Introduction

A solar tracker is a device that orients a solar panel towards the Sun to get maximum light energy. For flat-panel photovoltaic systems, trackers are used to minimize the angle of incidence between the incoming sunlight and a photovoltaic panel. This increases the amount of energy produced from a fixed amount of installed power generating capacity. Here we will use some simple and easily available components to construct the circuit.

Components required

Resistors  1 kΩ

Variable resistor 10 kΩ

Capacitor 0.01 µF

NE 555

LDR

BC 547

Relay

BO Motor

Diode 1N4007

Solar cell.

Components Description

Resistor

A resistor restricts the flow of current. The resistors used here are carbon film and quarter watt type.

LED (Light Emitting Diode)

It is a transducer which converts electrical energy into light energy.

Transistor

A transistor amplifies current. It can be used with other components to make an amplifier or switching circuit. BC 547 is a general purpose transistor. It is an npn epitaxial silicon transistor. Its maximum collector current (DC) is 100mA.

Capacitor

A capacitor stores electric charge. Capacitor used here is 0.01 µF and it is a mica type.

LDR

LDR Stands for Light Dependant Resistor. LDR is a kind of variable resistor and its resistance value varies depending on the intensity of light falling on it. In dark, LDR offers extremely high resistance as high as 10 Mega Ohm but it reduces to 100 Ohms or less in bright light. So LDR is an ideal light sensor when our circuit has a dependency parameter as sun light. You can use a 5mm diameter LDR here.

NE 555

The 8-pin NE 555 timer is the most useful ICs ever made in the world. Its popular name is timer IC. It is used in many electronics projects. Just adding a few external components, it can be used to construct so many circuits. The 555 has three operating modes: Monostable mode, Astable mode and Bistable mode. It can withstand maximum supply voltage up to 16 volt. It has a maximum power dissipation up to 600mW.

Relay

Generally relay is defined as an electromagnetic switch. The relay used here is a 12 volt ice cube type.

BO Motor

BO  stands for  Battery Operated . BO motors are suitable for electronics hobby activities especially for small projects. It consists of small DC motor with gear arrangement to increase the torque. It is used in many DIY Robotic applications that are operated through batteries.

Diode 1N4007

These are general purpose diodes. These diodes have high current capability and low forward voltage drop. The average rectified output current is one ampere.

Solar cell  

A solar cell (also called a photovoltaic cell) is an electrical device that converts the energy of light directly into electricity by the photovoltaic effect. It is a form of photoelectric cell, defined as a device whose electrical characteristics e.g. current, voltage, or resistance vary when exposed to light. Cells can be described as photovoltaic even when the light source is not necessarily the sunlight. Photons in sunlight hit the solar panel and are absorbed by semiconducting materials, such as silicon or germanium. Electrons are excited from their current molecular/atomic orbital. Once excited an electron can either dissipate the energy as heat and return to its orbital or travel through the cell until it reaches an electrode. Current flows through the material to cancel the potential and this electricity is captured for our use.

How it works

NE555 is the popular timer IC which is used in the circuit as a Schmitt trigger to get a bistable action. The set and reset activities of the IC is used to switch on/off the relay. Inside the IC there are two comparators. The upper threshold comparator trips at 2/3 Vcc while the lower trigger comparator trips at 1/3 Vcc. The inputs of these two comparators are tied together and connected at the junction of the LDR and variable resistor. Thus the voltage provided by the LDR to the inputs depends on the intensity of light.

When there is light, the LDR has less resistance and current flows through it to the threshold (Pin6) and the trigger (pin2) inputs of IC. As a result, the voltage at the threshold input goes above 2/3 Vcc which resets the internal Flip-Flop and the output remains low. At the same time, the trigger input gets more than 1/3Vcc. Both the conditions keep the output of timer IC low when there is light. The relay driver transistor is connected to the output of IC so that, the Relay remains de energized when there is light.

When there is dark, the resistance of LDR increases and the amount of current flowing through it reduces. As a result of this, the voltage at the threshold comparator input (pin6) drops below 2/3Vcc and the voltage at the trigger comparator input (pin2) less than 1/3Vcc. Both these conditions cause the output of the comparators to go high which sets the Flip-Flop. This changes the output of IC to high state and transistor triggers. When transistor conducts, relay energizes and completes the motor circuit. Here the operation of motor depends on the relay. The motor rotates the panel. The motor used is a BO motor with high torque and low rpm. The LDR is mounted on the solar panel axis with an approximately 10 cm long  black pipe so that sunlight reaches to the LDR as a narrow beam of light. When the sun light incidents on the LDR, this makes the motor to rotate through the normally connected pin of relay and consequently black pipe shifted with the panel axis and motor stops due to dark. Because motor can’t get power through the normally open pin of relay when LDR is at dark. This process continues in a step after step due to the movement of the sun from east to west. Thus, how we get a step rotation from a BO motor. Only 4V dc is supplied to the BO motor for slower rotation.

Watch the operation video of a very similar type of model in our You Tube Channel…