How do tides generate electricity?

The principle of tidal power generation is similar to that of ordinary hydropower generation. By leaving the reservoir, seawater is stored in the reservoir at high tide and stored as potential energy. Then, when the tide ebbs, seawater is released, and the turbine is driven to rotate by the difference of high and low tide levels, and the generator is driven to generate electricity.

tidal energy

In a bay or tidal estuary, you can see the fluctuation of sea water or river water twice a day. In the morning,

tidal power generation

Some are called tides while others are called sunsets at night. Tide, as a natural phenomenon, provides convenience for human navigation, fishing and salt drying. This phenomenon is mainly caused by the tidal force of the moon and the sun and the rotation effect of the earth. At high tide, a large amount of seawater flows in, with great kinetic energy; At the same time, the water level gradually rises, and kinetic energy is converted into potential energy. At low tide, the seawater rushes home, and the water level drops one after another, and the potential energy is converted into kinetic energy. The kinetic energy and potential energy of seawater in motion are collectively called tidal energy. [1] Tide is a kind of renewable energy with huge reserves, inexhaustible resources, no need for exploitation and transportation, and no pollution. To build tidal power stations, there is no need to emigrate or flood the land, and there is no problem of environmental pollution. In addition, it can also be combined with tidal power generation to develop comprehensive utilization projects such as reclamation, aquaculture and marine chemical industry.

use

The main utilization mode of tidal energy is tidal power generation. The principle of tidal power generation is similar to that of ordinary hydropower generation. Leaving the reservoir, seawater is stored at high tide.

Schematic diagram of tidal power generation

In the reservoir, it is stored in the form of potential energy, and then the seawater is released at low tide, and the turbine is driven by the high and low water level difference to drive the generator to generate electricity. The difference is that seawater is different from river water, and the accumulated seawater has a small drop, but a large flow and is intermittent, so the turbine structure of tidal power generation should be suitable for the characteristics of low head and large flow.

Tidal power generation is a kind of hydroelectric power generation. Dams, gates and factories are built in conditional bays or tidal ports to form reservoirs, so that the water level of the reservoirs and the tidal level in the open sea form a certain tidal difference (i.e. working head), thus driving the hydro-generator set to generate electricity.

The technology related to tidal power generation has made rapid progress, and a variety of mechanical equipment has been developed to convert tidal energy into mechanical energy, such as propeller turbine, axial flow turbine, open cycle turbine and so on. Japan even began to use satellites to provide tidal information. The utilization of tidal power generation is becoming more and more mature and has entered the practical stage.

2 Use historical editing

The main utilization mode of tidal energy is tidal power generation.

At the beginning of the 20th century, some countries in Europe and America began to study tidal power generation. 19 13 Germany established the first tidal power station on the North Sea coast. The first tidal power station with commercial and practical value was the French Reims Power Station built in 1967. The power station is located at the mouth of the Lance River in the Gulf of Saint Marlowe, France. The maximum tidal range at Langsi Estuary is13.4m, and the average tidal range is 8m. A 750-meter-long dam spans the Longs River. The dam is a highway bridge for traffic, and there are lock, sluice and generator room under the dam. There are 24 bidirectional turbine generators installed in the engine room of Langsi Tidal Power Station, which can generate electricity at high tide and low tide. The total installed capacity is 240,000 kilowatts, and the annual power generation is more than 500 million kWh, which is input into the State Grid.

1968, the former Soviet Union built an experimental tidal power station of 800 kilowatts in Yawan, Kiisla, near Murmansk in the north. 1980, Canada built an experimental tidal power station with 20,000 dry watts in the Bay of Fundy. Experimental power stations and pilot power stations are used to demonstrate and prepare for the construction of larger practical power stations.

Due to the competition of cheap electricity charges of conventional power stations, commercial tidal power stations are rarely built and put into operation. However, due to huge tidal energy reserves and many advantages of tidal power generation, people still attach great importance to the research and experiment of tidal power generation. [ 1]

The first tidal power station was built in Shandong in 1957. In August 1978, 1, Baishakou Tidal Power Station in Rushan County, Shandong Province started to generate electricity, with an annual output of 2.3 million kWh. On August 4th, 1980, China's first "single-reservoir bidirectional" tidal power station-Jiangxia tidal test power station was officially put into operation, with an installed capacity of 3,000 kilowatts and an average annual power generation of/kloc-0.07 million kwh, which was the second largest tidal power station in the world at that time, second only to the French Reims tidal power station (with an installed capacity of 240,000 kilowatts and an annual power generation of 540 million kwh [

Tidal power generation is simply to build a dam in a bay or tidal estuary to form a reservoir, and place a hydro-generator set in or near the dam, and use the fluctuation of seawater level during tidal fluctuation to drive the hydro-generator set to generate electricity when seawater passes through the hydro-turbine. From the point of view of energy, it is to use the potential energy and kinetic energy of seawater to convert it into electrical energy through hydro-generators.

