What is Tidal Power?

Tide energy The energy that occurs in the periodic fluctuations of seawater. The water level difference is represented by potential energy, and the speed of its tide is represented by kinetic energy. Both kinds of energy can be used and it is a renewable energy source. As the tide is the most trustworthy and most regular among the various movements of seawater, it also fluctuates on the shore, and it was also recognized and utilized by people for the first time. Among the various ocean energy uses, the use of tidal energy is the most mature . ^[1]

Chinese name: Tidal energy

Foreign name: Tide energy

The tide phenomenon is caused by the change of the gravity of the moon. The tide causes the sea level to rise and fall periodically. The energy generated by the fluctuation of the sea and the tide flow is called tidal energy. This energy is eternal, pollution-free energy. The energy of tidal energy is directly proportional to the tide volume and tide difference, or in other words, the square of the tide difference and the area of the reservoir. Compared with hydroelectric power, the energy density of tidal energy is very low, which is equivalent to the level of micro-hydropower.

Tidal energy applications

The tides of the ocean hold tremendous energy. During the high tide, the turbulent seawater has great kinetic energy, and as the seawater level rises,

The main way to use tidal energy is to generate electricity High, the huge kinetic energy of the seawater is converted into potential energy; during the ebb, the seawater gallops away, the water level gradually decreases, and the potential energy is converted into kinetic energy. The larger tidal range in the world is about 13-15m, but generally speaking, the average tidal range above 3m has practical application value. Tidal energy varies from place to place. Different regions often have different tidal systems. They all obtain energy from deep-sea tidal waves, but each has its own unique characteristics. Although the tides are complicated, the tides can be accurately forecasted everywhere. Tidal energy is mainly used to generate electricity. Tidal power generation uses the favorable terrain such as bays and estuaries to construct water embankments and form reservoirs to facilitate the accumulation of large amounts of seawater. Hydroelectric power plants are built in or near the dam to generate electricity through hydroelectric generators. It is only possible to extract energy from the tide when there is a high tide, when the energy is concentrated, and where the geographical conditions are suitable for the construction of a tidal power station. Although such sites are not everywhere, countries around the world have selected a considerable number of sites suitable for the development of tidal power stations.

Tidal energy meaning

The development of new energy sources such as tidal energy can indirectly slow the increase of the CO2 content in the atmosphere. Tide is a phenomenon of periodic sea level changes worldwide. Due to the two gravitational sources of the moon and the sun, sea level fluctuates twice a day and night. As a natural phenomenon, the tide provides convenience for human navigation, fishing, and salt drying. It is more worth pointing out that it can also be transformed into electricity, bringing light and power to people.

Tidal energy source

Tidal energy is the energy generated by the tidal phenomenon. It is related to celestial gravity. The attraction of the earth-moon-solar system and thermal energy are the sources of tidal energy.

Tidal energy formation

Tidal energy is a general term for periodic movements and changes in the lithosphere, hydrosphere, and atmosphere of the earth caused by the tidal force of the sun and the moon. The elastic-plastic deformation caused by the tide-inducing force of a solid earth is called solid tidal energy.

As a complete tidal science, the research object should regard the ground tide, ocean tide and air tide as a unified whole, but because the tide phenomenon is very obvious, and it is closely related to people's life, economic activities, transportation, etc., it is customary to make the tide The word energy can be interpreted narrowly as the ocean tide.

Tidal energy

The difference between the true lunar gravity and the average gravitational force is called interference force, and the horizontal component of the interference force forces the seawater to move to the earth, the moon line and produce water peaks. The water peak corresponding to the high tide occurs twice every 24 hours and 50 minutes (that is, the time required for the same longitude of the earth from the first time to face the moon to the second time to face the moon), that is, the moon is every 12 hours and 25 minutes. Causes seawater to ebb once. This kind of tide is called half-day tide.

The tide causes the sea level to rise and fall periodically. Full moon every month and

East China Sea At the new moon, the sun, the earth, and the moon are aligned. At this time, due to the cumulative gravitational effect of the sun and the moon, the tide produced is higher than usual, and this kind of tide is called the spring tide. When the Earth, the Moon, and the Earth and the Sun are at an angle, the gravitational forces cancel each other out, so the resulting tide is lower and is a small tide. The average tidal distance varies from place to place. For example, the coastline in some areas will cause resonance and increase the tidal distance, while the coastline in other areas will reduce the tidal distance. Another factor affecting the tidal distance is the Coriolis force, which is derived from the conservation of angular momentum of fluid flow. If the ocean current moves northward in the northern hemisphere, its movement is close to the axis of the earth, so the angular velocity increases. Therefore, the ocean current will be biased toward the eastern current, that is, the seawater on the eastern coast is higher. Similarly, if the northern current flows to the south, the seawater on the western coast is higher. .

