Wind is one of the most common natural phenomena, and it is an "airflow" caused by uneven heating of the earth's surface by the sun. The kinetic energy of flowing air is called wind energy. Therefore, wind energy is a kind of generalized solar energy. According to the analysis of the World Meteorological Organization (WMO) and the Institute of Meteorological Science of China Meteorological Bureau, the available wind energy resources on the earth are 20 billion kilowatts, which is 20 times of the available water energy on the earth. In China, the available wind energy at land 10m height is 253 million kW, the available wind energy at sea is three times that at land, and the available wind energy at 50m height is twice that at 10m height, so the wind energy resources are very rich.
Wind energy is one of the renewable energy sources with mature technology and broad prospects for development and utilization. The utilization of wind energy includes not only wind power generation, wind-driven water lifting, but also wind heating and sail-assisted navigation. Therefore, the development and utilization of wind energy has great charm for scientific and technological workers all over the world, which has aroused many scientists around the world to devote themselves to the research of wind energy utilization. This paper will discuss the current situation and development trend of wind power generation technology at home and abroad.
Basic knowledge of wind power generation Edit this paragraph 1 Calculation formula of wind energy.
Air motion has kinetic energy. Wind energy refers to the kinetic energy of wind. If the cross-sectional area of the wind turbine impeller is a, when the wind with the wind speed of V passes through the impeller, the wind energy transmitted to the impeller by the wind per unit time is
(1) where: mass flow per unit time m=ρAV(2) Actually, in (3):
PW- wind energy, that is, wind power, in which air flows through the cross-sectional area of the wind turbine impeller every second, w;
CP-wind energy utilization coefficient of impeller;
The mechanical efficiency of hm- gearbox and transmission system is generally 0.80-0.95, and that of direct-driven wind turbine is1.0;
He-generator efficiency, generally 0.70-0.98;
R-air density, kg/m3;
A- the area swept by the wind turbine impeller in one rotation, m2;
V- wind speed, m/s.
2 Bates theory
The first complete theory about wind turbines was established in 1926 by A. Bates of Gottingen Institute in Germany.
Bates assumes that the wind wheel is ideal, that is, there is no hub, the number of blades is infinite, and there is no resistance for airflow to pass through the wind wheel. So this is a pure energy converter. In addition, it is further assumed that the air flow is uniform on the whole sweeping surface of the wind wheel, and the direction of air flow speed is along the axis of the wind wheel before and after or when passing through the wind wheel.
By analyzing the "ideal" wind wheel placed in flowing air, it is concluded that the maximum power that the wind wheel can generate is
(4) Where: PMAX-the maximum power that the wind wheel can generate;
-air density, kg/m3;
A- the area swept by the wind turbine impeller in one rotation, m2;
V- wind speed, m/s.
This expression is called Bates formula. It is assumed that the wind speed is consistent with the direction of the wind wheel shaft and uniform across the whole wind wheel scanning surface.
The theoretical maximum efficiency of the fan can be obtained by dividing Equation (4) by the kinetic energy of the wind when the airflow passes through the scanning surface A..
The limit value of Bates theory. This shows that the energy obtained by wind turbine from natural wind is limited, and its power loss can be explained as the residual rotational kinetic energy in the wake.
The conversion of energy will lead to the reduction of power, which varies with the types of wind turbines and generators used. Therefore, the actual wind energy utilization coefficient CP of wind turbines.
3 Temperature, atmospheric pressure and air density
The ambient temperature and atmospheric pressure of the experimental site are measured by thermometer and barometer, and the air density is calculated according to the following formula.
Where: ρ-air density, kg/m3;
H—— local atmospheric pressure, pa;
T-temperature,℃.
It can be seen from the formula of air density that air density is related to atmospheric pressure and temperature.
4 Main components of wind turbine
1) small wind turbine
The main components of small horizontal axis wind turbine are: wind wheel, generator, tower, steering mechanism, energy storage system, inverter and so on.