Tidal energy is one of the most mature marine energy in the world, and the tidal power generation abroad is developing rapidly. European countries, with vast oceans and long coastlines, are rich, stable and cheap tidal resources, and have always been at the forefront of the world in tidal development and utilization. France, Canada, Britain and other countries keep the leading edge in the research and development of tidal power generation.

China's coastline is tortuous and long, mainly concentrated in the coastal areas of Fujian, Zhejiang, Jiangsu and other provinces. The development of tidal energy in China began in 1950s. After years of research and pilot projects on tidal power station construction, the tidal power generation industry in China has not only matured technically, but also made great progress in reducing costs and improving economic benefits. A number of tidal power stations with good performance and remarkable benefits have been built.

Insufficient power supply is an important factor restricting the development of China's national economy, especially in the eastern coastal areas. Tidal energy has the advantages of renewable, clean and predictable. Under the background of optimizing the power structure and promoting the upgrading of energy structure in China, the development of tidal power generation conforms to the social trend and is conducive to alleviating the energy shortage in the eastern coastal areas. The construction of tidal power station can create good economic, social and environmental benefits and has great investment potential.

3 details

Tidal law

Tides also appear regularly. The occurrence of tides is related to the sun and the moon, and also corresponds to the traditional lunar calendar in China. On the first day of each lunar month, that is, the new moon, the sun and the moon are on one side of the earth [1], so there is the largest tidal force, which will cause "spring tides". Near the fifteenth or sixteenth day of each lunar month, the sun and the moon are on both sides of the earth, and the tidal force of the sun and the moon will also cause "spring tide"; When the phases of the current month are the first quarter moon and the second quarter moon, that is, August and 23rd of the lunar calendar, the tidal force of the sun and the tidal force of the moon cancel each other out, so a "small tide" occurs. Therefore, there is a saying in agricultural proverbs that "the spring tide begins on the fifteenth day of the first lunar month, and beaches can be seen everywhere on the 23rd of the eighth lunar month". In addition, there was a climax on the first day. Because the moon moves eastward more than 13 degrees on the celestial sphere every day, which is about 50 minutes in total, that is, the transit time of the moon (1 lunar day =24: 50) is delayed by about 50 minutes every day, (there will be tides in the next transit, usually twice a day), so the time of high tide is also delayed by about 50 minutes every day. [ 1]

Working people in China have summed up thousands of years' experience and put forward many tidal calculation methods (tidal pushing time), such as the eight-point tidal calculation method, for example, the concise formula is:

High tide =0.8h×[=0.8h×[ Lunar date-1 (or 16)]+ high tide interval.

When the above formula can be regarded as one-day high tide, for the normal semidiurnal tide sea area, add or subtract 12: 25 (or add or subtract 12: 24 for calculation convenience) to get another high tide time. If you add or subtract 6: 00 and 12 points, you can get the time of low tide-low tide. However, due to the complexity of the movements of the moon and the sun, the spring tide may sometimes be delayed by one or several days, and the climax during lunar day is often one hour or several hours later than the transit time on the moon. In some places, the tide will rise as soon as the lunar calendar is over. Therefore, the time and interval of high tide and low tide are different every day.

Power generation conditions

There are two physical conditions for tidal power generation: first, the amplitude of tidal power generation must be large, at least several meters; The second coastal terrain must be able to store a large amount of seawater and can be used for civil engineering. In other words, it is very important to have enough tidal energy in this area. The method of general survey and calculation of tidal energy is to select suitable sites for building tidal power stations, and then calculate the exploitable installed capacity of power generation in these sites, and add them to get the estimated resources.

The working principle of tidal power generation is similar to that of general hydropower generation, that is, dams are built in estuaries or bays to form natural reservoirs, and hydro-generator sets are installed in seawalls. Because the water level difference of seawater tide is much lower than that of ordinary hydropower stations, the tidal power stations should adopt hydro-generator sets with low head and large flow. Full-tubular turbine generator set has the characteristics of small volume, light weight, short pipeline and high efficiency, and has been widely used in tidal power stations.

4 power generation type

Tidal power stations can be single reservoirs or double reservoirs. Single-reservoir tidal power station has only one dam and one reservoir, while double-reservoir tidal power station has two adjacent reservoirs.

Single reservoir unidirectional power station

That is, only one reservoir generates electricity only at high tide (or low tide), so it is also called single reservoir single program tidal power station. The Shashan tidal power station in Wenling City, Zhejiang Province, China is of this type.

