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Exploring Photovoltaics Student Guide

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SECONDARY

What Is Energy? We all use the word energy daily. We have energy drinks, we pay our energy bills, and politicians discuss energy policy almost daily. However, what energy actually is can be a difficult concept to explain precisely. Our bodies and objects all around us are using energy all the time. Energy allows us to do work, and to affect change. It provides the ability to do what we need to do, whether we can visibly see what is happening or on a microscopic level. Energy exists in two basic forms. Stored energy to use later is called potential energy, while energy in motion is called kinetic energy. Each of these two, broad categories can be broken down further into nine different forms of energy. One type of potential energy is gravitational potential energy (GPE), which is energy stored by position. A child at the top of a slide or water behind a dam both have gravitational energy. Elastic energy is potential energy that is stored by applying a force. When you wind up a toy car, you are storing energy in the spring inside of it. If you pull back on a rubber band, you are storing elastic energy in it. Nuclear energy is the potential energy within the nucleus of atoms. Very small changes in the nucleus of an atom can release tremendous amounts of energy. The most commonly used form of potential energy is chemical energy. It is the energy in the bonds between atoms of all the substances in the world. The food you eat, the fuel in the car you drive, the wood your campfire burns are all examples of chemical energy. Kinetic energy – energy in motion - can be broken down into five forms. When large-scale things are moving, they have motion or mechanical energy. A child on a bike, water moving through a stream, and the wind all have motion energy. Thermal energy is the energy that allows atoms and molecules to move around. The more thermal energy in a substance, the faster the molecules move, and the higher its temperature. Sound energy is a form of energy that we often overlook – because a sound is a vibration, it is an energy form. Radiant energy is energy that moves through space in transverse waves. Sunlight and radio waves are examples of radiant energy, as are microwaves and x-rays. Electrical energy is the energy of moving electrons. Electricity is the most common example of electrical energy, but small static electricity jolts and lightning strikes are also examples of electrical energy.

Conservation of Energy

Potential and Kinetic Energy

Potential Energy

Kinetic Energy

HILL Energy Energy Transformations Transformations

Chemical

Motion

Chemical

Motion

Radiant

Chemical

Electrical

Heat

Energy Efficiency Energy efficiency is the amount of useful energy you get from a system compared to the energy input. A perfect, energy-efficient machine would change all the energy put in it into useful work— an impossible dream. Converting one form of energy into another form always involves a loss of usable energy, often as waste heat. Most energy transformations are not very efficient. The human body is a good example. Your body is like a machine, and the fuel for your machine is food. Food gives you the energy to move, breathe, and think. Your body is very inefficient at converting food into useful work. Most energy in your body is released as wasted heat.

Conservation of energy is not just saving energy. The Law of Conservation of Energy says that energy is neither created nor destroyed. When we use energy, it doesn’t disappear. We simply change it from one form of energy into another. A car engine burns gasoline, converting the chemical energy in gasoline into motion energy. Solar cells change radiant energy into electrical energy. Energy changes form, but the total amount of energy in the universe stays the same.

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Sources of Energy We use many energy sources to meet our needs. All of them have advantages and disadvantages—limitation or reliability of supply, and economic, environmental, or societal impacts. Energy sources are usually classified into two groups—renewable and nonrenewable. In the United States, most of our energy comes from nonrenewable energy sources. Coal, natural gas, petroleum, propane, and uranium are nonrenewable energy sources. They are used to generate electricity, heat homes, move vehicles, and manufacture all kinds of products from candy bars to computers. They are called nonrenewable because their supplies are limited, and they cannot be replenished in a short period of time. Petroleum, for example, was formed hundreds of millions of years ago, before dinosaurs lived, from the remains of ancient sea plants and animals. We could run out of economically recoverable nonrenewable resources someday. Renewable energy sources include biomass, geothermal, hydropower, solar, and wind. They are called renewable because they are replenished in a short time, almost as quickly as they are used. Day after day the sun shines, the wind blows, and the rivers flow. We use renewable energy sources mainly to make electricity.

Energy Sources and Electricity Electricity is neither a renewable or nonrenewable energy source. Electricity is considered a secondary source of energy because it is created or generated using other sources of energy. In the United States, nine of the ten energy sources are regularly used to generate electricity; the only source that is not commonly used for electricity generation is propane. Natural gas is the leading source for electricity, followed by uranium and coal. Wind and hydropower are the leading renewable energy sources for electricity generation. The most common way to generate electricity is by using thermal energy to boil water into pressurized steam that can turn a turbine. Turbines change linear motion into rotational motion; in this case, the linear movement of the steam is changed to a rotation to turn a generator. The generator houses large magnets and coils of copper wire. The turbine blades spin the generator, moving either the coils of wire or the magnets relative to the other. This produces an electric current. Wind and hydropower use a flowing fluid, air or water respectively, to turn the turbine. Because no thermal energy is lost, wind and water are more efficient sources of energy for generating electricity. Solar energy, however, often generates electricity differently than other renewables. Solar energy can generate electricity by capitalizing on the photovoltaic effect with the use of solar panels. It can, under the right conditions, also be generated by heating a substance and using thermal energy to turn a turbine.

