“here comes the sun” – ieee tisp / engineers in the classroom 2010 arnold brenner 1 “here...

“Here Comes the Sun” – IEEE TISP / Engineers In the Classroom

2010 Arnold Brenner 1

“Here Comes the Sun”

A study of Electricity and Photovoltaics



Before we study how solar cells convert sunlight to electricity, we need to understand what electricity is, and what its properties are.

Let’s start with how we use electricity – what are some common uses of electricity?



What are some uses of electricity?

• Lighting



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……….



But what is electricity and what are it’s properties?

120 volts 220 volts 230 volts

1 ½ - 9 volts 6-24 volts

Alternating Current - AC

Direct Current -DC

Dry Cells

Wet Cell



We can’t see it, or smell it, or touch it, how do we relate to it?

All the matter around us is made from atoms. An atom of any element consists of two types of charge carriers: Those that carry the positive charge and are called Protons and those that carry the negative charges are called Electrons.

The positively charged Protons reside at the nucleus of the atom while the negatively charged Electrons orbit freely around it from a distance.

Give them a chance to jump to another atom and they will.

That is exactly what happens in conductors or wires connected to a power source such as a battery or a generator.

Electricity

Carbon atom



Electrical nature of matter

Substances that permit the free motion of a large number of electrons are called CONDUCTORS. Copper is a good conductor because it has many free electrons. Another way of saying this is that a good conductor has low opposition or low RESISTANCE to current (electron) flow.

Some substances such as rubber, glass, and dry wood have tightly bonded electrons. In these materials, large amounts of energy must be expended in order to break the electrons loose from the influence of the nucleus. These substances containing very few free electrons are called poor conductors, nonconductors, or INSULATORS.



Some of the best conductors and best insulators are listed in the order of their ability to conduct or resist the flow of electrons.

CONDUCTORS INSULATORSGoldSilver

Dry AirGlass

Copper MicaAluminum

BrassRubber

AsbestosZinc BakeliteIron PVC

TeflonPlastics



The uniform motion of free electrons or charges from one place to another is what we call Electricity or electric current.

We can relate to this electricity by using it or by measuring it.

So, we need to define some terms:

An electric circuit is formed when a path is created by a conductor to allow for the continuous movement of free electrons. The force that excites the electrons to "flow" in a circuit is called “V” voltage (volts).

Electric current “I” (Ampere or Amps) measures the rate or quantity of charge flow past a given point in an electric circuit.

The presence of friction or opposition to movement of free electrons is present in conductors. This opposition is called “R” Resistance and is measured in a unit called ohms.



In addition to voltage, current, and resistance there is another measure of electron activity in a circuit: “P” Power (watts)

Electric power is defined as the rate at which electrical energy is transferred by an electric circuit.

For example, the power consumed by an ordinary light bulb might be 100 watts, but from a compact fluorescent bulb (CFL), with the same light output might only be 15 watts.

Power is Voltage x Current, or P = V x I.



Some electricity terms:

• Voltage (volts, v) V

• Amperage (amps, a) I

• Resistance (ohms, Ω) R

• Power (watts, w) P



OHM’s LAW

V = I × R

P = V × I

V (voltage)

R resistance



We can’t see electricity, but we can see waterLet’s look at a tank of Water:Potential Energy – Height of water

“Voltage”Potential Energy

An equivalent electric circuit might be:

Fully charged battery

Fully discharged battery

Valve –“Switch”



When the valve is opened (switch is closed) the water flows (current).

When the potential (voltage) is equalized, it is equivalent to charging a battery from another battery.

Flow (“Current”)

Valve –“Switch”





=

Battery symbol



Solar Cells produce Direct Current (DC) similar to batteries, but batteries differ because they create electricity from a chemical reaction.

Dry Cells.1 ½ - 9 volts

Wet Cell6-24 volts

A “dry” battery is a primary (generally non-rechargeable) electrochemical device that stores chemical energy and releases it as electrical energy upon demand..

A lead-acid battery is a secondary (rechargeable) electrochemical device that works like a dry cell, but whose chemical reaction can be reversed so that the battery can be recharged.



Inside a Battery

Dry Cell Wet Cell



In any battery, an electrochemical reaction occurs. This reaction moves electrons from one pole to the other.