Single reservoir bidirectional power station

Use the reservoir, but the tide rises and falls

Types of tidal power generation

Power can be generated at tidal time, but it can't be generated at low tide when the water level inside and outside the reservoir is the same. This kind of power station is called single reservoir and double program tidal power station, which greatly improves the utilization rate of tidal energy. [1] The tidal power station in Zhenkou, Dongguan, Guangdong Province and Jiangxia tidal power station in Wenling, Zhejiang Province are all of this type.

Double reservoir bidirectional power station

In order to make the tidal power station generate electricity continuously all day, it is necessary to adopt the dual-reservoir tidal power station. It uses two adjacent reservoirs, so that one reservoir can supply water at high tide and the other reservoir can drain water at low tide, so that the former one

Tidal power generation practical device

The water level of one reservoir is always higher than the next, so the former is called upper reservoir (high-level reservoir) and the latter is called lower reservoir (low-level reservoir). The hydro-generator set is placed in the dam between the two reservoirs, and the water level difference between the two reservoirs is always maintained, so it can generate electricity all day. [2]

5 power generation characteristics

superiority

1. Tidal energy is a clean and renewable energy that does not pollute the environment and affect the ecological balance. The tide rises and falls, every day, and it is endless. It can be developed into an important supplementary energy source for life, production and national defense in coastal areas.

Wave and tidal current energy device

2. It is a relatively stable and reliable energy source, which is little influenced by natural factors such as climate and hydrology, and the total power generation is stable throughout the year, which is not affected by wet years and dry seasons.

3. Tidal power stations do not need to flood a large number of farmland to form reservoirs, so there are no complex problems such as population migration and flooding farmland. Moreover, seawalls can be used to promote the siltation and reclamation of large-scale tidal flats, and can be comprehensively utilized in combination with aquaculture, water conservancy, marine chemical industry and transportation. This is a prominent advantage for coastal areas with large population and little arable land.

4. Tidal power stations do not need to build high dams. Even if the dam is damaged by natural disasters such as war or earthquake, it will not cause serious disasters to downstream cities, farmland and people's lives and property.

5. Tidal energy can be used to develop primary energy and secondary energy, which does not need fuel, is not affected by the price of primary energy, and has low operating cost, so it is an economic energy. But like Hechuan hydropower station, it has the characteristics of large one-time investment and low power generation cost.

6. There are many units, so there is no need to set up spare units.

disadvantaged

1, tidal range and water head often change in one day, with intermittent output and no special adjustment measures, which brings inconvenience to users. However, the operation plan can be made in advance according to the tidal forecast and run in parallel with the large power grid to overcome its intermittence.

tidal power generation

2. When the tide changes for half a month, the tidal range can be doubled, so the annual utilization hours to ensure the output and installed capacity are also low.

3. The tidal power station is built at the estuary of the harbor, and the dam depth is generally long, so it is difficult to construct, treat the foundation and prevent siltation. Hometown construction and electromechanical investment are large and the cost is high.

4. Tidal power station is a form of power generation with low head and large flow. Tides rise and fall in opposite directions, so the turbine is large in size, uses a large amount of steel, and the structure of water inlet and outlet buildings is complex. Moreover, seawater and marine life have corrosive and polluting effects on metal structures and marine structures because they are immersed in seawater, so special anti-corrosion and anti-adhesion treatment is needed for marine life.

5. The tidal cycle is lunar day (24 hours and 50 minutes), the monthly cycle is about 14 days, and the daily high tide lags behind by about 50 minutes, which is not well matched with the daily electricity demand load diagram given according to the solar day. Although tidal power generation has the above shortcomings, it can be improved with the continuous improvement of modern technology. The first shortcoming can be made up by taking measures such as two-way or multi-reservoir power generation, pumped storage and power grid regulation. Adopting modern floating caisson construction can save civil investment; The corrosion of seawater and the attachment of marine life can be overcome by using stainless steel production equipment, vinyl resin series coatings and cathodic protection.

6 use status

domestic situation

As a kind of clean energy, tidal power generation not only gets the attention of government departments, but also becomes a new business opportunity for equipment manufacturing enterprises to enter strategic emerging industries. As a kind of renewable energy, tidal energy has become an important part of new energy in the "Twelfth Five-Year Plan" of strategic emerging industries. Compared with wind energy and solar energy, tidal energy is more reliable, the power generation will not fluctuate greatly, and it does not occupy farmland and pollute the environment, and the cost is only one-eighth of that of thermal power. China is rich in tidal resources, which provides ample opportunities for the development of tidal power generation. With the decrease of traditional fossil energy such as coal, oil and natural gas and the aggravation of energy shortage, people have shifted the focus of energy development to a wider ocean. Tidal power generation has the characteristics of rich resources, large reserves, renewable, environmental protection and pollution-free, and has become the focus of developing "blue energy". Under the background of vigorously developing marine economy, tidal power generation has been listed as an important part of new energy in China's strategic emerging industries in the Twelfth Five-Year Plan, which also provides huge business opportunities for equipment manufacturing industry to enter strategic emerging industries and has great development potential. Tidal power generation requires higher natural conditions and equipment conditions. Tidal power generation is to make use of favorable topography such as tidal bays and estuaries, build a dam to form a reservoir, and place a hydro-generator set in or near the dam, and use the tidal level difference during tidal fluctuation to drive the turbine to rotate, so as to convert the potential energy and kinetic energy of seawater into electric energy. In addition, because tidal power generation takes seawater as the medium, power generation equipment is immersed in seawater all the year round, so there are strict requirements for equipment anticorrosion and prevention of marine life adhesion.

