Introduction to small wind turbines
1. Conditions for use of small wind turbines
Small wind turbines should generally be used in areas with abundant wind resources. That is, the annual average wind speed is more than 3m/s, the cumulative number of effective wind speeds of 3-20m/s throughout the year is more than 3000h; the annual average effective wind energy density of 3-20m/s is more than 100W/m2. When choosing to use a wind turbine, you must be aware of it and avoid blindness. Only in this way can you make full use of local wind resources, maximize the efficiency of the wind turbine, and achieve higher economic benefits.
It should be pointed out that in areas rich in wind resources, it is best to choose a wind turbine whose rated design wind speed matches the local best design wind speed. If this can be achieved, it will be of great significance both in the selection of wind turbines and in the economic sense of utilizing wind resources. Wind tunnel tests have proven that the conversion power of the wind wheel is proportional to the cube of the wind speed, that is to say, the wind speed has the greatest impact on the power. For example, if a wind turbine with a rated design wind speed of 8m/s is installed in an area where the local optimal design wind speed is 6m/s, its annual rated output power will only reach 42% of the original design output power, that is to say, The rated output power of the wind turbine is reduced by 58% compared with the design value. If the rated design wind speed of the selected wind turbine is higher, the rated power output effect will be even more unsatisfactory. However, it must also be pointed out that the rated design wind speed of the wind turbine is relatively low, and the diameter of the wind wheel and motor will be relatively larger, and the cost of the whole machine will also increase accordingly. It is uneconomical from both a manufacturing and product economics perspective.
2. General requirements for the use of small wind power generators
At present, small wind turbines use batteries to store energy, and the electricity used by household appliances is provided by batteries. Therefore, the general principle when using electricity is that the battery can be replenished by the wind turbine in time after it is discharged. In other words, the amount of electricity charged into the battery and the amount of electricity consumed by the electrical appliance should be roughly equal (usually calculated in days). The following is an example to illustrate this problem: a wind turbine is used in a certain area, and the rated wind speed output power is IOOW. Assume that the wind blowing hours equivalent to the rated wind speed in the area on a certain day are 4 hours continuously, then the daily output of the wind turbine And the energy stored in the battery is 400Wh. Considering that the conversion efficiency of lead-acid batteries is 70, the actual energy available for user appliances is 280Wh. If the electrical appliances used by the user include:
(1) Two 15W light bulbs, used for 4 hours, the energy consumption is 120Wh;
(Z) One 35W TV, used for 3 hours, The energy consumption is 105Wh;
(3) A 15W radio cassette player, used for 4 hours, consumes 60Wh energy.
The total energy consumption above is 285Wh.
In this way, the total daily energy consumption of electrical appliances exceeds the energy provided by the wind turbine by 5Wh, which is the so-called "pay-for-pay" electricity consumption. , will cause the battery to work in a state of power loss. If you use electricity like this for a long time, the battery will be seriously depleted and damaged, shortening its service life.
The above example assumes the power consumption of the wind turbine at the rated wind speed. In fact, due to the variability and intermittent nature of the wind, the wind has different sizes (wind speed) and The difference in blowing time (wind frequency). Therefore, when using electrical appliances, you should use more electricity when the wind conditions are good and use less electricity when the wind conditions are bad. This requires users to carefully summarize their experience when using it.
In addition, qualified regions and users can prepare a kilowatt-class diesel generator set to recharge the battery when wind conditions are bad, so that the battery can provide uninterrupted power supply.
3. Reasonable matching of small wind turbines
The electric energy generated by small wind turbines is first stored in batteries, and then the batteries provide power to electrical appliances.
Therefore, issues such as the reasonable matching of wind turbine power and battery capacity and energy storage during quiet wind periods must be carefully and scientifically considered.
At present, the capacity of small wind turbines and batteries is generally matched according to the principle that input and output are equal, or input is greater than output. That is: a 100W wind turbine is matched with a 120Ah battery (60Ah 2 pieces); a 200W wind turbine is matched with a 120-180Ah battery (60 or 90Ah 2 pieces); a 300W wind turbine is matched with a 240Ah battery (120Ah 2 pieces); a 750W wind turbine is matched with a 240Ah battery (120Ah 2 pieces); 1000W wind turbine is matched with 360Ah battery (120Ah 3 pieces).
Practice has proved that if the matching battery capacity does not meet the energy requirements of the wind turbine, the following problems will occur:
(1) When the battery capacity is too large, the wind turbine will The energy emitted cannot ensure that the battery is fully charged in a timely manner, causing the battery to often be in a state of power loss. Shorten battery life. In addition, the battery capacity is large, and the price and usage costs increase accordingly, causing unnecessary waste in the economy.
(2) If the battery capacity is too small, the battery will often be in an overcharged state. If the wind turbine is stopped due to sufficient charging, the working efficiency of the wind turbine will be seriously affected. Long-term overcharging of the battery will cause early damage to the battery and shorten its service life.
In addition, the reasonable matching of small wind turbines and the matching of electrical appliances are also items that cannot be ignored. When selecting electrical appliances, the matching principle of batteries and wind turbines should also be followed. That is, the energy consumed by the optional electrical appliances must match the energy output by the wind turbine. However, it should be pointed out that the matching indicator emphasizes "energy" and should not be confused with power. When selecting electrical appliances, you must also pay attention to the voltage requirements. At present, small wind turbine distribution boxes are equipped with 12V, 24V and special sockets for TVs. When users use them, they must choose the corresponding voltage value according to the required voltage value of the electrical appliances. The TV should be specifically plugged into the TV socket.