(1) wind wheel
The wind wheel is a part of the wind turbine that absorbs energy from the wind, and its function is to convert the kinetic energy of airflow into the mechanical energy of the wind wheel. The rotor of horizontal axis wind turbine consists of 1~3 blades. There are various structural forms of blades, and the material depends on the model and power of the fan, such as FRP blades covered with wood core and FRP resin blades.
(2) Generator
In wind turbines, there are three kinds of generators, namely DC generators, synchronous alternators and asynchronous alternators. Small wind turbines mostly use synchronous or asynchronous alternators, and the generated alternating current is converted into direct current through rectifier devices.
(3) Tower
The tower is used to support the generator and steering mechanism. Because the wind speed increases with the height above the ground, the higher the tower, the more wind energy the wind turbine captures per unit area, but the cost and installation cost also increase.
(4) Steering mechanism
Vertical axis wind turbines can accept wind blowing from any direction, so there is no need for steering mechanism. For the horizontal axis wind turbine, in order to obtain the highest wind energy utilization efficiency, the rotating surface of the rotor should always be aligned with the wind direction, so the wind power device is needed. The commonly used steering mechanisms mainly include tail rudder, steering wheel and electric wind power device.
(5) Speed limiting mechanism
When the wind speed is higher than the design wind speed of the wind turbine, it is necessary to control the speed of the wind turbine to prevent the blades from being damaged.
(6) Energy storage device
Energy storage device is very important for small wind turbines operating independently. Its energy storage methods include thermal energy storage and chemical energy storage.
(7) Inverter
It is used to convert DC into AC to meet the requirements of AC electrical equipment.
2) Large wind turbines
Large-scale wind turbine consists of two parts: pneumatic mechanical part and electrical part. The pneumatic machinery part includes a wind wheel, a low-speed shaft, a speed-increasing gearbox and a high-speed shaft, and its function is to drive the generator rotor and convert wind energy into mechanical energy. The electrical part includes asynchronous generator, power electronic frequency converter, transformer and power grid, and its function is to convert mechanical energy into electric energy with constant frequency. In recent years, the direct-drive variable-speed constant-frequency wind turbine (gearbox without speed increase) has been successfully developed.
Editor of Wind Turbine and Wind Power Generation Technology 1 History of Wind Turbine and Wind Power Generation Technology
Wind energy is one of the earliest energy sources used by human beings. As early as 2000 BC, sailing boats and windmills appeared in Egypt, Persia and other countries. In the Middle Ages, Holland and America used transverse windmills for irrigation and drainage. China is one of the earliest countries in the world to use wind energy. As early as 1800 years ago, there was a record of water pumping by wind in China. 1890, Danish company P Lacour successfully developed wind turbines. 1908, hundreds of small wind power stations were built in Denmark. From the beginning of 20th century to the end of 1960s, the development of wind energy resources in some countries was still in the stage of small-scale utilization.
With the adoption of large hydropower and thermal power units and the development of power system, medium and large wind turbines developed before 1970 were gradually eliminated due to high cost and poor reliability, and all of them stopped running at the end of 1960s. The experimental research at this stage shows that these medium and large units are generally feasible in technology, which laid the foundation for the great development in the late 1970 s.
Since 1980, wind turbine technology has been commercialized in the world. The main unit capacity is 300kW, 600kW, 750kW, 850kW, 1MW and 2MW. 199 1 year, Denmark built the world's first offshore wind farm in Winderby, which was composed of 1 1 Denmark plus 450kW single machine with a total installed capacity of 4.95MW. Subsequently, the Netherlands, Sweden and the United Kingdom also built their own offshore wind farms.
At present, the manufacturers with commercial production capacity of offshore wind power generation equipment mainly include Danish Vestas (including NEG-Micon integrated by it), American GE Wind Energy, Nordex, Repower, Pfleiderer/Prokon, German Bonus and the famous German Enercon Company. The rated power coverage of a single machine ranges from 2MW, 2.3MW, 3.6MW, 4.2MW and 4.5MW to 5MW. Impeller diameters range from 80m, 82.4m, 100m,10m, 1 14m, 1 16m to 126th.
