Misplaced Pages

#898101

42-410: The tidal barrage makes use of a seawall constructed in 1994 for flood mitigation and agricultural purposes. Ten 25.4 MW submerged bulb turbines are driven in an unpumped flood generation scheme; power is generated on tidal inflows only, and the outflow is sluiced away, i.e. as one-way power generation. This slightly unconventional and relatively inefficient approach has been chosen to balance

84-399: A bay or river due to tidal forces. Instead of damming water on one side like a conventional dam , a tidal barrage allows water to flow into a bay or river during high tide , and releases the water during low tide . This is done by measuring the tidal flow and controlling the sluice gates at key times of the tidal cycle. Turbines are placed at these sluices to capture the energy as

126-487: A barrage is dependent on the volume of water. The potential energy contained in a volume of water is: where: The factor half is due to the fact, that as the basin flows empty through the turbines, the hydraulic head over the dam reduces. The maximum head is only available at the moment of low water, assuming the high water level is still present in the basin. Assumptions: Mass of the sea water = volume of sea water × density of sea water Potential energy content of

168-603: A basin where it is not sealed by caissons. The sluice gates applicable to tidal power are the flap gate, vertical rising gate, radial gate, and rising sector. Only a few such plants exist. The first was the Rance Tidal Power Station , on the Rance river , in France, which has been operating since 1966 and generates 240MW. A larger 254MW plant began operation at Sihwa Lake , Korea, in 2011. Smaller plants include

210-471: A complex mix of existing land use, water use, conservation, environmental and power generation considerations. The station's mean operating tidal range is 5.6 m (18 ft), with a spring tidal range of 7.8 m (26 ft). The working basin area was originally intended to be 43 km (17 sq mi) and has been reduced by land reclamation and freshwater dykes to 30 km (12 sq mi), likely to be reduced further. The power station

252-534: A small fraction of fish only. Research in sonic guidance of fish is ongoing. The Open-Centre turbine reduces this problem allowing fish to pass through the open centre of the turbine. Recently a run of the river type turbine has been developed in France. This is a very large slow rotating Kaplan-type turbine mounted on an angle. Testing for fish mortality has indicated fish mortality figures to be less than 5%. This concept also seems very suitable for adaption to marine current/tidal turbines. The energy available from

294-555: A tidal power plant was made at Aber Wrac'h in the Finistère in 1925, but due to insufficient finance, it was abandoned in 1930. Plans for this plant served as the draft for follow-on work. Use of tidal energy is not an entirely new concept, since tidal mills have long existed in areas exposed to tides , particularly along the Rance . The idea of constructing a tidal power plant on the Rance dates to Gerard Boisnoer in 1921. The site

336-478: A very low running cost. As a result, a tidal power scheme may not produce returns for many years, and investors may be reluctant to participate in such projects. It reportedly took around 20 years to recoup the $ 100m costs of building the Rance Tidal Power Plant. As of 2024 , it has been operating for 60 years with the cost of tidal power lower than nuclear or solar, so it has more than paid back

378-632: Is also possible to generate almost continuously. In normal estuarine situations, however, two-basin schemes are very expensive to construct due to the cost of the extra length of barrage. There are some favourable geographies, however, which are well suited to this type of scheme. Tidal pools are independent enclosing barrages built on high level tidal estuary land that trap the high water and release it to generate power, single pool, around 3.3 W/m . Two lagoons operating at different time intervals can guarantee continuous power output, around 4.5 W/m . Enhanced pumped storage tidal series of lagoons raises

420-476: Is raised 2 ft (61 cm) by pumping on a high tide of 10 ft (3 m), this will have been raised by 12 ft (3.7 m) at low tide. Another form of energy barrage configuration is that of the dual basin type. With two basins, one is filled at high tide and the other is emptied at low tide. Turbines are placed between the basins. Two-basin schemes offer advantages over normal schemes in that generation time can be adjusted with high flexibility and it

