The tidal power revolution has long been promised: a renewable form of energy that produces few greenhouse gas emissions and provides excellent energy security, but which can also be guaranteed to operate without interruption. Yet despite the development of the 240MW La Rance plant in 1966, the cost of generating electricity from tidal power has not come down and it remains a long term aspiration rather than an essential element in the generation mix. However, the world’s biggest tidal scheme is now being developed in South Korea, which means that enthusiasm for tidal power will again be rekindled.

South Korea has long relied heavily on gas imports to provide power sector and industrial feedstock. The country has virtually no oil, gas or coal reserves of its own and so has had to rely on imports to provide almost all of its energy needs. On the grounds of energy security, the government encouraged the development of nuclear reactors in the 1970s and the state owned Korea Hydro & Nuclear Power Company (KHNP) today operates 20 reactors with combined generating capacity of 16,840MW.

The state power company, Korea Electric Power Corporation (Kepco), which owns KHNP and which is currently undergoing a process of unbundling in preparation for selective privatisation, expects to increasingly rely on nuclear power as a result of government fears about high oil and gas import costs and supply security. It is predicted that the combined generating capacity of all of Kepco’s offshoots will reach 79GW by 2015, including 26,000MW from nuclear, 21,200MW from coal fired facilities and 18,900MW from gas fired plants.

However, the government is keen to boost the proportion of capacity that does not rely on foreign feedstock. The hydroelectric sector contributes just 1% of national energy consumption and there are few economically feasible hydro sites available to provide new generating capacity, so new hydro schemes do not appear to be an option. As a result, Seoul hopes to create a sizeable renewable energy sector from a virtual standing start. Solar and tidal power are the most favoured alternatives, and the government hopes that South Korea can become a technological leader in both fields.

As in Japan, the South Korean economy has been founded on importing foreign technology and then improving it. The first nuclear reactors were designed, manufactured and supplied by European and North American companies but Kepco signed a technology transfer and training deal with US firm Combustion Engineering in 1987. KHNP gradually introduced its own technology and by 1998 reactors were being commissioned using purely South Korean technology. It is hoped that a similar process can take place in the tidal sector. Denmark and Germany have built up sizeable industries exporting wind power technology and parts and Seoul believes that the time is ripe for it to adopt a similar role regarding tidal technology.

In order to encourage the development of tidal power and other renewable energy schemes, the South Korean government has introduced a target of boosting the proportion of renewable energy in the generation mix to 5% by 2011. This may not seem particularly impressive on paper, particularly as the UK and some other European states have set a goal of 20% and even China aims for 10% by roughly the same date, but the current proportion in South Korea is just 1.4%, so this will require a rapid increase in just five years.

The Sihwa power plant

With government backing, state owned Korea Water Resources Corporation (KWRC) is developing the 254MW Sihwa tidal power plant at Sihwa lake on Inchon bay. Funding of about US$250M is being provided by the government’s new renewable energy fund and KOWACO but environmental as well as energy considerations have driven the development of the project. A 12.4km sea wall separating the lake from the sea was built between 1987 and 1994 but pollution has become an increasing problem on the lake.

Large volumes of industrial waste are discharged into the lake and so it is hoped that the tidal power scheme will improve water quality through the movement of 60B tonnes of sea water a year. The process should help to disperse the pollution but South Korean environmental groups have attacked the venture on the grounds that industrial waste will be carried into the sea. They fear that it will affect sea life in the area and argue that the process will not encourage the producers of the industrial waste to reduce their emissions.

Daewoo Engineering & Construction was awarded the main engineering contract on the project and VA Tech Hydro secured a US$95.3M contract to design the turbine and generator equipment and to provide the main electromechanical components on the scheme. The power plant, which is located close to Ansan city in Gyeonggi province, is expected to come on stream in 2009.

Tidal power schemes that can make use of the movement of water in both directions produce more electricity but still face more technical problems than those with fixed turbines. As a result, electricity will be generated on Sihwa lake when the water moves from the sea to the lake only. A VA Tech Hydro spokesperson revealed that ten bulb type 25.4MW turbines will be installed along the sea wall, powered by the movement of water between the sea and the lake, ‘using the head between the high tide and reservoir levels’.

One of the main problems facing KWRC, Daewoo and VA Tech Hydro was the fact that almost all other commercial tidal power projects around the world are far smaller than the Sihwa scheme. As a result, almost all of the project’s components have been custom made for use on the scheme. However, the experience of developing the plant could be put to use on other similar projects in the future.

Sihwa will have 14MW generating capacity more than the French La Rance facility. It will also produce more electricity, with output estimated at 254,000kWh or 552GWh per year. This should be sufficient to supply the entire electricity needs of Ansan city, which has a population of about 500,000. Kim Jin-oh, the deputy director of the Korea Energy Economics Institute, said: ‘With the construction cost of the Sihwa tidal power plant, you could build a 340,000kW coal thermoelectric power plant, a 450,000kW diesel thermoelectric power plant, and a 670,000kW LNG thermoelectric power plant. But a tidal power plant has the merit of no additional fuel costs.’

Government funding has also enabled the development of other tidal power test and experimental facilities in South Korea. For instance, the Ministry of Maritime Affairs and Fisheries (MMAF) is backing an experimental hydraulic turbine at a sea bottleneck at Uldol-mok in Jeonnam province. MMAF has drawn up plans to develop a 1MW wave power hydraulic turbine at the site from 2007 to test the feasibility of a larger scale scheme. Water flows through the 300m wide bottleneck at a speed of up to 6.5m/sec. KWRC is considering carrying out feasibility studies on other likely tidal projects.