If you are using AC power equipment, you must prepare an "inverter" that can meet its power requirements to convert the DC power from the battery into AC power with a voltage of 220V and a frequency of 50Hz before it can be used.
Section 2 Selection of installation site for small wind turbines
Selection of installation site for small wind turbines is very important. A wind turbine with high performance will not work if there is no wind, while a wind turbine with lower performance will fully function if the installation site is well selected. The site selection conditions for small wind turbines include very complex factors. Some countries such as the United States have published monographs on wind turbine site selection. In principle, locations with very strong winds and low turbulence during the year should be considered the best, but sometimes it is difficult to select such a location.
The figures are: the annual average wind speed is more than 3m/s, the cumulative effective wind speed of 3-20m/s is more than 3000h, and the annual average effective wind energy density of 3-20m/s is more than 100W/m2. As long as the first condition is met, small wind turbines can be considered economically viable.
2. The site should have a relatively stable prevailing wind direction. The prevailing wind direction refers to the wind direction with the highest frequency. In meteorology, the wind direction is generally represented by 16 directions (Figure 4-1). The length and number of each azimuth arrow are the average wind speed in that wind direction, and can visually draw a wind rose (Figure 4-2).
It can be seen from the wind rose diagram that the prevailing wind directions are southwesterly wind (average wind speed 11.7m/s), south-southwest wind (average wind speed 11.5m/s) and northeasterly wind (average wind speed 5.9m/s). s). Our country is a country with strong monsoons, and the prevailing wind direction changes in different seasons. It is hoped that the prevailing wind direction will be more stable when selecting a site, so that the favorable influence of the terrain can be easily considered.
3. The "wind shear" within the fan height range should be small (the wind shear should be small). "Wind shear" refers to large changes in wind speed and direction within a short distance. Figure 4-3 shows the wind shear on the top of a flat-top mountain ridge. The shadow area in the figure shows that the wind speed decreases due to air flow separation, and the upper part of the separation area is a strong shear area. If the fan is installed in this shadow area, the blades will rotate in the unequal wind, and the blades will be unevenly loaded.
Figure 4-1 16 azimuth diagrams of the wind direction
Figure 4 -2 Wind rose diagram
Reduce performance and shorten the service life of the fan. Therefore, the wind turbine should avoid this strong shear area and be installed on the windward slope, or the tower should be raised.
4. The influence of meteorological factors should be considered
(1) Turbulence. The so-called turbulence refers to sharp changes in airflow speed, including changes in wind direction. Usually these two factors appear together. Turbulent flow can affect the power output of the wind turbine, while causing the entire device to vibrate and damaging the wind turbine. Small turbulence is mostly caused by the influence of ground obstacles, so when installing wind turbines, such areas must be avoided.
(2) Extremely strong wind. The wind speed at sea can reach more than 30m/s, and inland it is sometimes called extremely strong wind when it is greater than 20m/s. Of course, the installation site of wind turbines must choose a place with high wind speed
Figure 4-3 Wind field changes on the top of a flat-top ridge
However, it should be used in areas prone to extremely strong winds. Wind turbines require the unit to have sufficient strength. Once there is extremely strong wind, the wind turbine will become the target of attack.
(3) Icing and sticky snow. Wind turbines installed at the junction of mountains and sea-land are prone to ice and snow. Once ice forms on the blades, their weight distribution will change. At the same time, changes in the wing shape will cause violent vibrations and even damage.
(4) Thunder. Because wind turbines are installed high in flat areas without obstacles, lightning strikes often occur. For this reason, it is best to add lightning protection devices to the wind turbine.
(5) Salt spray damage. When installing wind turbines in areas within 10-15km from the coastline, measures to prevent salt spray damage must be taken. Because salt spray can corrode metal parts such as blades and destroy the insulator inside the device.
(6) Dust and sand. In areas with a lot of dust and sand, the life of wind turbine blades is significantly shortened. The method of protection is usually to prevent damage to the leading edge of the blade and treat the leading edge surface. However, dust and sand can sometimes invade the interior of machinery, causing damage to mechanical parts such as bearings and gear mechanisms. In factory areas, harmful gases floating in the air can also corrode the metal parts of wind turbines, so you should be careful.
2. Site selection on flat terrain
According to the wind rose diagram that can simultaneously express the relationship between wind direction and wind speed, if there are no obstacles on the upwind side of the wind direction, it can generally be considered This location is flat. When installing a wind turbine on flat land, the following two conditions should be considered:
(1) There should be no obstacles within a circle with a radius of 1km centered on the installation site.
(2) If there are obstacles, the height of the wind turbine should be more than three times the height of the highest point of the obstacles. This relationship is shown in Figure 4-4. This condition is extremely strict, but can be relaxed for small wind turbines (for example, the radius can be set to 400m).
3. Site selection for ridge or mountaintop terrain
Ridges and mountaintops have natural tower functions, and as the airflow approaches the ridge, due to the wind tunnel effect, the airflow is approximately The line is accelerated and the energy increases accordingly. As shown in Figure 4-5a. However, the direction of the wind and the direction of the ridge are opposite