The Sihwa tidal power plant is being developed as part of Korea’s drive to increase the share of renewable energy in its fuel mix. At 260 MW, Sihwa will be the largest power plant of its kind in the world, and will bring a number of socio-environmental benefits to the Lake Sihwa area.

Harald Schmid, VA Tech Hydro GmbH & Co., Linz, Austria

The world’s oceans are a potential source of enormous amounts of pollution-free energy that could be harnessed to meet increasing global energy demand. Oceans hold 97 per cent of all water resources and cover more than 70 per cent of the surface of the earth.

The tides are generated by the rotation of the earth within the gravitational fields of the moon and sun. The relative motions of these planets cause the surface of the oceans to be raised and lowered periodically. On most shorelines the tides go in and out twice a day, and energy can be captured from this movement with tidal power stations. A tidal power station can stretch over a delta, estuary, or beach, but energy is most easily harnessed where there is an estuary.

Figure 1. Sihwa will be the world’s largest tidal power plant, and the first plant of its kind in Korea
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The best sites for tidal power plants are those with big tidal ranges and a narrow estuary. Tidal barrages can provide protection against coastal flooding during very high tides by acting as storm surge barriers. Especially at large sites, the presence of a road across the dam is a major benefit.

The most noticeable benefit of tidal power plants is that they do not generate emissions. Like most renewable sources of energy, tidal energy displaces fossil fuels and reduces CO2 in the atmosphere.

Costs and benefits

While hydropower stations can operate around the clock, tidal power stations can only produce electricity during a short period of the day, provided that the water quantity and the tidal ranges are sufficient.

The cost of tidal power systems varies depending on the biological, geographical and geological features of the site. Generally speaking, rather high capital costs and long construction periods have prevented the construction of large tidal schemes. Only very large tidal power plants requiring a high investment volume will operate economically.

The major factors determining the cost effectiveness of a tidal power site are the size of the barrage required, and the difference in height between high and low tides. Although the initial cost of a tidal power plant is relatively high compared with other types of power plants, the benefits include low operating and maintenance costs, since no fuel is needed.

Tidal power generation has some additional advantages, including improved transportation due to the development of traffic or rail bridges across estuaries and reduced greenhouse gas emissions by utilizing non-polluting tidal power in place of fossil fuels.

One tidal project that will illustrate such benefits is the Sihwa tidal power plant, which is being constructed by Daewoo Engineering and Construction on Sihwa Lake in South Korea. This 260 MW, $250 million project is the first of its kind in the country and is expected to play a big role in improving the water quality of Lake Sihwa.

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Other benefits that this project will bring to Korea include the restoration of the Lake Sihwa ecosystem and water quality, local economic activation due to new tourist attractions, reduction of crude oil imports, and a reduction in emissions.

Renewable goals

Korea started its industrial development in the 1970s, focusing on energy-intensive heavy and chemical industries, including steel, chemicals, shipbuilding and cement. Korea is very much dependent on energy imports and as well as trying to secure supplies from elsewhere, for example gas from Russia, it is also developing a positive attitude towards renewables and energy efficiency.

Korea is the world’s fourth largest oil importer and is trying to diversify energy sources to increase security, meet rising energy demand and meet greenhouse gas emission reduction targets. It plans to increase spending on alternative energy sources and wants to increase the share of alternative energy in its fuel mix from 1.4 per cent to 5 per cent by 2011. Korea imports 2.5 million barrels of oil per day, representing a small proportion of its needs. The country is mainly targeting solar and wind projects in order to increase the share of renewables. In addition, Korea has been closely examining the potential for tidal power projects around its shores.

Korea ratified the Kyoto Protocol in 2002 and is looking to explore ways to carry out AIJ (Activities Implemented Jointly) and CDM (Clean Development Mechanism) projects.

The Korea Water Resources Corporation (Kowaco) is the governmental water authority of Korea and is responsible for irrigation, water supply and waste water. Kowaco is dedicated to fulfilling its role in improving the quality of life of Koreans and in supporting the national economic development.

Lake Sihwa

Lake Sihwa is located in the mid-west of the Korean Peninsula in Gyeonggi province, bordering the West Sea at the Lake Sihwa Dam around 4 km from the city of Siheung.

The lake was created by constructing a dam in 1994 to secure agricultural water for the region, for developing industrial/agricultural lands near the metropolitan area and to secure irrigation water.

Besides the 56.5 km2 freshwater lake (one of the largest tidal lakes in Korea), reclaimed land of 173 km2 and 330 million m3 volume was also created.

Due to the cut-off of tidal currents and the rapid increase of population and industrial waste loads from factories in the neighbourhood, the water quality of Lake Sihwa has deteriorated over the years since the construction of the dam. The water pollution is largely due to the lack of fresh water and disposal of sewage from nearby factories. The pollution situation is now considered to be severe and a solution is urgently required.

Because of rapid socio-environmental changes and the lowering of water quality in Lake Sihwa, it was decided that there was no choice but to open the lake to sea water. The dam will therefore be opened up allowing tidal flow into the lake, and the Sihwa tidal power plant will be built to harness the energy of the tides.

Plant design

The Sihwa tidal power plant is designed as a flood generating system. Flood generating systems generate power from the incoming tide i.e. from the sea to a basin. When the high tide comes in, water flows through the turbines to create electricity. Separate gates beside the turbines are designed to open during the ebb phase. When low tide comes, the gates are raised and the water flows out. The turbines operate in sluicing mode during the ebb phase and no energy is produced.