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U.S. Energy Consumption by Source, 2024 NONRENEWABLE, 90.89%

RENEWABLE, 9.11%

Petroleum

37.53%

Biomass

5.30%

Natural Gas

36.31%

Wind

Uses: electricity

1.64%

Uses: electricity, heating, manufacturing - Includes Propane

Uranium

8.68%

Solar

1.17%

Coal

8.37%

Hydropower 0.88%

Uses: electricity, heating, transportation

Uses: transportation, manufacturing - Includes Propane

Uses: electricity

Uses: electricity, heating

Uses: electricity, manufacturing

Uses: electricity

*Propane consumption figures are reported as part of petroleum and natural gas totals.

Geothermal 0.12%

Propane

Uses: electricity, heating

Uses: heating, manufacturing

Data: Energy Information Administration **Total may not equal 100% due to independent rounding.

U.S. Electricity Generation, 2024

RENEWABLES

URANIUM

22.56%

18.17%

WIND, 10.54% HYDROPOWER, 5.49%

NATURAL GAS

43.33%

SOLAR, 5.08% Other

COAL

15.17%

0.23%

Petroleum

0.35%

BIOMASS, 1.09% GEOTHERMAL, 0.36%

Data: Energy Information Administration *Total may not equal 100% due to independent rounding

Solar Energy

THE SUN

What is Solar Energy? Solar energy is radiant energy from the sun. It is vital to us because it provides the world—directly or indirectly—with almost all of its energy. In addition to providing the energy that sustains the world, solar 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 each day than the world uses in one year. Solar energy comes from within the sun itself. Like other stars, our sun is an enormous mass of the smaller elements—mostly hydrogen and helium. The nuclei from smaller elements combine to form larger nuclei and radiant energy in a process called nuclear fusion. Because the sun is so massive, its gravitational pull produces extremely high temperatures and pressure. It is high enough to cause nuclei to separate from their electrons, forming plasma. At this extremely energized state, the nuclei are able to fuse, or combine. In one fusion reaction, two hydrogen nuclei fuse to become one helium nucleus of a higher atomic number and greater mass, and one neutron remains free. This new helium atom, however, contains less mass than the combined masses of the hydrogen isotopes that fused. This transmutation of matter results in some mass being lost. The lost matter is emitted into space as radiant energy. The process of fusion occurs most commonly with lighter elements like hydrogen, but can also occur with heavier nuclei, until iron (Fe) is formed. Because iron is the lowest energy nucleus, it will neither fuse with other elements, nor can it be fissioned (split) into smaller nuclei. Scientists theorize that the time for the energy in the sun’s core to make its way to the solar surface takes on average, 200,000 years. The nuclear fusion process in the sun’s core produces, among other things, extremely high energy photons. What is a photon? It is a specific amount of energy that has a specific wavelength. The highest energy photons are also called gamma rays. The high-energy photons produced by fusion are constantly absorbed and re-emitted as they move through the sun, essentially bouncing in random directions. By the time this “random walk” takes them to the sun’s surface the wavelengths have increased and the energy of each photon is decreased. Some of these photons have wavelengths in the visible part of the electromagnetic spectrum, which we see as light. The photons, as radiant energy, escape from the photosphere, the visible surface of the sun, and arrive at Earth about eight minutes later. The solar energy travels to the Earth at a speed of 3.0 x 108 meters per second (186,000 miles per second), the speed of light. Thermal energy is not transmitted from the sun because the space between the sun and Earth is mostly a vacuum. Rather, radiant energy transforms into thermal energy when it is absorbed by molecules in the atmosphere or on the surface of the Earth. Only a small portion of the energy radiated by the sun into space strikes the Earth—one part in two billion. Yet, this amount of energy is enormous. It was mentioned before that the sun provides more energy in a day than the world uses in a year. The sun also provides more energy in an hour than the United States uses in a year! Where does all this energy go? About 30 percent of the sun’s energy that hits the Earth is

Image courtesy of NASA

This image of our sun was captured by NASA’s Solar Dynamics Observatory—a space telescope designed to study the sun.

Fusion The process of fusion most commonly involves hydrogen isotopes combining to form a helium atom with a transformation of matter. This matter is emitted as radiant energy. Hydrogen Isotope

Hydrogen Isotope Energy Helium

Neutron

Albedo Thin clouds 25% to 30%

Thick clouds 70% to 80%

Snow

Forest

50% to 90%

5% to 10%

Asphalt

5% to 10%

Dark roof

10% to 15%

Light roof 35% to 50%

Water

5% to 80% (varies with sun angle)

Average reflectivity of solar radiation for various surfaces.

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reflected back into space. Another 25 percent powers the water cycle; it evaporates water that is then drawn into the atmosphere, turns into clouds, condenses, and falls back to Earth as precipitation. Plants, the land, and the oceans also absorb a portion of solar energy. The rest is reflected and could be used to supply our energy needs. A surface’s albedo describes how much solar energy it reflects.

