Photovoltaics Student Guide

8/12/2019 Photovoltaics Student Guide

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Exploring PhotovoltaicsStudent Guide

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2 Exploring Photovoltaics

Solar Energy

What is Solar Energy?Solar energy is radiant energy from the sun. It is vital to us becauseit provides the worlddirectly or indirectlywith almost all of itsenergy. In addition to providing the energy that sustains the world,solar energy is stored in fossil fuels and biomass, and is responsiblefor powering the water cycle and producing wind.

Every day the sun radiates, or sends out, an enormous amount ofenergy. The sun radiates more energy each day than the world usesin one year. Solar energy comes from within the sun itself. Like otherstars, the sun is a big ball of gasesmostly hydrogen and helium. The hydrogen atoms in the suns core combine to form helium andradiant energy in a process called nuclear fusion .

During nuclear fusion, the suns extremely high pressure andtemperature cause nuclei to separate from their electrons. At thisextremely energized state, the nuclei are able to fuse, or combine.

Hydrogen nuclei fuse to become one helium atom of a higher atomicnumber and greater mass, and one neutron remains free. This newhelium atom, however, contains less mass than the combinedmasses of the hydrogen isotopes that fused. This transmutation ofmatter results in some mass being lost. The lost matter is emittedinto space as radiant energy. The process of fusion occurs mostcommonly with lighter elements like hydrogen, but can also occurwith heavier nuclei, until iron (Fe) is formed. Because iron is thelowest energy nucleus, it will neither fuse with other elements, norcan it be ssioned (split) into smaller nuclei.

Scientists theorize that the time for the energy in the suns core tomake its way to the solar surface takes about 150,000 years. Thenuclear fusion process in the suns core produces, among otherthings, gamma rays . These gamma rays are constantly absorbedand re-emitted as they move through the sun, essentially bouncingin random directions. By the time this random walk takes themto the suns surface they have been transformed into visible light. This light escapes from the photosphere , the visible surface of thesun, and arrives at Earth about eight minutes later. The solar energytravels to the Earth at a speed of 3.0 x 10 8 meters per second (186,000miles per second), the speed of light. Heat energy is not transmittedfrom the sun because the space between the sun and Earth is mostlya vacuum. Rather, radiant energy transforms into thermal energy when it strikes the molecules in the atmosphere or on the surfaceof the Earth.

Only a small portion of the energy radiated by the sun into spacestrikes the Earthone part in two billion. Yet, this amount of energyis enormous. It was mentioned before that the sun provides moreenergy in a day than the world uses in a year. The sun also providesmore energy in an hour than the United States uses in a year!

Where does all this energy go? About 30 percent of the suns energythat hits the Earth is reected back into space. Another 25 percentpowers the water cycle; it evaporates water that is then drawn intothe atmosphere, turns into clouds, condenses, and falls back toEarth as precipitation. Plants, the land, and the oceans also absorba portion of solar energy. The rest is reected and could be used tosupply our energy needs.

Image courtesy of NASAThis image of our sun was captured by NASAs Solar DynamicsObservatorya space telescope designed to study the sun.

FusionThe process of fusion most commonly involves hydrogen isotopes cform a helium atom with a transformation of matter. This matter is eradiant energy.

Hydrogen IsotopeHydrogen Isotope

Neutron Helium

Energy

THE SUN

Forest5% to 10%

Water5% to 80%

(varies with sun angle)

Light roof 35% to 50%

Dark roof 10% to 15%

Asphalt5% to 10%

Thick clouds70% to 80%

Thin clouds25% to 30%

Snow50% to 90%

Albedo

Average reectivity of solar radiation for various surfaces.


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Solar energy is considered a renewable energy source. Renewablesources of energy are resources that are continually replenishedby nature, and hence will never run out. Solar power is consideredrenewable because the nuclear fusion reactions that power the sunare expected to keep generating sunlight for many billions of years.

History of Solar EnergyPeople have harnessed solar energy for centuries. As early as the 7thcentury B.C., people used simple magnifying glasses to concentratethe light of the sun into beams so hot they could cause wood tocatch re.

In the 1860s in France, a scientist named Auguste Mouchout usedheat from a solar collector to make steam to drive a steam engine.Around the same time in the United States, John Ericsson developedthe rst realistic application of solar energy using a solar reector todrive an engine in a steam boiler. With coal becoming widely used,neither of these inventions became part of the mainstream.

Early in the 1900s, scientists and engineers began seriouslyresearching ways to use solar energy. The solar water heater gainedpopularity during this time in Florida, California, and the Southwest. The industry was in full swing just before World War II. This growthlasted until the mid-1950s, when low-cost, natural gas became theprimary fuel for heating homes and water, and solar heating lostpopularity.

The public and world governments remained largely indifferent tothe possibilities of solar energy until the energy crises of the 1970s.Research efforts in the U.S. and around the world since that timehave resulted in tremendous improvements in solar technologies forheating water and buildings and making electricity.

Solar CollectorsHeating with solar energy is relatively easyjust look at a car parkedin the sun with its windows closed. Getting the right amount of heatin a desired location, however, requires more thought and carefuldesign. Capturing sunlight and putting it to work effectively isdifficult because the solar energy that reaches the Earth is spreadout over a large area. The sun does not deliver that much energy toany one place at any one time.

How much solar energy a place receives depends on severalconditions. These include the time of day, the season of the year, thelatitude of the area, the topography, and the clearness or cloudinessof the sky.

Asolar collector is one way to collect heat from the sun. A closed caron a sunny day is like a solar collector. As the sunlight passes through

the cars glass windows, it is absorbed by the seat covers, walls, andoor of the car. The light that is absorbed changes into heat. Thecars glass windows let light in, but do not let all the heat out. Thisis also how greenhouses are designed to stay warm year-round. Agreenhouse or solar collector:allows sunlight in through the glass; absorbs the sunlight and changes it into heat; and traps most of the heat inside.

TRAPPED HEAT

SOLAR ENERGY

Solar CollectorOn a sunny day, a closed car becomes a solar collector. Light energy passethrough the window glass, is absorbed by the cars interior, and convertedheat energy. The heat energy becomes trapped inside.

JOHN ERICSSONS SOLAR ENGINE

John Ericssons Sun Motor. Built in New York in 1872. Ericsson hadintended Californian agriculturists to take up his sun-motor forirrigation purposes, but in the end nothing came of the project.

Image courtesy of www.stirlingengines.org


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Photovoltaic SystemsPhotovoltaic (or PV)systems convert light directly into electricity. The term photo comes from the Greek phos , which means light. Theterm volt is a measure of electricity named for Alessandro Volta (1745-1827), a pioneer in the development of electricity. Photovoltaicsliterally means lightelectricity.

Commonly known as solar cells, PV cells are already an important

part of our lives. The simplest PV systems power many of the smallcalculators, wrist watches, and outdoor lights we see every day.Larger PV systems provide electricity for pumping water, poweringcommunications equipment, and even lighting homes and runningappliances.

In certain applications, such as motorist aid call boxes on highwaysand pumping water for livestock, PV power is the cheapest form ofelectricity. Some electric utility companies are building PV systemsinto their power supply networks.

History of PhotovoltaicsFrench physicist Edmond Becquerel rst described the photovoltaic

effect in 1839, but it remained a curiosity of science for the next halfcentury. At the age of 19, Becquerel found that certain materialswould produce small amounts of electric current when exposed tolight. In the 1870s, William Adams and Richard Day showed that lightcould produce an electric current in selenium. Charles Fritts theninvented the rst PV cell using selenium and gold leaf in 1883, whichconverted light to electricity at about one percent efficiency .

The conversion efficiency of a PV cell is the proportion of radiantenergy the cell converts into electrical energy, relative to the amountof radiant energy that is available and striking the PV cell. This isvery important when discussing PV devices, because improvingthis efficiency is vital to making PV energy competitive with moretraditional sources of energy, such as fossil fuels.

