1. “HERE COMES THE SUN” A STUDY OF ELECTRICITY AND PHOTOVOLTAICS
Institute Of Electrical And Electronic Engineers, Phoenix Section
Teacher In Service Program / Engineers In The Classroom (TISP/EIC)
“Helping Students Transfer What Is Learned In The Classroom To The World Beyond”

2. Copyright Notice This presentation includes material copied from the web sites: HowStuffWorks “How Solar Cells Work,” (Copyright ©   HowStuffWorks, Inc.) Explain that stuff! “Solar Cells” Wikipedia, The Sun, Tennessee Valley Authority, Coal-Fired Power Plant, The Electricity Book, and “Here Comes The Sun” from the “Abbey Road” album, 1969, by the Beatles This presentation may only be used free of charge and only for educational purposes, and may not be sold or otherwise used for commercial purposes
May 2012
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3. Comments on Solar Cars
A solar car is an electric car powered from solar panels on the surface (generally, the roof) of the vehicle
Solar vehicles are not practical day-to-day transportation devices at present, but are primarily demonstration vehicles.
Several solar powered cars have been built and tested but practically these are not ready for the market.
In order for Solar cars to be used as regular family cars tremendous improvements are required in the development of small, light weight, rechargeable batteries. First of all batteries would be needed just to start the car after being parked all night in the garage. Secondly, what would happen on cloudy/rainy days?
Major improvements would also be needed in the efficiency of solar cells so that adequate power would be available to both charge the batteries and run the car on cloudy days, as you will see when we go over the technology.
Look at these models, do you see any room for a family of four? Do you see any possibility of having an SUV that is solar powered? These definitely are demonstration vehicles that show the application of a technology, and no more.
You will be building a small, light weight solar car only to show you that solar energy has to potential to be an alternative to gasoline power. So to get there we need to review some basic engineering concepts. After that review, you will get the chance to build one solar demonstration car, as shown on the next slide.
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May 2012

4. The Solar Model Car You Will Build
Motor
Solar panels
Cardboard Chassis
Rear Wheel Axle with Gear Assembly
You are going to build a solar car that is driven by a motor and a set of gears.
The electric motor will get its power from the solar cells.
The motor has a gear that will be connected to gears, mounted around one of the wheel assemblies, and that will make the wheel assembly turn. Therefore, the turning of the motor causes the turning of the wheels which then causes the car to move.
If you wish you can make some mention about gear ratios and the fact that the motor turns at an rpm that is much higher than what the wheels will be turning, so there is a gear ratio assembly to assure that the wheels will turn at the proper speed. Most important is that the gears must be meshed together in order for this to happen.
Front Wheel Axle Assembly
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5. What is the Sun???
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6. What Is The Sun? The Sun is the STAR at the center of our Solar System
The Sun has a diameter of about 1,392,000 kilometers (865,000 mi).
By itself accounts for about 99.86% of the Solar System's mass
1,300,000 Earths
27,000,000°F Center
10,000°F Surface
The purpose of this slide is to emphasize that the Sun is a Star, that is it at the center of our solar system and show its relative size to the planets, in particular the Earth.
The last click brings home the point of its magnitude with respect to the Earth.
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7. Solar Energy From 400 Million Years Ago
Coal, petroleum and natural gas formed from buried plant life
The sunlight is transformed through photosynthesis
Sunlight
Photosynthesis
Plant Life Cycle
Carbon Based Compounds
Heat, Pressure & Time
They are carbon-based fossil fuels
Coal, Oil and Gas were formed million of years ago from plants that were buried in the crust of the planet and crushed by the succeeding formations of upper soil.
The process diagram shows all the processes involved in transforming the sun’s energy into fossil fuel.
With this concept we consider these energy sources to be “buried sunshine”, because the plants would not otherwise have existed without the presence of the sun.
First we will look at the most common method used today to generate electricity.
These are often referred to as "buried sunshine”
How do we convert this energy into useful work?
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8. Coal (Or Gas Or Oil) Fired Electric Power Plant
This is the most common power plant found in the world. Some burn coal and some burn Oil to create the necessary steam to turn the turbines that then cause the generators to produce electricity.
Basically the fire under the boiler creates steam.
The steam, in turn goes through the turbine, causing it to rotate.