JOHN ERICSSON’S SOLAR ENGINE

Solar energy is considered a renewable energy source because the nuclear fusion reactions that power the sun are expected to keep generating sunlight for many billions of years.

History of Solar Energy People have harnessed solar energy for centuries. As early as the 7th century BCE, people used simple magnifying glasses to concentrate the light of the sun into beams so hot they could cause wood to catch fire. In the 1860s in France, a scientist named Auguste Mouchout used heat from a solar collector to make steam to drive a steam engine. Around the same time in the United States, John Ericsson developed the first realistic application of solar energy using a solar reflector to drive 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 seriously researching ways to use solar energy. The solar water heater gained popularity during this time in Florida, California, and the Southwest. The industry was in full swing just before World War II. This growth lasted until the mid-1950s, when low-cost, natural gas became the primary fuel for heating homes and water, and solar heating lost popularity. The public and world governments remained largely indifferent to the possibilities of solar energy until the energy crises of the 1970s. Research efforts in the U.S. and around the world since that time have resulted in tremendous improvements in solar technologies for heating water and buildings and generating electricity. Today, solar energy accounts for about one percent of U.S. energy consumption.

Solar Collectors Heating with solar energy is relatively easy—just look at a car parked in the sun with its windows closed. Getting the right amount of heat in a desired location, however, requires more thought and careful design. Capturing sunlight and putting it to work effectively is difficult because the solar energy that reaches the Earth is spread out over a large area. The sun does not deliver that much energy to any one place at any one time.

Image courtesy of www.stirlingengines.org

John Ericsson’s Sun Motor. Built in New York in 1872. Ericsson had intended Californian agriculturists to take up his sun-motor for irrigation purposes, but in the end nothing came of the project.

Solar Collector On a sunny day, a closed car becomes a solar collector. Radiant energy from the sun passes through the window glass, is absorbed by the car’s interior, and converted into thermal energy, which becomes trapped inside.

SOLAR ENERGY TRAPPED HEAT

How much solar energy a place receives depends on several conditions. These include the time of day, the season, the latitude of the area, the topography, and the amount of clouds in the sky. A solar collector is one way to collect heat from the sun. A closed car on a sunny day is like a solar collector. As the sunlight passes through the car’s glass windows, it is absorbed by the seat covers, walls, and floor of the car. The light that is absorbed changes into heat. The car’s glass windows let light in, but do not let all the heat out. This is also how greenhouses are designed to stay warm year-round. A greenhouse or solar collector: allows sunlight in through the glass; absorbs the sunlight and changes it into heat; and traps most of the heat inside. ©2026 The NEED Project

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Using Sunlight to Generate Electricity

SOLAR TRAFFIC SIGNAL

Photovoltaic (or PV) systems convert light directly into electricity. The term photo comes from the Greek phos, which means “light.” The term volt is a measure of electricity named for Alessandro Volta (17451827), a pioneer in the development of electricity. Photovoltaics literally means light–electricity. Commonly known as solar cells, PV cells are already an important part of our lives. The simplest PV systems power many of the small calculators, wrist watches, and outdoor lights we see every day. Larger PV systems generate electricity for factories and warehouses, provide electricity for pumping water, powering communications equipment, and lighting homes and running appliances. In certain applications and remote settings, such as motorist aid call boxes on highways and pumping water for livestock, PV power is the cheapest form of electricity. Electric utility companies are building and include PV systems in their power supply networks. Today solar energy, mostly from PV systems, generates about five percent of U.S. electricity.

Image Credit: Semiglass/ Adobe Stock

Solar cells provide power to traffic signals and road signs. Attached to the support pole are boxes that store control panels and batteries for operation when the sun is not available.

History of Photovoltaics French physicist Edmond Becquerel first described the photovoltaic effect in 1839, but it remained a curiosity of science for the next half century. At the age of 19, Becquerel found that certain materials would produce small amounts of electric current when exposed to light. In the 1870s, William Adams and Richard Day showed that light could produce an electric current in selenium. Charles Fritts then invented the first PV cell using selenium and gold leaf in 1883, which converted light to electricity at about one percent efficiency.

ALESSANDRO VOLTA

EDMOND BECQUEREL

The conversion efficiency of a PV cell is the proportion of radiant energy the cell converts into electrical energy, relative to the amount of radiant energy that is available and striking the PV cell. This is very important when discussing PV devices, because improving this efficiency is vital to making PV energy competitive with more traditional sources of energy, such as fossil fuels. During the second half of the 20th century, PV science was refined and the process more fully developed. Major steps toward commercializing photovoltaics were taken in the 1940s and 1950s, when the Czochralski process was developed for producing highly pure crystalline silicon.