During the second half of the 20th century, PV science wasrened and the process more fully developed. Major steps towardcommercializing photovoltaics were taken in the 1940s and 1950s,when the Czochralski process was developed for producing highlypure crystalline silicon.

In 1954, scientists at Bell Laboratories depended on the Czochralskiprocess to develop the rst crystalline silicon photovoltaic cell, whichhad a conversion efficiency of four percent.

As a result of technological advances, the cost of PV cells hasdecreased signicantly over the past 25 years, as the efficiency hasincreased. Todays commercially available PV devices convert 18 to 24percent of the radiant energy that strikes them into electricity.

In the laboratory, combining exotic materials with specialized celldesigns has produced PV cells with conversion efficiencies as highas 43 percent. The current expense of these technologies typicallyrestricts their use to aerospace and industrial applications, wherethe unit cost of a solar array that powers, for example, a satellite is a

minor concern.

ALESSANDRO VOLTA EDMOND BECQUERE

SOLAR PANELS ON THE INTERNATIONAL SPACE STATION

Image courtesy of NASA

High efficiency photovoltaic cells power the International Space Station.

Solar cells provide powerto this traffic signal.Attached to the supportpole are two boxes: onethat stores batteries foroperation while its dark,and one that houses acontrol panel.

SOLAR TRAFFIC SIGNAL


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Photovoltaic Effect The photovoltaic effect is the basic physical process through which

a PV cell converts sunlight directly into electricity. PV technologyworks any time the sun is shining, but more electricity is producedwhen the light is more intense and when it is striking the PV modulesdirectlywhen the rays of sunlight are perpendicular to the PVmodules.

Unlike solar systems for heating water, PV technology does notproduce heat to make electricity. Instead, PV cells generate electricitydirectly from the electrons freed by the interaction of radiant energywith the semiconductor materials in the PV cells.

Sunlight is composed of photons , or bundles of radiant energy.When photons strike a PV cell, they may be reected, absorbed, ortransmitted through the cell.

Only the absorbed photons generate electricity. When the photonsare absorbed, the energy of the photons is transferred to electrons inthe atoms of the solar cell, which is actually a semiconductor .

With their new-found energy, the electrons are able to escape fromtheir normal positions associated with their atoms to become partof the current in an electrical circuit. By leaving their positions, theelectrons cause holes to form in the atomic structure of the cell intowhich other electrons can move.

Special electrical properties of the PV cella built-in electric eldprovide the voltage needed to drive the current through a circuit andpower an external load, such as a light bulb.

Photovoltaic Cells The basic building block of PV technology is the photovoltaic cell .Different materials are used to produce PV cells, but siliconthemain ingredient in sandis the most common basic material. Silicon,a common semiconductor material, is relatively cheap because it iswidely available and used in other things, such as televisions, radios,and computers. PV cells, however, require very pure silicon, whichcan be expensive to produce.

The amount of electricity a PV cell produces depends on its size, itsconversion efficiency, and the intensity of the light source. Efficiencyis a measure of the amount of electricity produced from the sunlighta cell receives. A typical PV cell produces 0.5 volts of electricity. It

takes just a few PV cells to produce enough electricity to power asmall watch or solar calculator.

The most important parts of a PV cell are the semiconductor layers,where the electric current is created. There are a number of differentmaterials suitable for making these semi-conducting layers, andeach has benets and drawbacks. Unfortunately, there is no oneideal material for all types of cells and applications.

Photovoltaic Technology

Silicon Atom

Silicon is used as a semiconductor because it has four valence electronsand does not want to lose or gain electrons. Therefore, the electrons owacross it from the boron side to the phosphorus side without the siliconinterfering with the movement.

Photovoltaic cellElectric Load

Sun

(-)

(+)

DC currentow

Boron-doped (p-type) silicon layer

Phosphorous-doped (n-type) silicon lay

Sunlight to Electricity

Types of PV Cells

PV cells come in manyshapes and sizes. The mostcommon shapes are circles,rectangles, and squares. The size and the shape ofa PV cell, and the numberof PV cells required for onePV module, depend on thematerial of which the PVcell is made.


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How a Traditional PV Cell is MadeLets look more closely at how a PV cell is made and how it produces

electricity.

Step 1A slab (or wafer) of pure silicon is used to make a PV cell. The top of theslab is very thinly diffused with an n dopant, such as phosphorous.On the base of the slab, a small amount of a p dopant , typicallyboron, is diffused. The boron side of the slab is 1,000 times thickerthan the phosphorous side. Dopants are similar in atomic structureto the primary material. The phosphorous has one more electron inits outer shell than silicon, and the boron has one less. These dopantshelp create the electric eld that motivates the energetic electronsout of the cell created when light strikes the PV cell.

The phosphorous gives the wafer of silicon an excess of free

electrons; it has a negative character. This is called the n-typesilicon (n = negative). The n-type silicon is not chargedit has anequal number of protons and electronsbut some of the electronsare not held tightly to the atoms. They are free to move to differentlocations within the layer. This silicon has a negative character, butnot a negative charge.

The boron gives the base of the silicon wafer a positive character,which will cause electrons to ow toward it. The base of the silicon iscalled p-type silicon (p = positive). The p-type silicon has an equalnumber of protons and electrons; it has a positive character, but nota positive charge.

Step 2Where the n-type silicon and p-type silicon meet, free electrons fromthe n-layer ow into the p-layer for a split second, then form a barrierto prevent more electrons from moving between the two sides. Thispoint of contact and barrier is called the p-n junction.

When both sides of the silicon slab are doped, there is a negativecharge in the p-type section of the junction and a positive chargein the n-type section of the junction due to movement of theelectrons and holes at the junction of the two types of materials. This imbalance in electrical charge at the p-n junction produces anelectric eld between the p-type and n-type.

Step 3If the PV cell is placed in the sun, photons of light strike the electronsin the p-n junction and energize them, knocking them free of theiratoms. These electrons are attracted to the positive charge in then-type silicon and repelled by the negative charge in the p-typesilicon. Most photon-electron collisions actually occur in the siliconbase.

Step 4A conducting wire connects the p-type silicon to an external loadsuch as a light or battery, and then back to the n-type silicon, forminga complete circuit. As the free electrons are pushed into the n-typesilicon, they repel each other because they are of like charge. Thewire provides a path for the electrons to move away from each other. This ow of electrons is an electric current that can power a load,such as a calculator or other device, as it travels through the circuitfrom the n-type to the p-type.

In addition to the semi-conducting materials, solar cells consist of atop metallic grid or other electrical contact to collect electrons fromthe semiconductor and transfer them to the external load, and aback contact layer to complete the electrical circuit.

Photovoltaic Cell


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PV Modules and ArraysFor more power, PV cells are connected together to form larger unitscalled modules . Photovoltaic cells are connected in series and/or parallel circuits to produce higher voltages, currents, and powerlevels. A PV module is the smallest PV component sold commercially,and can range in power output from about 10 watts to 300 watts.

A typical PV module consists of PV cells sandwiched between a clear

front sheet, usually glass, and a backing sheet, usually glass or a typeof tough plastic. This protects them from breakage and from theweather. An aluminum frame can be tted around the PV moduleto enable easy affixing to a support structure. Photovoltaic arrays include two or more PV modules assembled as a pre-wired, eld-installable unit. A PV array is the complete power-generating unit,consisting of any number of modules and panels.

PV System ComponentsAlthough a PV module produces power when exposed to sunlight,a number of other components are required to properly conduct,control, convert, distribute, and store the energy produced by thearray. Depending on the type of system, these components mayinclude:

Power InverterPV modules, because of their electrical properties, produce directcurrent rather than alternating current. Direct current (DC) iselectric current that ows in a single direction. Many simple devices,such as those that run on batteries, use direct current. Alternatingcurrent (AC) , in contrast, is electric current that reverses its directionof ow at regular intervals (120 times per second). This is the type ofelectricity provided by utilities, and the type required to run mostmodern appliances and electronic devices.