Tidal power generation principle

The main principle of tidal power generation is to use the kinetic energy of the celestial body to induce the horizontal flow of seawater to produce electrical energy .

Tidal power generation

The flow of tidal water is different from the flow of river water. It is constantly changing direction. There are three forms of tidal power generation:

Tidal energy

Single-reservoir and one-way power stations use only one reservoir and generate electricity only at high tide (or low tide). This is the type of Shashan Tidal Power Station in Wenling City, Zhejiang Province, China.

A single reservoir two-way power station uses a reservoir, but it can generate electricity at high and low tides, but it cannot generate electricity at low tide. Zhenkou Tidal Power Station in Dongguan City, Guangdong Province and Jiangxia Tidal Power Station in Wenling City, Zhejiang Province are this type.

Shuangku bidirectional power station uses two adjacent reservoirs to make one reservoir enter water at high tide and the other reservoir discharge at low tide. In this way, the water level of the former reservoir is always higher than the water level of the latter reservoir, so the former is called The upper reservoir, which is called the lower reservoir. The hydro-generator unit is placed in a dam between the two reservoirs. The two reservoirs always maintain a water level difference, so they can generate electricity throughout the day.

Tidal energy is available

The use of tidal power must have two physical conditions.

First, the tide must be large, at least a few meters.

Second, the terrain of the coast must be able to store large amounts of seawater and be able to carry out civil works.

Advantages and disadvantages of tidal energy

The main way tidal energy is used is power generation. The working principle of tidal power generation is similar to that of conventional hydroelectric power generation. It uses the potential energy of the water level difference generated by the rise and fall of tidal water to generate electricity. The difference is that seawater is different from river water. The accumulated seawater has a small drop, but the flow is large and intermittent. Therefore, the structure of the tidal turbine should be suitable for low head and large flow. Specifically, it is to build dams, gates and workshops in conditional bays or tidal estuaries, separate the bay (or estuary) from the open sea to form a reservoir, and install hydro-generator units in the dams or power plant buildings. . The periodic fluctuation curve of the ocean tide level is similar to a sine wave. A certain height difference (that is, the working water head), thereby driving the hydro-generator to generate electricity. From the perspective of energy, it is the process of converting the potential energy and kinetic energy of seawater into electrical energy through a hydro-generator set. Characteristics of tidal energy resources in China

A) The reserves are considerable.

2. The geographical distribution of tidal energy resources in China is very uneven. Coastal tidal range is highest in the East China Sea, followed by the Yellow Sea, and smallest in the southern Bohai Sea and South China Sea. The estuary tidal energy resources are most abundant in the Qiantang Estuary, followed by the Yangtze River Estuary, followed by the estuaries such as the Pearl River, Jinjiang, Minjiang, and Minjiang. In terms of regions, it is mainly concentrated on the coast of East China, with Fujian, Zhejiang, and the northern branch of the Yangtze River as the largest, accounting for 88% of China's developable tidal energy.

(3) In terms of topography and geology, the coastal areas of China are mainly of the plain type and the bay type. They are bounded by Hangzhou Bay and north of Hangzhou Bay. Most of them belong to the plain coast. The coastline is straight and the terrain is flat. The difference is small, and there is no better harbor dam site. South of Hangzhou Bay, there are many harbors and coasts, the terrain is steep, the coastline is tortuous, the slope is steep, the water depth is large, and the bay and the coast have a large tide difference. Dam site. However, the coasts of gradually and Fujian provinces are muddy harbors. Although there are abundant tidal energy resources, there are major difficulties in development. It is necessary to focus on the research to solve the problem of sediment deposition in reservoirs.

