Sun tracking of solar panel with MPPT charge controller.

Achieving  Optimal  Power Point  Of  Solar  Cell Using  Sun   Tracking And  Maximum Power Point Tracking  Method

Basics of solar cell:

A solar cell or photovoltaic cell is a device that converts light directly into electricity by the photovoltaic effect. Sometimes the term solar cell is reserved for devices intended specifically to capture energy from sunlight, while the term photovoltaic cell is used when the light source is unspecified. Assemblies of cells are used to make solar panels, solar modules, or photovoltaic arrays.

Objective:

•         Longer Backup

•         Required Efficiency>15%

Modification:

•         Modification of solar panel by LDR sensors

•         Rotation of panel by Dc gear motors

•         Optimal point achievement by MPPT

Hardware Implementations:

•         Sun Tracking through Motors and Driver circuit

•         Protection of batteries through PIC controller and RELAYS

•         Optimal point achievement by buck circuit

•         Conversion of DC power into AC power by full wave INVERTER

Proposed Solution:

Using Hardware:

We have designed all the following circuits.

·         Sensor placement on the panel for tracking

·         Motors placement for tracking

·         Motor driver circuit for tracking of panel

·         Charging protection circuit for battery

·         Buck circuit for MPPT implementation

·         Full wave inverter for DC to AC conversion

I.Sensor placement on the panel for tracking:

First we have to select proper sensor for the tracking to detect the light from our source. Now we have choice between different sensors as LDR sensors and PHOTO DIODE and different other sensors which were available in market .LDRare commonly used in market and photo diode are not so common as LDR are. For real time analysis photo diode are best and as LDR are very sensitive for light as compared to photo diode .we are using LDR  as we are using it in demo but these will be replaced by photo diode in case of real time analysis .

            

We have put sensors in 7 different to fully track the source. Four sensors in four sides of panel and one sensor in center of the panel and two in the bottom side to check that either source is in back position or in the front .our first priority are these sensors then we will compare other sensors for movement. We will get the output from these sensors and give it to comparator and comparator compares this and these comparators are in pic micro controller.

II.Motors placement for tracking:

We have placed two dc gear motors in two different positions for the two dimensional rotation of panel. DC gear motors are very efficient in rotation and especially in our case of tracking. These motors are very sensitive to movement and polarity. And movement control is easy as compared to stepper and servo motors. And to stand on one position is very necessary in our case and stepper motor can’t do it because it needs constant energisation for this purpose and it will drain the battery after some time and we could not risk the efficiency of our system and we need two movements and one is azimuth and other is             movement .we have used chains that are used in bikes as timing chains to rotate the panel

              

III. Motor driver circuit for tracking of panel:

We have chosen PIC microcontroller (18F452) for this sun tracking circuit because it has 8 pins for ADC and two pins for PWM pulse width modulation. We have applied 5 volt across LDR’s in series with resistors. Then we have given an input through a wire to the ADC of PIC microcontroller and we took this wire connection from B/W the LDR and resistor. After that we took four outputs from PIC micro controller and then we put these wires as input into the ic ULN 2003 for the relay driver operation. As PIC controller gives us 5 volts and to drive the relay we need 12 volts so to reach that voltage level we fulfill these volts by the help of this ULN 2003.And we put 12 volts into the pin #9 of ULN 2003.Then we took four wires as output from ULN 2003 and connect them into the four points of relays and give 12 volts to the other remaining points of relays.

Fig .3

Then we took a MOSFET and we ground its source pin and attached its drain with the switching pin of relay and at its gate we connect a pin from PIC controller by which PWM input will be sent to the relay and its working is according to the PIC input. After that we design another part of the circuit same as like we have design before with two relays and one MOSFET.And after that we apply another 12 volt on one pin of all relays and attach remaining pins to the two DC gear motors .

IV. Charging protection circuit for battery:

In this circuit we are using PIC controller. And we have taken two inputs one from solar panel and one from the battery. And we are checking the solar panel and battery voltage level and we are then indicating this voltage level and displaying these levels on the LCD attracted on D port. Then we take a relay and a ic ULN 2003 and a MOSFET .We connect this ULN 2003 with the PIC controller by the four wire connection  which are coming from PIC controller  as output as going into the ULN 2003.And we have connected this MOSFET which we have connected in our circuit.

The source of this MOSFET is grounded and drain is connected to the relay and its gate is attached to the controller and PWM is coming as input to the MOSFET from the controller. And we have attached a resistor and diode in parallel to the relay and capacitor also in parallel to the relay these all things prevent the back current and protect our relay from damage. When this circuit works relay trips and these LED’s blink and show the battery condition that either it is low or high or it is in medium state.

V. Buck circuit for MPPT implementation:

For the MPPT implementation to get our required power for charging purpose we have designed a buck circuit whose input is variable as input voltages coming from the panel vary from time to time as intensity of light increases or decreases depending on the weather condition. Our input varies from 12 to 17 volt and we need 13 volt for the proper battery charging and our inductor setting is so that it gives us 13 volt on the output terminal and from this we are charging our battery. And we could control the chopping frequency by the pulse width modulation and the PWM input sense the voltages and then change its input to make it 13 volt to charge the battery.