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Our goal is to design a systemthat tracks the sun and converts it to electricity which can be used to start any electronic device. In our projectit is used to powerthe college TV.
It is mentioned in the definition report that LDR sensors will be used in the form of right angle (as shown in figure 1) so a testing circuit is designed to check the reaction of the sensors according to sunlight. It was a successful experiment as the sensors responded properly. Also a sample servo motor has been tested with the sensors to check the rotation despondence depending on sensors reading.
(The descriptions are detailed in the system block diagram section)
The main parts of this project are listed below in two sections, theory and technical description.
(Also known as photovoltaic panel) consists of interconnected solar cells which are electronic devices. Solar cells are used to convert the light energy from the sun to generate electricity through the photovoltaic effect.
The following is copied verbatim from (Gevorkian, P. (2008) Solar Power in Building Design. USA. The McGraw-Hill Companies):
Figure 1 pd-panel
Solar cell physics
"Most solar cells are constructed from semiconductor material which has the combined properties of a conductor and an insulator, such as silicon.
Conductors such as gold have loosely bound electrons in the outer shell or orbit of their atomic configuration. These electrons can be detached when subjected to an electric voltage or current. But in the insulators such as the glass, the atoms have very strongly bonded electrons in the atomic configuration and do not allow the flow of electrons even under the severest application of voltage and current. Semiconductor materials, on the other hand, bind electrons midway between that of metals and insulators.
Semiconductor elements used in electronics are constructed by fusing two adjacently doped silicon wafer elements. Doping implies impregnation of silicon by positive and negative agents, such as phosphor and boron. Phosphor creates a free electron that produces so-called N-type material. Boron creates a "hole" or a shortage of an electron, which produces so called P-type material. Impregnation is accomplished by depositing the previously referenced dopant on the surface of silicon using a certain heating or chemical process.
When N-type and P-type doped silicon wafers are fused together, they form a PN junction. The negative charge on P-type material prevents electrons from crossing the junction, and the positive charge on the N-type material prevents holes from crossing the junction. A space created by the PN, wafers creates a potential barrier across the junction.
In solar cells, when a PN junction is exposed to sunshine, the device converts the stream of photons that form the visible light into electrons, making the device behave like a minute battery with a unique characteristic voltage and current, which is dependent on the material dopants and PN-junction physics.
Solar Cell Electronics
An electronics field is produced at a PN junction of a solar cell by impinging photons that create 0.5 V of potential energy, which is characteristic of most PN junctions and all solar cells. This miniscule potential resembles in function a small battery with positive and negative leads, these are then connected front to back in series to achieve higher voltages.
In addition to the previously discussed PN-junction device, solar cells contain construction components, for mechanical assembly purpose, that are laid over a rigid or flexible holding platform or a substrate, such as a glass or a flexible film, and are interconnected by micron-thin, highly conductive metals. A typical solar panel used in photovoltaic power generation is constructed from a glass supportive plate that houses solar PV modules, each formed from several hundreds of interconnected PN devices."
(Also known as Charge Regulators) are electronics devices designed to protect batteries from overcharging. They are installed between the solar array termination boxes and batteries.
Figure 2 Charge Controller
Storage batteries are a group of one or more electrochemical cells. Because of their reversible reactions they are known as secondary cells.
The solar panel is not used to store energy so a dc voltage is used to charge an appropriate set of batteries.
The reserve capacity of batteries is referred to as the system autonomy. This varies according to the specific application requirements. Batteries in applications that require autonomy form a critical component of a solar power system. Battery banks in photovoltaic applications are designed to operate at deep-cycle discharge rates and are generally maintenance-free.
Figure 3 Storage Batteries
DC to AC converter
There are two basic types of electricity: Alternative Current (AC) and Direct Current (DC). An inverter is an electrical device that converts DC to AC; the converted AC can be at any desired voltage and frequency with the use of suitable transformer, switching, and control circuits.
Figure 5 shows a simple inverter circuit, DC power is connected to a transformer through the center tap of the primary winding. A switch is rapidly switched back and forth to allow current to flow back to the DC source following two alternate paths through one end of the primary winding and then the other.The alternation of the direction of current in the primary winding of the transformer produces alternating current (AC) in the secondary circuit.
Figure 5 Inverter Block Diagram
Figure 4 DC to AC convertor
LDR or Light Depended Resisters
An LDR is very sensitive towards light and its resistance can get as high as 1000,000 ohms. This resister works in such a way that if a bright light level of 1000 lux is directed towards it, the LDR's resistance drops. On the other hand, if a very low light level of 10 lux is directed towards it the resistance will rise dramatically to mega ohms. In voltage divider circuits with the other resistors' values held constant. Sensitivity of the circuit is varied by replacing the constant resistors with potentiometers.
Figure 6 LDR
A Servo is a small device that has an output shaft. This shaft can be positioned to specific angular positions by sending the servo a coded signal. As long as the coded signal exists on the input line, the servo will maintain the angular position of the shaft. As the coded signal changes, the angular position of the shaft changes. A servo is used to control an angular motion between 0 and 180 degrees it is also mechanically not capable of turning any farther due to a mechanical stop built on to the main output gear. In practice, there are many different uses of a servo motor; they can be used in radio controlled airplanes to position control surfaces like the elevators and rudders, they can also be used in radio controlled cars and puppets.