The actual metals and electrolytes used control the voltage of the battery -- each different reaction has a characteristic voltage. Here's what happens in one cell of a car's lead-acid battery:

• The cell has one plate made of lead and another plate made of lead dioxide, with a strong sulfuric acid electrolyte in which the plates are immersed.

• The acid reacts with the lead plates and electrons are given off.

When a load like a starter motor is connected, the electrons flow from the battery to the motor. A lead-acid battery has a nice feature -- the reaction is completely reversible. If you apply current from an alternator to the battery, the chemical action reverses so you can reuse the battery over and over.



How to connect circuits

Series Circuit

Parallel Circuit




Series Circuit

Parallel Circuit



1.5V

3.0V3 W light bulb

3 W light bulb

1.0A

0.5A

1.0A

0.5A

1.0A

1.5V

3.0V

Series Circuit

Series - Parallel Circuit

Power = Voltage × Current

We can also connect power sources (batteries, solar cells) in series and/or parallel



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)), and by itself accounts for about 99.86% of the Solar System's mass; the remainder consists of the planets (including Earth), asteroids, meteoroids, comets, and dust in orbit. Why is the mass of the sun so important?

What is the Sun???



Because of the axial tilt of the Earth, the inclination of the Sun's trajectory in the sky varies over the course of the year. When the northern pole is tilted toward the Sun the day lasts longer and the Sun climbs higher in the sky. This results in warmer average temperatures from the increase in solar radiation reaching the surface. When the northern pole is tilted away from the Sun, the reverse is true and the climate is cooler. Above the arctic circle, an extreme case is reached where there is no daylight at all for part of the year. This variation in the climate (because of the direction of the Earth's axial tilt) results in the seasons.

This tilt is also important when aligning solar cells so that they receive the maximum direct rays of the sun.



Average Distance from the sun = 93,000,000 miles = radiusTime to orbit the sun = 1 year = 365 days = (365 X 24) = 8,760 hoursCircumference of orbit = 2 π r = 2* 3.14 * 93,000,000 = 584,336,234 milesSpeed of earth’s orbit = 584,336,234/8760 = ??

NOTE: The earth is closer to the sun by about 3 million miles in our winter than in our summer!

How fast is the earth orbiting around the sun?



Average Distance from the sun = 93,000,000 miles = radiusTime to orbit the sun = 1 year = 365 days = (365 X 24) = 8,760 hoursCircumference of orbit = 2 π r = 2* 3.14 * 93,000,000 = 584,336,234 milesSpeed of earth’s orbit = 584,336,234/8760 = 66,705 mph!!

NOTE: The earth is closer to the sun by about 3 million miles in our winter than in our summer!

How fast is the earth orbiting around the sun?



Solar Energy – a 100 million years ago?

Coal is formed from plant life buried in the Earth millions of years ago. Like Petroleum and natural gas, it is a carbon-based fossil fuel. Coal is called a fossil fuel because it was formed from the remains of vegetation that grew as long ago as 400 million years. It is often referred to as "buried sunshine" because the plants which formed the coal captured the energy from the sun through photosynthesis to create the compounds that make up plant tissues. The main element in the plant material is carbon, which gives coal most of its energy.

So, if we use fossil fuel, how do we convert this energy into useful work?



Electric Power Plant



What are the two main properties of the sun?




1. Heat




1.Heat2.Light

How can we convert the sun’s light into fuel immediately, not in millions of years?



Solar CellSolar Cell Symbol



A solar cell is a device that converts the energy of sunlight directly into electricity by the photovoltaic effect.. The energy generated this way is an example of solar energy. Solar cells are also called photovoltaic or “PV” cells.

The term "photovoltaic" comes from the Greek word “photo” meaning "light", and "voltaic", meaning electric, from the name of the Italian physicist Volta, after whom a unit of electro-motive force, the volt, is named..

Albert Einstein explained the photoelectric effect in 1905 for which he received the Nobel prize in Physics in 1921.



Photovoltaic (PV) cells are made of special materials called semiconductors such as silicon, which is the most commonly used.

When light strikes the cell, photons are absorbed within the semiconductor material. (A photon is a discrete bundle of light energy. Photons are always in motion and have a constant speed of light.) Electrons (negatively charged particles) are knocked loose from their atoms, allowing them to flow through the material to produce electricity.