462-894: The Annapolis Royal Generating Station on the Bay of Fundy , and another across a tiny inlet in Kislaya Guba , Russia . A number of proposals have been considered for a barrage across the River Severn , from Brean Down in England to Lavernock Point near Cardiff in Wales . Barrage systems are dependent on high civil infrastructure costs associated with what is in effect a dam being placed across estuarine systems. As people have become more aware of environmental issues, they have opposed barrages because of

SECTION 10

#1732773132899

504-461: The capacity factor is approximately 24%. The turbines are "bulb" Kaplan turbines , of nominal power 10 MW; their diameter is 5.35 m, each has 4 blades, their nominal rotation speed is 93.75  rpm and their maximal speed 240 rpm. Half of the turbines were built from martensitic stainless steel , the other half from aluminium bronze . The plant is equipped with cathodic protection against corrosion . It supplies 0.12% of

546-425: The power demand of France . The power density is of the order of 2.6 kW/m . The cost of electricity production is estimated at € 0.12/kWh. The barrage is 750 m (2,461 ft) long, from Brebis point in the west to Briantais point in the east. The power plant portion of the dam is 332.5 m (1,091 ft) long and the tidal basin measures 22.5 km (9 sq mi). An early attempt to build

588-558: The La Rance to pay for itself. In spite of the high development cost of the project, the costs have now been recovered, and electricity production costs are lower than that of nuclear power generation (1.8 ¢/kWh versus 2.5 ¢/kWh for nuclear). However, the capacity factor of the plant is 28%, lower than 85–90% for nuclear power. The barrage has caused progressive silting of the Rance ecosystem. Sand-eels and plaice have disappeared, though sea bass and cuttlefish have returned to

630-407: The abandoned space, which caused a shift in diversity. Also as a result of the construction, sandbanks disappeared, the beach of St. Servan was badly damaged and high-speed currents have developed near sluices, which are water channels controlled by gates. Turbidity (the amount of matter in suspension in the water) decreases as a result of smaller volume of water being exchanged between the basin and

672-414: The adverse effects associated with changing a large ecosystem that is habitat for many varieties of species. The basin is filled through the sluices until high tide. Then the sluice gates are closed. (At this stage there may be "Pumping" to raise the level further). The turbine gates are kept closed until the sea level falls, in order to create sufficient head across the barrage. The gates are opened so that

714-562: The available power varies with the square of the tidal range, a barrage is best placed in a location with very high-amplitude tides. Suitable locations are found in Russia, the US, Canada, Australia, Korea, and the UK. Amplitudes of up to 17 m (56 ft) occur for example in the Bay of Fundy , where tidal resonance amplifies the tidal range. Tidal barrage power schemes have a high capital cost and

756-528: The construction costs. Governments may be able to finance tidal barrage power, but many are unwilling to do so also due to the lag time before investment return and the high irreversible commitment. For example, the energy policy of the United Kingdom recognizes the role of tidal energy and expresses the need for local councils to understand the broader national goals of renewable energy in approving tidal projects. The UK government itself appreciates

798-498: The ecosystem. "Tidal Lagoons" do not suffer from this problem. Estuaries often have high volume of sediments moving through them, from the rivers to the sea. The introduction of a barrage into an estuary may result in sediment accumulation within the barrage, affecting the ecosystem and also the operation of the barrage. Fish may move through sluices safely, but when these are closed, fish will seek out turbines and attempt to swim through them. Also, some fish will be unable to escape

840-411: The energy potential, instead of enhancing it as in ebb generation. Of course this is not a problem with the "lagoon" model, without river inflow.. Turbines are able to be powered in reverse by excess energy in the grid to increase the water level in the basin at high tide (for ebb generation). Much of this energy is returned during generation, because power output is strongly related to the head. If water

882-609: The environment. The main environmental impact of turbines is their impact on fish. If the turbines are moving slowly enough, such as low velocities of 25–50 rpm, fish kill is minimalized and silt and other nutrients are able to flow through the structures. For example, a 20 kW tidal turbine prototype built in the St. Lawrence Seaway in 1983 reported no fish kills. Tidal fences block off channels, which makes it difficult for fish and wildlife to migrate through those channels. In order to reduce fish kill, fences could be engineered so that