In the simplest systems, DC current produced by PV modules is useddirectly. In applications where AC current is necessary, an inverter can be added to the system to convert DC to AC current.

Battery SystemPV systems cannot store electricity, so batteries are often added. APV system with a battery is congured by connecting the PV arrayto an inverter. The inverter is connected to a battery bank and to anyload. During daylight hours, the PV array charges the battery bank. The battery bank supplies power to the load whenever it is needed.A device called a charge controller keeps the battery properlycharged and prolongs its life by protecting it from being overchargedor completely discharged.

PV systems with batteries can be designed to power DC or AC

equipment. Systems operating only DC equipment do not need aninverter, only a charge controller.

It is useful to remember that any time conversions are made in asystem, there are associated losses. For example, when an inverteris used there is a small loss of power that can be described by theinverters conversion efficiency. Likewise, when batteries are usedto store power, not only is there additional expense to purchasethe batteries and associated equipment, but due to the internalresistance of the batteries there is a small loss of power as the chargeis drawn out of the batteries.

module

PV cell

array

CELLS

MODULES

ARRAY

CELLS

MODULES

ARRAY

Parts of a Photovoltaic Array

Photovoltaic Arrays Are Made of IndividuCells


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PV Systems Two types of PV systems are grid-connected systems and stand-alone systems. The main difference between these systems is thatone is connected to the utility grid and the other is not.

Grid-Connected SystemsGrid-connected systems are designed to operate in parallel with,and interconnected with, the national electric utility grid. What

is the grid? It is the network of cables through which electricity istransported from power stations to homes, schools, and other places.A grid-connected system is linked to this network of power lines.

The primary component of a grid-connected system is the inverter,or power conditioning unit (PCU). The inverter converts the DCpower produced by the PV system into AC power, consistent withthe voltage and power quality requirements of the utility grid. Thismeans that it can deliver the electricity it produces into the electricitynetwork and draw it down when needed; therefore, no battery orother storage is needed.

Stand-Alone SystemsAs its name suggests, this type of PV system is a separate electricitysupply system. A stand-alone system is designed to operateindependent of the national electric utility grid, and to supplyelectricity to a single system. Usually a stand-alone system includesone or more batteries to store the electricity.

Historically, PV systems were used only as standalone systems inremote areas where there was no other electricity supply. Today,stand-alone systems are used for water pumping, highway lighting,weather stations, remote homes, and other uses away from powerlines.

Grid-Connected Systems Stand-Alone SystemsPV Array

Inverter/Power Conditioning Unit

Distribution Panel

AC Loads Electric Utility

Energy Source

Energy Conversion

Energy Inversionand Conditioning

Energy Distribution

EnergyStorage

GridEnergy Use

PG&Es Vaca-Dixon Solar Station in California is a 2-MW grid-connected system.

The Mars Rovers, Spirit and Opportunity, are powered by stand-alone systems because they operate far away from Ear th.

Image courtesy of PG&E Image courtesy of NASA


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Scale of PV Systems There are three general scales at which photovoltaic systems aregenerally installed. They are:

ResidentialA residential system is designed to offset power usage at an individualresidence. While usually unable to provide all power used by thehomeowners, the system could help to offset the homes electricityusage. This type of system might produce enough electricity topower part, or all, of one homes electricity needs.

CommercialA commercial system is designed to offset power usage at a businessor industrial site. These systems are much larger than residentialsystems that can produce more power due to the often expansiveroof-top space available for their installation. An example would be agrocery store that contracts with a company to place a solar array ontheir at roof while simultaneously contracting to buy power fromthe installer at a xed rate for many years. This type of system mightproduce enough electricity to operate all or part of the business orindustrial site.

UtilityUtility systems are employed by energy companies to produce base-load or peak-load power for sale to consumers. Large areas of landare typically required for their installation. An example would bea large PV array that is employed to produce power at peak usagetimes in the summer months when air conditioning accounts for alarge part of the electrical usage. The array produces the most powerwhen the sun is at its peak and causing consumers to turn down theirthermostatsrequiring the extra electricity produced by the array.

Other Solar TechnologiesLike solar cells, solar thermal systems use solar energy to makeelectricity. Concentrated solar power (CSP) technologies focusheat in one area to produce the high temperatures required tomake electricity. Since the solar radiation that reaches the Earth isso spread out and diluted, it must be concentrated to produce thehigh temperatures required to generate electricity. There are severaltypes of technologies that use mirrors or other reecting surfaces toconcentrate the suns energy up to 2,000 times its normal intensity.

Parabolic troughs use long reecting troughs that focus the sunlightonto a pipe located at the focal line. A uid circulating inside thepipe collects the energy and transfers it to a heat exchanger, whichproduces steam to drive a turbine. The worlds largest parabolictrough power plant is located in the Mojave Desert in California. Thisplant has a total generating capacity of 354 megawatts, one-thirdthe size of a large nuclear power plant.

Solar power towers use a large eld of rotating mirrors to track thesun and focus the sunlight onto a thermal receiver on top of a talltower. The uid in the receiver collects the heat and either uses it togenerate electricity or stores it for later use.

Dish/engine systems are like satellite dishes that concentrate

sunlight rather than signals, with a heat engine located at the focalpoint to generate electricity. These generators are small mobile unitsthat can be operated individually or in clusters, in urban and remotelocations.

Concentrated solar power technologies require a continuous supplyof strong sunlight, like that found in hot, dry regions such as deserts.Developing countries with increasing electricity demand willprobably be the rst to use CSP technologies on a large scale.

RESIDENTIAL COMMERCIAL UTILITY

Average Size of Grid-Connected Photovoltaic Systems, 2011

U.S. Total Installed Solar Electricity Capacity

18 kW5.7 kW

4.6 MW

CSP

PV

0

1000

2000

3000

4000

5000

2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010Data: DOE EERE 2011 Renewable Energy Data Book, IREC

20112001 2002 2003 2004 2005 2006 2007 2008 2009 20100

100

200

300

400

500

600

700

800

900

1000

Annual Installed Grid-Connected PV Capacity by Sector

Utility

Non-Residential

Residential

Data: Interstate Renewable Energy Council2011

2000

1100

1200

1300

1400

1500

1600

1700

1800


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Emerging PV Technologies Today there are many new PV technologies either on the market, inthe pipeline, or in the research phase. These technologies will havea direct effect on how much of our energy we derive from solarpower in the future. Look for technologies that will make things lessexpensive or serve multiple purposes as they are applied to newdesigns.

Ribbon Silicon Thin crystalline silicon sheets are drawn out of molten silicon ratherthan being sawed from an ingot . This method is less expensive andless wasteful to produce silicon. However, the nished product isusually a lower quality material. In some cases, they will have cells ofa higher conversion efficiency.

Amorphous Silicon / Thin-Film Technologies This new class of materials allows the production of PV cells that aresmaller and more exible than the delicate silicon wafer technologythat has dominated PV cell production in the past. These materialsare not crystalline, but amorphous , in structure. This type of PV cellcan actually be applied to a variety of materials to make any numberof materials that you might use for another purposesuch as glazingfor a window, or shingles for a roof. Imagine windows that produceelectricity! Materials used for dual purposes (building material andPV cell) are called Building Integrated Photovoltaics (BIPV).

CdTe: Cadmium Telluride This thin-lm technology has higher solar spectrum absorptionand lower costs to manufacture, however, there are concernsabout the toxicity and scarcity of chemicals necessary for itsproduction.

CIGS: Copper Indium Gallium Diselenide The gallium is added to these thin-lm cells to increase theenergy absorption of the cells, which increases efficiency.

Earth Abundant Materials Manufacturing PV cells from abundant, low cost resources is aresearch priority. One of the promising technologies issulfoselenide or CZTS. The drawback to CZTS is a lower efficiencythan other PV cells.