Two types of wind turbines
Wind turbines are devices that convert wind energy into electrical energy. In view of the wide variety of wind turbines, there are also many classifications. According to the number of blades, there are single blades, double blades, three blades, four blades and multiple blades; According to the relative position between the main shaft and the ground, it is divided into horizontal shaft and vertical shaft (vertical shaft); According to the working principle of blades, there are lift type and drag type. At present, there are many types of three-blade horizontal shafts of wind turbines.
Horizontal axis wind generator, the rotation axis of the wind wheel is parallel to the wind direction; Vertical axis wind turbine, the rotation axis of the wind wheel is vertical to the ground or the direction of airflow.
Editor of current situation of wind power generation at home and abroad. This paragraph 1 Current situation of wind power generation in the world.
At present, more than 40 countries in the world have connected large and medium-sized wind turbines on land and at sea, and the trend that the growth rate of wind power is higher than other power sources continues. As shown in table 1, by the end of February 2005, the global installed capacity had reached 58,982MW, and the annual installed capacity was1100 MW, with an increase rate of 24%. Wind power generation accounts for 1% of global electricity, and some countries and regions reach more than 20%. The ten countries with the largest cumulative installed capacity of wind power in the world in 2005 are shown in Table 2. The top ten countries total 5 1750.9MW, accounting for 87.7% of the total installed capacity in the world.
In 2005, the diversification of international wind power market share showed a trend of sustainable development: 1 1 countries had installed capacity higher than 1 000MW, including 7 European countries (Germany, Spain, Italy, Denmark, Britain, Netherlands and Portugal) and 3 Asian countries (India, China and Japan). Asia is becoming a new force in global wind power development, with a growth rate of 48%.
In 2002, the European Wind Energy Association (EWEA) and Greenpeace published a report entitled "Wind Power 12", which outlined the blueprint for wind power to reach the world power 12% in 2020. The report points out that this document is not a forecast, but demonstrates the possibility of wind power reaching the world power 12% from the aspects of world wind energy resources, the growth of world power demand and power grid capacity, the development trend and potential growth rate of wind power market, the comparison with other power technologies such as nuclear power and large hydropower, and the requirement of reducing greenhouse gases such as CO2. The report also points out that the installed capacity of wind power in China may reach 65.438+0.7 billion kilowatts in 2020.
2 Current situation of wind power generation in China
According to the estimation of National Meteorological Research Institute, the theoretical exploitable amount of wind energy at land 10 meter height in China is 3.2 billion kW, and the actual exploitable amount is 253 million kW. The exploitable amount of offshore wind energy is three times that of onshore wind energy reserves.
The actual exploitable amount in Inner Mongolia is 0.610.80 billion kW.
The actual exploitable amount in Tibet is 40.8 million kilowatts.
The actual exploitable amount in Xinjiang is 34.3 million kilowatts.
The actual exploitable amount in Qinghai is 24.2 million kilowatts.
The actual exploitable amount of Heilongjiang is 0.10.72 billion kW.
In 2005, in addition to Taiwan Province Province, China added 592 wind turbines with an installed capacity of 503,000 kilowatts. Compared with the new installed capacity of 6.5438+0.98 million kilowatts in 2004, the growth rate of new installed capacity in 2005 was 254%.
By the end of 2005, China, except Taiwan Province Province, had accumulated 1.864 wind turbines with an installed capacity of 1.266 million kilowatts and 62 wind farms. It is distributed in 15 provinces (cities, autonomous regions and special administrative regions), and their ranking by installed capacity is shown in Table 3. Compared with the cumulative installed capacity of 764,000 kilowatts in 2004, the cumulative installed capacity increased by 65.6% in 2005. In 2005, the on-grid electricity consumption of wind power was about 65.438+53 million kW h [9].
