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					SCHOOLS GOING
SOLAR ACTIVITIES
Activities to incorporate school PV systems into the classroom
                                                                                 GRADE LEVEL


                                                                            SUBJECT AREAS
                                                                                         K–12


learning environment.                                                                   Science
                                                                                 Social Studies
                                                                                          Math
                                                                                Language Arts
                                                                                   Technology




                              Activities for Schools with Solar Installations
                           Teacher Advisory Board
                               Shelly Baumann, Rockford, MI
                              Constance Beatty, Kankakee, IL
                            Sara Brownell, Canyon Country, CA
                                 Scott Burch, New Albany, IN
                                 Amy Constant, Raleigh, NC
                              Joanne Coons, Clifton Park, NY
                                 Darren Fisher, Houston, TX
                          Deborah Fitton, Cape Light Compact, MA
                            Linda Fonner, New Martinsville, WV
                                 Melanie Harper, Odessa, TX
                                Linda Hutton, Kitty Hawk, NC
                                 Kim Jenkins, Cynthiana, KY
                              Barbara Lazar, Albuquerque, NM
                              Robert Lazar, Albuquerque, NM
                                Catherine Norris, Raleigh, NC
                                   Don Pruett, Sumner, WA
                                  Larry Richards, Eaton, IN
                                Barry Scott, French Camp, CA
                                Regina Sizemore, Letcher, KY
                               Joanne Spaziano, Cranston, RI
                                Nancy Stanley, Pensacola, FL
                             Scott Sutherland, Providence, RI
                               Robin Thacker, Henderson, KY
                                Bob Thompson, Glen Ellyn, IL
                                 Doris Tomas, Rosenberg, TX
                            Patricia Underwood, Anchorage, AK
                                 Jim Wilkie, Long Beach, CA
                                Carolyn Wuest, Pensacola, FL
                           Debby Yerkes, Ohio Energy Project, OH
                            Wayne Yonkelowitz, Fayetteville, WV



                               NEED Mission Statement
  The mission of the NEED Project is to promote an energy conscious and educated society by
creating effective networks of students, educators, business, government and community leaders
             to design and deliver objective, multi-sided energy education programs.

                      Teacher Advisory Board Vision Statement
   In support of NEED, the national Teacher Advisory Board (TAB) is dedicated to developing
               and promoting standards-based energy curriculum and training.
              TABLE OF CONTENTS
         Why Introduce PV Projects in Schools ............................... 4
         What Do Solar Schools Receive? ...................................... 4
         What Students Should Know About Solar Energy............... 5
         Suggested Activities ...................................................... 6-9
         Resources ..................................................................... 10
         Backgrounder on Solar Energy & PV Technology ......... 11-21
         PV Glossary .............................................................. 22-23




 These suggested activities are for solar schools to use to incorporate
the solar arrays into their solar/energy curriculum, in conjunction with
                  the NEED solar curriculum and kits.
                                       Why Introduce PV Projects In Schools?
Schools around the country are being offered the opportunity to partner with governmental agencies, community
foundations, utilities, businesses, and corporations to install PV systems. The Solar Electric Power Association
states that, “…bringing solar to schools is an important first step to increasing the use of solar energy in the
community at large. Schools make an excellent showcase for the benefits of solar photovoltaic electricity, solar
thermal energy, and passive solar. Changes and improvements at schools are highly visible and closely followed.
As has been the case with recycling programs, which were introduced to many communities by schoolchildren
educating their parents, students can carry good ideas from the fringe into the mainstream.”

The PV system installed at your school can provide energy savings. Depending on geographical location, a 2kW PV
system produces an average of 7kW of electricity per day (enough electricity to power 10 computers) and an
average annual output of 3000 kW. The environmental benefits include offsetting carbon dioxide (CO2) produced
by coal-fired power plants.

For most schools, however, the decision to install PV systems is more about education and inspiration for their
students than about cost savings. The students get a head start on real-world energy concerns. Integrating the
data supplied by the PV systems into the school curriculum helps students learn about how solar electricity works
and involves them in the study of the benefits of renewable energy and energy efficiency. The PV system also
provides students with an opportunity to learn first-hand about employment opportunities in emerging renewable
energy technology fields.

                                           What Do Solar Schools Receive?
Many schools that choose to enter into a PV demonstration partnership receive all of the hardware and software
needed for complete integration into the curriculum system. The systems typically range from 500 watts to 10
kilowatts in size and are usually designed to be mounted on peaked or flat roofs. Some systems are designed for
ground or wall mounts for increased public visibility.

In order for students to be able to explore the PV system’s effects on electricity use, many schools also receive
interactive educational monitoring software designed to produce educational value from the PV system. The goal
of the monitoring software is to provide interaction with students and teachers, while also logging PV system data
to a database for simple integration into class curricula. Adding an optional Internet component to the data
acquisition hardware will allow data to be sent directly to a centralized database for interactive web explorations.

The data acquisition systems allow schools to monitor the daily and cumulative production of electricity from the
system. The Internet-compatible data collection monitoring systems supplied to many schools allows teachers
and students to monitor local atmospheric conditions (i.e. wind speed, temperature, solar radiations, etc.) and
compare this data to the electrical production of the system.

Most schools cannot afford to install these systems without assistance from a local power company, community
foundation, or a government agency. If your school has installed a PV system with funding and support supplied by
local utilities and/or state agencies, it has entered into a partnership with the organization(s) who generously
supplied the hardware and software. In return for the hardware, software, expertise, and/or curriculum materials
supplied by your solar partner(s), your school has agreed to actively use and promote the PV system as a real-
world teaching tool in your community.

In order to make full use of your PV system as a real-world teaching tool, teachers must find ways to integrate its
use throughout the school’s curricula. This booklet has been designed to provide teachers with ideas for integrating
the system into your science, math, language arts, and social studies class curricula. The ideas in this booklet
will help your students master the concepts they need to know about solar energy and PV systems.




 PAGE 4   Schools Going Solar Activities             © 2006 THE NEED PROJECT • PO BOX 10101 • MANASSAS, VA 20108 • 1-800-875-5029
                         What Your Students Should Know About Solar Energy
According to energy experts convened by the National Energy Education Development (NEED) Project, your students
should know the following upon high school graduation:

All students should know:

   1. Solar energy provides the world—directly and indirectly—with most of its energy. As well as providing the
      light and heat energy that sustain the world, solar energy is stored in fossil fuels and biomass, and is
      responsible for hydropower and wind energy.

   2. Radiant energy is produced as a result of nuclear fusion in the sun’s core.

   3. Solar energy is a renewable energy source. Its potential as an energy source is vast.

   4. Using solar energy produces no air pollution.

   5. Solar energy is abundant, but it is diffuse and not available at all hours. It is not yet economical to harness
      on a large scale to produce electricity.

   6. Most of the solar energy we use for heat and light cannot be measured. Harnessed solar energy provides
      a small amount (0.1%) of the nation’s total energy consumption.

   7. Photovoltaic cells convert sunlight directly into electrical energy. Today, they are mainly used in remote
      areas and for special applications.

   8. Solar energy is used directly to light and heat buildings and heat water.

   9. Back-up energy systems are usually needed when using solar energy.

Advanced students also should know:

   1. Photovoltaic–produced electricity costs more than conventionally produced power; however, PV
      manufacturing costs are decreasing and cell efficiencies are increasing.

   2. Concentrating solar energy and directing it toward a receiver can produce high temperatures capable of
      producing electricity.

   3. Using proven construction techniques, solar heated and lighted buildings decrease the need for
      conventional energy sources.

   4. Solar resources are affected by time of day, season, and location. Using solar energy for heating and
      lighting is a feasible choice in many areas of the country with current technologies.