Thin-lm materials are much cheaper to produce. They are veryversatile in how they can be applied to many structural materials. They are also less efficient than current silicon crystal PV cells.However, what they lack in efficiency may be overcome by theirexibility of application and low cost.

Multijunction Technologies This category actually combines multiple layers of materials thatare designed to absorb different wavelengths of solar energyimproving the efficiency of the cell by combining the output of thevarious layers. Multijunction cells are a high-cost PV technology, butcan reach efficiencies of over 43 percent.

Dye Sensitized Solar CellsWhile not yet in production, this organic-inorganic hybrid technologyshows promise to be a very low cost technology. Using a small-molecule dye that absorbs photons, an acceping material such aszinc ozide, and an electrolyte, this technology is easy to manufacturefrom abundant materials. Research continues to improve durability.

The Schapfen Mill Tower is a our mill in Germany. The southern facadeis faced with 1,300 thin-lm solar modules.

THIN FILM TECHNOLOGY


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Benets and LimitationsBenets

Solar electric systems offer many advantages:

they are safe, clean, and quiet to operate;

they are highly reliable;

they require virtually no maintenance;

they are cost-effective in remote areas and for some residential andcommercial applications;

they are exible and can be expanded to meet increasing electricalneeds;

they can provide independence from the grid or backup duringoutages; and

the fuel is renewable and free.

Limitations There are also some practical limitations to PV systems:

PV systems are not well suited for energy-intensive uses such asheating; and

grid-connected systems are rarely economical, primarily becausethe current cost of the PV technology is much higher than the costof conventional electricity in the United States.

In August 2002, BP Solar installed a new photovoltaic facility on the roof of the new Terminal 2 at the Munich International Airport. It is one ofthe largest solar facilities of its kind and produces an average of approximately 500,000 kWh a yearrepresenting the electricity needs of about200 households. High production of energy is guaranteed even in winter through the use of the latest polycrystalline silicon cells and the optimalalignment of the solar modules at a 20 angle facing south.

Image courtesy of BP Solar

MUNICH INTERNATIONAL AIRPORT


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Electricity makes our lives easier, but it can seem like a mysteriousforce. Measuring electricity is confusing because we cannot see it.We are familiar with terms such as watt, volt, and amp, but we donot have a clear understanding of these terms. We buy a 60-wattlight bulb, a tool that requires 120 volts, or an appliance that uses 8.8amps, but we do not think about what those units mean.

Using the ow of water as an analogy can make electricity easierto understand. The ow of electrons in a circuit is similar to waterowing through a hose. If you could look into a hose at a given point,you would see a certain amount of water passing that point eachsecond. The amount of water depends on how much pressure isbeing appliedhow hard the water is being pushed. It also dependson the diameter of the hose. The harder the pressure and the largerthe diameter of the hose, the more water passes each second. Theow of electrons through a wire depends on the electrical pressurepushing the electrons and on the cross-sectional area of the wire.

Voltage The pressure that pushes electrons in a circuit is called voltage. Usingthe water analogy, if a tank of water were suspended one meterabove the ground with a one-centimeter pipe coming out of thebottom, the water pressure would be similar to the force of a shower.If the same water tank were suspended 10 meters above the ground,the force of the water would be much greater, possibly enough tohurt you.

Voltage (V) is a measure of the pressure applied to electrons tomake them move. It is a measure of the strength of the current in a

circuit and is measured in volts (V) . Just as the 10-meter tank appliesgreater pressure than the 1-meter tank, a 10-volt power supply (suchas a battery) would apply greater pressure than a 1-volt powersupply.

AA batteries are 1.5-volt; they apply a small amount of voltage forlighting small ashlight bulbs. A car usually has a 12-volt batteryitapplies more voltage to push current through circuits to operate theradio or defroster. The standard voltage of wall outlets is 120 voltsadangerous voltage. An electric clothes dryer is usually wired at 240voltsa very dangerous voltage.

Current The ow of electrons can be compared to the ow of water. Thewater current is the number of molecules of water owing past axed point; electric current is the number of electrons owing pasta xed point.

Electric current (I) is dened as electrons owing between twopoints having a difference in voltage. Current is measured in amperes or amps (A). One ampere is 6.25 x 10

18 electrons per second passing

through a circuit.

With water, as the diameter of the pipe increases, so does the amountof water that can ow through it. With electricity, conducting

wires take the place of the pipe. As the cross-sectional area of thewire increases, so does the amount of electric current (number ofelectrons) that can ow through it.

ResistanceResistance (R) is a property that slows the ow of electrons. Usingthe water analogy, resistance is anything that slows water ow, suchas a smaller pipe or ns on the inside of a pipe.

In electrical terms, the resistance of a conducting wire depends onthe properties of the metal used to make the wire and the wiresdiameter. Copper, aluminum, and silvermetals used in conductingwireshave different resistance.

Resistance is measured in units called ohms () . There are devicescalled resistors, with set resistances, that can be placed in circuits

to reduce or control the current ow. Any device placed in a circuitto do work is called a load. The light bulb in a ashlight is a load. Atelevision plugged into a wall outlet is also a load. Every load hasresistance.

Measuring Electricity

Water Tank

1 m

Water Tank

10 m

Voltage

Water Tank

1 cm diameterpipe

Water Tank

10 cm diameterpipe

Current


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Ohms LawGeorge Ohm, a German physicist, discovered that in many materials,especially metals, the current that ows through a material isproportional to the voltage. He found that if he doubled the voltage,the current also doubled. If he reduced the voltage by half, thecurrent dropped by half. The resistance of the material remained thesame.

This relationship is called Ohms Law and can be described using a

simple formula. If you know any two of the measurements, you cancalculate the third using the following formula:

voltage = current x resistanceV = I x R or V = A x

Electric PowerPower (P) is a measure of the rate of doing work or the rate at whichenergy is converted. Electric power is the rate at which electricity isproduced or consumed. Using the water analogy, electric power isthe combination of the water pressure (voltage) and the rate of ow(current) that results in the ability to do work.

A large pipe carries more water (current) than a small pipe. Water at aheight of 10 meters has much greater force (voltage) than at a height ofone meter. The power of water owing through a 1-centimeter pipe froma height of one meter is much less than water through a 10-centimeterpipe from 10 meters.

Electric power is dened as the amount of electric current owing dueto an applied voltage. It is the amount of electricity required to start oroperate a load for one second. Electric power is measured in watts (W) . The formula is:

power = voltage x currentP = V x I or W = V x A

Electrical EnergyElectrical energy introduces the concept of time to electric power. In

the water analogy, it would be the amount of water falling throughthe pipe over a period of time, such as an hour. When we talk aboutusing power over time, we are talking about using energy. Using ourwater example, we could look at how much work could be done bythe water in the time that it takes for the tank to empty.

The electrical energy that an appliance or device consumes can bedetermined only if you know how long (time) it consumes electricpower at a specic rate (power). To nd the amount of energyconsumed, you multiply the rate of energy consumption (measuredin watts) by the amount of time (measured in hours) that it is beingconsumed. Electrical energy is measured in watt-hours (Wh).

energy = power x timeE = P x t or E = W x h = Wh

Another way to think about power and energy is with an analogyto traveling. If a person travels in a car at a rate of 40 miles per hour(mph), to nd the total distance traveled, you would multiply therate of travel by the amount of time you traveled at that rate.

If a car travels at 40 miles per hour for 1 hour, it would travel 40 miles.distance = 40 mph x 1 hour = 40 miles

If a car travels at 40 miles per hour for 3 hours, it would travel 120miles.

distance = 40 mph x 3 hours = 120 miles

The distance traveled represents the work done by the car. When welook at power, we are talking about the rate that electrical energy isbeing produced or consumed. Energy is analogous to the distancetraveled or the work done by the car.