Development and utilization of tidal energy

Tidal energy is an inexhaustible source of renewable energy that does not consume fuel, has no pollution, is not affected by floods or dry water. Among marine energy sources, the development and utilization of tidal energy is the most realistic and simple. China has begun to use tidal energy as early as the 1950s, and in this respect it is the earliest country in the world. The Fujian Junbian Tidal Turbine Pumping Station, built in 1956, uses tides as motive power to pour water into the fields. By 1958, the tidal power station blossomed throughout the country. According to the statistics of the "First National Tidal Power Generation Conference" held in October 1958, there are 41 tidal power stations completed and 88 under construction. The installed capacity can be as large as 144 kilowatts or as small as 5 kilowatts. Mainly used for lighting and driving small agricultural facilities. For example, the Shashan Tidal Power Station in Wenling County, Zhejiang Province, completed in 1959, was further built as a power station in 1961, with an installed capacity of only 40 kilowatts and an annual power generation of 100,000 kilowatts · hour. with). According to 1986 statistics, its cumulative income from power generation has exceeded 10 times the investment. There are still nearly 10 tidal power stations in operation in China. The Jiangxia Tidal Power Station in Yueqing Bay, Zhejiang, costs about the same as a small hydropower station below 600 kilowatts. The first unit started generating power in 1980 and was fully completed at the end of 1985. The amount can reach 10.7 million kilowatt-hours, and the electricity price per kilowatt-hour is only 0.067 yuan. Each year's own economic benefits include generating 670,000 yuan in power generation, 740,000 yuan in aquaculture, and 1.9 million yuan in farm reclamation, totaling 3.3 million yuan. Social benefits, calculated as 5 yuan per kilowatt-hour of electricity, can reach 50 million yuan. This is China and the largest tidal power station in Asia, second only to France's Lance Tidal Power Station and Canadian Annapolis Tidal Power Station, ranking third in the world.

Tidal energy is the potential energy of the tidal range. The basic method of development and utilization is similar to the construction of a hydropower station: firstly set up a sluice in the bay or estuary. "Single storage and one-way power generation". This type of power station can only generate electricity at low tide, twice a day for a maximum of 5 hours each time.

In order to improve the utilization of the tide, as far as possible to generate electricity at high tide and low tide, people have used clever circuit facilities or two-way turbine units to generate electricity when high tide flows into and out of the tide. This is the "single storehouse" "Two-way power generation", like the Jiangxia Tidal Power Station mentioned above, belongs to this type.

However, neither of these types can generate a relatively stable voltage when the water in the reservoir is discharged when the tide is low (no water level difference) or when the tide is stopped. So people came up with two different reservoirs, high and low, for two-way power generation. This method can not only generate electricity continuously during the whole ebb and flow, but also make the power output relatively stable. It is especially suitable for those isolated islands, so that the islands can get a smooth power supply at any time without interruption. Such as Haishan Tidal Power Station on Maozhi Island, Yuhuan County, Zhejiang Province. It has two tidal storage reservoirs, and is equipped with small pumped storage power stations. In this way, it can generate electricity for 25 days per month and produce 10,000 kilowatt-hours of electricity. In order to pump water for energy storage, it needs to use 5000 kWh of electricity at the cost of 3 kWh for 1 kWh to obtain the continuity and balance of power supply, so there is a certain power loss.

On the whole, the technical problems in the development and utilization of Chaoneng Energy have been basically solved, there are many successful examples at home and abroad, and the technology is also updated quickly.

The French Lance Tidal Power Station, a symbol of foreign technological progress, was completed in 1968. It is equipped with 24 light bulb-type generator units with forward and reverse power generation. The diameter of the runner is 5.35 meters, and the single unit capacity is 10,000 kilowatts. 540 million kilowatt-hours. The Annapolis Tidal Power Station in Canada, completed in 1984, is equipped with one of the world's largest 20,000-kilowatt unidirectional turbine units with a rotor diameter of 7.6 meters. The generator rotor is located on the outer edge of the turbine blade. Sealing technology, fast cooling, high efficiency,

Louis estuary, saint malo, france The cost is 15% lower than that of the French bulb type unit, and the maintenance is also very convenient. Among China's self-designed tidal power stations, Jiangxia Power Station is more formal and mature in technology. The power station was originally designed with 6 bulb-type units with a capacity of 500 kilowatts. In fact, only 5 were installed, and the total capacity reached 3,200 kilowatts. There are three specifications of 500 kW, 600 kW and 700 kW, and the diameter of the runner is 2.5 meters. It has also achieved good results in more advanced methods in anti-corrosion of marine buildings and units and prevention of marine organisms. In particular, the last two units have reached the advanced foreign technology level, with multiple functions of bidirectional power generation, drainage and pumped water storage, and adopting a high-tech planetary gear speed-up transmission mechanism, so that it is not necessary to increase the unit size. , Which increases the power generation, and also reduces the cost of construction.