   5. The environmental and economic advantages and disadvantages of using solar energy.

   6. How photovoltaic cells and concentrated solar power systems transform sunlight into electricity.

   7. How passive and active solar systems operate.




© 2006 THE NEED PROJECT • PO BOX 10101 • MANASSAS, VA 20108 • 1-800-875-5029         Schools Going Solar Activities PAGE 5
                                      Suggested PV System Learning Activities
Tour Your School’s PV System
(Primary, Elementary, Intermediate, Secondary) (Science)

Take your students on a tour of your school’s PV system. Point out the basic components of the system and explain
the role each plays in the production of electricity. If your school also has a data acquisition system, explain what
information each component provides.
Important components of the system include the PV module(s), PV cells, inverter, transformer, electric meter,
electric distribution panel, disconnect switches and your data logger or data acquisition system. If your school
also has a weather station, point out the thermometer, anemometer, and pyronometer.
An excellent lesson plan (Introduction To Your School’s Solar Electric System) with background information and
student worksheets can be downloaded from the Watts On Schools website at www.wattsonschools.com/
activities.htm.

Explore Your Data Website
(Primary, Elementary, Intermediate, Secondary) (Computer Science)

Many of the providers of PV equipment link the schools to each other through a website on the Internet. Depending
upon the site, there may be opportunities for students and teachers to communicate with each other, explore the
electrical and atmospheric data from their school and compare it with data from other schools, develop their own
inquiry projects, and ask questions of experts.
While the options provided on these websites may differ, many of the websites provide similar opportunities to
teachers and students. A lesson plan for providing an overview of a data website (What’s On Your Website) can be
downloaded from the Watts On Schools website at www.wattsonschools.com/activities.htm. The lesson and
accompanying worksheet can be modified to provide an overview of the data website provided by your solar
partner.

Put Together Educational Displays Throughout the School
(Primary, Elementary, Intermediate, Secondary) (Art, Language Arts, Social Studies)
One of the main reasons that schools are selected to become solar partners is that they make an excellent
showcase for the benefits of solar photovoltaic electricity. Changes and improvements at schools are highly
visible and closely followed. As with recycling programs, which were introduced to many communities by
schoolchildren educating their parents, students can carry good ideas from the fringe into the mainstream.
One way to make your PV project highly visible and to promote the benefits of renewable energy technologies is to
have students design displays that can be placed in strategic areas throughout your school. Possible themes for
the displays include the history of solar energy (past, present, future), uses of solar energy, and documenting your
school’s PV project.

Graph PV System Data
(Primary, Elementary, Intermediate, Secondary) (Math)

Have students download data from your data acquisition system (DAS) and then use the data to create graphs
incorporating different variables. Students at lower levels can make pictographs and older students can create
line, bar, and circle graphs. Students should first decide which variables they want to use in their graphs (i.e.,
energy generated in kW and time of day, season, or different types of weather conditions). After downloading the
data, students should decide which type of graph is most appropriate for displaying the data.
After students have created their graphs, they can generate questions for other students to answer by analyzing
the graphs.


 PAGE 6     Schools Going Solar Activities                 © 2006 THE NEED PROJECT • PO BOX 10101 • MANASSAS, VA 20108 • 1-800-875-5029
Conduct An Energy Audit of Your School
(Primary, Elementary, Intermediate, Secondary) (Science, Math)

Physically, schools are ideal places to use solar energy. The energy demand in school buildings is significant and
concentrated during the daytime, when the energy from the sun can be used to maximum benefit. However, the
value of solar energy is multiplied when using different solar technologies in concert and in combination with
other new and efficient uses of resources, including low-wattage lighting, heat pumps, and better insulating windows,
walls, and roofs.
Your students can experience the multiplying effect of energy conservation by having them perform an energy
efficiency audit of their classroom and school. An energy audit allows students to use their school building as a
real-world laboratory for applying science knowledge and math skills. The NEED Project publishes three energy
conservation booklets (Building Buddies, Monitoring and Mentoring, and Learning and Conserving) for primary
through high school students. These curriculum materials introduce students to basic concepts of energy use
and conservation; teach methods of measuring energy usage, determining costs, and quantifying environmental
effects; guides students through comprehensive surveys of the school building and school energy consumption–
–gathering, recording and analyzing data, and monitoring energy usage; and assist students in developing a
comprehensive energy management plan for the school that includes suggestions for retrofits, systems
management and conservation practices.

Create a PV Brochure
(Elementary, Intermediate, Secondary) (Language Arts)
In this activity, students research energy alternatives and produce a collection of brochures that can be distributed
to adults to provide a basic understanding of the need for alternative energy sources and the strengths of PV
systems. A complete lesson plan for this activity (Energy Solutions: A Brochure) with background information,
student worksheets, and a grading rubric can be downloaded from the Solar Power…Naturally website at
www.nyserda.org/schools/curricular.html.


Calculate How Your Energy Usage Impacts the Environment
(Elementary, Intermediate) (Science, Math, Geography)

A set of interactive online calculators at the Texas State Energy Conservation Office website at www.infinitepower.org/
calculators.htm can help students understand energy production and consumption in a variety of ways. Students
can use the calculators to develop a personal profile of their own energy use and the resulting contribution to
atmospheric pollution. The site includes a Carbon Pollution Calculator and an Electric Power Pollution Calculator.
Additional calculators on this site allow students to determine the trade-offs involved in installing PV systems,
determine whether a solar water heater could save money, and explore how different measurements of energy and
power relate to one another.

Compare Data From Different Schools
(Elementary, Intermediate, Secondary) (Math, Geography, Computer Science)

If your school is connected to a website in which students can download data from your school’s PV system, they
can use this data to compare their system’s performance and draw inferences as to the causes for differences in
performance. This is a good activity for teaching students about variables. Depending upon the capabilities of
your DAS, students can compare such factors as power generation, temperature, wind speed, and solar irradiation.
A lesson plan (Comparison of Schools) with background information, method, and student worksheets for this
activity can be downloaded from the Watts On Schools website at www.wattsonschools.com/activities.htm.




© 2006 THE NEED PROJECT • PO BOX 10101 • MANASSAS, VA 20108 • 1-800-875-5029           Schools Going Solar Activities PAGE 7
Convert Your PV System’s Output to Other Forms of Energy Using Interactive Calculator
(Elementary, Intermediate, Secondary) (Math, Science)

It is often difficult for students to picture how much electricity the school’s PV system is producing. This activity
helps them by providing an interactive calculator that converts electrical energy into equivalent amounts of other
forms of energy (chemical, mechanical, thermal) and other everyday energy measures (exercise, pollution). An
interactive energy calculator for this activity can be found on the Watts On Schools website at
www.wattsonschools.com/activities.htm.

Analyze the PV System’s Performance
(Intermediate, Secondary) (Science, Math, Computer Science, Geography)

Have your students calculate the efficiency of the school’s PV system. In this case, efficiency refers to the effectiveness
of the PV system in converting solar energy to electrical energy and is expressed as a percentage. Another way to
look at efficiency is to compare how much electrical energy could have been produced by the solar energy striking
your school (at any given time) to the actual amount of electrical energy your system produced. To complete this
activity, your DAS will need to provide access to three kinds of historical data: time, solar irradiation striking your
local area, and energy output of your system.
A lesson plan (Calculating the Efficiency of a SE System) explaining the background information and calculations for
this activity can be downloaded from the Watts On Schools website at www.wattsonschools.com/activities.htm.