A person would not say he took a 40-mile per hour trip because thatis the rate. The person would say he took a 40-mile trip or a 120-miletrip. We would describe the trip in terms of distance traveled, notrate traveled. The distance represents the amount of work done.

The same applies with electric power. You would not say youused 100 watts of light energy to read your book, because a wattrepresents the rate you use energy, not the total energy used. Theamount of energy used would be calculated by multiplying the rateby the amount of time you read.

If you read for ve hours with a 100-W light bulb, for example, youwould use the formula as follows:

energy = power x time (E = P x t)energy = 100 W x 5 hours = 500 Wh

One watt-hour is a very small amount of electrical energy. Usually,we measure electric power in larger units called kilowatt-hours(kWh) or 1,000 watt-hours (kilo = thousand). A kilowatt-hour is theunit that utilities use when billing most customers. The average costof a kilowatt-hour of electricity for residential customers is about$0.12.

To calculate the cost of reading with a 100-W light bulb for ve hours,you would change the watt-hours into kilowatt-hours, then multiply thekilowatt-hours used by the cost per kilowatt-hour, as shown below:

500 Wh / 1,000 = 0.5 kWh0.5 kWh x $0.12/kWh = $0.06

Therefore, it would cost about six cents to read for ve hours with a 100-W light bulb.

Water Tank Water Tank

Resistance

Water Tank Water Tank

Electric Power


14/40


1. Identify and explain the nuclear reaction in the sun that produces radiant energy.

2. Dene renewable energy. Explain why solar energy is considered renewable.

3. Explain why a car parked in the sun becomes hot inside.

4. Why is a solar cell called a PV cell? What does the word photovoltaic mean?

5. Explain the conversion efficiency of a PV cell. How efficient are PV cells today?

6. How do new thin-lm technologies compare to conventional PV cells?

7. Explain briey how a PV cell converts radiant energy into electricity.

8. Do PV modules produce AC or DC current? Which type of current do most appliances use? What device converts DC to AC current?

9. Dene the following electrical measures and the unit of measurement for each.

voltage:

current:

resistance:

power:

10. What is the average cost of a kilowatt-hour of electricity for U.S. residential customers?

Review Questions


15/40


Power (P) is a measure of the rate of doing work or the rate at which energy is converted. Electric power is dened as the amount of electric currentowing due to an applied voltage. Electric power is measured in watts (W) . The formula is:

power = voltage x current

P = V x I or W = V x A

Calculation of Power

Itotal = I1 = I2 = I3Vtotal = V1 + V2 + V3

In series circuits, the current remains constant whilethe voltage changes. To calculate total voltage, addthe individual voltages together:

Series Circuits+

1.5 V

+

1.5 V

+

1.5 V

4.5 V

1 2 3 4 5 6- + - + - +

Single PV Module

1.5 V0.1 A

1 2 3 4 5 6- + - + - +

Series - 2 PV Modules

3.0 V0.1 A

1 2 3 4 5 6- + - + - +

Series - 3 PV Modules

4.5 V0.1 A

Itotal = I1 + I2 + I3Vtotal = V1 = V2 = V3

In parallel circuits, the voltage remains constantwhile the current changes. To calculate totalcurrent, add the individual currents together:

Parallel Circuits+

1.5 V

+

1.5 V

+

1.5 V

1.5 V

1 2 3 4 5 6- + - + - +

Single PV Module

1.5 V0.1 A

1 2 3 4 5 6- + - + - +

Parallel - 2 PV Modules

1.5 V0.2 A

1 2 3 4 5 6- + - + - +

Parallel - 3 PV Modules

1.5 V0.3 A


16/40


Basic Measurement Values in Electronic

SYMBOL VALUE METER UNIT

V Voltage (the force) Voltmeter Volts (V)I Current (the ow) Ammeter Amps/Amperes (A)

R Resistance (the anti-ow) Ohmmeter Ohms ()

1 Ampere = 1 coulomb/second

1 Coulomb = 6.24 x 10 18 electrons (about a triple axle dump truck full of sand where one grain of sand is one electron)

Prexes for Units Smaller

(m)illi x 1/1000 or .001() micro x 1/1000000 or .000001

(n)ano x1/100000000 or .000000001

(p)ico x 1/1000000000000 l or .000000000001

Bigger(K)ilo x 1,000

(M)ega x 1,000,000

(G)iga x 1,000,000,000

Formulas for Measuring ElectricityV = I x R

I = V/R

R = V/I

Series Resistance (Resistance is additive)RT= R1 + R2 + R3 +Rn

Parallel Resistance (Resistance is reciprocal)1/RT= 1/R 1 + 1/R 2+ 1/R 3 +1/R n

Note: ALWAYS convert the values you are working with to the BASE unit. For exampledont plug kilo-ohms (K ) into theequationconvert the value to frst.

The formula pie works for any threevariable equation. Put your nger onthe variable you want to solve for andthe operation you need is revealed.

V


17/40


OFF750

200

200

2000 20m

200m

10

hFE

1000

200

20

2000m

200m

2000K

200K

20K

2000200

V --- V

A ---

CEDIGITALMULTIMETER

NPN PNP

E

E

B

B

C

EE

C

10ADC

V mA

COM

!

!

10A maxunfused

750VAC

1000VDC200m A max

500V max

DirectionsDC Voltage ( )1. Connect RED lead to VmA connector and BLACK to COM.

2. Set SWITCH to highest setting on DC VOLTAGE scale (1000).

3. Connect leads to the device to be tested using the alligator clips provided.

4. Adjust SWITCH to lower settings until a satisfactory reading is obtained.

5. With the solar modules or array the 20 setting usually provides the best reading.

DC Current ( )1. Connect RED lead to VmA connector and BLACK to COM.

2. Set SWITCH to 10 ADC setting.

3. Connect leads to the device to be tested using the alligator clips provided.Note: The reading indicates DC AMPS; a reading of 0.25 amps equals 250 ma (milliamps).

YOUR MULTIMETER MIGHT BE SLIGHTLY DIFFERENT FROM THE ONE SHOWN. BEFORE USING THE MULTIMETER READ THE OPERATORS

INSTRUCTION MANUAL INCLUDED IN THE BOX FOR SAFETY INFORMATION AND COMPLETE OPERATING INSTRUCTIONS.

Digital Multimeter


18/40


Solar 1

? QuestionHow do similar PV modules in an array vary in electrical output? Think about which

varies more, current or voltage.

HypothesisDevelop a hypothesis to address the question using the following format: If(manipulated variable) then (responding variable) because ...

Materials

Procedure1. Test each PV module in the array by connecting the electrical load to each cell.

2. With the multimeter, measure the current and voltage of each PV module in thearray under identical external conditions.

3. Record the data below and compare.

4. Calculate the power (current x voltage), or wattage of each trial. Record results in the chart below.

Observations

DataCURRENT A VOLTAGE V POWER W

LEFT PV MODULE

CENTER PV MODULE

RIGHT PV MODULE

Conclusion

ReectionsWere the output currents of the PV modules similar?

Were the output voltages of the PV modules close to one another?

Bright light source Alligator clips Electrical load (motor, fan, light, or buzzer) PV array

2 Multimeters

TO MEASURE CURRENT,Ampmeter (set to DC Amps)

TO MEASURE VOLTAGE,Voltmeter (set to DC Volts)

Note : Solid and dashed lines in the diagramrepresent different sets of clips or wires.


19/40


Solar 2

? QuestionHow does a PV array wired in series affect the electrical output? Thinkabout what will happen to current and voltage output.

HypothesisDevelop a hypothesis to address the question using the followingformat: If (manipulated variable) then (responding variable) because ...

Materials PV array Electrical load 2 Multimeters Alligator clips

Procedure1. Attach the multimeter to the PV array wired in series with an

electrical load. See diagram to the right.

