# How to calculate a wind generator using the formulas

Alternative energy received from wind power plants causes high interest in society. Evidence of this at the level of real household practice abounds.

Owners of suburban real estate build windmills with their own hands and are satisfied with the result, although the effect is also short-lived. The reason is that during the assembly the wind generator was not calculated properly.

Agree, I would not want to spend time and money on the project, to get inefficient installation. Therefore, it is important to understand how to make a calculation of the wind generator, and by what parameters to choose the main working units of the windmill.

The article is devoted to solving these issues. The theoretical part of the material is supplemented by illustrative examples and practical recommendations for assembling a wind generator installation.

The content of the article:

• Calculation of wind generator installation
• How to calculate the power of the windmill
• Calculation of screws wind turbines
• Selection of generators for wind turbines
• Calculation and selection of charge controller
• Selection of the battery for the system
• Calculation of the inverter for home windmill
• Conclusions and useful video on the topic

## Calculation of wind generator installation

How to start counting the system of reproduction of electricity from wind energy? Given that we are talking about a wind generator, a preliminary analysis of the wind rose in a specific area seems logical.

Such design parameters as wind speed and its characteristic direction for a given territory are important design parameters. They to some extent determine the power level of the windmill, which will be really achievable.

Wind turbines of such power is difficult to even imagine. But such designs exist and work effectively. However, calculations of such structures show relatively low power compared to traditional energy sources.

What is remarkable, this process is long-term (at least 1 month), which is quite obvious. Calculate the maximum probable parameters of wind speed and its most frequent direction is impossible with one or two measurements.

Dozens of measurements will be required. Nevertheless, this operation is really necessary if there is a desire to build an effective productive system.

### How to calculate the power of the windmill

Domestic wind turbines, especially those made with their own hands, have not yet had to surprise people with high power. It is understandable. One has only to imagine a massive mast with a height of 8-10 m, equipped with a generator with a span of the propeller blades of more than 3 m. And this is not the most powerful installation. Only about 2 kW.

For servicing wind turbines of such power, helicopters and teams of specialists, numbering up to ten people, are used. To calculate such a power plant, an even greater number of performers are involved.

In general, if you rely on a standard table showing the ratio of the power of the wind generator and the required span of the propeller blades, there is something to be surprised at. According to the table, a 2-meter propeller is required for a 10 W windmill.

For a 500-watt design, a screw with a diameter of 14 m is required. In this case, the parameter of the blade span depends on their number. The larger the blades, the smaller the swing.

But this is only a theory, due to the wind speed not exceeding 4 m / s. In practice, everything is somewhat different, and the power of domestic installation, actually operating for a long time, has never exceeded 500 watts.

Therefore, the choice of power here is usually limited to the range of 250-500 W with an average wind speed of 6-8 m / s.

Table of the dependence of the power of the wind energy system on the diameter of the working screw and the number of blades. This table can be used for calculations, but taking into account its compilation under the wind speed parameter up to 4 m / s (+)

From a theoretical position, the power of the wind power station is considered according to the formula:

N = p * s * v3/2,

Where:

• p - density of air masses;
• S - total blown area of ​​the propeller blades;
• V - air velocity;
• N - air flow rate.

Since N is a parameter that drastically affects the power of a wind generator, the actual capacity of the installation will be close to the calculated value N.

### Calculation of screws wind turbines

When designing a windmill, two types of screws are usually used:

• winged - rotation in the horizontal plane;
• Savonius rotor, Darier rotor - rotation in the vertical plane.

The design of screws with rotation in any of the planes can be calculated using the formula:

Z = L * W / 60 / V

Where:

• Z - the degree of rapidity (low speed) of the screw;
• L - the size of the length described by the blades of a circle;
• W - speed (frequency) of the screw;
• V - air flow rate.

Based on this formula, you can easily calculate the number of revolutions W - the speed of rotation.

This looks like a screw design called “Rotor Daria”. This version of the propeller is considered effective in the manufacture of wind turbines of small capacity and size. Screw calculation has some features

A working ratio of speed and wind speed can be found in the tables that are available on the network. For example, for a screw with two blades and Z = 5, the following relationship holds true:

 Number of blades Degree of rapidity Wind speed m / s 2 5 330

Also one of the important indicators of a windmill's screw is a step.

This parameter can be determined by using the formula:

H = 2πR * tg α,

Where:

• - constant (2 * 3.14);
• tg α - section angle.

Additional information on the choice of the shape and number of blades, as well as instructions for their manufacture is given in this article.

### Selection of generators for wind turbines

Having the calculated value of the screw speed (W), obtained by the above method, you can already select (make) the corresponding generator.

For example, when the degree of rapidity is Z = 5, the number of blades is 2, and the speed is 330 rpm. With a wind speed of 8 m / s. generator power should be approximately 300 watts.

Generator wind power plant "in the section." An exemplary copy of one of the possible designs of a generator of a home wind power system assembled independently

With such parameters, a motor that is used in the construction of modern electric bicycles can be a suitable choice as a generator for a household wind power plant. The traditional name of the part is the cycle motor (made in China).

