Sun tracker. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Alternative energy sources

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Until now, when operating solar panels, we have been content with the total dispersion of sunlight. True, some seasonal changes were taken into account, as well as the time of day (orientation in the east-west direction). Nevertheless, the solar panels remained more or less fixed in the working position once found. In a number of cases, we did not even attach much importance to this, approximately exposing the battery in the direction of the sun.

However, it is known from experience that solar cells generate maximum energy only when they are exactly perpendicular to the direction of the sun's rays, and this can happen only once a day. The rest of the time, the efficiency of solar cells is less than 10%.

Suppose you were able to track the position of the Sun in the sky? In other words, what would happen if you rotated the solar array during the day so that it always pointed directly at the sun? By changing this parameter alone, you would increase the total efficiency of solar cells by approximately 40%, which is almost half of the energy produced. This means that 4 hours of useful solar intensity automatically turns into almost 6 hours. Tracking the sun is not difficult at all.

The principle of operation of the tracking device

The tracking device consists of two parts. One of them combines a mechanism that drives the receiver of solar radiation, the other - an electronic circuit that controls this mechanism.

A number of solar tracking methods have been developed. One of them is based on mounting solar cells on a holder parallel to the polar axis. You may have heard of similar devices called equatorial tracking systems. This is a popular term used by astronomers.

Due to the rotation of the Earth, it seems to us that the Sun moves across the sky. If we took into account this rotation of the Earth, the Sun, figuratively speaking, "stopped" would.

The equatorial tracking system works in a similar way. It has a rotating axis parallel to the Earth's polar axis.

If you attach solar cells to it and rotate them back and forth, you will get an imitation of the rotation of the Earth (Fig. 1). Axis co-directional with the axis of rotation of the Earth.

Ris.1

The tilt angle (polar angle) is determined by the geographic location and corresponds to the latitude of the place where the device is mounted. Suppose you live in an area corresponding to 40°N. Then the axis of the tracking device will be rotated at an angle of 40° to the horizon (at the North Pole, it is perpendicular to the Earth's surface (Fig. 2).

Ris.2

The rotation of solar cells to the east or west about this inclined axis will imitate the movement of the sun across the sky. If we rotate the solar cells with the angular velocity of the Earth's rotation, we can completely "stop" the Sun.

This rotation is carried out by a mechanical tracking system. A motor is needed to rotate solar cells around an axis. At any moment of the daily movement of the sun, the plane of the solar panels will now be perpendicular to the direction of the sun's rays.

The electronic part of the tracking device gives the leading mechanism information about the position of the Sun. By electronic command, the panel is installed in the desired direction. As soon as the sun moves to the west, the electronic controller will start the electric motor until the correct direction of the panel to the sun is restored again.

Tracker characteristics

The novelty of our tracking device lies not only in the implementation of the orientation of solar cells to the sun, but also in the fact that they feed the control electronic "brain". This is achieved through a unique combination of structural and electrical characteristics of the device.

Let us first consider the design features of the device, referring to Fig. 3.

Ris.3

The solar battery consists of two panels containing three elements each, connected in series and placed on the planes of a transparent plastic case. The panels are connected in parallel.

These panels are mounted at right angles to each other. As a result, at least one of the modules will be constantly illuminated by the sun (subject to the limitations discussed below).

First consider the case where the entire device is positioned so that the bisector of the angle formed by the panels is directed exactly at the sun. In addition, each panel is tilted at an angle of 45° to the sun (Fig. 4) and generates electrical energy.

Ris.4

If you rotate the device 45° to the right, the right panel will be parallel and the left panel will be perpendicular to the sun's rays. Now only the left panel generates energy, the right panel is idle.

Rotate the device another 45°. The light continues to hit the left panel, but at a 45° angle. As before, the right side is not illuminated and therefore does not generate any power.

You can repeat a similar rotation to the left side, while the right panel will generate energy, and the left panel will be idle. In any case, at least one battery generates electricity. Since the panels are connected in parallel, the device will always produce electricity. During our experiment, the module rotated 180°.

Thus, if a particular device is fixed so that the joint of the panels is directed to the midday sun, the output of the solar battery will always generate electrical voltage, regardless of the position of the sun in the sky. From dawn to dusk, some part of the device will be illuminated by the sun.

Great, but why all this? Now you will know.

Electronic sun tracking system

To follow the movement of the sun across the sky, the electronic control circuit must perform two functions. First of all, she must decide whether there is a need for tracking at all. It makes no sense to waste energy on the operation of the electric motor if there is not enough sunlight, for example, in the presence of fog or clouds. This is the purpose for which the above device is needed in the first place!

