SOLAR PWM CHARGING AND TRACKING SYSTEM

Introduction    

 The PV applications could be grouped according to the scheme of interaction with utility  grid: grid connected, stand alone, and hybrid. PV systems consist of a PV generator (cell, module, and array), energy storage devices (such as batteries), AC and DC consumers and elements for power conditioning. The most common method uses the PV cells in the grid network. However, to understand the performance and to maximize the efficiency of the irradiation of the PV cells, the standalone PV cells have spurred some interest, especially, in the area of the solar tracker system.

      Over the years, test and researchers had proven that development of smart solar tracker maximizes the energy generation. In this competitive world of advanced scientific discoveries, the introductions of automated systems improve existing power generation methods. Before the introduction of solar tracking methods, fixed solar panels were positioned within a reasonable tilted direction based on the location. The tilt angle depending on whether a slight winter or summer bias is preferred in the system. The PV systems would face “true north” in the northern hemisphere and “true south” in the southern hemisphere. Solar tracking is best achieved when the tilt angle of the tracking PV systems is synchronized with the seasonal changes of the sun’s altitude. Several methods of sun tracking systems have been surveyed and evaluated to keep the PV cells perpendicular to the sun beam. An ideal tracker would allow the PV cells to point towards the sun, compensating for both changes in the altitude angle of the sun (throughout the day), latitudinal offset of the sun (during seasonal changes) and changes in azimuth angle. In the light of this, two main types of sun trackers exist: passive (mechanical) and active (electrical) trackers

       One class of the passive solar trackers is the fixed solar panel. It is placed horizontally on

the fixed ground and face upwards to the sky. But most of the passive solar trackers are based on manual adjustment of the panel, thermal expansion of a shape memory alloy or two bimetallic strips made of aluminum and steel. Usually this kind of tracker is composed of a couple of actuators working against each other, which are, by equal illumination, balanced. By differential illumination of actuators, unbalanced forces are used for orientation of the apparatus in such direction where equal illumination of actuators and balance of forces is restored.

       Another passive tracking technology is based on the mass imbalance between both ends of the panel. This kind of trackers does not use any kind of electronic control or motor. Two identical cylindrical tubes are filled with a fluid under partial pressure. The sun heats the fluid causing evaporation and transfer from one cylinder to another, which creates the mass imbalance. Passive solar trackers, compared to active trackers, are less complex but works in low efficiency. Although passive trackers are often less expensive, they have not yet been widely accepted by

Consumers.

On the other hands, major active trackers can be categorized as a microprocessor based,

computer-controlled date and time based, auxiliary bifacial solar cell based and a combination of these three systems. In the microprocessor based solar tracker systems, a controller is connected to DC motors OR linear actutor also called super jack. Once the location is selected, the azimuth elevation range is determined, and the angular steps are calculated. Usually for monitoring the power generation, they also connected this tracking device to a PC by a code written in Assembly

or  picbasic languages. In this solar tracker design, sensors were often used. For example, a

photo-resistor was put in a dark box with a small holes on the top to detect the

illumination, and a light sensor or photosensor called light-dependent resistor (LDR)

to indicate the intensity of the radiation (that changes its electrical resistance from several

thousand Ohms in the dark to only a few hundred Ohms when light falls upon it). The

signals were then captured by the microcontroller that provides a signal to the motors to

rotate the panel.

In this design, unreliable and expensive components like batteries and driving electronics were completely eliminated. Hence, it is a very simple, reliable solar tracker for space and terrestrial applications. On the other hands, the method use combination of microprocessor with sensor and date/time based system, the sensors such as or light sensors send the signal to the microprocessor. Using the realtime clock (RTC), the tracker computes the position of the sun based on the date/time

information of its clock. The data gathered during the day are analyzed, and a new

improved set of parameters for the installation errors is computed. These data are used in

the next day to compute more accurate positions of the sun, and the cycle continues.

       In this solar tracking system that we are designing, the required position was calculated in advance and was programmed into Programmable Logic Control (PLC) that in term controls the motor to adjust the panel to maintain position perpendicular to the sun.

MECHANICAL STRUCTURE

After the solar panels and other components were selected, the overall structural design of

the solar tracker as seen in Fig.1 was fabricated. The solar tracker weight 10 kg and has an

overall dimension of 1480mm x 680mm x 30mm. The compactness of the proposed solar

tracker enables it to be mounted on the wall. It consists of the PV panel, linear actutor also called super jack; the motor and electronics boards support and the vertical pillar with base plate support. The entire structure was fabricated using the metal plates. The pillar holding panel is aligned to a ratio of 48:100 for better flexibility during the panel jacking. The tracker is designed to have a single-axis rotation (East to West), and the superjack is mounted in such a way that the tracker systems have only a single-axis freedom of rotation. The fixture to hold the sensors are then assembled and aligned at both ends of the PV panel to sense the sun irradiance.

The PV panel frame support has a support rod that runs across the PV panel width.