The Sihwa tidal power plant project is the first of its kind in Korea. The plan is to open the existing dam to allow the circulation and exchange of water between the Lake Sihwa and the sea. The tidal plant will improve the lake by circulating 60 billion tonnes of seawater annually.

Figure 2. Opening up the dam will allow sea water to circulate around Lake Sihwa. Plant operation is scheduled to start in 2009
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The Sihwa tidal power plant will generate power from the incoming tide, taking advantage of the differing tide water levels between the sea and the artificial lake. Kowaco, as the project developer/owner, will implement the tidal power plant with a total turbine output of 260 MW and an annual power generation of 543 GWh.

The Sihwa tidal power plant consists of powerhouses for ten bulb type turbines and with direct driven generators including gates and other equipment. Each unit has a capacity of 26 MW, a runner diameter of 7.5 m, speed of 64.29 r/min and operates under a rated head of 5.82 m.

The dewatering of the basin will be accomplished with eight new gates and the existing gates plus all turbines in reverse sluicing mode. The total project cost will be around $250 million.

Competitive bids

The project was a strictly domestic bidding project with civil engineering companies as lead companies and suppliers and engineering companies as sub-contractors. Three groups bid for the project. Leaders of these groups were Korean civil companies with internal engagements with equipment suppliers and engineering companies.

The Daewoo Construction Consortium with Daewoo Engineering and Construction Co., Ltd. as leader participated in and won the bidding with Saman Engineering Consultant Co., Ltd. Kowaco awarded the contract.

Kowaco selected from the bidders according to the evaluation criteria: price (35 per cent), technical concept (45 per cent) and references (20 per cent). It announced Daewoo as the preferred bidder, which has to perform the detailed design before being awarded with the project. In the bidding, Daewoo presented a price which was higher than its competitor, Hyundai Construction Consortium.

As Daewoo’s sub-contractor, VA Tech Hydro will be responsible for certain supplies and services with respect to the electro-mechanical portion. VA Tech Hydro will act as the technology provider for the Sihwa tidal power plant project and carry out the detailed design for the turbine/generator equipment. Additionally, VA Tech Hydro will supply all the major equipment for the turbines and generators, while Daewoo will supply non-core components for the plant.

The delivery of VA Tech Hydro will include the turbine runners, the turbine shaft seals, bearings and oil heads, the wicket gates, stator cores and windings, rotor poles, combined bearings, excitation, protection, and the SCADA system. The first deliveries of electro mechanical equipment will commence at the beginning of 2007.

Since the installation of the tidal plant will be accomplished in a staggered mode and there is not much storage space available at the site, the electro mechanical parts and components have to be delivered on time.

Figure 3. VA Tech Hydro will act as the technology provider for the Sihwa tidal power plant project and carry out the detailed design for the turbine/generator equipment
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In addition, VA Tech Hydro will supply a comprehensive services package that includes supervision of manufacturing for parts to be delivered by Daewoo, supervision of preassembly and installation, supervision of commissioning and a training package for the operators.

The contract value for VA Tech Hydro amounts to approximately €75 million ($93 million). Due to environmental reasons the project is of extreme urgency and the Sihwa tidal power plant is scheduled to be completed by 2009.

Project team

A team of specialists from Daewoo, Sam-An Engineering and VA Tech Hydro worked out the technical and commercial issues and finally succeeded by signing the contract documents.

The Sihwa tidal power plant opens up a new chapter in the domestic renewable energy development in South Korea. It will reduce oil imports by approximately 860 000 barrels ($43 million) as well as make a great contribution to the water quality improvement of Lake Sihwa through the continuing circulation of sea water.

With the enhancements planned around Lake Sihwa the quality of life of Koreans will be improved and the national economic development will be supported. With this award, VA Tech Hydro takes an important position in the realization of the world’s largest tidal power plant.

VA Tech Hydro is planning to continue its efforts to participate in the construction of further large hydro power plants and its involvement in similar projects. There are investigations for several large scale projects on the western shorelines of the Korean peninsula and prospective sites have been targeted for tidal power development.

Tidal power: past, present and future

Tidal power plants were invented in the early 1900s. At that time only one tidal direction was utilized. Tidal mills were built in the 18th century when their major competition were windmills and water wheels. The tidal mills disappeared with the invention of cheap steam engines. Rather few tidal plants have been built so far. The important reference plants are:

La Rance: The first and largest tidal plant in operation is the 240 MW plant built for commercial production across the La Rance estuary in north-western France between 1961 and 1967. A 75 m dam (including sluices, powerhouse, ship lock and embankment) encloses a 17 km2 basin. The tidal power plant has 24 bulb-type Kaplan turbines with a rated capacity of 10 MW each.

Annapolis: The second commercially operated tidal power plant in the Western hemisphere is a 18 MW plant at Annapolis Royal on the Nova Scotia coast of the Bay of Fundy in Canada. Built in 1984, the project utilises an existing flood control dam with a 7.8 m diameter Straflo turbine.

Other sites: Other plants include the 400 kW experimental unit at Kislaya Guna, built in 1968 in Russia on the Barents Sea, and the 3.4 MW Jianxia station built in China between 1980 and 1986. Most of the technically available tidal resources in Europe are in the UK. The site in the Severn estuary in south-western England represents a potential of 8 GW and has been the object of several feasibility studies. Large potential also exists in northern France, at the Cotentin Peninsula in Normandy.

There are several other possible sites, in Argentina, Chile, Australia, Canada, China, India, Korea and Russia, with a tidal range between 4.8 and 11.5 m. Many of these sites are remote from centres of demand and therefore, although representing very substantial resources at rational equipment cost, stand little chance of development at present.