SECTION 20

#1732773132899

924-493: The estuary basin, bay, or river. These systems are similar to a hydro dam that produces static head or pressure head (a height of water pressure). When the water level outside of the basin or lagoon changes relative to the water level inside, the turbines are able to produce power. The basic elements of a barrage are caissons , embankments, sluices , turbines , and ship locks . Sluices, turbines, and ship locks are housed in caissons (very large concrete blocks). Embankments seal

966-456: The mouths of estuaries pose similar environmental threats as large dams. The construction of large tidal plants alters the flow of saltwater in and out of estuaries, which changes the hydrology and salinity and could possibly harm marine mammals that use the estuaries as their habitat. The La Rance plant, off the Brittany coast of northern France, was the first and largest tidal barrage plant in

1008-498: The river. By definition, tides still flow in the estuary and the operator, EDF , endeavours to adjust their level to minimize the biological impact. A tourist facility at the dam is open to visitors. The facility attracted approximately 40,000 visitors in 2011. A lock for navigation at the west end of the dam allows the passage of 1,600-tonne vessels between the English Channel and the Rance . Departmental road 168 crosses

1050-454: The sea. This lets light from the Sun penetrate the water further, improving conditions for the phytoplankton . The changes propagate up the food chain , causing a general change in the ecosystem . Tidal fences and turbines, if constructed properly, pose less environmental threats than tidal barrages. Tidal fences and turbines, like tidal stream generators , rely entirely on the kinetic motion of

1092-426: The spaces between the caisson wall and the rotor foil are large enough to allow fish to pass through. Larger marine mammals such as seals or dolphins can be protected from the turbines by fences or a sonar sensor auto-braking system that automatically shuts the turbines down when marine mammals are detected. As a result of less water exchange with the sea, the average salinity inside the basin decreases, also affecting

1134-544: The technical viability and siting options available, but has failed to provide meaningful incentives to move these goals forward. Rance Tidal Power Station The Rance Tidal Power Station is a tidal power station located on the estuary of the Rance River in Brittany , France. Opened in 1966 as the world's first tidal power station, the 240- megawatt (MW) facility was the largest such power station in

1176-409: The tidal currents and do not use dams or barrages to block channels or estuarine mouths. Unlike barrages, tidal fences do not interrupt fish migration or alter hydrology , thus these options offer energy generating capacity without dire environmental impacts. Tidal fences and turbines can have varying environmental impacts depending on whether or not fences and turbines are constructed with regard to

1218-435: The turbines generate until the head is again low. Then the sluices are opened, turbines disconnected and the basin is filled again. The cycle repeats with the tides. Ebb generation (also known as outflow generation) takes its name because generation occurs as the tide changes tidal direction. The basin is filled through the turbines, which generate at tide flood. This is generally much less efficient than ebb generation, because

1260-423: The volume contained in the upper half of the basin (which is where ebb generation operates) is greater than the volume of the lower half (filled first during flood generation). Therefore, the available level difference – important for the turbine power produced – between the basin side and the sea side of the barrage, reduces more quickly than it would in ebb generation. Rivers flowing into the basin may further reduce

1302-469: The water flows in and out. Tidal barrages are among the oldest methods of tidal power generation, with tide mills being developed as early as the sixth century. In the 1960s the 1.7 megawatt Kislaya Guba Tidal Power Station in Kislaya Guba , Russia , was built. Around the same time, the 240 MW la Rance Tidal Power Station was built in Brittany , France, opened in November 1966. La Rance

Sihwa Lake Tidal Power Station - Misplaced Pages Continue

1344-500: The water in the basin at high tide = ½ × area × density × gravitational acceleration × tidal range squared Now we have 2 high tides and 2 low tides every day. At low tide the potential energy is zero. Therefore, the total energy potential per day = Energy for a single high tide × 2 Therefore, the mean power generation potential = Energy generation potential / time in 1 day Assuming the power conversion efficiency to be 30%: The daily-average power generated = 104 MW * 30% Because