Compare Solar Power Production, Sunlight, Temperature, and Electrical Production
(Intermediate, Secondary) (Science, Math, Computer Science)
If your school’s DAS provides a measurement of solar irradiation and temperature, you can have your students
design inquiry projects that will help them understand the relationship between three variables of their photovoltaic
system: power, temperature and solar irradiation.
A lesson plan (The Relationship Between Solar Power Production, Temperature, and Sunlight) explaining the background
information and calculations for this activity can be downloaded from the Watts On Schools website at
www.wattsonschools.com/activities.htm.

Design Your Own PV System
(Intermediate, Secondary) (Science, Math, Geography, Computer Science)

The PVWATTS website at http://rredc.nrel.gov/solar/codes_algs/PVWATTS/ allows students to calculate the
electricity produced by a grid-connected PV system. PVWATTS calculates monthly and annual energy production in
kWh and monthly savings in dollars for localities throughout the United States. Two different versions of the
calculator allow students to compare the electrical output of identical PV systems in different geographical locations.
Students can also compare electrical output of different PV systems by specifying the PV system size, local electric
costs, fixed or tracking PV array, and the PV array tilt and azimuth angles.

Determine Whether a PV System in Your Area Is Cost Effective
(Intermediate, Secondary) (Math, Economics)

PV systems are more cost-effective in some situations than in others, depending on the size and nature of the
load, the availability of the solar resource, and the cost of alternative sources of power. In many situations, PV
systems can be more cost-effective than many alternatives. Have students determine whether installing a PV
system is cost-effective for their needs and whether or not there are any financial incentives for installing a PV
system in your locality. A lesson plan for this activity can be downloaded from the Montana Green Power website
at www.montanagreenpower.com/solar/curriculum/lesson8.html.




 PAGE 8    Schools Going Solar Activities               © 2006 THE NEED PROJECT • PO BOX 10101 • MANASSAS, VA 20108 • 1-800-875-5029
Community PV Decision Simulation
(Intermediate, Secondary) (Social Science, Language Arts)

Have your students participate in a simulation that lets students evaluate the feasibility of installing a PV system
on the roof of a school in their community. In this simulation students research the topic and then each student
assumes the role of a community member participating in the decision-making process. A complete lesson plan
for this activity (To Go Solar or Not To Go Solar!) with all needed materials, background information and student
worksheets can be downloaded from the Solar Power…Naturally website at www.nyserda.org/schools/
curricular.html.

Size Up A PV System for YOUR Home or School
(Secondary) (Math, Science, Geography)
This activity allows students to determine the size of the PV system they would need to provide electricity needed
to operate all of the loads in their classroom, school, and/or home. In sizing a PV system, students will need to
determine the sunlight levels or insolation values of their area and the daily power consumption of their electrical
loads. Background information (Estimating PV System Size and Cost) for this activity can be download from the
Texas State Energy Conservation Office website at www.infinitepower.org/calculators.htm.
A worksheet for this activity can be downloaded from the e-Marine, Inc website at www.e-marine-inc.com/articles/
size.html.
An interactive website and sizing calculator can be found at AAASolar’s website at http://aaasolar.com/design/
pvsizing/PVSIZING.htm.
 In addition, a complete lesson plan for sizing up a PV system can be found on the Montana Green Power website
at www.montanagreenpower.com/solar/curriculum/lesson7.html.

Determine Circuit Wiring for a PV System
(Secondary) (Science, Math)

In this activity, students study different types of circuits and then describe how photovoltaic cells are optimally
connected in arrays. A complete lesson plan for this activity (Series or Parallel) with background information and
student worksheets can be downloaded from the Solar Power…Naturally website at www.nyserda.org/schools/
curricular.html.




© 2006 THE NEED PROJECT • PO BOX 10101 • MANASSAS, VA 20108 • 1-800-875-5029         Schools Going Solar Activities PAGE 9
PV Related Websites

BP Solar
www.bpsolar.com/ContentMap.cfm?page=3&BreadCrumb=yes

National Renewable Energy Laboratory – About Solar Energy
www.nrel.gov/clean_energy/solar.html

US Department of Energy – Solar Technologies Program
www.eere.energy.gov/solar/

Sandia National Laboratories – PV Systems Research and Development
www.sandia.gov/pv/

Florida Solar Energy Center – PV and Distributed Generation
www.fsec.ucf.edu/pvt/

How Stuff Works – How Solar Cells Work
www.howstuffworks.com/solar-cell.htm

Solar Electric Power Association
www.solarelectricpower.org/

IEA – Basics of PV
www.oja-services.nl/iea-pvps/pv/home.htm


Solar Schools Websites
www.solarconnection-bp.com/index.asp

www.chicagosolarpartnership.com/splash.htm

www.mge.com/environment/solar/schools.htm

www.wattsonschools.com/

www.schoolpowernaturally.org/

www.montanagreenpower.com/solar/schools/sun4schools.html

www.soltrex.com/


Solar Radiation Data

Solar radiation data is available from NASA—you’ll need to register (free) to log in and access data at:
http://eosweb.larc.nasa.gov/cgi-bin/sse/sizer.cgi?email=na

Solar radiation data previously hosted by REPP is available from the National Renewable Energy Laboratory’s (NREL) Solar
Radiation Resource Information database at the Renewable Resource Data Center (RReDC) at:
http://rredc.nrel.gov/

World Solar Radiation data is available from NREL at:
http://wrdc-mgo.nrel.gov/




 PAGE 10     Schools Going Solar Activities              © 2006 THE NEED PROJECT • PO BOX 10101 • MANASSAS, VA 20108 • 1-800-875-5029
What Is Solar Energy?                                                 Only a small portion of the energy radiated by the
Solar energy is radiant energy from the sun. It is vital              sun into space strikes the earth, one part in two
to us because it provides the world––directly or                      billion. Yet this amount of energy is enormous. Every
indirectly––with almost all of its energy. In addition                day enough energy strikes the United States to supply
to providing the energy that sustains the world, solar                the nation’s energy needs for one and a half years!
energy is stored in fossil fuels and biomass, and is
responsible for powering the water cycle and
producing wind.
Every day the sun radiates, or sends out, an enormous
amount of energy. The sun radiates more energy in
one second than people have used since the
beginning of time! Solar energy comes from within
the sun itself. Like other stars, the sun is a big ball
of gases––mostly hydrogen and helium. The
hydrogen atoms in the sun’s core combine to form
helium and radiant energy in a process called nuclear
fusion.




                                                                      Where does all this energy go? About 15 percent of
                                                                      the sun’s energy that hits the earth is reflected back
                                                                      into space. Another 30 percent powers the water
                                                                      cycle: it evaporates water that is then drawn into the
                                                                      atmosphere, turns into clouds, and falls back to earth
                                                                      as precipitation. Plants, the land, and the oceans also
                                                                      absorb solar energy. The rest could be used to supply
                                                                      our energy needs.
                                                                      Solar energy is considered a renewable energy
                                                                      source. Renewable sources of energy are resources
                                                                      that are continually renewed by nature, and hence
During nuclear fusion, the sun’s extremely high                       will never run out. Solar power is considered
pressure and temperature cause hydrogen atoms to                      renewable because the nuclear (fusion) reactions that
come apart and their nuclei (the central cores of the                 power the sun are expected to keep generating
atoms) to fuse or combine. Four hydrogen nuclei fuse                  sunlight for many billions of years to come. 
to become one helium atom. But the helium atom
contains less mass than the four hydrogen atoms                       History of Solar Energy
that fused. Some matter is lost during nuclear fusion.                People have harnessed solar energy for centuries.
The lost matter is emitted into space as radiant                      As early as the 7th century B.C., people used simple
energy.                                                               magnifying glasses to concentrate the light of the
                                                                      sun into beams so hot they would cause wood to
It takes millions of years for the energy in the sun’s                catch fire.
core to make its way to the solar surface, and then
just a little over eight minutes to travel the 93 million             More than 100 years ago in France, a scientist used
miles to earth. The solar energy travels to the earth                 heat from a solar collector to make steam to drive a
at a speed of 186,000 miles per second (3.0 x 108                     steam engine. In the 1860s in the U.S., John
meters per second), the speed of light. No heat from                  Ericsson developed the first realistic application of
the sun travels to the earth; the light turns into heat               solar energy using a solar reflector to drive an engine
when it is absorbed by molecules on earth.                            in a steam boiler.


