Heliostat. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Alternative energy sources

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One of the areas of solar energy is the direct conversion of solar energy into electrical energy using solar panels. The article describes a simple device that allows you to automatically orient the solar battery to the sun.

As is known, the power of the light flux at the Earth's surface at the equator reaches 1,1 kW/m2 (at the latitude of Moscow, about 0,5 kW/m2).

Approximately 40% of this energy can be converted into electrical energy by solar batteries created by the British company Sandia National Laboratories based on indium gallium arsenide nitride. In some cases, it is advisable to use conventional solar batteries with an efficiency of 20% [1].

The efficiency of solar batteries depends on many factors, but the orientation of its elements relative to the radiation source is decisive. To maintain optimal illumination of solar batteries, various tracking systems have been developed - from the simplest analog to analog-digital ones [2]. The adjustment of such devices is complicated by the fact that the threshold for their operation varies depending not only on the differential, but also on the total intensity of illumination. In addition, the intervention of maintenance personnel is required to restore such systems to their original state.

The proposed device (heliostat) uses pulse control and without outside interference is able to orient the solar battery to the best illumination. The schematic diagram of the heliostat is shown in fig. 1. It consists of a clock generator (DD1.1, DD1.2), two integrating circuits (VD1R2C2, VD2R3C3), the same number of shapers (DD1.3, DD1.4), a digital comparator (DD2), two inverters (DD1.5 .1.6, DD1) and a transistor switch (VT6-VT1) for the direction of rotation of the electric motor MXNUMX, which controls the rotation of the platform on which the solar battery is installed.

(click to enlarge)

With the power supply (from the solar battery itself or from the battery), the generator on the elements DD1.1, DD1.2 begins to generate clock pulses that follow at a frequency of about 300 Hz. When the device is in operation, the durations of the pulses generated by the inverters DD1.3, DD1.4 and the integrating circuits VD1R2C2, VD2R3C3 are compared. Their steepness varies depending on the integration time constant, which, in turn, depends on the illumination of the photodiodes VD1 and VD2 (the charging current of capacitors C2 and C3 is proportional to their illumination).

The signals from the outputs of the integrating circuits are fed to the level shapers DD1.3, DD1.4 and then to a digital comparator made on the elements of the DD2 microcircuit. Depending on the ratio of the durations of the pulses input to the comparator, a low-level signal appears at the output of the element DD2.3 (pin 11) or DD2.4 (pin 4). With equal illumination of the photodiodes, high-level signals are present at both outputs of the comparator.

Inverters DD1.5 and DD1.6 are required to control transistors VT1 and VT2. A high signal level at the output of the first inverter opens the transistor VT1, at the output of the second - VT2. The loads of these transistors are keys on powerful transistors VT3, VT6 and VT4, VT5, which switch the supply voltage of the electric motor M1. The R4C4R6 and R5C5R7 circuits smooth out ripples at the bases of the control transistors VT1 and VT2.

The direction of rotation of the motor changes depending on the polarity of the connection to the power source. The digital comparator does not allow all key transistors to open at the same time, and thus ensures high reliability of the system.

With sunrise, the illumination of the photodiodes VD1 and VD2 will be different and the electric motor will begin to turn the solar panel from west to east. As the difference in the duration of the pulses generated by the shapers decreases, the duration of the resulting pulse will decrease and the rotation speed of the solar battery will gradually slow down, which will ensure its accurate positioning. Thus, with pulse control, the rotation of the motor shaft can be transmitted directly to the platform with a solar battery, without the use of a gearbox.

During the day, the solar-powered platform will rotate to follow the movement of the sun. With the onset of twilight, the duration of the pulses at the input of the digital comparator will be the same and the system will go into standby mode. In this state, the current consumed by the device does not exceed 1,2 mA (in orientation mode, it depends on the motor power).

The heliostat battery is used to store the energy generated by the solar battery and power the electronic unit itself. Since the motor is only turned on to turn the battery (ie, for a short time), there is no power switch.

The described device orients the solar battery in a horizontal plane. However, when positioning it, one should take into account the geographical latitude of the area and the time of year. If the design is supplemented with a vertical deflection block assembled according to a similar scheme, it is possible to fully automate the orientation of the battery in both planes.

In addition to those indicated in the diagram, microcircuits of the K564, K176 series can be used in the device (with a supply voltage of 5 ... 12 V). Transistors KT315A are interchangeable with any of the KT201, KT315, KT342, KT3102 series, and KT814A - with any of the KT814, KT816, KT818 series, as well as germanium P213-P215, P217 with any letter indices. In the latter case, resistors with a resistance of 3 ... 6 kOhm should be connected between the emitters and the bases of transistors VT1-VT10 to prevent their accidental opening due to a significant reverse current.

Instead of FD256 photodiodes, it is permissible to use separate solar cells of the battery itself (connected with polarity), phototransistors without bias circuits, as well as photoresistors, for example, SF2, SFZ or FSK of any modification. It is only necessary to select (by changing the resistance of the resistor R1) the frequency of the clock generator according to the reliable operation of the digital comparator.

All parts of the device are mounted on a printed circuit board (Fig. 2) made of double-sided foil fiberglass. Transistors VT3 - VT6 are screwed to the board and equipped with L-shaped heat sinks with an area of ​​about 10 cm2, bent from strips of aluminum alloy sheet 1,5 mm thick. When using a more powerful electric motor, these transistors are placed outside the board on separate heat sinks that provide efficient heat dissipation. The board is placed in a sealed plastic case, fixed at the same level with the solar battery.

A green light filter is used to protect the photodiodes from excessive irradiation. An opaque curtain is placed between the photo sensors. It is fixed perpendicular to the board in such a way that when the angle of illumination changes, it obscures one of the photodiodes.

The solar battery is installed on a platform, under which an MP-3-015 electric motor (supply voltage 6 V) is mounted, which rotates it in a horizontal plane. It is possible to use a more powerful motor, in which the direction of rotation of the shaft also changes depending on the polarity of the voltage.

A battery is connected to the battery through a current collector, the charging current of which corresponds to the maximum current generated by the battery.

Assembled from serviceable parts, the device does not require adjustment and immediately starts working. Its sensitivity is such that the battery is confidently guided by the light flux from the MN 2,5 V-0,15 A lamp located at a distance of 3 m from the photo sensors.

Literature

1. Zinoviev K., Pantuev V. Solar batteries for powering REA. - Radio, 1995, No. 1, p. 44; No. 2, p. 43, 44.
2. Bayere T. 20 designs with solar cells. - M.: Mir, 1988.

Author: I. Tsaplin, Krasnodar

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