MITES Middle School Introduction To Engineering Systems

A couple of reminders…

Today’s lecture will be quite brief, (yay!)so

please stay as quiet as you can and avoid

playing with any of the items on the tables (including your own pencils, sticky notes, and

notebooks = only use these for note-taking

and questions!)

Please DON’T SWIVEL IN THE CHAIRS!!! I know

it’s tempting (even for me), but it’s distracting

to your peers!

Don’t forget that you are responsible for

creating a poster on a topic we have

covered, so please pay attention!

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Objectives of Today’s Lesson

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Understand solar energy and describe

the ways we can use it.

Understand the basic structure and

function of a Photovoltaic Cell (and

how it creates electricity).

Understand what a Microgrid is and

how we will use it (Dr. Islam).

Harnessing Solar Energy to

Create Electricity

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Solar Energy – A Bright Idea!

“I’d put my money on the sun and solar

energy. What a source of power! I hope we

don’t have to wait ‘til oil and coal run out

before we tackle that.”

- Thomas Edison

Bet ‘ya didn’t know: People have been

harnessing solar energy for a long time!

Solar collector for heating water

A home in California in 1906

SO, WHERE IN AMERICA DO

YOU THINK WE CAN GET THE

MOST SOLAR ENERGY?

WHY?

Sun Angles

A little review of the sun

and the seasons….

Now that we have reviewed some

facts about the sun, let’s focus on

how we can use the HUGE amount

of energy it makes available to us!

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Two Main Categories: Solar Thermal Solar Photovoltaic (PV)

Water heating and cooking Electricity production

*OUR FOCUS

Solar Thermal Energy Technology

Cooking Water

Heating

Solar Water Heating

How Does it Work?

Solar Thermal Energy Technology

Cooking Water Heating

Solar Cooking

Benefits of Solar Cooking

Consumes no

fuels/wood

Generates no air

pollution and no

greenhouse gases

Produces no

smoke

Eliminates fire

dangers

More Benefits of Solar Cooking

Eliminates work ▫ No daily search for

firewood 2 Billion people rely on

wood for cooking fuel!

• Cooks foods slowly and thoroughly

• Preserves nutrients • Foods will not burn

Solar Cooking How Long Does it Take?

Vegetables/Rice

/Wheat:

▫ 1.5-2 hrs

Beans:

▫ 2-3 hrs

Meats:

▫ 1-3 hrs

Bread:

▫ 1-1.5 hrs

Two Main Categories: Solar Thermal Solar Photovoltaic (PV)

Water heating and cooking Electricity production

*OUR FOCUS

Solar Electric Systems

(Photovoltaic Cells)

Photovoltaic (PV) systems

convert light energy

directly into electricity.

Commonly known as “solar

cells.”

The simplest systems power

the small calculators we

use every day! More

complicated systems will

provide a large portion of

the electricity in the near

future.

Solar Electric Systems

How Does it Work?

Sunlight is composed of photons, or bundles

of radiant energy. When photons strike a PV

cell, they may be reflected or absorbed

(transmitted through the cell). Only the

absorbed photons generate electricity. When the photons are absorbed, the energy

of the photons is transferred to electrons in

the atoms of the solar cell.

How Does it Work?

• Solar cells are usually made of two thin pieces of

silicon, the substance that makes up sand and the second most common substance on earth.

• One piece of silicon has a small amount of the

element boron added to it, which gives it a

tendency to attract electrons. It is called the p-

layer because of its positive tendency.

• The other piece of silicon has a small amount of the element phosphorous added to it, giving it an

excess of free electrons (and a negative tendency). This is called the n-layer because it has

a tendency to give up negatively charged

electrons.

How Does it Work?

• When a photon strikes the PV cell, its energy is

used to “push” one of the extra electrons

contained on the n-layer (negative layer) of

silicon into the circuit.

• The “pushed” electron will travel through the

circuit until it reaches a “hole” in the p-layer

(positive layer) of silicon, giving us an electrical

current as it travels (*remember, + and –

charges attract one another).

How Does it Work?

Helpful PV Animations

Let’s keep it quick and simple!

Some cool pictures…

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What is this guy DOING?

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Why do you

think we

included this

picture?

How can

this apply to

harnessing

solar

energy?

Solar Concentrators

The concentrators use an array of mirrors to focus sunlight onto high-efficiency solar cells. Four supports hold the cells in front of the mirrors. The supports also supply cooling water and electrical connections

Concentrators are COOL!