© 2006 THE NEED PROJECT • PO BOX 10101 • MANASSAS, VA 20108 • 1-800-875-5029                 Schools Going Solar Activities PAGE 11
Early in the 1900s, scientists and engineers began          A solar collector is one way to collect heat from the
seriously researching ways to use solar energy. The         sun. A closed car on a sunny day is like a solar
solar water heater gained popularity during this time       collector. As the sunlight passes through the car’s
in Florida, California, and the Southwest. The industry     glass windows, it is absorbed by the seat covers,
was in full swing just before World War II. This growth     walls, and floor of the car.
lasted until the mid-1950s when low-cost natural gas
                                                            The light that is absorbed changes into heat. The
became the primary fuel for heating homes and water,
                                                            car’s glass windows let light in, but don’t let all the
and the use of solar energy lost popularity.
                                                            heat out. This is also why greenhouses work so well
The public and world governments remained largely           and stay warm year-round. A greenhouse or solar
indifferent to the possibilities of solar energy until      collector:
the energy crises of the 1970s. Research efforts in            –     allows sunlight in through the glass;
the U.S. and around the world since that time have
                                                               –     absorbs the sunlight and changes it into
resulted in tremendous improvements in solar
                                                                     heat; and
technologies for heating water and buildings and
making electricity.                                            –     traps most of the heat inside.

Solar Collectors                                            Solar Space Heating
Heating with solar energy is relatively easy––just look     Space heating means heating the space inside a
at a car parked in the sun with its windows closed.         building. Today many homes use solar energy for
Getting the right amount of heat in a desired location,     space heating. There are two general types of solar
however, requires more thought and careful design.          space heating systems: passive and active.
Capturing sunlight and putting it to work effectively
is difficult because the solar energy that reaches the      Passive Solar Homes
earth is spread out over a large area. The sun does         In a passive solar home, the house operates as a
not deliver that much energy to any one place at any        solar collector. A passive house does not use any
one time.                                                   special mechanical equipment such as pipes, ducts,
                                                            fans, or pumps to transfer the heat that the house
How much solar energy a place receives depends on           collects on sunny days. Instead, a passive solar home
several conditions. These include the time of day,          relies on properly oriented windows and is designed
the season of the year, the latitude of the area, and       with added thermal mass to store and release heat.
the clearness or cloudiness of the sky.                     Since the sun shines from the south in North America,
                                                            passive solar homes are built so that most of the
                                                            windows face south. They often have few or no
                                                            windows on the north side.
                                                            A passive solar home converts solar energy into heat
                                                            just as a closed car does. Sunlight passes through a
                                                            home’s windows and is absorbed in the walls and
                                                            floors. Materials such as tile, stone and concrete are
                                                            often used, because they can store more heat than
                                                            wood or sheetrock. To control the amount of heat in
                                                            a passive solar house, the designer must determine
                                                            the appropriate balance of mass in the floors and
                                                            walls and admission of sunlight.
                                                            Windows let in the sunlight, which is converted into
                                                            heat when it is absorbed by the walls and floors. The
                                                            mass stores the heat from the sun and releases it
                                                            when the air temperature inside drops below the
                                                            temperature of the mass. Heating a house by warming
                                                            the walls or floors is more comfortable than heating
                                                            the air inside a house.


 PAGE 12   Schools Going Solar Activities         © 2006 THE NEED PROJECT • PO BOX 10101 • MANASSAS, VA 20108 • 1-800-875-5029
Additionally, the doors and windows can be closed to                  Solar Water Heating
keep heated air in or opened to let it out to keep the                Solar energy is also used to heat water. Water heating
temperature in a comfortable range. At night, special                 is usually the second leading home energy expense,
heavy curtains or shades can be pulled over the                       costing the average family over $400 a year.
windows to keep the daytime heat inside the house.
In the summer, awnings or roof overhangs help to                      Depending on where you live, and how much hot water
shade the windows from the high summer sun to                         your family uses, a solar water heater can pay for
prevent the house from overheating. Passive homes                     itself in as little as five years. A well-maintained solar
are quiet, peaceful places to live. A well-designed                   water heating system can last 15-20 years, longer
passive solar home can harness 50 to 80 percent of                    than a conventional water heater.
the heat it needs from the sun.                                       A solar water heater works in the same way as solar
Many passive homeowners install equipment, such                       space heating. A solar collector is mounted on the
as fans to help circulate air, to further increase the                roof, or in an area of direct sunlight. It collects
comfort and energy efficiency of their homes. When                    sunlight and converts it to heat. When the fluid
special equipment is added to a passive solar home,                   becomes hot enough, a thermostat starts a pump.
it is called a hybrid system.                                         The pump circulates the fluid through the collector
                                                                      until it reaches the required temperature, called the
Active Solar Homes                                                    set point. Then the heated fluid is pumped to a
Unlike a passive solar home, an active solar home                     storage tank where it is used in a heat exchanger to
uses mechanical equipment, such as pumps and                          heat water.
blowers, to gain greater control of when, where and                   The hot water may then be piped to a faucet or
how much of the collected heat from the sun gets                      showerhead. Most solar water heaters that operate
used. The active solar home is designed to deliver                    in cold climates use a heat transfer fluid similar to
the heat from where it is collected to where it is                    antifreeze that will not freeze and damage the system.
needed.
                                                                      Today, over 1.5 million homes in the U.S. use solar
Storing Solar Heat                                                    heaters to heat water for their homes or swimming
The challenge confronting any solar heating system—                   pools. Besides heating homes and water, solar
whether passive, active, or hybrid—is heat storage.                   energy also can be used to produce electricity. Two
Solar heating systems must have some way to store                     ways to generate electricity from solar energy are
the heat that is collected on sunny days to keep people               photovoltaics and solar thermal systems.
warm at night or on cloudy days.
In passive solar homes, heat is stored by
using dense interior materials that retain
heat well—masonry, adobe, concrete, stone,
or water. These materials absorb surplus
heat and radiate it back into the room when
the air temperature is lower than the surface
temperature of the material. Some passive
homes have walls a foot thick.
In active solar homes, heat may be stored
in one of two ways—a large tank may store
a heated liquid, or rock bins beneath the
house may store warm mass. Houses with
active or passive solar heating systems may
also have furnaces, wood-burning stoves, or
other heat sources to provide heat during
long periods of cold or cloudy weather. These
are called backup systems.