Tidal power uses tidal potential energy. The highest tidal range in the world is only over 10 meters. In China, the tidal range is only 9 meters high. Therefore, it is impossible to use tens of meters or more than 100 meters of hydroelectric power like tidal power. The hydropower generating unit must adapt to the characteristics of "low head and large flow". But as the water wheel becomes larger, the cost of supporting facilities will increase accordingly. Therefore, how to solve this problem has become a sign reflecting the level of technology. The Hongchao Power Station in Ganzhutan, Guangdong, which was put into operation in 1974, is a successful representative. It is characterized by both flood and tide, and can generate electricity as long as there is a drop of 0.3 meters. The total installed capacity of the Ganzhutan Hydropower Station is 5000 kilowatts, with an average annual power generation of 10.3 million kilowatt-hours. Its runner has a diameter of 3 meters, plus a large number of cement substitute components, and the cost is low, which is very significant for private small-scale tidal power stations.

Application Status of Tidal Energy

Due to the competition of cheap electricity costs of conventional power stations, not many commercial tidal power stations have been completed and put into operation. However, due to the huge amount of tidal energy and the many advantages of tidal power generation, people still attach great importance to the research and experiment of tidal power generation.

According to calculations by oceanographers, the world s tidal energy resources are more than 1 billion kilowatts, which is also an astronomical figure. The tidal energy census calculation method is to first select sites suitable for the construction of tidal power stations, and then calculate the installed power generation capacity that can be developed at these sites, which is added up to the estimated resource amount.

In the early 20th century, some countries in Europe and the United States began to study tidal power generation. The first tidal power station with commercial value was the French Langs Power Station, which was completed in 1967. The power station is located at the estuary of the Rance in Saint-Malo, France. The maximum tidal range of the Langs Estuary is 13.4 meters, with an average tidal range of 8 meters. A 750-meter-long dam crosses the Lance River. Above the dam is a highway bridge for passing vehicles, and ship locks, sluice gates and generator rooms are set under the dam. There are 24 two-way turbine generators installed in the machine room of the Lance Tidal Power Station, which can generate electricity at high and low tides. The total installed capacity is 240,000 kilowatts, and the annual power generation is more than 500 million kWh, which is imported into the national power grid.

In 1968, the former Soviet Union built an 800-kilowatt test tidal power station in the Kislya Bay near Murmansk in the north. In 1980, Canada built a 20,000-kilowatt intermediate test tidal power station in Fundy Bay. The test and pilot power stations are used for demonstration and preparation for the construction of larger practical power stations. More than 20 places in the world suitable for the construction of tidal power stations are studying, designing and constructing tidal power stations. These include: Cook Bay, Alaska, USA, Bay of Fundy, Canada, Severn Estuary, San Jose Bay, Argentina, Van Diemen Bay, Darwin, Australia, Campbell Estuary, India, Far East Okhotsk, Russia, South Korea Incheon Bay and other places. With the advancement of technology, the cost of tidal power generation continues to decrease. In the 21st century, large modern tidal power stations will be built and used.

The theoretical reserves of tidal energy in China reach 110 million kilowatts. There are many high energy densities along the coast of China, especially the southeast coast, with an average tidal range of 4-5m and a maximum tidal range of 7-8m. Among them, Zhejiang and Fujian have the largest reserves, accounting for about 80.9% of the country. China's Jiangxia Tidal Experimental Power Station, built in Jiangxia Port on the north side of Yueqing Bay in Zhejiang Province, has an installed capacity of 3,200kW and was officially put into operation in 1980.

China's hydropower reserves reach 680 million kW, accounting for about 1/6 of the world, ranking first in the world. After completion, the Yangtze River Three Gorges Hydropower Station will be the world's largest hydroelectric power station with an installed capacity of 18.2 million kW.

The first grid-connected tidal energy project in the United States is put into operation. The project is located in the Bay of Fundy between Maine and Canada. Here, 100 billion tons of water flows turbulently every day, forming waves about 15 meters high and bringing 5884 kilowatts of electricity. The project will be completed in several phases, and will eventually reach 4 megawatts of power generation and be able to supply 1,000 households and commercial institutions.

The first phase of the project was officially connected to the grid last week. The daily generating capacity is 180 kilowatts, which is enough to meet the needs of 25 to 30 households. But so far, it has not really contributed one kilowatt of electricity to the power grid because of insufficient government support. The European government's stable policy preferences and subsidies have given the European marine energy industry a firm foothold.

This tidal energy project in Maine is not the first tidal energy project in North America (the first was a tidal power station in Nova Scotia, Canada in 1984), but it was the first to have no dam. The tidal energy generating unit of the body will basically not affect the normal life of marine life.