How do the photovoltaic cells turn sunlight ("photo") into electricity ("voltaic")?

A solar cell is composed of a material, called silicon, sandwiched between metal strips and covered with glass to protect it.

The silicon is made by melting and then cooling sand. This material is then sliced into wafers like potato chips.



Silicon is a good material for solar cells, but by itself, it is a poor conductor. So the cell's are “doped” by inserting impurities into the top and bottom of the wafer.

The top, phosphorus-doped layer contains more electrons, or negatively charged particles, than pure silicon does, while the bottom, boron-doped layer contains fewer electrons than silicon.



To generate electricity, we first need to establish an electric field. It's like a magnetic field: just as the opposite poles of two magnets attract each other, so do the positive and negative charges in an electric field.

This electric field is created in the cell when its two different silicon layers are first brought together. The "extra" electrons in the phosphorus-doped top layer move into the boron-doped bottom layer—a process that occurs only very close to the junction (the point at which the two layers meet)..

Now the cell is ready for the sun.



As sunlight hits the cell, its photons begin "knocking loose" electrons in both silicon layers. These newly freed electrons dart around each layer but are useless for generating electricity until they reach the electric field at the junction.

The electric field pushes electrons that do reach the junction towards the top silicon layer. This force essentially slingshots the electrons out of the cell to the metal conductor strips, generating electricity.



Electrons flow as electricity via the metal conductor strips into a wire and then to an inverter inside the house. This device converts the direct current coming from the PV cell into the alternating current our appliances can use.

Electrons also flow out of the house and back to the solar panel, creating the closed loop necessary to maintain the flow of electricity. The cell keeps generating electricity, even on cloudy days, until the sun goes down at night.



Video: How Solar Cells Work



36 LED Solar Security Light Solar Two-Tier Light

Solar Spotlight with LED lamps

Solar Pathway Marker Light



Solar Demo Circuit

400 watt, dc/ac convertor

110v ac

A AA

A

VV

Charge Controller(Peak Power Tracker)



A solar car is an electric car powered by a type of renewable energy, by solar energy obtained 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.

Solar Cars



Gear Drive Solar Car



Belt Drive Solar Car



Motor Speed, Gear or Pulley ratios, Wheel Speed, Car Speed

1) Motor Speed (from spec. sheet) = 6990 rpm.2) Gear ratio, 48 teeth/12 teeth = 4; Pulley ratio 8mm/24mm = 33) Wheel speed, 6990 /4 = 1747 rpm



Pi (π) – The Special Relationship between the Circumference and the Diameter of a

Circle

Diameter (Across)

For any circle of any size:

d3.14 C:So

3.14

)()(

)(

×=

=

×=

==

dC

or

PidDiameter

CnceCircumfere

Across

Around



So, for one revolution of a wheel whose diameter (d) = 1 inch,

the distance around the wheel is π (3.14) x 1inch = 3.14 inches.



Motor Speed, Gear or Pulley ratios, Wheel Speed, Car Speed

1) Motor Speed (from spec. sheet) = 6990 rpm.2) Gear ratio, 48 teeth/12 teeth = 4; Pulley ratio 5mm/20mm = 43) Wheel speed, 6990 /4 = 1747 rpm4) Car speed:

a) For 1” Diameter wheel, one full revolution = π × D = 3.14”

b) 1747 rpm × 60min. = 104,820 rev per hour c) 104,820 rph × 3.14 = 329,135 inches per hour.d) 329,135 in/hr ÷ 12 inches = 27,428 ft per houre) 27,428 ft/hr ÷ 5,280 feet = 5.2 miles per hour



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• Decide on a belt drive (small pulley) or a gear drive (small gear)• Assemble the wheels and gear / pulley on the axles with the axles through

straws (use washers between the end of the straw and the wheels / gear / pulley)

• 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• Make sure the axles are parallel• Clip the motor to the chassis on the same side as the wheel axle and,• Align the gears (if used), or align the pulley and rubber band (if used)• Assemble a tilted platform for the solar array• 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

“here comes the sun” – ieee tisp / engineers in the classroom 2010 arnold brenner 1 “here...

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