Image courtesy of Wikimedia Commons via Public Domain

SOLAR PANELS ON THE INTERNATIONAL SPACE STATION

In 1954, scientists at Bell Laboratories depended on the Czochralski process to develop the first crystalline silicon photovoltaic cell, which had a conversion efficiency of four percent. As a result of technological advances, the cost of PV cells has decreased significantly over the past 25-30 years, as the efficiency has increased. Today’s commercially available PV devices convert 13 to 30 percent of the radiant energy that strikes them into electricity. In the laboratory, combining exotic materials with specialized cell designs has produced PV cells with conversion efficiencies as high as 50 percent. The current expense of these technologies typically restricts their use to aerospace and industrial applications, where the unit cost of a solar array that powers, for example, a satellite is a minor concern. Image courtesy of NASA

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Photovoltaic Technology Photovoltaic Effect The photovoltaic effect is the basic physical process through which a PV cell converts sunlight directly into electricity. PV technology works any time the sun is shining, but more electricity is produced when the light is more intense and when it is striking the PV modules directly—when the rays of sunlight are perpendicular to the PV modules.

Silicon Atom

Unlike solar systems for heating water, PV technology does not produce heat to make electricity. Instead, PV cells generate electricity directly from the electrons freed by the interaction of radiant energy with 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 reflected, absorbed, or transmitted through the cell. Only the absorbed photons generate electricity. When the photons are absorbed, the energy of the photons is transferred to electrons in the atoms of the solar cell, which is actually a semiconductor. With their new-found energy, the electrons are able to escape from their normal positions associated with their atoms to become part of the current in an electrical circuit. By leaving their positions, the electrons cause holes to form in the atomic structure of the cell into which other electrons can move. Special electrical properties of the PV cell—a built-in electric field— provide the voltage needed to drive the current through a circuit and power an external load, such as a light bulb.

Silicon is used as a semiconductor because it has four valence electrons and does not want to lose or gain electrons. Therefore, the electrons flow across it from the boron side to the phosphorus side without the silicon interfering with the movement.

Sunlight to Electricity Sun Electric Load (-)

Photovoltaic Cells The basic building block of PV technology is the photovoltaic cell. Different materials are used to produce PV cells, but silicon—the main ingredient in sand—is the most common basic material. Silicon, a common semiconductor material, is relatively cheap 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 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 semiconductor layers, where the electric 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.

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DC current flow

Phosphorous-doped (n-type) silicon layer

(+)

Boron-doped (p-type) silicon layer

Types of PV Cells 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.

How a Traditional PV Cell is Made Let’s look more closely at how a PV cell is made and how it produces electricity.

Photovoltaic Cell

Step 1

A slab (or wafer) of pure silicon is used to make a PV cell. The top of the slab is very thinly diffused with an “n” dopant, such as phosphorous. On the base of the slab, a small amount of a “p” dopant, typically boron, is diffused. The boron side of the slab is 1,000 times thicker than the phosphorous side. Dopants are similar in atomic structure to the primary material. The phosphorous has one more electron in its outer shell than silicon, and the boron has one less. These dopants help create the electric field that motivates the energetic electrons out 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-type silicon (n = negative). The n-type silicon is not charged—it has an equal number of protons and electrons—but some of the electrons are not held tightly to the atoms. They are free to move to different locations within the layer. This silicon has a negative character, but not a negative charge. The boron gives the base of the silicon wafer a positive character, which will cause electrons to flow toward it. The base of the silicon is called p-type silicon (p = positive). The p-type silicon has an equal number of protons and electrons; it has a positive character, but not a positive charge.

Step 2

Where the n-type silicon and p-type silicon meet, 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 the two sides. This point of contact and barrier is called the p-n junction. When both sides of the silicon slab are doped, there is now a negative charge in the p-type section of the junction and a positive charge in the n-type section of the junction due to movement of the electrons and “holes” at the junction of the two types of materials. This imbalance in electrical charge at the p-n junction produces an electric field between the p-type and n-type.

Step 3

If the PV cell is placed in the sun, photons of light strike the electrons in the p-n junction and energize them, knocking them free of their atoms. These electrons are attracted to the positive charge in the n-type silicon and repelled by the negative charge in the p-type silicon. Most photonelectron collisions actually occur in the silicon base.

Step 4

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

Image courtesy of National Laboratory of the Rockies

Because PV cells are semiconductor devices, they share many of the same processing and manufacturing techniques as other semiconductor devices, such as computer and memory chips.

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

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Basic Principles of Electricity You have already learned how the photovoltaic effect causes electrons to move within a solar cell, and that providing a pathway on a conducting wire for the energized electrons allows them to power things like a flashlight. This section will give you a basic understanding of what is happening in an electric circuit.

Circuits are Electron Roads Unless an energized electron has someplace to transfer that energy, nothing will really happen. Most materials on Earth are insulators, meaning they do not allow free movement of electrons. However, many materials are conductors, and allow electrons to move around, transferring their energy to each other or to a device that needs that energy. The paths created with conducting materials are called circuits. If you connect a battery to a light emitting diode (LED) bulb with some wires, you have created a simple circuit. If you connect a solar panel to an LED, you have also created a simple circuit. As the name suggests, a simple circuit is the most basic circuit type–one pathway, one power source, one item to draw power. Whether a simple circuit such as a battery and LED, or a complex network of circuits such as the wiring in your home, they all operate in a similar fashion. For electricity to move, the pathway must be a closed loop, or a closed circuit. At home you close a circuit by turning on a switch. The switch connects two wires in the circuit and turns on whatever it is you are wanting to operate. Electricity will not move through an open, or disconnected, circuit.