2. Measure the current and voltage. Record data in the chart below.

3. Calculate the power (current x voltage), or wattage and recordresults in the chart below.

Observations

Data

CURRENT A VOLTAGE V POWER WATTS

SERIES

Conclusion

ReectionsHow did the current produced in a series circuit compare to the current of an individual PV module?

How did the voltage produced in a series circuit compare to the voltage of an individual PV module?





20/40


Solar 3

? Question

How does light intensity affect the electrical output of a PV array wired in series?


Materials 2 Multimeters PV array Bright light source Dim light source

Electrical load Alligator clips

Procedure1. Attach the multimeter to the PV array wired in series with an electrical load.2. Place the PV array under the bright light source.3. Measure the current and voltage produced by the PV array.4. Record data in the chart below.5. Place the PV array under the dim light source.6. Measure the current and voltage produced by the PV array.7. Record data in the chart below.8. Calculate the power (current x voltage), or wattage of each trial. Record results in the chart below.

Observations

Data

CURRENT A VOLTAGE V POWER WA

BRIGHT LIGHT

DIM LIGHT

Conclusion

ReectionsWhat differences did you observe in the variables of the two light intensities?

How does light intensity affect the output of the PV array?

NoteWhen comparing light outputof different sources (e.g., bulbs),lumens should be used tocompare light intensity ratherthan watts, which comparepower consumption.





21/40


Solar 4

? QuestionHow does the angle of a PV array wired in series with a light source affect theelectrical output?


Materials

Procedure1. Attach the multimeter to the PV array wired in series with an electrical load.

2. Measure current and voltage when the PV module is at an angle of 90 relative to the light. Record data in the chart.

3. Using the protractor to adjust the angle, measure current and voltage when the PV module is at an angle of 75 relative to the light.Record data in the chart.

4. Using the protractor, measure current and voltage when the PV module is at an angle of 60, 45, 30, and 15 relative to the light. Recorddata in the chart.

5. Calculate the power (current x voltage), or wattage of each trial. Record results in the chart.

6. Graph your experimental results, wattage (y) vs. degrees (x).

Data

DEGREES CURRENT A VOLTAGE V POWER WATTS

90

75

60

45

30

15

Conclusion

ReectionsFrom the graph of your data, what is the relationship between the angle of a PV array to wattage produced?

PV array Bright light source Electrical load 2 Multimeters

Alligator clips Protractor





22/40


Solar 5

? QuestionHow does the distance from a light source affect the electrical output of a PVarray wired in series?


Materials


2. Place the PV array at increasing distances from a light source according to the data chart below.

3. At each distance, measure current and voltage, and record data in the chart.


5. Graph your experimental results, wattage (y) versus distance (x) from light source.

Data

DISTANCE CM CURRENT A VOLTAGE V POWER WATTS

10 CM

20 CM

25 CM

50 CM

75 CM

100 CM

Conclusion

ReectionsFrom the graph of your data, what is the relationship of wattage to distance from the light source?

PV array Bright light source Electrical load 2 Multimeters

Alligator clips Measuring tape or meter stick





23/40


Solar 6

? QuestionHow does covering different parts of the PV array wired in series affect its electrical output?

HypothesisDevelop a hypothesis to address the question using the following format: If (manipulatedvariable) then (responding variable) because ...

Materials Bright light source Electrical load PV array 2 Multimeters

Alligator clips 3x5 Piece of cardboard

Procedure1. Attach the multimeter to the PV array wired in series with an electrical load. Measure current

and voltage and record in the data chart as trial 1.

2. Using the cardboard, cover half the PV array horizontally as in diagram 1. Measure and recordthe current and voltage in the data chart as trial 2.

3. Using the cardboard, cover half of the complete cells vertically as in diagram 2. Measure andrecord the current and voltage in the data chart as trial 3.


Data

TRIALS CURRENT A VOLTAGE V POWER WATTS

1 NO COVER2 COVER HORIZONTALLY

3 COVER VERTICALLY

Conclusion

ReectionsWhat did you observe about the differences in your data?

What function does the silver strip perform in the PV array?



CARDBOARD

TOMEASURE CURRENT,Ampmeter (set to DC Amps)

TOMEASURE VOLTAGE,Voltmeter (set to DC Volts)

C A R D B O A R D

Diagram 1

Diagram 2

Note : Solid and dashed lines in the

diagram represent different sets of clipsor wires.


24/40


Solar 7

? QuestionHow does concentrating the light from a light source affect the electrical output of a PVarray wired in series?


Materials


2. Measure the current and voltage and record data in the chart.

3. Lay the Fresnel lens over the PV array.

4. Measure the current and voltage. Record data in the chart.

5. Conduct additional trials with the lens, changing the distance from the lens to the PV array.



Data


NO LENS

LENS 0 cm

LENS ____cm

LENS ____cm

LENS ____cm

Conclusion

ReectionsFrom your observations, what is the affect of concentrating the light on a PV array?



PV array Electrical load Bright light source

2 Multimeters Alligator clips Fresnel lens

Metric ruler

Note: Solid and dashed lines in thediagram represent different sets ofclips or wires


25/40


Solar 8

? QuestionHow does surface temperature affect the electrical output of a PV array wired in series?


Materials PV array Electrical load 2 Multimeters Alligator clips

Ice water Bright light source Stopwatch


2. Place the array in the bright light for 10 minutes.

3. After the 10 minutes, record data in the chart.

4. With the conductors at the top of the array, hold the PV array at an angle of 45, and carefully pour ice water across the surface of the PVarray.Caution: DO NOT LET WATER TOUCH LEADS.

5. Measure change in voltage every 15 seconds as the surface of the PV module cools. Record data in the chart.

6. Graph data with voltage (y) vs. time (x).

Data

TIME SEC VOLTAGE V

0

15

30

45

60

Conclusion

ReectionsHow does cooling down the surface of the PV array affect the voltage produced? Why do you think this is?





26/40


Solar 9

? QuestionHow does a PV array wired in parallel affect the electrical output? Think about what will happen to current and voltage output.

HypothesisDevelop a hypothesis to address the question using the following format: If (manipulated variable) then (responding variable) because ...

Materials PV array Electrical load 2 Multimeters

Alligator clipsBright light source

Procedure1. Attach the multimeter to the PV array wired in parallel with an electrical load. See in

the diagram to the right.


3. Calculate the power (current x voltage), or wattage. Record results in the chart.

Data


PARALLEL

Conclusion

ReectionsIn previous investigations the array was wired in series. How has the current changed in parallel connections?

In previous investigations the array was wired in series. How has the voltage changed in parallel connections?





27/40


Extension 1

? QuestionHow do changes in supply current and voltage affect operation of electrical device loads?


Materials PV array 2 Fan motors

2 Multimeters Bright light source

Procedure1. Assemble 2 PV modules in series with 2 fan motors.2. Measure current and voltage. Record data and observations below.

3. Assemble 3 PV modules in series with 2 fan motors.4. Measure current and voltage. Record data and observations below.5. Assemble 2 PV modules in parallel with 2 fan motors.6. Measure current and voltage. Record data and observations below.7. Assemble 3 PV modules in parallel with 2 fan motors.8. Measure current and voltage. Record data and observations below.9. Calculate the power (current x voltage), or wattage. Record data and observations below.

Data

CIRCUIT TYPE # MODULES CURRENT AMPS VOLTAGE VOLTS POWER WATTS OBS

SERIES 2

SERIES 3

PARALLEL 2

PARALLEL 3

Conclusion

ReectionsHow did the current change when the PV module was connected in series versus in parallel?

What was observed when two modules were used? When three modules were used?

What was the difference in fan performance between series and parallel circuits?


28/40


Extension 2

? QuestionHow do changes in different circuit congurations affect the operation of multiple loads in the circuit?


Materials

2 PV arrays3 Fan motors

2 Multimeters Alligator clips

Bright light source

Procedure1. Connect three PV modules in series and three PV modules in parallel.2. Measure the changes in current and voltage of two fans and then three fans connected in series to each of the PV module congurations.