Physically connected to the turbine is a generator that creates the electricity.
After the steam goes through the turbine it goes through a condenser, which cools the steam down and converts it back to water. The resulting water is then cycled through the boiler again. Some of the steam is lost in this process, so a good source of nearby water.
It is important that these plants be near water sources, such as rivers or lakes and have railroad tracks coming to them to deliver the fuel.
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9. What Are The Two Main Properties Of The Sun?
1. Heat
Solar Thermal Power Arrays generate steam to drive Turbine
AC OUT
No Turbines/Generators!
2. Light
When we use the heat property of the sun the sun rays are concentrated on pipes that have water running in them. The intense concentration of the sunlight causes the water in the pipes to boil creating steam. At this point the generation of electricity is the same as with the coal burning plants. The steam is piped into a turbine with drives a generator that produces the electricity.
When we use the light property of the sun solar arrays convert the sunlight directly into electricity. This electricity is then processed by an inverter which provides the same type of electricity that comes out of a generator.
Solar Cell Power
Arrays generate electricity directly
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10. What Are Some Uses Of Electricity?
Lighting
Air conditioning
Cooking
Ironing
Electric Motors
Toasters
Television
Computers
iPods
Cell Phones
Electric Guitars
Welding
Electric drill
Table saw
And on and on and on……….
In fact, life as you know it today would be completely impossible without electricity!
May 2012
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11. Types of Electricity Batteries Alternating Current - AC
Direct Current - DC
Batteries
With this slide get the students to think a little bit about the different sources of electricity that are available around the home, before showing the examples.
This is a good lead-in then to talk about the general properties of electricity
Dry Cells
Wet Cells
Solar Cells
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12. Direct Current Sources
Batteries produce Direct Current (DC) like solar cells.
Batteries create electricity by an electrochemical action.
Solar cells create electricity by exposure to light.
A “dry” battery is primarily an electrochemical device that stores chemical energy and releases it as electrical energy upon demand. This process depletes the characteristics of the material until it can no longer release any electrical energy – commonly known as a “dead” battery.
A lead-acid (car) battery is an electrochemical device that works like a dry cell, but whose chemical reaction can be reversed so that the battery can be recharged. Charging the battery is a process through which an external electric source replenishes the chemical energy of the material. Unfortunately there is a limit to how many times a battery can be recharged.
A solar cell needs a strong light source in order to directly produce electricity. The best light source is being exposed to sunlight. There is not time limit in the use of a solar cell. It should be noted that it does not store any energy … It is operational only in the presence of a light source. As a practical application in a home one needs to have large batteries to store electrical energy during the day so that, at night, one can use the charged batteries energy as a source of electrical power.
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13. But What Is Electricity And What Are It’s Properties?
Electricity is the result of electrons moving in a uniform direction in material.
This occurs best when the material is made up of atoms with “free” outer electrons
Copper Atom
Deuterium Atom
All the matter is made up of tiny particles called atoms
Atoms consist of even smaller particles called electrons, protons and neutrons
Protons and Neutrons represent % of the weight of an atom.
The protons and electrons contain equal and opposite charge ( + & - )
A neutron can be considered of a proton/electron pair and thus has no electrical charge.
Outer most electrons can be easily moved from one atom to another.
In the absence of an external electrical source, this is a random motion within the material.
When an external electrical source is provided, then the outer most electrons will move in a specific direction, in and out of the material. This then is electrical current.
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14. The movement of free electrons forms an electric current
It is important on this slide to explain that the circle areas are really cross sections of the wire – looking straight across the wire, as if it was cut. On the left side the electrons are just moving randomly amongst themselves. When the switch is closed the battery caused electrons to move in a specific direction, in and out of the area.
Look at around 9 O’clock on the right hand side and see an electron arriving in the area and then at 3 O’clock an electron moves out of the area. This movement is what creates an electric current – the motions of electrons through the wire, in a specific direction.
An Electric Circuit is formed by a Conductor to allow for the continuous movement of free electrons
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15. What Is A Solar Cell?
Solar Cell Symbol
It converts the energy of sunlight directly into electricity
The photovoltaic effect discovered in 1905
Albert Einstein explained the photoelectric effect in 1905 for which he received the Nobel prize in Physics in 1921.