© 2006 THE NEED PROJECT • PO BOX 10101 • MANASSAS, VA 20108 • 1-800-875-5029                   Schools Going Solar Activities PAGE 13
Photovoltaics                                                In 1954, scientists at Bell Laboratories depended
Photovoltaic (or PV) systems                                 on the Czochralski process to develop the first
conver t light directly into                                 crystalline silicon photovoltaic cell, which had a
electricity. The term photo                                  conversion efficiency of four percent.
comes from the Greek phos,                                   As a result of technological advances, the cost of PV
which means light. The term                                  cells has decreased significantly over the past 25
volt is a measure of electricity                             years, as the efficiency has increased. Today’s
named for Alessandro Volta                                   commercially available PV devices convert seven to
(1745-1827), a pioneer in the                                17 percent of the radiant energy that strikes them
development of electricity.                                  into electricity.
Photovoltaics literally means
light–electricity.                                           In the laboratory, combining exotic materials with
                                                             specialized cell designs has produced PV cells with
Commonly known as solar cells, PV cells are already          conversion efficiencies as high as 38 percent.
an important part of our lives. The simplest PV
systems power many of the small calculators and              Solar Systems
wrist watches we use every day. Larger PV systems            The photovoltaic effect is the basic physical process
provide electricity for pumping water, powering              through which a PV cell converts sunlight directly into
communications equipment, and even lighting homes            electricity. PV technology works any time the sun is
and running appliances. In certain applications, such        shining, but more electricity is produced when the
as motorist aid call boxes on highways and pumping           light is more intense and when it is striking the PV
water for livestock, PV power is the cheapest form of        modules directly––when the rays of sunlight are
electricity. Some electric utility companies are             perpendicular to the PV modules.
building PV systems into their power supply networks.
                                                             Unlike solar systems for heating water, with which
History of Photovoltaics                                     you might be more familiar, PV technology does not
French physicist Edmond Becquerel first described            produce heat to make electricity. Instead, PV cells
the photovoltaic (PV) effect in 1839, but it remained        generate electricity directly from the electrons freed
a curiosity of science for the next half century. At the     by the interaction of radiant energy with the semi-
age of 19, Becquerel found that certain materials            conductor materials in the PV cells.
would produce small amounts of electric current              Sunlight is composed of photons, or bundles of
when exposed to light. The effect was first studied          radiant energy. When photons strike a PV cell, they
in solids, such as selenium, by Heinrich Hertz in the        may be reflected or absorbed, or transmitted through
1870s. Soon selenium PV cells were converting light          the cell. Only the absorbed photons generate
to electricity at one to two percent efficiency.             electricity. When the photons are absorbed, the
The conversion efficiency of a PV cell is the proportion     energy of the photons is transferred to electrons in
of sunlight energy that the cell conver ts into              the atoms of the solar cell, which is actually a semi-
electrical energy relative to the amount of sunlight         conductor.
that is available and striking the PV cell. This is very     With their newfound energy, the electrons are able to
important when discussing PV devices, because                escape from their normal positions associated with
improving this efficiency is vital to making PV energy       their atoms to become part of the current in an
competitive with more traditional sources of energy,         electrical circuit. By leaving their positions, the
such as fossil fuels.                                        electrons cause holes to form in the atomic structure
During the second half of the 20th century, PV science       of the cell into which other electrons can move.
was refined and the process more fully explained.            Special electrical properties of the PV cell—a built-
Major steps toward commercializing PV were taken             in electric field—provide the voltage needed to drive
in the 1940s and 1950s, when the Czochralski                 the current through a circuit and power an external
process was developed for producing highly pure              load, such as a light bulb.
crystalline silicon.




 PAGE 14   Schools Going Solar Activities          © 2006 THE NEED PROJECT • PO BOX 10101 • MANASSAS, VA 20108 • 1-800-875-5029
                                                                      Different materials are used to produce PV cells, but
                                                                      silicon––the main ingredient in sand––is the most
                                                                      common basic material. Silicon is a relatively cheap
                                                                      material because it is widely available and used in
                                                                      other things, such as televisions, radios and
                                                                      computers. PV cells, however, require very pure
                                                                      silicon, which can be expensive to produce.
                                                                      The amount of electricity a PV cell produces depends
                                                                      on its size, its conversion efficiency and the intensity
                                                                      of the light source. Efficiency is a measure of the
                                                                      amount of electricity produced from the sunlight that
                                                                      a 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 a small watch or solar
                                                                      calculator.
                                                                      The most important parts of a PV cell are the semi-
                                                                      conductor layers, where the electron current is
                                                                      created. There are a number of different materials
                                                                      suitable for making these semi-conducting layers, and
                                                                      each has benefits and drawbacks. Unfortunately,
                                                                      there is no one ideal material for all types of cells
                                                                      and applications.
                                                                      When sunlight strikes the surface of a PV cell, the
                                                                      electrical field provides momentum and direction to
                                                                      light-stimulated electrons, resulting in a flow of
   Photovoltaic Cells                                                 electric current, or flow of electrons, when the solar
   The basic building block of PV technology is the                   cell is connected in a circuit.
   photovoltaic cell. PV cells come in many shapes
   and sizes. The most common shapes are circles,
   rectangles and squares. The size and the shape
   of a PV cell and the number of PV cells required
   for one PV module depend on the material of
   which the PV cell is made.




© 2006 THE NEED PROJECT • PO BOX 10101 • MANASSAS, VA 20108 • 1-800-875-5029                  Schools Going Solar Activities PAGE 15
How a PV Cell is Made                                          them, knocking them free of their atoms. These
Let’s look more closely at how a PV cell is made and           electrons are attracted to the positive charge in the
how it produces electricity.                                   n-layer and repelled by the negative charge in the p-
                                                               layer.
Step 1
Pure silicon is used to form very thin wafers. In half
                                                               Step 4
of the wafers, a small amount of the element                   If the n-layer is attached by a conducting wire to the
phosphorous is added. In the other wafers, a small             p-layer, a circuit is formed. As the free electrons are
amount of the element boron is added. This process             pushed into the n-layer, they repel each other because
is called doping. Dopants are similar in atomic                they are of like charge. The wire provides a path for
structure to the primary material. The phosphorous             the electrons to move away from each other. This
has one more electron in its outer shell than silicon,         flow of electrons is an electric current that can power
and the boron has one less. These dopants help                 a load, such as a calculator or other device, as it
create the electric field that makes it easier for the         travels through the circuit from the n-layer to the p-
electrons to become dislodged when light strikes               layer.
the PV cell.                                                   In addition to the semi-conducting materials, solar
The phosphorous gives the wafer of silicon an excess           cells consist of a top metallic grid or other electrical
of free electrons; it has a negative character. This           contact to collect electrons from the semi-conductor
wafer with the phosphorous is called the n-layer (n =          and transfer them to the external load, and a back
negative). The n-layer is not a charged wafer—it has           contact layer to complete the electrical circuit.
an equal number of protons and electrons—but some
of the electrons are not held tightly to the atoms in
the wafer. They are free to move to different locations
within the layer.
The boron gives its wafer of silicon a positive
character, because it has a tendency to attract
electrons. The layer has an equal number of
protons and electrons; it has a positive character
but not a positive charge. This wafer with boron is
called the p-layer (p = positive).

Step 2
When the two wafers are placed together, the free
electrons from the n-layer are attracted to the p-
layer. At the moment of contact between the two
wafers, free electrons from the n-layer flow into the
p-layer for a split second, then form a barrier to
prevent more electrons from moving between
layers. This point of contact and barrier is called
the p-n junction.
When the layers are joined, there is a negative
charge in the p-layer section of the junction and a
positive charge in the n-layer section of the junction.
This imbalance in electrical charge at the p-n
junction produces an electric field between the p-
layer and the n-layer.