Measuring Electricity You’ve heard of electric current and voltage – but what do they really mean? If you imagine a wire down to the atomic level, envisioning all of the atoms within the wire bumped up against each other, and then imagine energized electrons moving through that wire, you can imagine how current is measured. Each electron is a charged particle, and if we could stand at a point along the wire and count how many electrons are moving past a point in the wire each second, we would be describing current. Current is literally defined as the amount of charge (related to the number of electrons) moving through a cross-section of wire in one second. The more electrons moving, the higher the current. The unit for measuring current is Amperes, or just Amps, named after André-Marie Ampere. Ampere was a French physicist who did the earliest work in “electrodynamics”, or what we now call electromagnetism. If current describes the number of energized electrons moving through a circuit; voltage is how we describe the degree to which they have been energized. Imagine two pieces of sheet metal with a gap between them. One piece is positively charged, and one is negatively charged. Moving the plates closer and closer together will eventually cause electrons to jump the gap and negate the charges on both pieces of metal. The more energy the electrons have, the greater the distance they can jump. This is how voltage is determined. It is the potential electrons have to jump a gap between charged plates. The more energy the electrons have, ©2026 The NEED Project

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the greater the voltage. ELECTRIC CIRCUIT POWERING A LIGHTBULB The unit for measuring voltage is Volts, named after Alessandro Volta. He was an Italian physicist who invented the electric battery. In an electric circuit, the electrons do the work. The amount of work that can be done is a measure of the current needed – doing a lot of work requires a lot of current. For example, running Image courtesy of Adobe Stock/yusufdemirci an electric heater all day Electricity can only move in a completed uses a lot of current. The circuit. difficulty of work those electrons can do is related to the voltage. The motor inside your electric toothbrush isn’t nearly as difficult to operate as the motor on a blender, for example. The toothbrush needs lower voltage than the blender because the blender’s parts are bigger and therefore more difficult to move. Power is the combination of current and voltage. Mathematically, multiplying the current in Amps by the voltage in Volts will give you power in Watts. Power is how solar panels are rated, and power is the basis for the amount we pay for electricity. Power does not give us the complete picture of what is happening in a circuit. For example, if we have a power source providing 100 volts through a circuit through which 10 Amps of current is moving, that’s 1,000 watts of power. But 1,000 volts with 1 Amp or 1 volt with 1,000 Amps would also be 1,000 watts. We could be doing a little bit of really difficult work or a lot of really easy work and it would be the same amount of power. Suppose we need to move a pile of 100 bricks from here to there. We could have 20 people each move five bricks, or we could have two people each move 50 bricks. The people represent the current, and their strength represents voltage. The same amount of work gets done but the manner in which it is done is not the same. Voltage and current are related through a property called resistance. Resistance in a material — even in conductors — gets in the way of electrons moving through a circuit. The thicker the wire, the lower the resistance. Ohm’s Law defines resistance, mathematically relating voltage, current, and resistance through the expression V=IR, where V is voltage in volts, I is current in amps, and R is resistance measured in ohms (Ω). At a constant voltage, a high resistance results in a lower current, and a low resistance results in a higher current. Think of it like cars moving on a highway. The road represents the conductor, the cars represent the current, and the speed of the cars represents the voltage. Suppose the cars encounter a tollbooth — that’s the resistance. If the tollbooth has only a few lanes open (high resistance), fewer cars can pass through (low current). If the

temperature of the road rises and the pavement buckles, cars slow down — just like electrons do when wires heat up. The hotter the wire, the higher its resistance. If the road has potholes or unexpected construction, cars slow down even more. In our analogy, those obstacles represent impurities in the conductor.

Series Circuit with LED Diagram 1

LED

If the work being done is difficult — V like powering a blender motor — the wires need to be thicker (lower resistance) to supply enough current. + If the wires are too thin, they can overheat and become a fire hazard.

BATTERY

Mapping the Electron Highway 100Ω Circuits are the “roads” for electrons. The number of electrons moving is the current, and the degree to which the electrons are energized is the voltage. A simple circuit has one power source and one load. A load is a 68Ωfrom as simple as a LED to as complicated as all device that uses power, the devices in your school. As you are probably aware, there is not just one circuit that A provides electricity to your home or school; there are many circuits. Circuits can be planned two ways: series, or parallel. Series circuits provide only one pathway for electrons. If you have a battery powering 2 LEDs in a line, that is a series circuit (see Diagram 1). One loop describes the trip electrons take: From the battery, through the first LED, through the second LED, and back to the battery. Parallel circuits provide two or more pathways for electrons. If you have a battery powering 2 LEDs LED parallel to each other, that is a parallel circuit, with two possible loops (see Diagram 2). The first loop leaves the battery, goes through LED 1, and back to the battery. The second loop leaves the battery, goes through LED 2, and back to the battery. When we measure current in a circuit, we measure it in line, or in series, with the load. When we measure voltage in a circuit, we measure it across, or in parallel, to the load. LED