To understand the principle of its operation, let us turn to the electronic circuit shown in Fig. 3. Let's focus on the RL1 relay first. To simplify the discussion below, let's assume that transistor Q1 is saturated (conducting) and transistor Q2 is not present.

Relay RL1 is a circuit element that reacts to the current flowing through it. The relay has a wire coil in which the energy of the electric current is converted into the energy of a magnetic field. The field strength is directly proportional to the strength of the current flowing through the coil.

With an increase in current, there comes a moment when the field strength increases so much that the relay armature is attracted to the winding core and the relay contacts close. This moment corresponds to the so-called relay threshold.

Now it is clear why the relay is used when measuring the threshold intensity of solar radiation using solar cells. As you remember, the current of a solar cell depends on the intensity of light. In our circuit, two solar panels are actually connected to the relay, and until they generate a current that exceeds the trip threshold, the relay does not turn on. Thus, it is the amount of incident light that determines the response threshold.

If the current strength is slightly less than the minimum value, then the circuit does not work. The relay and the solar panel are matched so that the relay is activated when the light intensity reaches 60% of the maximum value.

This is how the first task of the tracking system is solved - determining the level of solar radiation intensity. Closed relay contacts turn on the electric motor, and the system starts to look for orientation to the sun.

So we come to the next task, namely, to find the exact orientation of the solar battery to the sun. To do this, let's go back to transistors Q1 and Q2.

There is a relay in the collector circuit of transistor Q1. To turn on the relay, it is necessary to short the transistor Q1. Resistor /?1 sets the bias current, which opens the transistor Q1.

Transistor Q2 is a phototransistor, its base region is illuminated by light (in conventional transistors, an electrical signal is applied to the base). The collector current of a phototransistor is directly proportional to the light intensity.

Resistor R1, in addition to setting the bias current of transistor Q1, is also used as a load for transistor Q2. When the base of transistor Q2 is not illuminated, there is no collector current and all the current through resistor R1 flows through the base, saturating transistor Q1.

As the illumination of the phototransistor increases, the collector current begins to flow, which flows only through the resistor R1. According to Ohm's law, an increase in current through a fixed resistor R1 leads to an increase in the voltage drop across it. Thus, the voltage at the collector of Q2 also changes.

When this voltage drops below 0,7V, the predicted phenomenon will occur: transistor Q1 will lose bias due to the fact that it needs at least 0,7V to carry the base current. Transistor Q1 will stop conducting current, relay RL1 will turn off and its contacts will open.

This mode of operation will only take place when transistor Q2 is pointed directly at the sun. In this case, the search for an exact orientation to the sun is terminated due to the opening of the engine power supply circuit by the relay contacts. The solar array is now pointing exactly at the sun.

When the sun leaves the field of view of transistor Q2, the transistor

Q1 turns on the relay and the mechanism starts moving again. And finds the sun again. The search is repeated many times as the sun moves across the sky during the day.

By evening, the intensity of illumination decreases. The solar panel can no longer generate enough energy to power the electronic system, and the relay contacts open for the last time. In the early morning of the next day, the sun illuminates the battery of the tracking system, oriented to the east, and the operation of the circuit begins again.

Similarly, the relay contacts open if the illumination decreases due to bad weather. Suppose, for example, that in the morning the weather is fine and the tracking system has started working. However, at noon the sky began to frown and the decrease in illumination caused the tracking system to stop working until the sky cleared up again in the afternoon, or maybe the next day. Whenever this happens, the tracking system is always ready to resume operation.

Design

Making a tracking device is quite simple, since a significant part of the parts is made of organic glass.

However, a very important point is to match the characteristics of solar panels and relays. It is necessary to select elements that generate a current of 80 mA at the maximum intensity of solar radiation. Selection can be done through testing. For this purpose, this tester is quite suitable.

I have found that the crescent cells put out about 80 mA on average. Therefore, of all the types of elements that are on sale, I used these elements for my device.

Both solar panels are similar in design. Each contains three elements that are connected in series and attached to Plexiglas plates measuring 10x10 cm2. The elements will be constantly exposed to the environment, so protection measures must be provided for them.

It would be nice to do the following. Place the finished battery on a Plexiglas plate placed on a flat metal surface. From above, cover the battery with a relatively thick (0,05-0,1 mm) layer of lavsan film. Thoroughly heat the resulting structure with a blowtorch so that the plastic parts melt and solder together.

At the same time, be careful. If you place a Plexiglas plate on a surface that is not flat enough or if it is overheated, it may warp. Everything should be similar to cooking a grilled cheese sandwich.

Ris.5

When finished, check the tightness of the seal, especially around the edges of the solar cells. You may need to lightly crimp the edges of the Dacron while it is still hot.