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Photovoltaic Cell Conversion

Efficiency

= A fancy way of saying “the amount of

solar energy that shines on a PV device

that is actually converted into electrical

energy we can use.”

What variables can have an effect on the

amount of PV Cell Conversion Efficiency?

▫ Wavelength of light hitting the PV device

▫ Recombination of electrons with “holes”

before ever entering the current

Continued……

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▫ Natural Resistance of certain materials to

electron flow

▫ Temperature (works best under low temp; too

hot = not very efficient)

▫ Reflection of photons by the materials

(=antireflection is super important!)

▫ Electrical Resistance (must maintain constant

contact with grid for good conduction)

▫ Angle of the PV cell (must be at optimum angle to absorb the most photons)

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Photovoltaic Cell Conversion

Efficiency (continued…)

PV Panel Installation and Angle

Efficiency

Let's think about how you would place a

photovoltaic (PV) panel on a roof to get

the maximum amount of energy output

from it: Should the PV panel be installed flat against

your roof so that it has the same slope as the

roof, or would it be better for it to lie

horizontally and point straight up into the sky?

Should it stand up on its edge, vertically?

Would the direction you oriented it matter?

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What do you think?

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From the our review, you learned that the angle at

which the sun hits the Earth changes quite often. How

could we compensate for this with the installation of

our PV panel?

PV Cell Angle Efficiency INQUIRY

What is the best angle and orientation

at which to install the PV panel so you

can get the most efficient use of the

sun’s energy over the course of the

year at your specific location?

“A New Angle on PV Efficiency”:

Activity 1 ONLY

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A New Angle on PV Efficiency INQUIRY

Each group of 5-6 will need the following

materials:

▫ Mini PV panel

▫ Multimeter and 2 wires with alligator clips

▫ 100-watt lamp

▫ 2 pieces of cardboard (same size as panel)

▫ Protractor

▫ Duct tape

▫ 1 set of instructions with 1 investigation worksheet per group ONLY

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THIS IS CALLED AN “INQUIRY” FOR A

REASON – YOU AND YOUR LAB MATES ARE

“INQUIRING” ABOUT THIS TOPIC, SO SOME

CONFUSION AT FIRST IS NORMAL AND

EXPECTED!

PLEASE FOLLOW YOUR DIRECTIONS AND IF

YOU ARE HAVING TROUBLE, MAKE SURE

YOU CONSULT THOSE BEFORE GIVING UP!

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A New Angle on PV Efficiency INQUIRY

Experimental Set-Up

▫ Step 1: Go to your station with your lab mates

▫ Step 2: Support your solar panel (using

cardboard pieces and tape) See Fig. 1

▫ Step 3: Connect the + and – pins to the mulitimeter and to the the PV panel

▫ Step 4: Turn multimeter on (make sure it is on DC

and measuring in mA) and place the panel 1-2 feet directly under the lamp.

▫ Step 5: Point the PV panel directly at the lamp

and tape the base to the table to prevent movement.

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A New Angle on PV Efficiency INQUIRY

Experimental Set-Up

▫ Step 6: SKIP

▫ Step 7: Lay the panel completely flat and

record the current for this angle (0º) on your worksheet.

▫ Step 8: Make sure your protractor is centered at

the front edge of the PV panel EACH TIME YOU MEASURE for accurate data.

▫ Step 9: Repeat the procedure in STEP 7 with

varying increments by 10º and continue to record data on your worksheet. Graph results!

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A New Angle on PV Efficiency INQUIRY

Now, please direct your

attention to Dr. Islam who is

here to discuss the Microgrid!

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THE PARKING LOT ANY questions you may have, POST ‘EM HERE!

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References The KidWind Project

▫ http://learn.kidwind.org/teach (Accessed

6.13.2012)

A New Angle on PV Efficiency

▫ http://www.teachengineering.org/view_activity.ph

p?url=collection/cub_/activities/cub_pveff/cub_pv

eff_lesson01_activity1.xml (Accessed 6.13.2012)

The Solar Panel and Electric Motor

▫ http://www.swe.org/regionb/b007/documents/sola

rsource.pdf (Accessed 6.13.2012)

U.S. Department of Energy (Energy Basics)

▫ http://www.eere.energy.gov/basics/renewable_en

ergy/pv_cell_conversion_efficiency.html (Accessed

6.18.2012)

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