The development and demonstration of high-power wind turbines, a major project of the 11th Five-Year National Science and Technology Support Plan of China, supports the development of doubly-fed variable-speed constant-frequency wind turbines with a capacity of more than 2.5MW 1.5~2.5MW. 1.5~2.5MW and above direct-drive variable-speed constant-frequency wind turbine development: 1.5MW and above wind turbine blades, gear boxes, doubly-fed generators and direct-drive permanent magnet generators development and industrialization; 1.5MW doubly-fed wind turbine control system and converter, direct-drive wind turbine control system and converter development and industrialization; Research on key technologies of offshore wind farm construction: development of special equipment for installation and maintenance of offshore wind turbines; The formulation of relevant standards for large-scale wind turbines and the analysis of wind power technology development 16 research. By the end of the 11th Five-Year Plan, the independent research and development capability of wind power technology in China will be close to the world leading level.
3 small wind turbines
Present situation of small wind turbine industry
As one of the main pillars of rural renewable energy, small-scale wind power industry has made great progress in 2005, with 70 units engaged in the development, research and production of small-scale wind power industry. According to the statistics of 23 production enterprises, in 2005, * * * produced 33,253 small wind turbines operating independently under 30kW, an increase of 34.4% over the previous year, of which 24 123 units were produced by 200W, 300W and 500W units, accounting for 72.5% of the total annual output; 15 * * * exported 5,884 small wind turbines, up 40.7% over the previous year, and earned 2.827 million US dollars, mainly exported to 24 countries and regions such as the Philippines and Vietnam. Moreover, due to the soaring prices of gasoline, diesel and kerosene, the supply channels are not smooth, and users who use diesel generators in inland areas, rivers and lakes, fishing boats, border posts, military units, weather stations, microwave stations, etc. gradually switch to wind turbines or wind-solar complementary power generation systems.
Development trend of small wind turbine industry
1) due to the improvement of the living standards of farmers and herdsmen and the increase of electricity consumption, the single power of small wind turbines continues to increase, and 50W units are no longer produced. The output of 100W and 150W units has decreased year by year, while the output of 200W, 300W, 500W and 1kW units has increased year by year, accounting for 800% of the total annual output.
2) Because farmers are eager to use electricity continuously, the popularization and application of "wind-solar hybrid power generation system" is obviously accelerated, and the development of multi-unit combination will become the development direction in the future.
3) With the formulation of the national renewable energy law and the guidance catalogue of renewable energy industry, there will be a variety of supporting measures and preferential tax policies, which will certainly improve the production enthusiasm of production enterprises and promote industrial development.
4) At present, there are still 28,000 villages, 7 million households and 28 million people in China without electricity, and they live in remote mountainous areas, agricultural and pastoral areas and conventional power grids, which are difficult to reach. According to experts' analysis, among the 7 million users without electricity, 3 million can use micro-hydropower to solve the problem of electricity consumption, and 4 million can use small wind power generation or wind-solar complementary power generation to meet the electricity demand of farmers and herdsmen.
Concentrated wind energy wind turbine
The concentrated wind energy type wind turbine was developed by the Institute of New Energy Technology of Inner Mongolia Agricultural University, and has obtained the patent of utility model in China (patent number: ZL94244 155.9). This type of wind turbine accelerates, rectifies and homogenizes the thin wind energy through the centralized wind energy device, and then drives the impeller to rotate to generate electricity, thereby increasing the energy flow density of wind energy, reducing the turbulence of natural wind, improving the instability of wind energy, improving the grade of wind energy and reducing the cost of wind power. The wind turbine has the characteristics of low wind speed, large power generation, low noise, high safety, long service life and low kWh cost.
Concentrated wind energy wind turbines can operate independently, with complementary wind and light, multi-machine networking and integration into low-voltage power grid. At present, a series of products have been developed, including 200W, 300W, 600W, 1kW, 2kW and other units. After the pilot test, the concentrated wind energy wind turbine can be developed to medium and large units. The application of this new wind power technology in China and even the whole world will effectively improve the power supply level and quality of the wind power system, effectively utilize low-grade wind energy and improve the competitiveness of wind power products, which has important economic and ecological benefits.
conclusion
In the next 20 years, wind power industry will be the fastest growing industry in the world, and wind power technology will also enter the golden age of rapid development; In China, the installed capacity of grid-connected wind turbines will increase significantly, attracting worldwide attention. Off-grid wind turbines have a wide range of development fields and great potential, and the total installed capacity will eventually exceed that of grid-connected wind turbines.