LED

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Parallel Circuit with LED Diagram 2

BATTERY

LED

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The diagrams shown are called circuit schematics. They use standard symbols, as designated by the Institute of Electrical and Electronics Engineers (IEEE), to represent parts of a circuit. A series of long and short stacked lines indicates a battery; lines represent connections or wires making the connections; the strange triangle with arrows represents an LED (arrows indicate the direction of light travel). The first schematic shows a series circuit with a battery and 2 LEDS. The second shows a parallel circuit with a battery and 2 LEDs. The third schematic shown, (Diagram 3), has more components added and is more representative of the circuit you will build when you conduct the solar panel activities in this guide. The circle with the + and -, plus arrows leading in, represents a photovoltaic cell. The circle with an A is an ammeter, measuring current, and the circle with a V is a voltmeter, measuring voltage. Note that the ammeter is in series with the LED load, and the voltmeter is parallel to the LED load. A multimeter can serve as an ammeter or a voltmeter depending on the setting you use; thus the name multimeter.

LED

Circuit Schematic Symbols

+ 10

LED

Wire

Direction of Light

Switch

Resistor

PV Cell

measuring V A Meter volts(V) or Amps(A)

Solar LED Circuit with Meters Diagram 3

PV CELL

LED

Battery

LED

A Schematic of a simple circuit with a PV cell and meters measuring current (A) and voltage (V).

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

Parts of a Photovoltaic Array CELL

A typical PV module consists of PV cells sandwiched between a clear front sheet, usually glass, and a backing sheet, usually glass or a type of tough plastic. This protects them from breakage and from the weather. An aluminum frame can be fitted around the PV module to enable easy affixing to a support structure. Photovoltaic arrays include two or more PV modules assembled as a pre-wired, fieldinstallable unit. A PV array is the complete power-generating unit, consisting of any number of modules and panels.

PV System Components Although 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 the array. Depending on the type of system, these components may include:

Power Inverter

PV modules, because of their electrical properties, produce direct current rather than alternating current. Direct current (DC) is electric current that flows in a single direction. Many simple devices, such as those that run on batteries, use direct current. Alternating current (AC), 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.

MODULE

ARRAY

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

Battery System

PV systems cannot store electricity, so batteries or large battery systems are often added. A PV system with a battery is configured by connecting the PV array to an inverter. The inverter is connected to a battery bank and to any load. 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 properly charged and prolongs its life by protecting it from being overcharged or completely discharged. PV systems with batteries can be designed to power DC or AC equipment. Systems operating only DC equipment do not need an inverter, only a charge controller. Utility-scale systems can be set up to charge large systems and deploy electricity as needed to the grid. It is useful to remember that any time conversions are made in a system, there are associated losses. For example, when an inverter is used there is a small loss of power that can be described by the

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Photovoltaic arrays are made of individual cells.

inverter’s conversion efficiency. Likewise, when batteries are used to store power, not only is there additional expense to purchase the batteries and associated equipment, but due to the internal resistance of the batteries there is a small loss of power as the charge is drawn out of the batteries.

To Connect or Not to Connect Two types of PV systems are grid-connected systems and stand-alone systems. The main difference between these systems is that one is connected to the utility grid and the other is not.

Grid-Connected Systems

Stand-Alone Systems

The primary component of a grid-connected system is the inverter, or power conditioning unit (PCU). The inverter converts the DC power produced by the PV system into AC power, consistent with the voltage and power quality requirements of the utility grid. This means that it can deliver the electricity it produces into the electricity network and draw it down when needed. While no battery or other storage is needed for solar systems, many large-scale grid-connected systems may employ battery storage to help manage demand.

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

Grid-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 is transported from power stations to homes, schools, and other places. A grid-connected system is linked to this network of power lines.

Grid-Connected SolarSystems Grid-connected System PV Array

Inverter/ Power Conditioning Unit

Distribution Panel

As its name suggests, this type of PV system is a separate electricity supply system. A stand-alone system is designed to operate independent of the national electric utility grid, and to supply electricity to a single system. Usually a stand-alone system includes one or more batteries to store the electricity.

Solar Standalone System Stand-Alone Systems PV Array

Charge Controller

DC Load (Energy Use)

Energy Storage (Battery)

Inverter AC Load

AC Loads

Electric Utility

Energy Distribution

Image courtesy of PG&E

Image courtesy of NASA

PG&E’s Vaca-Dixon Solar Station in California is a 2-MW gridconnected system.

The Mars Rovers, Spirit and Opportunity, are powered by standalone systems because they operate far away from Earth.