Step 3
If the PV cell is placed in the sun, photons of light
strike the electrons in the p-n junction and energize

 PAGE 16    Schools Going Solar Activities           © 2006 THE NEED PROJECT • PO BOX 10101 • MANASSAS, VA 20108 • 1-800-875-5029
PV Modules, Panels and Arrays                                         In the simplest systems, DC current produced by PV
For more power, cells are connected together to form                  modules is used directly. In applications where AC
larger units called modules. Photovoltaic cells are                   current is necessary, an inverter can be added to the
connected in series and/or parallel circuits to                       system to convert DC to AC current.
produce higher voltages, currents and power levels.                   Battery System: PV systems cannot store electricity,
A PV module is the smallest PV component sold                         so batteries are often added. A PV system with a
commercially, and can range in power output from                      battery is configured by connecting the PV array to
about 10 watts to 300 watts.                                          an inverter. The inverter is connected to a battery
A typical PV module consists of PV cells sandwiched                   bank and to any load. During daylight hours, the PV
between a clear front sheet, usually glass, and a                     array charges the battery bank. The battery bank
backing sheet, usually glass or a type of tough plastic.              supplies power to the load whenever it is needed. A
This protects them from breakage and from the                         device called a charge controller keeps the battery
weather. An aluminum frame can be fitted around the                   properly charged and prolongs its life by protecting
PV module to enable easy affixing to a support                        it from being overcharged and completely discharged.
structure. Photovoltaic panels include one or more                    PV systems with batteries can be designed to power
PV modules assembled as a pre-wired, field-                           DC or AC equipment. Systems operating only DC
installable unit. A PV array is the complete power-                   equipment do not need an inverter, only a charge
generating unit, consisting of any number of modules                  controller.
and panels.
                                                                       PV Systems
                                                                       Two types of PV systems are grid-connected systems
                                                                       and stand-alone systems. The main difference
       cell                                                            between these systems is that one is connected to
                                        module
                                                                       the utility grid and the other is not.

                                                                       Grid Connected Systems
                                                                       Grid-connected PV systems are designed to operate
                                                                       in parallel with and interconnected with the national
              array                            panel                   electric utility grid. What is the grid? It is the network
                                                                       of cables through which electricity is transported
                                                                       from power stations to homes, schools and other
                                                                       places. A grid connected PV system is linked to this
PV System Components
                                                                      network of power lines.
Although a PV module produces power when exposed
to sunlight, a number of other components are                         The primary component of a grid-connected PV system
required to properly conduct, control, conver t,                      is the inverter, or power conditioning unit (PCU). The
distribute, and store the energy produced by the array.               inverter converts the DC power produced by the PV
Depending on the type of system, these components                     system into AC power consistent with the voltage
may include:                                                          and power quality requirements of the utility grid.
Power Inver ter: PV modules, because of their
electrical properties, produce direct current (DC)
rather than alternating current (AC). Direct current is
electric current that flows in a single direction. Many
simple devices, such as those that run on batteries,
use direct current. Alternating current, in contrast, is
electric current that reverses its direction of flow at
regular intervals (120 times per second). This is the
type of electricity provided by utilities and the type
required to run most modern appliances and
electronic devices.


© 2006 THE NEED PROJECT • PO BOX 10101 • MANASSAS, VA 20108 • 1-800-875-5029                   Schools Going Solar Activities PAGE 17
This means that it can deliver the electricity it               Benefits and Limitations
produces into the electricity network and draw it down
                                                                Benefits
when needed; therefore, no battery or other storage
is needed.                                                      Solar electric systems offer many advantages:
                                                                They are safe, clean and quiet to operate.
Stand-alone Systems
                                                                They are highly reliable.
As its name suggests, this type of PV system is a
separate electricity supply system. A stand-alone               They require virtually no maintenance.
system is designed to operate independent of the
electric utility grid and to supply electricity to a single     They are cost-effective in remote areas and for some
system. Usually a stand-alone system includes one               residential and commercial applications.
or more batteries to store the electricity.                     They are flexible and can be expanded to meet
Historically, PV systems were used only as stand–               increasing electrical needs.
alone systems in remote areas where there was no                They can provide independence from the grid or
other electricity supply. Today, stand-alone systems            backup during outages.
are used for water pumping, highway lighting, weather
stations, remote homes and other uses away from                 The fuel is renewable and free.
power lines.
                                                                Limitations
                                                                There are also several practical limitations to PV
                                                                systems:
                                                                PV systems are not well suited for energy-intensive
                                                                uses such as heating.
                                                                Grid-connected systems are rarely economical,
                                                                primarily because the current cost of the PV
                                                                technology is much higher than the cost of
                                                                conventional electricity in the United States.




 PAGE 18    Schools Going Solar Activities            © 2006 THE NEED PROJECT • PO BOX 10101 • MANASSAS, VA 20108 • 1-800-875-5029
Measuring Electricity
Electricity makes our lives easier, but it can seem
like a mysterious force. Measuring electricity is
confusing because we cannot see it. We are familiar
with terms such as watt, volt, and amp, but we do not
have a clear understanding of these terms. We buy a
60-watt lightbulb, a tool that needs 120 volts, or a
vacuum cleaner that uses 8.8 amps, and don’t think
about what those units mean.
Using the flow of water as an analogy can make
                                                                                   Voltage
electricity easier to understand. The flow of electrons
in a circuit is similar to water flowing 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 each second.
The amount of water depends on how much pressure
is being applied–– how hard the water is being
pushed. It also depends on the diameter of the hose.
The harder the pressure and the larger the diameter
of the hose, the more water passes each second.
The flow of electrons through a wire depends on the
electrical pressure pushing the electrons and on the
                                                                      Current
cross-sectional area of the wire.
                                                                      The flow of electrons can be compared to the flow of
Voltage                                                               water. The water current is the number of molecules
                                                                      flowing past a fixed point; electrical current is the
The pressure that pushes electrons in a circuit is
                                                                      number of electrons flowing past a fixed point.
called voltage. Using the water analogy, if a tank of
                                                                      Electrical current (I) is defined as electrons flowing
water were suspended one meter above the ground
                                                                      between two points having a difference in voltage.
with a ten-centimeter pipe coming out of the bottom,
                                                                      Current is measured in amperes or amps (A). One
the water pressure would be similar to the force of a
                                                                      ampere is 6.25 X 1018 electrons per second passing
shower. If the same water tank were suspended 10
                                                                      through a circuit.
meters above the ground, the force of the water would
be much greater, possibly enough to hurt you.                         With water, as the diameter of the pipe increases, so
                                                                      does the amount of water that can flow through it.
Voltage (V) is a measure of the pressure applied to
                                                                      With electricity, conducting wires take the place of
electrons to make them move. It is a measure of the
                                                                      the pipe. As the cross-sectional area of the wire
strength of the current in a circuit and is measured
                                                                      increases, so does the amount of electric current
in volts (V). Just as the 10-meter tank applies
                                                                      (number of electrons) that can flow through it.
greater pressure than the 1-meter tank, a 10-volt
power supply (such as a battery) would apply greater
pressure than a 1-volt power supply.
AA batteries are 1.5-volt; they apply a small amount
of voltage or pressure for lighting small flashlight
bulbs. A car usually has a 12-volt battery––it applies
more voltage to push current through circuits to
operate the radio or defroster. The voltage of typical
wall outlets is 120 volts––a dangerous amount of                                         Current
voltage. An electric clothes dryer is usually wired at
240 volts––a very dangerous voltage.



