Tracking Solar Panel

This small 12 V solar power source maintains its orientation towards the sun under control of a timer rather than the more  usual light-sensitive arrangement. All the  parts needed to build the project can be found in a well-stocked hardware shop or DIY store.

Tracking Solar Panel Project Image:

Tracking Solar Panel Project

The axle is made from the core of a roller blind with two bearings. Suitable angle brackets are readily available to hold these  bearings. The axis of rotation is set vertically, and the whole thing is directly driven by a battery-powered rotisserie motor. This motor already includes a gearbox to give a slow rotation and is capable of turning in either direction, and so one could hardly ask for a more perfect device for the job.

The upper end of the roller blind axle  must be filed down to a suitable (generally square) cross section to allow it to be  driven by the rotisserie motor. Now to the electrical department to find a cheap electronic mains time switch. The switch must be programmable for at least four on-off cycles per day. For the solar panel itself any 12 V solar charger designed for car, camping or boat use is ideal. It should be at most 0.25 m2 in area as other-wise the force of the wind may be too great for the gears in the rotisserie motor’s gear-box to withstand. The angle of inclination of the module is fixed, and depends on the latitude at which it is installed.

Tracking Solar Panel Circuit Diagram:

Solar Panel Circuit Diagram

The mains portion of the times witch and  the switching relay are not required and are removed. The remainder of the time-switch will act as a clock which causes the  axle to be rotated eight times during the  course of each day: each on-to-off or off-to-on transition of the clock will advance the  axle by 22.5 degrees from east to west via  south. The angle through which the roller blind axle turns is defined by its octagonal  shape: the corners operate a micro-switch  S1, which is fitted with an actuation lever.

The position of the micro switch must be set  carefully so that the switch is closed when  the lever is pushed aside by a corner and  open when between corners. Each time  the time-switch changes state IC2, a CMOS  4011 which contains four NAND gates,  switches the drive motor on via p channel MOSFET T3 for as long as necessary  until the micro-switch also changes state.  Reasonable settings for the time switch  have been found to be as follows: 7.30 am  on; 9.00 am off; 10.30 am on; 12 noon off;  2.00 pm on; 4.00 pm off; 6.00 pm on; and  9.00 pm off.

After eight moves the solar panel has rotated through a total of 180 degrees and points directly west. Counter IC1,  constructed from the two CMOS JK flip-flops in a 4027, detects the eighth clock  pulse and turns on relay Re1 via IC3. This in turn reverses the polarity of the power  to the motor and the panel starts to turn  back from west to east. When it reaches  its original position facing due east limit  micro-switch S2, actuated directly by the  solar panel, opens. The connected load  is also switched on and off by S2, which is  open during the night and closed during  the day. The author uses his solar panel to operate a small water pump. For this purpose  the output of the panel is regulated to 5 V  using a highly efficient switching regulator.  Alternatively, 12 V lighting could be powered from the panel, with no need for the  regulator.

Of course, both the control electronics and the time-switch need to be housed in a waterproof enclosure. Energy storage to  cover for the inevitable cloudy days can  be provided by a 12 V battery comprising ten 2800 mAh AA-size NiMH cells in a  suitable battery holder, which can be fit-ted inside an ordinary electrical junction  box. A 3000 mAh D cell is fitted in the battery compartment of the rotisserie motor,  wired in series with the 12 V battery and  also charged from the solar panel.

The motor and battery connections from the rotisserie motor are taken to the con-trol circuit using a four-core cable. The  rotisserie motor’s switch is removed. Resistor and capacitor values shown in the cir-cuit are not particularly critical, and other  similar types can be substituted for T1, T2  and T3. A Schottky diode should be used  for D3, which prevents current flow back  into the solar panel, in order to minimise  power losses. The 5 V regulator operates  at around 250 kHz and so a high-speed  switching diode is needed for D4. Using  an ordinary 1N4007 considerably reduces  the efficiency of the regulator and is there-fore not a good idea. A small toroidalcore inductor is used for L1.

Author : Manfred Schmidt-Labetzke - Copyright : Elektor


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