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Scale of PV Systems

Other Solar Technologies

Like solar cells, solar thermal systems use solar energy to make electricity. Concentrated solar power (CSP) technologies focus heat in one area to produce the high temperatures required to make electricity. Since the solar radiation that reaches the Earth is so spread out and diluted, it must be concentrated to produce the high temperatures required to generate electricity. There are several types of technologies that use mirrors or other reflecting surfaces to concentrate the sun’s energy up to 2,000 times its normal intensity.

There are three general scales at which photovoltaic systems are generally installed. They are:

Residential

A residential system is designed to offset power usage at an individual residence. While usually unable to provide all power used by the homeowners, the system could help to offset the home’s electricity usage. This type of system might produce enough electricity to power part, or all, of one home’s electricity needs.

Parabolic troughs use long reflecting troughs that focus the sunlight onto a pipe located at the focal line. A fluid circulating inside the pipe collects the energy and transfers it to a heat exchanger, which produces steam to drive a turbine. The U.S. has several large parabolic trough systems located in California and Arizona. However, the world’s largest, a 600 megawatt trough system, is located in Dubai. The solar park which houses the trough also includes a power tower system that will be the tallest in the world.

Commercial

A commercial system is designed to offset power usage at a business or industrial site. These systems are much larger than residential systems that can produce more power due to the often expansive roof-top space available for their installation. An example would be a grocery store that contracts with a company to place a solar array on their flat roof while simultaneously contracting to buy power from the installer at a fixed rate for many years. This type of system might produce enough electricity to operate all or part of the business or industrial site.

Solar power towers use a large field of rotating mirrors to track the sun and focus the sunlight onto a thermal receiver on top of a tall tower. The fluid in the receiver collects the heat and either uses it to generate electricity or stores it for later use. The Ivanpah Solar Electric Generating System, located in California, uses three power towers and 170,000 heliostats to generate electricity for over 140,000 homes. The facility generates 392 megawatts, and is among the largest CSP facility in the world, but is set to shut down in 2026. Dubai and Morocco are home to facilities that surpass this facility in generating capacity.

Utility

Utility-scale systems are employed by energy companies to produce base-load or peak load power for sale to consumers. Large areas of land are typically required for their installation. An example would be a large PV array that is employed to produce power at peak usage times in the summer months when air conditioning accounts for a large part of the electrical usage. The array produces the most power when the sun is at its peak and causing consumers to turn down their thermostats—requiring the extra electricity produced by the array.

Average Size of Grid-Connected Photovoltaic Systems RESIDENTIAL: 5 - 10 kW

Dish/engine systems are like satellite dishes that concentrate sunlight rather than signals, with a heat engine located at the focal point to generate electricity. These generators are small mobile units that can be operated individually or in clusters, in urban and remote locations. Concentrated solar power technologies require a continuous supply of strong sunlight, like that found in hot, dry regions such as deserts. Developing countries with increasing electricity demand will probably be the first to use CSP technologies on a large scale.

Annual Installed Grid-Connected PV Capacity by Sector

Annual Installed Grid-Connected PV Capacity by Sector 50000 Utility Non-Residential Residential

40000

COMMERCIAL: 30 - 110 kW

30000

20000

10000

UTILITY: 1 - 10 MW 0

2012

2013

2014

2015

2016

2017

2018

2019

2020

2021

2022

2023

2024

Data: Interstate Renewable Energy Council, LBNL, EIA Images (left, top to bottom): Adobe Stock, Performance Services Incorporated, jeson/Adobe Stock

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Developing PV Technologies

THIN-FILM TECHNOLOGY

Today there are many new PV technologies either on the market, in the pipeline, or in the research phase. These technologies will have a direct effect on how much of our energy we derive from solar power in the future. Look for technologies that will make things less expensive or serve multiple purposes as they are applied to new designs.

Ribbon Silicon

Thin crystalline silicon sheets are drawn out of molten silicon rather than being sawed from an ingot. This method is less expensive and less wasteful to produce silicon. However, the finished product is usually a lower quality material. In some cases, they will have cells of a higher conversion efficiency.

Thin-Film Technologies

This new class of materials allows the production of PV cells that are smaller and more flexible than the delicate silicon wafer technology that has dominated PV cell production in the past. These materials are not crystalline, but amorphous, in structure. This type of PV cell can actually be applied to a variety of materials to make any number of materials that you might use for another purpose—such as glazing for a window, or shingles for a roof. Imagine windows that produce electricity! Materials used for dual purposes (building material and PV cell) are called Building Integrated Photovoltaics (BIPV).

CdTe: Cadmium Telluride

This thin-film technology has higher solar spectrum absorption and lower costs to manufacture. It can have a conversion efficiency of up to 19%. There are concerns about the toxicity and scarcity of chemicals necessary for its production.

CIGS: Copper Indium Gallium Diselenide

The gallium is added to these thin-film cells to increase the energy absorption of the cells, which increases efficiency. This technology, although slightly more complicated, has a similar conversion efficiency of 20%.

� Earth Abundant Materials

Manufacturing PV cells from abundant, low cost resources is a research priority. One of the promising technologies is sulfoselenide or CZTS. The drawback to CZTS is a lower efficiency than other PV cells.