© 2006 THE NEED PROJECT • PO BOX 10101 • MANASSAS, VA 20108 • 1-800-875-5029                 Schools Going Solar Activities PAGE 19
Resistance                                                 Ohm’s Law
Resistance (R) is a property that slows the flow of        George Ohm, a German physicist, discovered that in
electrons. Using the water analogy, resistance is          many materials, especially metals, the current that
anything that slows water flow, a smaller pipe or fins     flows through a material is proportional to the
on the inside of a pipe.                                   voltage.
In electrical terms, the resistance of a conducting        In the substances he tested, he found that if he
wire depends on the metal the wire is made of and          doubled the voltage, the current also doubled. If he
its diameter. Copper, aluminum, and silver––metals         reduced the voltage by half, the current dropped by
used in conducting wires––have different resistance.       half. The resistance of the material remained the
                                                           same.
Resistance is measured in units called ohms (W).
There are devices called resistors, with set               This relationship is called Ohm’s Law, and can be
resistances, that can be placed in circuits to reduce      written in a simple formula. If you know any two of
or control the current flow.                               the measurements, you can calculate the third using
                                                           the following formula:
Any device placed in a circuit to do work is called a
load. The lightbulb in a flashlight is a load. A                    voltage = current x resistance
television plugged into a wall outlet is also a load.
                                                                    V=IxR              or        V=AxW
Every load has built-in resistance.
                                                           Electrical Power
                                                           Power (P) is a measure of the rate of doing work or
                                                           the rate at which energy is converted. Electrical power
                                                           is the rate at which electricity is produced or
                                                           consumed. Using the water analogy, electric power
                                                           is the combination of the water pressure (voltage)
                                                           and the rate of flow (current) that results in the ability
                                                           to do work.
                                                           A large pipe carries more water (current) than a small
                                                           pipe. Water at a height of 10 meters has much greater
                                                           force (voltage) than at a height of one meter. The
                                                           power of water flowing through a 1-centimeter pipe
                                                           from a height of one meter is much less than water
                                                           through a 10-centimeter pipe from 10 meters.
                                                           Electrical power is defined as the amount of electric
                                                           current flowing due to an applied voltage. It is the
                                                           amount of electricity required to start or operate a
                                                           load for one second. Electrical power is measured in
                                                           watts (W). The formula is:
                                                                    power = voltage x current
                                                                    P= V x I                or   W=VxA




                                                                                    Power



 PAGE 20   Schools Going Solar Activities        © 2006 THE NEED PROJECT • PO BOX 10101 • MANASSAS, VA 20108 • 1-800-875-5029
Electrical Energy                                                     The same applies with electrical power. You would
Electrical energy introduces the concept of time to                   not say you used 100 watts of light energy to read
electrical power. In the water analogy, it would be the               your book, because 100 watts represents the rate
amount of water falling through the pipe over a period                you used energy, not the total energy used. The
of time, such as an hour. When we talk about using                    amount of energy used would be calculated by
power over time, we are talking about using energy.                   multiplying the rate by the amount of time you read.
Using our water example, we could look at how much                    If you read for 5 hours with a 100-W bulb, for example,
work could be done by the water in the time that it                   you would use the formula as follows:
takes for the tank to empty.
                                                                               Energy = Power x Time            (E = P x t)
The electrical energy that an appliance or device
consumes can be determined only if you know how                                Energy = 100 W x 5 hour = 500 Wh
long (time) it consumes electrical power at a specific                One watt-hour is a very small amount of electrical
rate (power).                                                         energy. Usually, we measure electrical power in larger
To find the amount of energy consumed, you multiply                   units called kilowatt-hours (kWh) or 1,000 watt-
the rate of energy consumption (measured in watts)                    hours. (kilo = thousand). A kilowatt-hour is the unit
by the amount of time (measured in hours) that it is                  that utilities use when billing most customers. The
being consumed. Electrical energy is measured in                      average cost of a kilowatt-hour of electricity for
watt-hours (Wh).                                                      residential customers in the U.S. is about $0.09.

        Energy (E) = Power (P) x Time (t)                             To calculate the cost of reading with a 100-W bulb
                                                                      for five (5) hours, you would change the watt-hours
        E = P x t or       E = W x h = Wh                             into kilowatt-hours, then multiply the kilowatt-hours
                                                                      used by the cost per kilowatt-hour, as shown below:
Another way to think about power and energy is with
an analogy to traveling. If a person travels in a car                          500 Wh divided by 1,000 = 0.5 kWh
at a rate of 40 miles per hour (mph), to find the total                        0.5 kWh x $0.09/kWh = $0.045
distance traveled, you would multiply the rate of travel
by the amount of time you traveled at that rate.                      It would cost about four and a half cents to read for
                                                                      five hours with a 100-W bulb.
If a car travels for 1 hour at 40 miles per hour, it
would travel 40 miles.
        Distance = 40 mph x 1 hour = 40 miles
If a car travels for 3 hours at 40 miles per hour, it
would travel 120 miles.
        Distance = 40 mph x 3 hours = 120 miles
When we look at power, we are talking about the rate
that electrical energy is being produced or consumed.
Energy is analogous to the total distance traveled.
A person wouldn’t say he took a 40-mile per hour trip
because that is the rate. The person would say he
took a 40-mile trip or a 120-mile trip. Just as the
total distance is calculated by multiplying miles per
hour by time, the amount of energy is calculated by
multiplying power (work/time) by time.




© 2006 THE NEED PROJECT • PO BOX 10101 • MANASSAS, VA 20108 • 1-800-875-5029                 Schools Going Solar Activities PAGE 21
                                                          PV Glossary
Alternating Current (AC): an electric current that reverses direction at frequent, regular intervals.

Angle of Incidence: angle between the normal to a surface and the direction of incident radiation; applies to the aperture plane
of a solar collector.

Azimuth: angle between due north and the direction the surface of the PV array faces, measured clockwise from north. As applied
to the PV array, 180-degree azimuth means the array faces due south.

Carbon Dioxide (CO2) Saved: amount of carbon dioxide that would have been produced by burning fossil fuels (such as coal) to
generate an equivalent amount of electricity measured in pounds.

Current: the rate of flow of electricity.

Direct Current (DC): electric current in which electrons flow in one direction only. This is the type of electricity produced by a PV
system.

Disconnect Switches: safety devices that start and stop the flow of electricity in the PV system. They are used when qualified
personnel need to work on the system. There are two disconnect switches (an AC switch and a DC switch).

Distribution Panel: the place where the electrical energy produced by the PV system is integrated with the school’s electric
system. This allows solar energy to be used for lighting, computers, and other electric loads in the school building.

Dual-Axis Tracking: a sun-tracking system capable of rotating independently about two axes (e.g., vertical and horizontal) and
following the sun for maximum efficiency of the solar array. This type of system allows the array to point directly at the sun at all
times. Two-axis tracking arrays capture the maximum possible daily energy.

Electric Circuit: path followed by electrons from a power source (generator or battery) through an external line (including devices
that use the electricity) and returning through another line to the source.

Electric Meter: a device that keeps track of the amount of electrical energy produced by the PV system.

Energy: the ability to do work or make a change.

Energy Conservation: the practice of extending the useful life of the Earth’s energy resources through reduced and more efficient
energy use.

Energy Totals: amount of electricity produced in one day, and since the beginning of the year, measured in kilowatt-hours.

Grid: an integrated system of electricity distribution, usually covering a large area.

Grid-Connected (PV system): a PV system in which the PV array acts like a central generating plant, supplying power to the grid.

Insolation: the amount of sunlight reaching an area, usually expressed in milliwatts per square centimeter, or langleys.

Inverter: a device that converts DC electricity into AC electricity.

Kilowatt-hour: a unit of energy equal to 1000 watts being used for one hour.

Life-Cycle Cost: the estimated cost of owning and operating a PV system for the period of its useful life.

Load: anything in an electrical circuit that, when the circuit is turned on, draws power from that circuit.

Monthly Data: total amount of energy produced each day for a calendar month, measured in kilowatt-hours.

Photon: an elemental unit of light energy or a tiny particle of light.

Photovoltaic (PV) Array: a group of PV modules connected together.




 PAGE 22      Schools Going Solar Activities                © 2006 THE NEED PROJECT • PO BOX 10101 • MANASSAS, VA 20108 • 1-800-875-5029
Photovoltaic (PV) Cell: the basic building block in photovoltaic systems that turn sunlight directly into electricity. Sometimes
called “solar cells.”

