Prototype of PIC Based Automatic Solar Tracking System

Introduction

One of the most important problem facing the world today is the energy problem.Therefore, demand of electrical energy and cost of fuel is increasing. The solution is to using more  renewable energy sources such as solar energy, wind energy etc. Nowadays , solar energy has been widely used in our life.

Concepts related to the solar energy constantly been  under heavy research and development. The basic objective related to the energy produced from photovoltic cells and by making the overall systems more efficient and cost effective. There are several factors that affect that affect the efficiency of the collection process. Major  influences on overall efficiency include solar cell efficiency, intensity of solar radiation and storage Technics.

The materials used in solar cell manufacturing limit the efficiency of a solar cell. Therefore this restricts the efficiency of the overall collection process. Therefore most attainable method of improving the performance of solar power collection is to increase the mean intensity of radiation received from source.  Most solar panels statistically aligned , they have a fixed position at a certain angle towards the sky.The time and intensity of direct sunlight falling upon the solar panel is greatly reduced, resulting in low output power from the panel.

The major approach for maximizing power extraction is sun tracking.solar tracking system is used sun tracking for maximize the power output.

Solar Tracking system

A solar tracker is a device orienting a solar panel or solar lens towards the sun. The sun position of the sky varies both season and time of the day as the sun moves across the sky. Power output of the solar panel maximum when pointed to towards the sun. so a solar tracker can increase the effectiveness of such equipment over any fixed position at the cost of a additional system complexity.
There are  many types of tracker of varying costs, sophistication, and performance.

Tracking Systems

There are several forms of tracking systems are available. And these vary in the method of implementing the designs. The two general forms of tracking used  as fixed control algorithms and Dynamic tracking.

The inherent difference between the two methods is the manner in which the path of the sun is determined. in the fixed control algorithms systems, the path  of the sun is determined by referencing an algorithm that calculates the position of the sun for each time period. That is , the control system does not actively find the position of the sun but works it out the current time ,day month and year.

                        The dynamic tracking system, on the other hand, actively searches for the sun's position at any time of day (or night).Common to both forms of tracking is the control system. This system consists of some method of direction control, such as DC motors, stepper motors, and servo motors, which are directed by a control circuit, either digital or analog.

Types of Solar Trackers

                  There are many different types of solar tracker which can be grouped into single axis and double axis models.

Single Axis Trackers

                            Single axis solar trackers can either have a horizontal or a vertical axle. The horizontal type is used in tropical regions where the sun gets very high at noon, but the days are short. The vertical type is used in high latitudes (such as in UK) where the sun does not get very high, but summer days can be very long. These have a manually adjustable tilt angle of 0 - 45 °and automatic tracking of the sun from East to West. They use the PV modules themselves as light sensor to avoid unnecessary tracking movement and for reliability. At night the trackers take up a horizontal position.

                             

 Dual Axis Trackers

Double axis solar trackers have both a horizontal and a vertical axle and so can track the Sun's apparent motion exactly anywhere in the world. This type of system is used to control astronomical telescopes, and so there is plenty of software available to automatically predict and track the motion of the sun across the sky. Dual axis trackers track the sun both East to West and North to South for added power output (approx. 40% gains) and convenience

                 

                    

 Construction of the solar tracker prototype

Below figure shows the model of the solar tracker prototype. As illustrated the solar tracker prototype accommodates both degrees of freedom: azimuth and vertical. Note that two LDR sensors module and thus same control algorithm are implemented in both degrees of freedom.

For the each of axis, use two sensor modules. The sensor module which used to vertical axis should be normal to motor of vertical axis. Then that motor can align the vertical axis with sun.

In this prototype another axis is azimuth. Then the sensor module which used to azimuth axis should be normal to another sensor module. Then the motor belongs to that axis can align azimuth axis with sun.

When we use two sensors, we have to install separately. Therefore these can integrate in to one sensor which can align two axes with sun.

The Materials used in the construction of the prototype include Perspex 2mm sheets. The vertical axis was constructed by using Perspex sheets and motor connected to the panel as above figure shows.

  Solar Tracker Control Circuit

 Solar tracker control circuit consist power supply, two motor drivers and micro-controller(16f877A).

Above shows the schematic for the solar tracker control circuit. A voltage supply of 12V is applied to the circuit which is then passed through a 5V voltage regulator. The regulated voltage is then supplied to the PIC.

Notice that the four Analogue pins are connected to port RA0 to RA3 of the PIC from the sensor modules. The output which drives the motor is obtained from two PWM pins RC1 and RC2, and direction controlling from RC0, RC3 for motor1 and RC4, RC5 for motor2. MCLR reset input port is also connected to 5V supply via 10k resistor. In order to supply power to the PIN11, PIN 32 is set to positive 5V and the PIN12, PIN 33 is set to ground. 4MHz crystal is connected to PIN12 and PIN13.

Sensor

               The most important part in this project is select suitable sensor for detect the maximum light intensity position. Then the below sensor which have two LDRs is so easy to make and find maximum light intensity position.

The resistance of LDR is inversely proportional to the light intensity. It is difficult to measure the light intensity by resistance of LDR. Therefore we convert resistance in to voltage signal where voltage signal is proportional to the light intensity. For that LDR is placed with resister

in series.  The 5V is supplied to LDR and ground the remaining end of resister as above figure.

The voltage signal father convert to digital value using ADC module of microcontroller.

                             The sensor has object between to LDRs. When sensor is normal to the sun, there is no shadow of object on the LDRs. Then, the light intensity which on the LDRs is same.  Therefore digital values are also same. If sensor is not normal to the sun, there should be shadow of object on one of the LDRs. Then the digital value of the LDR which get dark is less than the digital value of another LDR. Therefore this sensor can find the position of sun.

Operation of the solar tracker program

                                                                                                                                                                      The operation of the solar tracker is easy to understand, it works by using a PIC16F877A which compares the ADC values which proportional to light intensity illuminated onto the LDRs in each sensor module. PIC16F877A have ADC modules to get digital values. Each LDR have bridge circuit produce analog voltage which proportional to light intensity. That analog voltage connected to the ADC module of Microcontroller. The logic that works on the Microcontroller to get the analog values as inputs and compare two analogue values form LDRs belongs to each sensor and find which LDR is under shadow. Then rotate motors which belongs to each sensor until minimize the difference between two ADC values with an error margin of ±5 points. Simultaneously two motors are rotate according to minimize the difference between two ADC values. 

Whereas in the above figure, if one of the sensors comes under a shadow, then the PIC will detect this change through ADC values and thus it will actuate the motor to move the sensor module to a position where equal light is being illuminated on both of them.

The PIC is programmed so that it can obtain analog voltages which proportional to light intensity   from the each bridge circuit of LDRs and to move motor either clock wise or anti clock wise depending on which LDR is under shadow. The basic concept of the software design is illustrated in the below flowchart.


Programming Algorithm