China is rich in tidal energy resources, from the mouth of Yalu River in the north to the mouth of Beilun River in the south, with coastline18,000 kilometers and coastline of more than 5,000 islands14,000 kilometers. * * About 32,000 kilometers of coastline is rich in tidal energy resources. According to incomplete statistics, the national tidal energy reserves are 65.438+0.9 billion kilowatts, of which about 38.5 million kilowatts can be developed, and the annual power generation is 87 billion kWh, equivalent to more than 40 Xin 'anjiang hydropower stations. At present, the total installed capacity of tidal power stations in China has reached more than 1 10,000 kilowatts. According to the results of marine energy resources zoning in China, there are 424 tidal power station dam sites along the coast of China, with Zhejiang and Fujian having the largest number.

Coastal areas of Zhejiang province

According to the Marine Functional Zoning of Zhejiang Province issued by the Zhejiang Provincial Government, the marine energy utilization area in this province includes four tidal energy areas, with the key areas being Nantiandao Bay tidal energy area, Sanmen Bay tidal energy area, Jiangxia tidal energy area and seamount tidal energy area. There are 1 tidal energy zones, that is, the tidal energy zone of Guishan waterway. Zhoushan Archipelago accounts for about half of tidal energy in China, and has great development potential.

It is understood that the coastal areas of Zhejiang are all strong tidal areas. The average tidal range along the coast of Zhejiang is 4.29 meters, the theoretical installed capacity of tidal energy is 28.96 million kilowatts, and the exploitable installed capacity of tidal energy is 8.8 million kilowatts, accounting for about 40% of the whole country. The average wave height along the coast is 1.3m, the theoretical wave energy density is 5.3kW/m, the installed capacity is 2.5m, and the wave energy accounts for 16.5% of the whole country.

Fujian Province

1980 65438+February 16, Fujian Provincial Department of Hydropower, Provincial Research Institute of Water Conservancy, Provincial Institute of Agricultural Machinery and other units organized technicians to inspect tidal energy in Pingtan. 1983 10 the provincial science and technology commission decided to build a tidal power station in the Xiao Jiu fish seawall in Xingfuyang reclamation area of Pingtan county. The project was designed by Fujian Water Conservancy and Electric Power Survey and Design Institute and constructed by Xingfuyang Experimental Tidal Power Station Project Headquarters in Pingtan County. The tidal power station takes the flood drainage ditch and deep-water aquaculture pond (with an area of 73 hectares) in the reclamation area as storage reservoirs, with a storage capacity of 6,543.8+0.67 million cubic meters and an effective storage capacity of 6,543.8+0.33 million cubic meters, and adopts one-way ebb tide to generate electricity.

1984 10 started cofferdam and foundation blasting. Construction of the main and auxiliary workshops started at Xiao Jiu Fish Bank, with the construction area of 522.7 m2 for the main workshop and 184.4 m2 for the auxiliary workshop. The installation elevation of the unit is -3.8m, and there are 4 turbines and 4 generators. The turbine is of domestic GDBWS- 190 tubular type, with the shaft power of 38 1.7 1 kW and the rotation speed of 155 rpm, with an efficiency of 83%. The generator is an AC synchronous hydraulic turbine TSWN99/37- 12, with a capacity of 320kW, rated voltage of 400V, rated current of 577A and rotating speed of 500rpm. The elevation of the equipment operation floor is-1.55m, including governor, control panel, power board, potentiostat, etc. It's already arranged. It is equipped with central control room, main transformer room, in-plant transformer room and 10 kV switchgear. The power transmission line of the power station is 10 kV secondary circuit, and the primary circuit goes to the county town through the standard sand factory, with the length of 13 km; The other time, it is connected to the county power grid through Zhonglou Township, with a length of 12km.

1988 The main project was completed,1989 was accepted in June, and it was connected to the county power grid for power generation in September. Total installed capacity of the power station 1 280 kW, and daily power generation 10 hour. The designed annual power generation is 3 1.5 1.7 million kwh, and the power generation in that year is 22,800 kwh. The total investment is 5.3 million yuan. 199 1 July, the motor was shut down for maintenance due to corrosion. Since then, it has been intermittent, and the power generation time is short and unstable. 65,438+0,995 generated 22,500 kWh.