Photovoltaic (PV) Conversion Efficiency: the ratio of the electric power produced by a photovoltaic device to the power of the
sunlight incident on the device.

Photovoltaic (PV) Effect: the phenomenon that occurs when photons, the particles of energy in a beam of light, knock electrons
loose from the atoms they strike. When this property of light is combined with the properties of semiconductors, electrons flow
in one direction across a junction, setting up a voltage. With the addition of circuitry, current flows and electric power is available.

Photovoltaic (PV) Efficiency: the ratio of electric power produced by a cell at any instant to the power of the sunlight striking the
cell. This is typically about 7–17 percent for commercially available cells.

Photovoltaic (PV) Module: the smallest replaceable unit in a PV array; an integral, encapsulated unit containing a number of PV
cells.

Photovoltaic (PV) System: a complete set of components for converting sunlight into electricity by the photovoltaic process,
including the array and other system components.

Pyronometer: an instrument for measuring total hemispheric solar irradiance on a flat surface.

Real Time Display: data readouts at a given moment from a photovoltaic and weather-monitoring system.

Renewable Energy: sources of energy that can be replenished in a short period of time or are inexhaustible because their use
today does not diminish their availability tomorrow. Solar, wind, biomass, and hydropower are examples.

Semiconductor: any material that has a limited capacity for conducting an electric current. A semiconductor generally falls
between a metal and an insulator in conductivity.

Single-Axis Tracking: a system capable of rotating about one axis, usually following the sun from East to West.

Solar Cell: another term for a photovoltaic (PV) cell.

Solar Energy: radiant energy from the sun.

Sunlight: amount of solar energy reaching the surface of a collector at a given moment, measured in watts per square meter.

Temperature: the ambient air temperature at a given moment in degrees Fahrenheit or Celsius.

Today’s Data: amount of power produced since midnight for the current calendar day, measured in kilowatts. Also the amount of
solar energy that reached the surface of the solar collectors since midnight for the current day, measured in watts per square
meter.

Tracking Array: a PV array that follows the path of the sun to maximize the solar radiation incident on the PV surface. The two most
common orientations are single-axis, where the array tracks the sun East to West, and dual-axis tracking, where the array points
directly at the sun at all times. Typically, a single axis tracker will provide 15 to 25 percent more power per day than a stationary
array, and dual axis tracking provide 20 to 30 percent more. Tracking arrays use both the direct and diffuse sunlight. Total output
depends somewhat on latitude and season.

Transformer: a device that changes the voltage of the electricity coming from the inverter to match the voltage of electricity that
is used in the school building.

Utility-Interactive System: a PV installation connected to a utility power line.

Voltage: a measure of the potential difference (push) of electric current. The higher the voltage, the more force there is to push
the current through the wire.

Watt: a metric unit of power that gives the rate at which work is done or energy is expended.

Wind Speed: how fast the wind is blowing at a given moment, measured in miles per hour or kilometers per hour.




© 2006 THE NEED PROJECT • PO BOX 10101 • MANASSAS, VA 20108 • 1-800-875-5029                      Schools Going Solar Activities PAGE 23
                             NEED National Sponsors and Partners
    Alabama Department of Economic and Community Affairs                                 Marathon Oil Company
   American Association of Blacks in Energy – Detroit Chapter                       Marianas Islands Energy Office
  American Association of Drilling Engineers – Houston Chapter              Massachusetts Division of Energy Resources
                     American Electric Power                                             Michigan Energy Office
         American Petroleum Institute – Houston Chapter                 Michigan Oil and Gas Producers Education Foundation
                American Public Power Association                  Minerals Management Service – U.S. Department of the Interior
                    Aramco Services Company                             Mississippi Development Authority – Energy Division
               Association of Desk & Derrick Clubs                        Narragansett Electric – A National Grid Company
                      BJ Services Company                                   National Association of State Energy Officials
                                BP                                          National Association of State Universities and
                             BP Solar                                                     Land Grant Colleges
  Bureau of Land Management – U.S. Department of the Interior                          National Biodiesel Board
                  Cape and Islands Self Reliance                                              National Fuel
                 Cape Cod Cooperative Extension                                     National Hydrogen Association
              Cape Light Compact – Massachusetts                                National Ocean Industries Association
              Chesapeake Public Schools – Virginia                       New Jersey Department of Environmental Protection
                             Chevron                                        North Carolina Department of Administration
                    Chevron Energy Solutions                                               State Energy Office
                       Cinergy Corporation                                          Nebraska Public Power District
                          Citizens Gas                                                    New Mexico Oil Corp.
                         ConEd Solutions                                         New Mexico Landman’s Association
Council of Great Lakes Governors – Regional Biomass Partnership      New York State Energy Research and Development Authority
     Cypress-Fairbanks Independent School District – Texas                                    Noble Energy
      D&R International – School Energy Efficiency Program                Offshore Energy Center/Ocean Star/OEC Society
              Dart Container Corporation Foundation                                        Ohio Energy Project
             Desk and Derrick of Roswell, New Mexico                                   Oil & Gas Rental Services
                          Devon Energy                                             Pacific Gas and Electric Company
                            Dominion                                            Permian Basin Petroleum Association
                                                                             Petroleum Equipment Suppliers Association
                     Duke Energy Indiana
                                                                                                 Premiere
                           Duke Energy Kentucky                               Puerto Rico Energy Affairs Administration
                           East Kentucky Power                                       Renewable Fuels Association
 Energy Information Administration – U.S. Department of Energy                                Roanoke Gas
                            Equitable Resources                                              Robert Gorham
              Escambia County School District – Florida                             Rogers Training and Consulting
          Florida Department of Environmental Protection                            Roswell Desk and Derrick Club
                              FMC Technologies                                        Roswell Geological Society
                               Fuel Cell Store                                     Rhode Island State Energy Office
                              Gerald Harrington                                               Saudi Aramco
                               GlobalSantaFe                                                  Schlumberger
                       Governors’ Ethanol Coalition                                           Sentech, Inc.
                             Guam Energy Office                                    Shell Exploration and Production
                          Halliburton Foundation                                    Society of Petroleum Engineers
                                    Hydril                                                   Southwest Gas
            Illinois Clean Energy Community Foundation                   Spring Branch Independent School District – Texas
  Illinois Department of Commerce and Economic Opportunity                           Strategic Energy Innovations
              Independent Petroleum Association of NM                          Tennessee Department of Economic and
                 Indiana Community Action Association                                    Community Development
         Indiana Office of Energy and Defense Development                    Texas Education Service Center – Region III
                       Indianapolis Power and Light                  Texas Independent Producers & Royalty Owners Association
                  Interstate Renewable Energy Council                                      TransOptions, Inc.
                             Iowa Energy Center                                   University of Nevada – Las Vegas
                              Johnson Controls                                               Urban Options
                      Kentucky Clean Fuels Coalition                            U.S. Environmental Protection Agency
                     Kentucky Office of Energy Policy               U.S. Department of Agriculture – Biodiesel Education Program
                    Kentucky Oil and Gas Association                                  U.S. Department of Energy
          Kentucky Propane Education & Research Council                                  U.S. Fuel Cell Council
                      Kentucky River Properties LLC                                               Vectren
                         Kentucky Soybean Board                                       Virgin Islands Energy Office
                     Lee Matherne Family Foundation                         Wake County Public Schools – North Carolina
                        Llano Land and Exploration                                      W. Plack Carr Company
                      Maine Energy Education Project                                           Xcel Energy
                      Maine Public Service Company                                          Yates Petroleum


     The NEED Project           PO Box 10101           Manassas, VA 20108     1-800-875-5029          www.NEED.org

				
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