Pros and cons

The attractiveness of tidal energy compared to other forms of electricity generation is that it can be guaranteed. A lack of sunshine or wind makes solar and wind power unreliable for core energy use unless and until economically and scientifically viable electricity storage is developed, but tides are more reliable. However, tides run according to the lunar clock, while demand for electricity is generally set by the sun. Consumption peaks during certain times of the day and year, whereas electricity is produced by tidal power plants at varying times of the day. As part of a wide generation mix this should not be a problem but could prevent tidal power ever becoming the mainstay of any country’s generation stock.

The great stumbling block with regards to promoting tidal power schemes is the relatively high cost of the electricity produced. Even European governments that are keen to encourage renewable energy schemes have found wind power more economically viable than tidal and most other forms of electricity. However, KWRC in South Korea believes that electricity will be generated at Sihwa at a cost of about 100 won ($0.08) per kW, which is slightly cheaper than the existing wind farms in South Korea.

Supporters of tidal energy are keen to promote the possibility that tidal plants could become a staple of generating capacity in all countries with access to the sea. At the Energy Ocean 2006 Conference in San Diego, US, speakers argued that the world’s total current demand for electricity would be satisfied by just 0.2% of available tidal, wave and marine current energy. However, the vast bulk of available ocean based energy is not located in easily accessible places and all forms of ocean energy are far more expensive than thermal power plants.

Investment in ocean based power generation needs to be stepped up if generation costs are to be reduced to politically acceptable levels. Wind energy is currently favoured in the UK, Germany, Denmark and other European states precisely because production costs have fallen. While renewable sources of energy comprise only part of the generation mix and their production costs per unit of electricity are only 20-40% higher than more conventional forms of power generation, such as nuclear and thermal plants, then the impact on overall electricity tariffs is minimal.

The challenge for tidal power is to reduce its costs to a similar level. MMAF in South Korea may calculate that electricity at Sihwa will be cheaper than power from wind farms but this is not generally accepted. Development costs at Sihwa are being divided between environmental protection and power generation, a factor which is not likely to be shared by other comparable schemes. In addition, South Korea is not as well furnished with wind suitable for power production as northwest Europe.

Nevertheless, tidal power production costs have remained so high precisely because so few commercial schemes have been developed. As with all other forms of renewable energy, increased investment will yield technological advances, which in turn will help to lower costs. The South Korean government’s decision to place tidal power at the heart of its renewable energy strategy and its plan to turn the country into a centre of renewable energy research and development indicates that enthusiasm for tidal power is once again on the rise.

There are other examples of new tidal energy investment around the world. China’s first ever tidal power plant was brought on stream in Zhejiang province in January. With generating capacity of just 40kW, the project is largely experimental in focus and was developed by Harbin Engineering University and Daishan Technology Bureau. A second 150kW Chinese project has secured funding from the United Nations Industrial Development Organization (UNIDO) and a raft of other ventures are being considered, as part of the Chinese government’s new found enthusiasm for renewable energy.

The Yalu river tidal project is particularly ambitious. British firm Tidal Electric is currently carrying out a feasibility study into the venture and the proposed 300MW generating capacity would outstrip even the South Korean Sihwa scheme. It is hoped that locating the scheme 1km offshore will avoid many of the environmental problems encountered by existing tidal power projects, most of which employ tidal barrage technology.

Another UK company, Neptune Power, is assessing a prototype turbine for use in the Cook Strait, between the North and South islands of New Zealand. Up to 7000 turbines could eventually be employed at the site over 200km2 of maritime territory. Electricity production costs are estimated at 7 US cents per kWh, which is low by the standards of tidal energy. In neighbouring Australia, Tidal Energy Australia is assessing the feasibility of two sites in western Australia. The company’s previous attempt to develop a tidal project in the area failed on financial grounds but its efforts have now secured political support.

A report by energy analysts Douglas Westwood last year concluded that US$13.6B would be spent on all forms of ‘marine renewable energy projects’ between 2005 and 2010, mainly in Europe. The Refocus Marine Renewable Energy Report assessed all projects under development and argued that around 7770MW of new generating capacity would be brought on stream over that period. Most of this new capacity would be provided by offshore wind farms, but the report added that tidal was also finally taking off.

With regard to tidal power, the author of the report, Adam Westwood, said: ‘The first orders for multiple unit farms are now being placed with the developers of market leading technologies. By 2007 annual installations could exceed 10MW per year – a small beginning but a very real achievement. Waves and tidal currents contain massive amounts of energy and the prize awaiting a commercially successful technology is considerable. The UK is strong in the wave and tidal sectors, having both an excellent natural resource coupled with a portfolio of successful technologies.’

Westwood continued: ‘Portugal and Spain are both important players, and government support is strong with a 12-year index linked tariff available to developers. This market-leading incentive is attracting the interest of many developers who view the country as ideal for future projects. Australia is also in the running, being home to some excellent wave energy technology.’

There have also been a string of potentially important technological advances in recent years. Irish firm OpenHydro is developing turbines that it insists will account for 6% of Ireland’s generating capacity within five years. A research team at Oregon State University in the US has developed a buoy that can convert wave power into electricity. A single prototype buoy has generating capacity of 250kW. In the longer term, projects that employ vortex induced vibrations (VIV), through an oscillating wing or other means, could overcome many environmental objections to tidal projects, as VIV technology converts the energy of flowing water into electricity without affecting the flow.

If enthusiasm to reduce greenhouse gas emissions continues to rise, then tidal power and other forms of sea energy could eventually become the preferred form of renewable energy. While production costs will always be an issue, their inability to provide reliable electricity will prevent wind and solar schemes from becoming the mainstay of any generation mix. Turning the huge potential of all forms of sea based electricity production into economic reality is the big challenge – but it is a challenge being attempted by increasing numbers of scientists.