Record data and observations below.3. Measure the changes in current and voltage of two fans and then three fans connected in parallel to each of the PV module congurations.

Record data and observations below.4. Calculate the power (current x voltage), or wattage. Record data and observations below.

Data

CIRCUIT TYPEPV ARRAY

NUMBEROF FANS

CIRCUITTYPE FANS

CURRENTAMPS

VOLTAGEVOLTS

POWERWATTS OBSERVATIONS

SERIES 2 SERIES

SERIES 3 SERIES

SERIES 2 PARALLEL

SERIES 3 PARALLEL

PARALLEL 2 SERIES

PARALLEL 3 SERIES

PARALLEL 2 PARALLEL

PARALLEL 3 PARALLEL

Conclusion

ReectionsWhat was observed when two fans were used? When three fans were used?

Give examples of loads in parallel and series circuits that you have at home?

What might happen if too many loads are drawing power in your classroom?


29/40


Extension 3

? QuestionWhat effects on current and voltage will using different light sources have?


Materials 1 PV array Electrical load

1 Multimeter Alligator clips

Various light sources

ProcedureDesign a procedure to compare the output of the PV array using natural sunlight and a variety of articial light sources (e.g., incandescent,CFL, halogen, LED).

Data

Conclusion

ReectionsHow would you do this activity differently to improve the electrical output of your circuit?


30/40


48V DC INVERTER

+ + + +

+ + + +

+ + + +

+

Extension 4

? QuestionBelow are twelve 12 volt photovoltaic modules rated at 80 watts each.Design an array to deliver 48 volts to the inverter by using a combination of series and parallel circuits.

Use dashed lines to represent the black (-) wires, and solid lines to represent the red (+) wires.

ReectionsWrite an algebraic equation representing the 48 volt circuit you created.

Is there more than one design that could have created the 48 volt circuit?


31/40


Can Solar Energy Meet Your ElectricityDemands?

Part One: How much energy do you need per day?1. How much electricity does your family consume each month (in kilowatt hours, kWh)? _____________ kWh

2. What is your daily electricity use in kWh? _____________ kWh3. What is your daily electricity use in watt-hours? _____________ watt-hours

Part Two: How much energy can a module produce on an average day where YOU live?1. Peak sun hours are the number of hours per day where solar insolation equals 1,000 watts/square meter. Use the U.S. Solar Resource Map

to determine how many peak sun hours your home city receives each day. _____________ peak sun hours2. How much energy will one 235-watt solar module generate on the average day?

235 watts x _______ peak sun hours = ________watt-hours daily production per module

Part Three: How big does your system need to be for where you live?1. How many 235-watt solar modules would you need to produce enough electricity for your home?

Answer: _______modules2. If each module costs $800.00 installed, how much would it cost for the number of solar modules you need? Answer: $______________

Part Four: How many years will it take before the system has paid for itself?1. Calculate your current cost for electricity (multiply your monthly total kWh use by the rate in your city/town).

2. A) How much do you pay each month? $___________ B) How much do you pay each year? $_____________

3. The payback period is the time it will take for your system price to be offset by the electrical energy bills that will be avoided. Divide thetotal system cost (Part 3, Step 2) by your annual cost for electricity (Part 4, Step 2B).

Answer:_______________ years

Part Five: Reect

1. What are the different factors that impact payback period?

2. Under what circumstances is it NOT worth installing a solar generating system?

3. Think about when you use the most electricity. Do these hourscoincide with peak sun hours? What would you need in orderto use solar energy around the clock?


32/40


U . S . S o l a r R

e s o u r

c e M

a p

A nn

u a l A v

er

a g e S ol a r

C on

c en

t r a t i on ( K Wh / m

2

/ D a y )

M or e t h an

6

5 t o 6

4 t o 5

3 t o4

L e s s t h an 3

HI GH

L OW

N o t e : A l a

s k a a n

d H

a w

a i i n o

t s h own

t o s c a l e

D a t a : N R E L


33/40


Your Solar-Powered Cabin

Your crazy old Uncle Ed has just willed you a cabin that he has on a river near Page, AZ. The only problem is that thecabin has no electricity. Uncle Ed believes in hard work and hes specied one conditionif you are to take possessionof this prime parcel, you must plan and install a PV system to support the following four specications:

a light for the kitchen (LED, 12 volts at 15 watts); a power supply for charging your laptop (12 volts at 90 watts); an electric pump for the well (12 volts at 100 watts intermittent); and a refrigerator (12 volts at 50 watts intermittent).

Before you can collect your inheritance, Uncle Eds lawyer will need to see: a description of the PV modules that you will use along with their ratings; a schematic diagram of your system design; and a spreadsheet detailing your budget and sources for parts.

Have fun!

ExtensionWhen you nish your plan, design a battery system to store the electrical energy generated for use at night or duringstorms.


34/40


Solar-Powered Cabin Planning Page

Description of Modules:

Diagram of Design:

Budget Information:


35/40


Glossary

alternating current (AC) an electric current that reverses its direction at regular intervals or cycles; in the U.S. the standard is 120

reversals or 60 cycles per second; typically abbreviated as ACampere (A) a unit of measure for an electric current; the amount of current that ows in a circuit at an electromotive

force of one volt and at a resistance of one ohm; abbreviated as amp

amorphous lacking shape or form

array a systematic arrangement, in rows, of photovoltaic cells

charge controller a device that controls or limits how much electric current is added to or removed from a storage deviceor battery

concentrated solar power technologies that focus the energy from the sun onto one smaller area creating high temperatures thatcan produce electricity

conversion efficiency a ratio of useful energy output compared to the energy input

Czochralski process a method of growing crystals for semiconductors

direct current (DC) an electric current that ows in only one direction through a circuit, as from a battery; typicallyabbreviated as DC

dopant an element that is inser ted into a substance to alter the conductivity or electrical proper ties

efficiency the ratio of useful energy delivered compared to energy supplied

electric current (I) the ow of charged particles like electrons through a circuit, usually measured in amperes

electric power the rate at which energy is transferred; electrical energy is usually measured in watts; also used for ameasurement of capacity

gamma rays energy in the form of high-energy, short wavelength, electromagnetic radiation released by thenucleus; gamma rays are similar to x-rays and are best stopped or shielded by dense materials, such aslead

grid the layout of an electrical distribution system

ingot a material (usually metal) cast into a shape; semiconductors in bulk cast by a mold

inverter device that converts direct current to alternating current

kilowatt-hour (kWh) a measure of electricity as a unit of work or energy, measured as 1 kilowatt of power expended for 1 hour

module multiple PV cells connected together in larger units

n-type silicon layer of silicon in a solar cell that has been doped with phosphorus to have a negative character andrepel electrons

nuclear fusion when the nuclei of atoms are combined or fused together; the sun combines the nuclei of hydrogenatoms into helium atoms in a process called fusion; energy from the nuclei of atoms, called nuclearenergy, is released from fusion

ohm () the unit of resistance to the ow of an electric current

Ohms Law a mathematical relationship between voltage (V), current (I), and resistance (R) in a circuit; Ohms Lawstates the voltage across a load is equal to the current owing through the load times the resistance ofthe load (V = I x R)

p-type silicon layer of silicon in a solar cell that has been doped with boron to have a positive character and attractelectrons

photons particles which transmit light

photosphere the outer layer of the sun or a star, light is radiated from the photosphere

photovoltaic cell a device, usually made from silicon, which converts some of the energy from light (radiant energy) intoelectrical energy; another name for a solar cell

a cb


36/40


photovoltaic effect creating electric current through exposure of a material to light; excited electrons become free,eventually being converted into electric energy

photovoltaic system an arrangement of components to supply power from the sun, often including the PV module(s),storage component, inverter, and connections