1386-559: The water level higher than the high tide, and uses intermittent renewables for pumping, around 7.5 W/m . i.e. 10 × 10 km delivers 750 MW constant output 24/7. These independent barrages do not block the flow of the river. The placement of a barrage into an estuary has a considerable effect on the water inside the basin and on the ecosystem. Many governments have been reluctant in recent times to grant approval for tidal barrages. Through research conducted on tidal plants, it has been found that tidal barrages constructed at

1428-434: The water speed near a turbine and will be sucked through. Even with the most fish-friendly turbine design, fish mortality per pass is approximately 15% (from pressure drop, contact with blades, cavitation , etc.). Alternative passage technologies ( fish ladders , fish lifts, fish escalators etc.) have so far failed to solve this problem for tidal barrages, either offering extremely expensive solutions, or ones which are used by

1470-401: The world by installed capacity for 45 years until the 254-MW South Korean Sihwa Lake Tidal Power Station surpassed it in 2011. The power station has 24 turbines . These reach total peak output at 240 MW, and produce an annual output of approximately 500  GWh (2023: 506 GWh; 491 GWh in 2009, 523 GWh in 2010); thus the average output is approximately 57 MW, and

1512-528: The world. It is also the only site where a full-scale evaluation of the ecological impact of a tidal power system, operating for 20 years, has been made. French researchers found that the isolation of the estuary during the construction phases of the tidal barrage was detrimental to flora and fauna, however; after ten years, there has been a "variable degree of biological adjustment to the new environmental conditions." Some species lost their habitat due to La Rance's construction, but other species colonized

1554-576: Was attractive because of the wide average-range between low and high tide levels, 8 m (26.2 ft) with a maximum perigean spring tide range of 13.5 m (44.3 ft). The first studies which envisaged a tidal plant on the Rance were done by the Society for the Study of Utilization of the Tides in 1943. Nevertheless, work did not actually commence until 1961. Albert Caquot , the visionary engineer,

1596-704: Was built in 2011 and started to operate in 2012. The project cost of US$ 560 million was borne by the South Korean Government . After the seawall was built in 1994, pollution built up in the newly created Sihwa Lake reservoir , making its water useless for agriculture. Concentrations of perfluorooctane sulfonate (PFOS) measured in Lake Sihwa were among the greatest ever measured in the environment. In January 2003, PFOS had been found at 730 ng/L in Lake Shihwa water. In 2004, seawater

1638-487: Was completed in 1966. Charles de Gaulle , then President of France , inaugurated the plant on 26 November of the same year. Inauguration of the road crossing the plant took place on 1 July 1967, and connection of the plant to the French National Power Grid was carried out on 4 December 1967. In total, the plant cost ₣ 620 million (approximately € 94.5 million). It took almost 20 years for

1680-445: Was instrumental in the construction of the dam, designing an enclosure in order to protect the construction site from the ocean tides and the strong streams. Construction necessitated draining the area where the plant was to be built, which required construction of two dams which took two years. Construction of the plant commenced on 20 July 1963, while the Rance was entirely blocked by the two dams. Construction took three years and

1722-403: Was reintroduced in the hope of flushing out contamination; inflows from the tidal barrage were envisaged as a complementary permanent solution. As of 2007 the power station was planned to provide this indirect environmental benefit, as well as renewable energy. Tidal barrage A tidal barrage is a dam -like structure used to capture the energy from masses of water moving in and out of

Sihwa Lake Tidal Power Station - Misplaced Pages Continue

1764-473: Was the largest tidal barrage in world for 45 years, until the 254 MW Sihwa Lake Tidal Power Station was commissioned in South Korea in 2011. However, there are few other examples worldwide. The barrage method of extracting tidal energy involves building a barrage across a bay or river that is subject to tidal flow. Turbines installed in the barrage wall generate power as water flows in and out of

#898101