However, in our project servo motor is used it to rotate the solar panel towards the sun to make it easier to pick up the signal. A servo motor consists of several main parts, the motor and gearbox, a position sensor, an error amplifier, motor driver and a circuit to decode the requested position.
Figure 8 Control Schematic diagram
Figure 7 Servo MotorC:\Users\H00083713\Desktop\ServoMotorControl.png
Basically, asolar powerwill be installed on the roof so that the TV will be ON during daytime by collecting sunlight and converting to electricity. The electricity will go through the charge controller before going to the TV. The charge controller controls the level of battery charging. Ourtarget will be achieved by making the solar base rotate towards the sun using two (LDR) sensors attached near the solar power in order to maximize captured sunlight.
During the daylight solar power will be charging the batteries constantly.
After sunset the process will be stopped. But the batteries cannot beignored because they will be fully charged and that may cause a major problem which is the transfer of energy. To avoid the transfer of the energy back to the solar panel and maybe the chance of destroying it charge controller will be attached between the solar panel and the batteries to conduct the electric current to only one direction.
Maximum Power (Wp)
Tolerance on technical data
Short circuit current (Isc)
Open circuit voltage (Voc)
Voltage at maximum power (Vmp)
Current at maximum power (Imp)
Typical Current at battery operating voltage
NOCT (Nominal operating cell temperature)
Change of Voc with temperature (ß)
Wind loading or surface pressure
Hailstone impact resistance
28mm at 23 m/s
Storage and operating temperature
from -40 up to +95 Â°C
Rated solar input
â‰¤ 30 m
-35 to 55*c
Nominal Capacity (20hr)
Internal Resistance( 25oC, 77oF)
~ 5.0 mâ„¦
Inverter (Dc to AC converter):
Nominal battery voltage
Input voltage range
10.5-16V (24V max.)
21-32V (44V max.)
Continuous power @ 25oC
Sine wave230Vac (120Vac*)0/-10%
50Hz (60Hz*)Â±0.05%(crystal controlled)
Max. battery voltage
Shut off @ 1.33 Ã-Unom - Automatic restart@<Umax
Explanation of characteristic values:
Continuous standstill torque
Continuous standstill current
SYSTEM BLOCK DIAGRAM
Block diagram 1 progress
For part one of the block diagram,the first three stages are performed in asingle circuit and linked with the servo motor. Later the motor will be connected to the mechanical part of the solar base. Actually in our final design these three stages will be replaced with a single microchip controller, it have not been decided yet which type to use.
(The full circuit and block diagram are attached in the appendix)
In this paragraph I will briefly describe what represents each stage in the circuit and how each part works.
Block one (LDR sensors):
There are two inputs for the circuit read by thedifferent angles of the LDRs. LDR sensors normally gives very high resistance values in the dark which ranges around (22-50) k ohms,on the other hand it ranges (0-10) ohms in the sunlight. The values significant variation is the main reason for using it in a divider circuit (as shown in figure 9) with two resisters of 68 ohms each. This resister value has been chosen to get the half of the voltage supply as an output for the next stage.
Figure 9 Divider Circuit
Block two (operational amplifier):
A voltage and current amplifiers (buffer)have been put in series for each input so there are four amplifiersin total (see figure 10). The reason behind using two different amplifiers in series is to gain a strong output.The four amplifiers are provided in one chip (LM 324).
Figure 10 Buffer Circuit
Block three (servo driving circuit):
Next four transistors are put in anH Bridge driver (such as figure 11) with four inputs referred as Q to drive the servo motors motion. For this part an NPN transistor is connected with the voltage supply of 12v and anotherPNP transistor withthe ground. The first output from the previous circuit is linked with Q1, Q4 and the other one with Q2, Q3. In addition the two outputs are connected to the servo motor. Basically what happens here is that if Q1 is more than Q3 then the motor will turn clockwise and if Q2 is more than Q4 it will turn anti clockwise.In short,the motor motion iscontrolledby using two PNP and two NPN types.
Figure 11 Driving Circuit
Block diagram 2 progress
The second block diagram describes the process of powering the TV. The output from the solar panel goes to the batteries through a charge controller. This is a crucial step; since the current cannot be allowed to go back from the batteries to the solar panel (this will ruin the solar panel).
The current going out of the battery is the one converted from DC to AC by the inverter, which in turn is used to power the TV.
Unit Price AED
Total Price AED
Solar Panel 40 watts
Charge controller- 15AH
Many things have been accomplished during this semester such as designing the testing circuit, creating system block diagram, ordering some of the componentsfrom different companies, studying and understanding solar systems. It is pleasing and satisfying that the circuit worked correctly although designing it waschallenging.
Listed are someof the works that has to be done in the coming semester:
Block diagram final check.
Getting an approval for ordering the remaining component.
Measuring the torque to choose an appropriate servo motor.
Recalculating the total cast depending on the real prices or any changes.
Designing the solar panel base and send it for manufacturing.
Choosing the appropriate microchip controller and then programming it.
Joining the parts and making the TV work.
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