power the rate at which energy is transferred, measured in watts

radiant energy any form of energy radiating from a source in electromagnetic waves

renewable fuels that can be easily made or replenished; we can never use up renewable fuels

resistance (R) a measure of the amount of energy per charge needed to move a charge through an electric circuit,usually measured in ohms

semiconductor any material that has a limited capacity for conducting an electric current; semiconductors arecrystalline solids, such as silicon, that have an electrical conductivity between that of a conductor and aninsulator

solar collector an item, like a car or greenhouse, that absorbs radiant energy from the sun and traps it within

thermal energy the total potential and kinetic energy associated with the random motions of the atoms andmolecules of a material; the more the molecules move and vibrate the more energy they possess

transmutation a process involving a change in the number of protons or neutrons in the nucleus, resulting in theformation of a different isotope; this occurs during alpha and beta emissions

volt (V) measure of electric potential or electromotive force; a potential of one volt appears across a resistance ofone ohm when a current of one ampere ows through that resistance

voltage the difference in electrical potential between any two conductors or between a conductor and the ground;it is a measure of the electric energy per electron that electrons can acquire and/or give up as they movebetween the two conductors

watt (W) a metric unit of power, usually used in electric measurements, which gives the rate at which work is doneor energy is used


37/40


B L A N K P A G E


38/40


B L A N K P A G E


39/40


NEEDs Online Resources

ENERGY EXCHANGE AND

CAREER CURRENTS NEWSLETTERS

NEED publishes two newsletters. Energy Exchange is published to keep teachers and partners informedabout new curriculum materials, current energy issues,and opportunities available for teachers and students.Career Currents is published to provide students withinformation about a variety of careers in the energyindustry. The newsletters are distributed to all NEEDteachers, partners, and sponsors. The latest edition ofeach newsletter and archived editions are available onthe NEED web site at www.NEED.org.

NEEDS SMUGMUG GALLERY

http://need-media.smugmug.com/

You can nd pictures of other NEED students learningand teaching about energy. You can also nd picturesfrom NEED workshops, and photos of energy fromaround the country that were submitted for the GreatAmerican Energy Scavenger Hunt. Would you like tosubmit images or videos to NEEDs gallery?

E-mail [email protected] for more information.

Use SmugMug for the following resources:

VideosNeed a refresher on The Science of Energy ? Watch the Science of

Energy videos. Also check out our Energy Chants videos!Find videos produced by NEED students teaching their peers andcommunity members about energy.

Online Graphics LibraryWould you like to use NEEDs graphics in your own classroompresentations? Download graphics for easy use in your classroom.

NEED Energy BooklistLooking for extra background reading on energy? NEEDs booklistprovides an extensive list of ction and nonction titles for allgrade levels to support energy units in the science, social studies,or language arts setting. Check it out at www.NEED.org.

U.S. Energy GeographyMaps are a great way to visualize the energy picture in the UnitedStates. This set of maps will support your energy discussion andenergy activities.

Go to www.NEED.org/maps to see energy production, consumption,and reserves all over the country!

E-PUBLICATIONS

The NEED Project now offers e-publication versions of variousguides for in-classroom and at-home use. Go to www.NEED.org/. Dont see what youre looking for? Check back often, asnew e-pubs will be added throughout the year.

SOCIAL MEDIA

Stay up-to-date with NEED, like us on Facebook! Search forThe NEED Project.

Follow us on Twitter. We share the latest energy news fromaround the country, @NEED_Project.

Read the latest from the NEED family in our blog! Visit it atwww.NEED.org.

NEED ANNUAL REPORT

NEEDs Annual Report gives summaries of the best state andnational Youth Awards projects for 20122013, as well asinformation about The NEED Project and our state programs.

Annual Report Upon RequestOnline at www.NEED.org


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National Sponsors and PartnersAmerican Electric PowerAmerican Wind Energy AssociationAppalachian Regional CommissionArizona Public ServiceArizona Science CenterArkansas Energy OfficeArmstrong Energy CorporationAssociation of Desk & Derrick ClubsAudubon Society of Western PennsylvaniaBarnstable County, MassachusettsRobert L. Bayless, Producer, LLCBPBP AlaskaBlue Grass EnergyBrady TraneCape Light CompactMassachusettsL.J. and Wilma CarrCenter for Teacher Success

Chabot Space and Science CenterChevronChevron Energy SolutionsColumbia Gas of MassachusettsComEdConEdison SolutionsConocoPhillipsConstellationDaniel Math and Science CenterDavid Petroleum CorporationDenver Public SchoolsDePaul UniversityDesk and Derrick of Roswell, NM

DominionDonorsChoose.orgDuke EnergyEast Kentucky PowerEastern Kentucky UniversityEl Paso CorporationE.M.G. Oil PropertiesEncanaEncana Cares FoundationEnergy Education for MichiganEnergy Training SolutionsFirst Roswell CompanyFJ Management. Inc.

Foundation for Environmental EducationFPL The Franklin InstituteFrontier AssociatesGeorgia Environmental Facilities AuthorityGeorgia PowerGovernment of ThailandEnergy Ministry

Harvard PetroleumHawaii EnergyGerald Harrington, GeologistHouston Museum of Natural ScienceHoustonWorksHydro Research FoundationIllinois Clean Energy Community FoundationIndependent Petroleum Association ofAmericaIndependent Petroleum Association of NewMexicoIndiana Michigan PowerInterstate Renewable Energy CouncilKentucky Clean Fuels CoalitionKentucky Department of EducationKentucky Department of Energy Develop-ment and IndependenceKentucky Power An AEP CompanyKentucky River Properties LLCKentucky Utilities CompanyLinn County Rural Electric CooperativeLlano Land and ExplorationLouisiana State University CooperativeExtensionLouisville Gas and Electric CompanyMaine Energy Education ProjectMaine Public Service CompanyMarianas Islands Energy OfficeMassachusetts Division of Energy ResourcesMichigan Oil and Gas Producers EducationFoundationMiller EnergyMississippi Development AuthorityEnergyDivisionMontana Energy Education CouncilNADA ScienticNASANational Association of State Energy OfficialsNational FuelNational GridNational Hydropower AssociationNational Ocean Industries AssociationNational Renewable Energy LaboratoryNebraska Public Power DistrictNew Mexico Oil CorporationNew Mexico Landmans AssociationNRG Energy, Inc.NSTAROCI EnterprisesOffshore Energy CenterOffshore Technology ConferenceOhio Energy Project

Petroleum Equipment Suppliers AssociationPhillips 66PNMRead & Stevens, Inc.Rhode Island Office of Energy ResourcesRiverWorks DiscoveryRobert ArmstrongRoswell Geological SocietySandia National LaboratorySaudi AramcoSchneider ElectricScience Museum of VirginiaC.T. Seaver TrustShellShell ChemicalsSnohomish County Public Utility DistrictWASociety of Petroleum EngineersDavid Sorenson

Southern CompanySouthern LNGSouthwest GasSpace Sciences UniversityLaboratory of theUniversity of California Berkeley Tennessee Department of Economic andCommunity DevelopmentEnergy Division Tioga Energy Toyota Tri-State Generation and Transmission TXU EnergyUnited Parcel ServiceUnited States Energy Association

United Way of Greater Philadelphia andSouthern New JerseyUniversity of NevadaLas Vegas, NVUniversity of TennesseeUniversity of Texas - AustinUniversity of Texas - TylerU.S. Department of EnergyU.S. Department of EnergyHydrogenProgramU.S. Department of EnergyOffice of EnergyEfficiency and Renewable EnergyU.S. Department of EnergyOffice of FossilEnergyU.S. Department of EnergyWind for SchoolsU.S. Department of EnergyWind PoweringAmericaU.S. Department of the InteriorBureau ofLand ManagementU.S. Energy Information AdministrationVan Ness FeldmanVestas

Photovoltaics Student Guide

Documents

Transcript of Photovoltaics Student Guide