It looks like an electric cycle motor, on the basis of which it is proposed to make a generator for a home windmill. The design of the cycle motor is ideal for implementation with little or no calculations and improvements. However, their power is small

Characteristics of an electric cycle motor are as follows:

 Parameter Meanings Voltage, V 24 Power, W 250-300 Rotational speed, rpm 200-250 Torque Nm 25

A positive feature of velomotors is that they practically do not need to be redone. They were constructively developed as electric motors with low revolutions and can be successfully used for wind generators.

For the manufacture of a windmill can use car generator or collect washing machine unit.

### Calculation and selection of charge controller

The battery charge controller is required for a wind power plant of any type, including a household structure.

The calculation of this device is reduced to the selection of the electrical circuit of the device, which would correspond to the calculated parameters of the wind system.

Of these basic parameters are:

• generator rated and maximum voltage;
• maximum possible generator power;
• maximum possible battery charge current;
• voltage on the battery;
• ambient temperature;
• environmental humidity level.

Based on the parameters presented, is charge controller assembly with your own hands or the selection of the finished device.

Battery charge controller used as part of a wind power plant. The device is an industrial manufacturer, choosing which you only need to carefully study the technical characteristics for precise coordination with the existing system

Of course, it is desirable to select (or assemble) a device whose circuit would provide the function of an easy start in conditions of the flow of weak air flows. A controller designed for operation with batteries of different voltages (12, 24, 48 volts) is also welcome.

Finally, when calculating (matching) the controller circuit, it is recommended not to forget about the presence of such a function as inverter control.

### Selection of the battery for the system

In practice, different types of batteries are used and almost all are quite suitable for use as part of a wind power system. But you have to make a concrete choice anyway. Depending on the parameters of the wind turbine system, the battery is selected for voltage, capacity, charge conditions.

Traditional components for home windmills are the classic acid-lead batteries. They showed good results in a practical sense. In addition, the cost of this type of battery is more acceptable compared to other types.

Lead-acid batteries are particularly unpretentious to charge / discharge conditions, but it is unacceptable to include them in a system without a controller.

Battery pack home wind generator. Not the best option of operation, given the chaos of the wires and storage requirements. With this state of energy storage devices, it is not necessary to rely on their long-term action.

In the presence of a wind generator set professionally executed charge controller, having a full-fledged automation system, the use of AGM batteries or helium.

Both types of energy storage devices are characterized by greater efficiency and long service life, but they place high demands on charge conditions.

The same applies to the so-called helium-type armored batteries. But the choice of these batteries for domestic windmill is significantly limited by the price. However, the life of these expensive batteries is the longest compared to all other types.

These batteries are also allocated a more significant charge / discharge cycle, but subject to the use of high-quality charger.

### Calculation of the inverter for home windmill

We should immediately make a reservation: if the design of a home energy wind installation contains one battery of 12 volts, it makes no sense to install an inverter on such a system.

On average, household power consumption is at least 4 kW at peak loads. Hence the conclusion: the number of batteries for such power should be at least 10 pieces and preferably under a voltage of 24 volts. On such a number of batteries, it already makes sense to install an inverter.

Small power inverter (600 W), which can be used for home small power plant. It is possible to power a TV or a small refrigerator from such 220-volt equipment. On the lamp in the chandelier current is not enough

However, to provide 10 batteries with a voltage of 24 W per each and to maintain their charge stably, a windmill with a capacity of at least 2-3 kW will be required. Obviously, for household unpretentious designs such power is not to pull.

However, the inverter power can be calculated as follows:

1. Sum up the power of all consumers.
2. Determine the time of consumption.

On a concrete example, it will look like this.

Let as a load there are household electrical appliances: lighting lamps - 3 pcs. 40 W each, TV receiver 120 W, compact 200 W refrigerator. We sum up the power: 3 * 40 + 120 + 200 and get 440 W at the output.

Determine the power of consumers for an average time period of 4 hours: 440 * 4 = 1760 W. Based on the obtained power value over the time of consumption, it seems logical to choose an inverter from among such devices with an output power of 2 kW.

Based on this value, the current-voltage characteristic of the required device is calculated: 2000 * 0.6 = 1200 V / A.

The classical scheme of reproduction and distribution of energy received from a domestic-type wind generator. However, to provide such a number of devices with long-term energy, a sufficiently powerful installation (+) is needed.

In reality, the load from a household to a family of three people, where there is a full-fledged equipment with household appliances, will be higher than that calculated in the example. Usually and in connection with the load time, the parameter exceeds the 4 hours taken. Accordingly, a wind power inverter will need a more powerful one.

Preliminary calculation of the windmill is useful not only for its self-assembly. To determine the optimal parameters is necessary and choosing a wind turbine.

## Conclusions and useful video on the topic

How the source data is analyzed and how the formulas are applied are presented in the video:

It is necessary to use the calculated data in any case. Whether it is an industrial power plant or manufactured for domestic conditions, the calculation of each node always carries with it the maximum efficiency of the device and, most importantly, operational safety.

Preliminary calculations determine the feasibility of the project, help to establish how costly or economical the project turns out.

Have experience in solving such problems? Or have questions on the topic? Please share your skills in calculating and designing a wind generator. You can leave comments and ask questions in the form below.

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