He was 26 years old!
The practical use of photovoltaic effect was not possible until we developed semiconductor technology in the late 1940’s, early 1950’s.
A Solar Cell is also known as a Photovoltaic (PV) Cell
“Photovoltaic” – combination of 2 Greek words Photo ≡ Light Voltaic ≡ Electric or Voltage
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16. What Makes A Solar Cell?
A solar cell is a sandwich of two different layers of silicon material.
The lower layer is p-type 
The upper layer  n-type
Then metal layers are placed on top and bottom. 
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17. How Do Solar Cells Work?
When sunlight shines on the cell, photons (light particles) bombard the upper surface.
The photons carry their energy down through the cell. 1
The photons give up their energy to electrons in the lower, p-type layer. 2 4
The electrons use this energy to jump across the barrier into the upper, n-type layer and escape out into the circuit. 5
This walks the student through the photovoltaic activity of a solar cell.
Use a click to go through each step of the process.
As a process appears its number appears on the image to show where the step is taking place. 3
Flowing around the circuit, the electrons make the lamp light up.
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19. Electrical Nature of Matter
Materials that permit the motion of free electrons are called Conductors.
Materials that oppose the motion of electrons are called Insulators
Conductors are said to have low resistance while insulators have high resistance
CONDUCTORS
Silver
Copper
Gold
Aluminum
Brass
Zinc
Iron
INSULATORS
Dry Air
Glass
Mica
Rubber
Asbestos
Bakelite
PVC
Teflon
Plastics
It is important here to emphasize that Resistance is a measure of the difficulty of electrons to slow through the material.
Most metals have low resistance with Silver being the best. Copper and Aluminum are used in the wires throughout a house. Gold is used on electronic boards because gold does not oxidize – which would increase its resistance significantly even to the point of having that part being an insulator.
Insulators have a very high resistance. So it takes a lot of voltage to make electrons flow through them. For instance in the case of air it takes about 2,000 volts per inch to have electrons flow through air. Just think of what it takes for a lightning bolt to come down to earth. If the cloud is 1500 feet up, then that’s 18,000 inches times 2,000 volts/inch your looking at 36,000,000 million volts and a lot of current.
When current goes through a conductor that has some resistance, the current heats up and can create light – which is the way incandescent lightbulbs work. Picking the material with the right resistance can give more or less light.
If a good conductor is connected directly to a relatively large voltage, say 120 volts, it will heat up to the point of melting. That’s how fuses operate they can allow a certain amount of current to go through. When that is exceeded the strip of metal melts and the electricity is cut off, thus protecting the house circuit from possible causing a fire.
Pure water is a fair conductor – it can be made better by dissolving salt in it. If you drop an electronic equipment in water it will “short” out all the connections. If the equipment was “ON” this will “kill” it. If it was “OFF” at the time it got wet, then if you wait a long time for all the water to dry you may have a chance to still have a good electronic equipment. Although the battery in it will probably need to be replaced or recharged.
May 2012
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20. Non Connected Electrical Circuit
Here we have the elements of a simple circuit.
We have a battery, wires, and a lightbulb.
Until these a are connected to form a complete loop, there is no current flow.
Once they are all connected we have current flowing through the circuit and the lightbulb gives of light.
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May 2012

21. Connected Electrical Circuit
At this point using several students, a battery, a buzzer and selected pieces of wire, form a series circuit and demonstrate that when all are connected there is a sound. Have anyone disconnect and the sound goes away. The more students are used the more effective this demonstration is. It is strictly a matter of time.
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22. Some Electrical Terms Voltage (volts, V) V Amperes (amps, A) I
Resistance (ohms, Ω) R
Power (watts, W) P
Explain the meaning of each term.
Voltage (v) is the measure of the electrical force that will cause electrons to move. Give examples: Most dry cell batteries are 1.5 volts, Car batteries are usually 12 volts, electrical voltage out of a wall socket is usually volts. Voltage for dryers, pool motors and air conditioners is 240 volts. Voltage is named after Allesandro Volta, , defined its properties.
Amperes (I) is a measure of the amount of electrons (current) that go through a circuit, or are supplied by the voltage source. Ampere is named after Andre Marie Ampere, , who defined the properties of electric current.
