currents, the DTP dam’s perpendicular design offers the key environmental advantage of not interfering with the tidal currents in and out of a tidal basin. As a result, the DTP design is expected to have less of an impact on the ecology of the basin and, in some cases such as the Bohai Sea in China, it may even improve water quality thanks to deliberately intensified circulation patterns. In addition, the design, with the dam running out to sea, does not have the dredging requirements of structures built close to shore.
Because Dynamic Tidal Power does not require a very large vertical range between low and high tide (which limits conventional tidal facilities to specific areas like the Bay of Fundy in Canada), DTP has greater potential in areas with modest natural tidal ranges, as long as the tides run parallel to the shore. The most promising sites are in Korea, China and the UK – areas with great demand for renewable energy sources.
Development in China
China, with its huge and ever-growing power demand, actively explores a range of renewable energy sources to reduce its dependence on imported fossil fuels and to help cut air pollution.
Overall, the total amount of theoretically available potential DTP power in China is estimated at a significant 80-150 GW. This total DTP potential capacity in China equals half the total river hydropower installed in China, the country with by far the largest installed hydropower capacity of the world. This includes the world’s largest dam, the Three Gorges Dam in the Yangtze River, with an installed capacity of 22.5 GW.
Early studies show that a large DTP dam along the Chinese coast has the potential to produce 5000 MW or more of installed capacity, placing it among the world’s largest hydropower projects.
In August 2012, China’s National Energy Administration formed a group of top Chinese power companies, design institutes and universities to carry out joint studies of Dynamic Tidal Power. The group signed an agreement with the Dutch consortium including Arcadis in Beijing in 2012. The programme’s targets have been registered under the United Nations’ Sustainable Energy for All initiative. The UN Industrial Development Organization (UNIDO) is also involved in the initiative.
The three-year development plan for Dynamic Tidal Power in China started with a feasibility study divided into three phases. Phase 1, proof of principle, was completed mid-2011. Phase 2 involved selection and initial feasibility studies of suitable locations in 2012; and phase 3 consisted of a detailed feasibility study of the most suitable location in 2014, to be continued into 2015. The feasibility studies cover diverse topics such as design and multiple functions of a tidal energy dam, economic costs and benefits, social and environmental impacts and mitigation measures, power generation and conversion to the grid.
At 30 months into the 36-month study period, the team began focusing on two locations in China. Since according to China’s Second Institute of Oceanography (SIO) a so-called “southern dam” experiences the most powerful tides, probably has better seabed conditions and can contain long arrays of turbine/generator units, the team built a higher-resolution numerical tidal model to study this location further. They are now analyzing a geological survey using ultrasound, which provides information about the sea depth and top sediment layer. The next step of the geologic survey is to drill bottom cores at the site of this dam.
Based on a preliminary assessment, the “southern dam” will accommodate 10 GW of generating capacity, with 3000 turbine units installed, capable of producing 3.5 MW each. At the same time, partner company Pentair Nijhuis has successfully produced and independently tested a physical scale model of a fish-friendly bi-directional ultra-low-head turbine. This design, with a proven efficiency of over 85 per cent, would enable the DTP installation to capture the power of both incoming and outgoing tides without harming the local fish population.
Challenges for DTP development
Now that testing has proven the basic concept – that is, a dam that can generate a significant head and ultra-low head turbines that can be made to operate efficiently under such head conditions – the partners are addressing the more specific challenges underpinning the need for a large-scale dam and the costs involved in building this type of development.
Since a DTP dam needs to be built on such a large scale to be economically viable, local authorities and investors need to see government support before moving forward with a project. The development team is optimizing the results of the technical and feasibility studies to provide the data the government leaders need for evaluation and decision-making.
The Chinese government has committed to the research for this technology and the partners are now building both the business case and the technical information needed to support continued investment. The economic assessment is making good progress. A large technical seminar took place in April this year in Hangzhou, followed by a smaller meeting to discuss turbine testing results in July. Progress on the joint development was presented in November, parallel to a meeting between Chinese and Dutch researchers at the Tidal Summit in London.
Working with Chinese partners, the team will continue the development of a Chinese DTP in the coming years. Co-operation from Chinese experts has enabled us to make great strides. The European Commission is investing heavily in the development of innovative technologies under its new Horizon 2020 programme. The DTP team is in close communication with Europe’s leaders to start similar R&D paths like those followed in China.
As the team continues to develop the potential of this innovative source of tidal power in Korea, the UK and Ireland, we need to keep in mind that this is a big idea on every level. Dynamic Tidal Power is huge in scale, electric output, investment and spatial interference and often goes beyond a person’s imagination. But already the research has spun off important advancements in science (tidal movement and hydraulic head in unsteady flow), technology (low-head turbines), and socioeconomic benefits (like governance issues). This alone is enormous and already worth the journey.
DTP, based on acceleration in an oscillating tidal flow, harnesses a power in nature that was not recognized before. More research on its potential is worth exploring further, to help humankind understand whether this source can satisfy our energy demand in an environmentally and socioeconomically acceptable way.
Rob Steijn is a civil engineer specializing in river and coastal morphodynamics. He is Director for River, Coast & Sea at Arcadis.
- High power output. It is estimated that some of the largest dams could accommodate over 15 GW of installed capacity. One DTP dam could supply energy for millions of households.
- Stable power. The generation of tidal power is highly predictable due to the deterministic nature of tides, and independent of weather conditions or climate change.
- High availability. DTP doesn’t require a very high natural tidal range, but instead an open coast where the tidal propagation is alongshore. The potential availability of DTP is very high.
- Potential for combined functions. The long dam can be combined with various other functions: coastal protection, LNG ports, aquaculture, land reclamation and connections between islands and mainland.
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