CHARGING AND TRACKING CONTROLLER CIRCUIT

       The overall mechanical and electrical subsystems were integrated into the solar tracker

system is shown below. The solar tracker system consists of mostly electrical components. The PV cells, LDR sensor,  the lead-acid battery, a voltage tracking control board based on pic16f72 .

The LDR sensors sense the sunlight intensity and send the signal to the microcontroller to move  the PV panel via the super jack. The electrical energy is then stored in the lead-acid battery that is later used to power the respective house hold device.

The PV cells are a device that helps to convert the solar energy into electrical energy. The

solar panel selected is capable of generating 130W  at maximum power with a maximum volage of 17.6V.

To calculate the charging AMP [CURRENT]

Power = voltage * current

Where:   power = 130w

               Voltage = 17.6v

               Current = ?

               Current = 130/ 17.6

               Current = 7.38 A

We requires 12.6V supply and is capable of handling a maximum of 10.32A. The charging and tracking controller sense battery voltage using a in-build analog to digital converter (ADC) to  prevents the over-charging of the battery. The LDR sensors (NORPS-12) are basically resistors that vary their resistance according to the sunlight intensity when exposed to irradiance. The output of the sensor circuit is an analogue voltage that is used as an input to the PIC microcontroller. To determine the value of resistor R, various values of different resistors were examined to finalize an appropriate resistor. The desired resistor value should provide a voltage that covers the sunny and cloudy conditions. The following resistor values as shown below based on self experiment. From the self experiment result, it was found that varying the value of resistors in the voltage divider circuit helps to improve the sensitivity of the output. The resistor of 100Ω was found to be suitable to differentiate between the sunny and cloudy day.

Fixed resistor (Ω)	Vout on sunny day	Vout on cloudy day	∆Vout
50	2.14	0.82	1.32
100	3.95	0.90	3.05
200	4.56	1.35	3.21
500	4.78	1.41	3.37
1000	5.01	1.89	3.12

        The driving mechanism includes the super jack and two 12v relay switching system. The super jack was main controlled using the microcontroller (16f72). The controller uses the high and low  signal to drive the super jack via two 12v relays at a controlled speed correspond to a maximum

voltage of 36Vdc which is been derived with a 12v - 15v supply from the solar panel...

       Solar Charging And Tracking controller regulates the voltage and current coming from your solar panels which is placed between a solar panel and a battery .It is used to maintain the proper charging voltage on the batteries. As the input voltage from the solar panel rises, the charge controller regulates the charge to the batteries preventing any over charging.

Types of Charge controller :

1.ON OFF

2. PWM

3. MPPT

The most basic charge controller(ON/OFF type) simply monitors the battery voltage and opens the circuit, stopping the charging, when the battery voltage rises to a certain level.

Among the 3 charge controllers MPPT have highest efficiency but it is costly and need complex circuits and algorithm.So think PWM charge controller is best for us which is treated as the first significant advance in solar battery charging.

Pulse Width Modulation (PWM) is the most effective means to achieve constant voltage battery charging by adjusting the duty ratio of the switches ( MOSFET ). In PWM charge controller, the current from the solar panel tapers according to the battery condition and recharging needs. When a battery voltage reaches the regulation set point, the PWM algorithm slowly reduces the charging current to avoid heating and gassing of the battery, yet the charging continues to return the maximum amount of energy to the battery in the shortest time.

 Advantages of PWM charge controller :

1. Higher charging efficiency

2. Longer battery life

3. Reduce battery over heating

4. Ability to desulfate a battery.

: CIRCUIT DIAGRAM

:  75% DUTY CYCLE AND POWER JACK ACTIVE

:  5% DUTY CYCLE 

       The microcontroller target board in the system was used to control the servo motor. It receives the signals from the LDR sensors. The analogue voltage is converted into digital signal (logic 1 or 0) for processing. The processor was a PIC16f72  from Microchip Inc.

: BOTTOM PCB

: TOP PCB

3.2.5   PV PANEL MODEL

The simplest equivalent circuit of a solar cell is a current source in parallel with a diode as shown below. The current source represents the current generated by the PV cell due to the photons received by it, and is constant under constant sun irradiance and temperature. During darkness, the solar cell is not an active device; it works as a diode. It produces neither a current nor a voltage. However, if it is connected to an external supply (large voltage) it generates a saturation current or dark current. The key parameters for a PV cell are short circuit current (Isc or the current from the solar cell when the voltage across the cell is zero), open circuit voltage (Voc) and sun irradiance value. Usually these values are given by the manufacturer in the data sheet.

 PV CELL MODEL

Normally a single PV cell produces a rather small voltage that have less practical use. The

real PV panel always uses many cells to generate a large voltage. For example the Eco-tree

130W, PV module used for our project comprises of 36 cells to generate a large enough

voltage to charge a 12 volt battery. The data sheet for Eco-tree 130W, is given in Table below.

Parameter	Value
Maximum Power (Pmax)	130 W
Voltage At Pmax	17.6v
Current At Pmax	7.41a
Open-Circuit Voltage (Voc)	21.6V
Short-Circuit Current (Isc)	0.6A
Weight	12kg
Module Size	1480*680*35(Mm)