After the panels have cooled down sufficiently, glue them together as shown in fig. 5 and connect them in parallel. Don't forget to solder the leads to the batteries before assembling the device.

Electronic brain

The next important design element is the relay. In practice, the relay is a coil wound around a small reed contact.

The relay winding consists of 420 turns of No. 36 enamelled copper wire wound around a frame small enough to fit the reed contact with interference. I used a cocktail straw as a frame. If you touch the ends of the straw with a hot knife blade, the cheeks of the frame are formed, as it were, protecting the winding from slipping over the edges. The impedance of the winding should be 20-30 ohms. Insert the reed switch into the frame and fix it with a drop of glue.

Then connect transistor Q1 and resistor R1 to the relay. Without connecting transistor Q2, apply power from the solar cells and check the operation of the circuit.

If everything is working correctly, the relay should trip when the sunlight intensity is around 60% of full intensity. To do this, you can simply cover 40% of the surface of the solar cells with an opaque material, such as cardboard.

Depending on the quality of the reed switch, there may be some deviation from the ideal value. It is acceptable to start the relay at a light intensity of 50-75% of the maximum possible value. On the other hand, if you do not meet these limits, you need to change either the number of turns of the relay winding or the current of the solar array.

The number of turns of the relay winding should be changed in accordance with the following rule. If the relay operates earlier, the number of turns must be reduced, if later - increased. If you want to experiment with changing the current of the solar array, connect a shunt resistor to it.

Now connect the phototransistor Q2 to the circuit. It must be placed in a light-tight case, otherwise it will not work correctly. To do this, take a copper or aluminum pipe about 2,5 cm long and with a diameter corresponding to the diameter of the transistor housing.

One end of the pipe should be flattened so that a gap of 0,8 mm wide remains. Attach the tube to the transistor.

The finished control circuit, containing the elements Q1, Q2, R1 and RL1, is filled with liquid rubber for the purpose of sealing.

Four drives are output from the device: two - from relay contacts, two - from solar panels. For pouring liquid rubber, a form made of thick paper (such as a postcard) is used. To make it with a sheet of paper, wrap a pencil and secure the paper so that it does not unfold. After the polymer layer around the diagram has dried, remove the paper form.

Working with the device

Operating the tracking device is quite simple. First, assemble a simple tracking mechanism.

Mount your battery on a rotating axle. You can attach the battery to a suitable frame and then attach the frame to the pipe using friction or rolling bearings. Then install a motor with a gearbox to rotate the frame around the axis. This can be done in many ways.

Since the relay only performs the functions of switching on and off in the electronic circuit, it is necessary to have elements that would switch the rotational voltage of the electric motor. This requires limit switches located in the extreme positions of the frame. They are connected according to the diagram shown in Fig. 6. Limit switch No. 1 is included in fig. 6 is incorrect. To ensure the correct operation of the circuit, the terminals of the limit switch must be connected in parallel with the contacts of the relay RL1, connected in series with the relay.

Ris.6

It can be seen from the figure that this is a simple polarity switch circuit. When power is applied, the electric motor starts to rotate. The direction of its rotation depends on the polarity of the power supply.

At the moment of power supply, the polarity switching relay RL1 does not work, because the power circuit of its winding is broken by normally open contacts. The electric motor rotates the frame towards limit switch No. 1. This switch is located so that the frame rests against it only in the extreme position of its rotation. The author equally designates various relays in the diagrams of Figures 3 and 6. To avoid confusion in the future, the relay RL1 in Fig. 3 is called the reed relay of the servo system, and its contacts in Fig. 6 are called reed switches. Relay RL1 in Fig. 6 is more powerful than the reed relay, with three groups of changeover contacts.

When this switch is closed, relay RL1 is activated, which reverses the polarity of the supply voltage of the electric motor, and the latter starts to rotate in the opposite direction. Although limit contact #1 opens again, the relay remains energized due to its contacts being closed.

When the frame is pressed on the limit switch No. 2, the power circuit of the relay RL1 opens and the relay turns off. The direction of rotation of the motor is reversed again and the sky tracking continues.

The cycle is interrupted only by the reed relay RL 1 from the solar tracking circuit, which controls the power circuit of the electric motor. However, the RL 1 relay is a low-current device and cannot directly switch the motor current. Thus, the reed relay switches the auxiliary relay, which controls the electric motor, as shown in fig. 6.

The tracking system's solar arrays must be located close to the rotation mechanism. The angle of their inclination should coincide with the angle of inclination of the polar axis, and the junction of the batteries is directed to the midday sun.

The electronic module is connected directly to the rotation device. Orient the slot of the phototransistor cover parallel to the polar axis. This takes into account seasonal changes in the position of the sun above the horizon.

Author: Byers T.

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