Resistance (R) is a measure (ohms) of the characteristics of the circuit. For a given voltage a circuit of higher resistance will have less current going through it. Good conductors have very low resistance, whereas insulators have very high resistance. It is named after Georg S.Ohm, , who defined the relationship between voltage and current – Ohm’s law.
Power (P) is a measure of energy used by a circuit – this is measured in Watts. That is what the electric company uses to charge your parents for the amount of energy it has supplied to your house.
Explain the simple circular charts to show how one can calculate any term of a circuit given two of the three parameters. Just cover the desired item and the chart shows the calculation that needs to be done in order to calculate the desired value. V I R P V I
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23. I = V R
P = V × I
OHM’s LAW
R resistance
V (voltage)
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25. How to connect circuits
Series Circuit
Parallel Circuit
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26. How to connect circuits
Series Circuit
Parallel Circuit
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27. How to connect circuits
Series Circuit
Parallel Circuit
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28. We Can Connect Batteries In Series And / Or Parallel
1.5V
3 W light bulb
1.0A
3.0V
Series Circuit P V I
Power = Voltage × Current
3.0V
3 W light bulb
0.5A
1.0A
Series - Parallel Circuit
First re-emphasize the equation for power, in terms of voltage and current.
If we have a 3 watt light bulb connected to a 3 volt source then we will have a current of 1 ampere. Click to show the “series” circuit. Point out the two batteries connected in series – the plus side of the bottom battery is connected the negative side of the upper. Since each battery is 1.5 volts then we have 3 volts across the two batteries.
Click to show the “series-parallel” circuit.
Note that we have two sets of series connected batteries, each providing 3 volts, and these are then connected in parallel. The light bulb will still need 1 A of current. But now this current is divided between the two sets of batteries. So each one only supplies 0.5 A of current. With this setup the batteries will last longer because they are each supplying less current than in the simple series connection. Click to show both circuits.
We will be applying this concept to the solar cars you will be building in this class.
May 2012
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29. Gear Drive Solar Model Car
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30. Applying the Series/Parallel Concept to the Solar Car
1.0V
1.5A
Series Circuit
Power = Voltage × Current
Solar cells can be considered to be just like batteries, except that in the absence of sunlight they provide no power.
Our solar cells will be used to provide power to the electric motor which will drive the car you will be building.
In order to start the car to move the motor will require an amount of current that is greater than what each cell can provide.
So in order to get more current to the motor we have to connect the solar cells in parallel, in a manner similar to what was shown with the batteries and the light bulb.
We will cover these details when we start to build the car.
Parallel Circuit
0.5V
3.0A
1.5A
1.5A
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31. Let’s Build Some Solar Powered Cars!
At this point have one member of each team come up and collect the necessary material to building their car. All the “instructors” can be a selected sections of the material line to make sure the proper components are collected.
At the end of the line a roll of tape and a pair of scissors are handed out.
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32. Elements of The Solar Model Car
Motor
Solar panels
Chassis
Rear Wheel Axle with Gear Assembly
Point out the elements of the solar car that will be built.
First click shows the chassis
Second click shows the solar panel which is connected to the motor with the red and black wires.
Third click show the motor, located above the chassis.
Fourth click points to the rear wheel axle assembly with the gear assembly.
Fifth click points to the front wheel axle assembly. Make sure that the two axle assemblies are parallel so that the car goes straight.
Once you test your car and it does not go straight then you’ll have to adjust the front wheel axle assembly to stop the car from turning.
Front Wheel Axle Assembly
May 2012
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33. Let’s Build Some Solar Powered Cars!
Use foam board or corrugated plastic for the chassis
Make sure the axles are wider than the chassis
Assemble the wheels and gears on the axles with the axles through straws (use washers between the end of the straw and the wheels / gear)
Cut the straw length the same as the gap between the wheels to prevent the wheels binding on the chassis, but leave a little slack between the wheels
Tape the straws firmly to the chassis; for rear axle needs to be on top of the chassis, NOT underneath the chassis, or the gears will not mesh properly
Make sure the axles are parallel
Clip the motor to the chassis on top of the chassis, NOT underneath the chassis (it will rub on the ground otherwise) and align the gears so they mesh, but not too tightly
Assemble the solar panel (directions on the following charts)
Assemble a tilted platform for the solar array; note the direction to the sun!
Fit the solar array on the platform and connect the wires from the motor to the array connection pads with clips, red to + and black to ─
Handle the solar panels gently; they are fragile! DON’T bend or cut them!
Keep the car as light weight as possible
Reverse the wires if the car runs backwards
SUGGESTION: HAVE ALL THE TEAMS PUT THE SOLAR PANEL ASSEMBLY TOGETHER FIRST, USING THE NEXT SET OF SLIDES. THEN GO ON TO THE REMAINDER OF THE ASSEMBLY INSTRUCTIONS.
On step 2 point out that they may need to trip the width of the chassis so that the axles extend, on both sides, beyond the chassis.
Have them assemble the front wheel axle first. The metal rod goes inside the straw, and the straw has to be trimmed to be smaller, I length than the metal rod. Then do the rear axle with the gear assembly on one side of the of the chassis.
On Step 7 make sure the motor is on top of the chassis. It is held on the chassis with a clip. It can be either in front of or behind the rear axle assembly. The key point is that the gear on the motor must mesh firmly with the gear assembly of the rear axle.
The solar panel assembly will be covered on the next charts.
The connection between the solar panel assembly and the motor is done with a red wire, attached to the “+” terminal on the solar assembly and a black wire to the “-” terminal. Once the car is first tested, if it moves in a reverse direction then it is these two wire that need to be switched on the solar panel assembly.
The last thing that needs to be done is to mount the solar pannel assembly on the car. Use of various foam pieces can be made to do this, making sure that the panel does not rub on any of the wheels. For mid-day running the solar panels can be in a horizontal position. For early morning or late afternoon then they need to be angled so that the sunlight can be most effective.
It is important the stress that the two axles must be parallel. At this stage of education students may not understand the meaning of parallel. A simple visual diagram on a board will do that. Furthermore, the front axle should be attached to the chassis with just to pieces of tape, as far apart as possible so that alignment can be easily adjusted if the car does not go straight.
May 2012
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34. Assembling Solar Cells Into A Panel
Solar panels are made by gluing solar cells onto an insulating sheet and connecting them electrically in series
The voltages add but the current is equal to that of a single cell
For our solar car project we are providing two panels, each with three cells in series
The current capability of a single cell is 1.5A and the voltage is 0.5V
So for the three cell panel the current capability if 1.5A and the voltage is 1.5V
The left side of the picture shows the schematic view of one panel.
The right side of the picture shows the actual physical view of a panel
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May 2012

35. Connecting The Panel To A Motor
The electric motor you will be using for the solar cars requires 1.5 – 3.0V and 2.1 – 2.2A in order to start to run from stop
If you connected two panels in series you would generate 3.0V and 1.5A
If you connected them in parallel you would generate 1.5V and 3.0A
Electric motors require current rather than voltage to start from stop so the parallel connection is recommended in this case
May 2012
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36. Panels Connected In Parallel
Aluminum Foil used here
This slide shows two methods of connecting the solar panels in parallel.
The next few slides show how to connect the method on the right side using aluminum foils, tapes and clips.
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37. Solar Car Solar Array Assembly Process
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38. Step #1: Add Positive (+) Aluminum Foil Strip To Panel #1
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39. Step #2: Add Negative (-) Aluminum Strip To Panel #2
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40. Step #3: Final Assembly
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41. Elements of The Solar Model Car
Motor
Solar panels
Cardboard Chassis
Rear Wheel Axle with Gear Assembly
Point out the elements of the solar car that will be built.
First click shows the chassis
Second click shows the solar panel which is connected to the motor with the red and black wires.
Third click show the motor, located above the chassis.
Fourth click points to the rear wheel axle assembly with the gear assembly.
Fifth click points to the front wheel axle assembly. Make sure that the two axle assemblies are parallel so that the car goes straight.
Once you test your car and it does not go straight then you’ll have to adjust the front wheel axle assembly to stop the car from turning.
Front Wheel Axle Assembly
May 2012
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43. Residential Solar System
Video of residential Solar System
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44. Solar Demo Circuit Solar Panels A A A A V V 400 watt, dc/ac inverter
Battery
Charge Controller A
110v ac V V
400 watt, dc/ac inverter
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