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

Multijunction Technologies

This category actually combines multiple layers of materials that are designed to absorb different wavelengths of solar energy— improving the efficiency of the cell by combining the output of the various layers. Multijunction cells are a high-cost PV technology, but can reach efficiencies of over 50 percent.

Image courtesy of Martin Grünvogel

The Schapfen Mill Tower is a flour mill in Germany. The southern facade is faced with 1,300 thin-film solar modules.

Dye Sensitized Solar Cells

This organic-inorganic hybrid technology shows promise to be a very low cost technology. Using a small-molecule dye that absorbs photons, an acceping material such as zinc ozide, and an electrolyte, this technology is easy to manufacture from abundant materials. Research continues to improve durability and efficiency.

Transparent Luminescent Solar Concentrators

In 2014, researchers at Michigan State University developed a material that absorbs nonvisible UV and infrared light, and emits and directs the energy as a different wavelength of near-infrared light. At the edge of the transparent material are thin photovoltaic cells, which use the near-infrared light to generate electricity. Currently the conversion efficiency is around one percent, but developers hope to reach seven percent. This technology is still in the research and development stage, but it could lead to windows and cell phone screens that generate electricity from sunlight. ©2026 The NEED Project

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Organic Photovoltaic Cells

Perovskites

A perovskite is a substance with the same crystalline structure as calcium titanium oxide, with the generalized formula ABX3. A and B represent positive ions, and X represents a negative ion. Perovskites are optically active and because they can be composed of a wide variety of elements, they can be fine-tuned to interact with specific wavelengths of light. Researchers have achieved conversion efficiencies of up to 25 percent in pure perovskite photovoltaics, and combined with silicon the maximum efficiency is almost 30 percent.

PEROVSKITE STRUCTURE

Imagine you are designing a residential, multi-family building. You want it to look good, but you also want it to be energy efficient. How can you keep the energy use of several residences under control, use renewable energy, and maintain a certain aesthetic? Organic photovoltaics might be the answer in the near future. OPV solar cells are polymer-based and are thin, lightweight, and flexible. Furthermore, they can be manufactured in different colors, so adding them to a building, or incorporating into a newly constructed building, does not necessarily sacrifice any design principles. Instead of a single layer doped with two dopants, as is the case in siliconbased photovoltaics, OPV uses two layers; one is an electron donor layer, and the other is an electron acceptor layer. Solar cells made using OPV currently have conversion efficiencies of around 13 percent, but that number is expected to improve in this rapidlyexpanding area of research.

ORGANIC PHOTOVOLTAIC

Image illustrated by graphic designer Toni Rigolosi

Figure 1 - Perovskite Structure (perovskite_ABO3)

Image Credit: Fraunhofer ISE

Image courtesy of vvoe/Adobe Stock

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Benefits and Limitations of PV Systems Benefits

Limitations

they are safe, clean, and quiet to operate;

PV systems cannot operate all the time;

they are highly reliable; they require virtually no maintenance;

PV systems are not well suited for energy-intensive uses such as heating;

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

grid-connected systems are becoming more economical, but can be expensive to buy and install;

they are flexible and can be expanded to meet increasing electrical needs for homes and businesses;

large amounts of land or space are required for utility or large scale generation; and

they can provide independence from the grid or back-up during outages; and

the process to make PV technologies can have harmful effects on the environment.

PV systems offer many advantages:

There are also some practical limitations to PV systems:

the fuel is renewable, domestically available, and free.

Up On the Roof MUNICH INTERNATIONAL AIRPORT

DISTRIBUTION CENTER IN NEW JERSEY

Image courtesy of BP Solar

Image courtesy of Constellation

In 2002, BP Solar installed a photovoltaic facility on the roof of Terminal 2 of the Munich International Airport in Germany. This facility produces an average of approximately 500,000 kWh a year – equivalent to the electricity needs of around 200 households. The project used otherwise unused space and helps the airport offset its operational costs. High production of energy is guaranteed even in winter through the use of polycrystalline silicon cells and the optimal alignment of the solar modules at a 20 degree angle facing south. Germany is a global leader in PV generation because of projects like this. However, many airports and businesses across the United States and the globe have taken on similar projects. U.S. companies take the opportunity for similar solar installations. On what was once a Toys “R” Us warehouse, Constellation Energy installed over 37,000 thin-film solar panels on the roof of the Flanders, New Jersey, distribution center. This rooftop installation has a generating capacity of 5.38 MW and can help the tenants of the facility offset over 60 percent of their annual electricity needs. Stadiums, businesses, warehouses, and airports are becoming prime locations for solar installations like these. Companies can help reduce their long-term operating costs while reducing their environmental impact.

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Careers in the Solar Energy Industry As is the case with many industries, the solar energy industry employs a wide variety of people with many different career paths and educational backgrounds. The list below is a sample of some representative careers and a brief description of each.

DRONE

Accountant All organizations need someone to keep track of the finances. School districts, businesses, colleges and universities, hospitals, and governments will typically have at least one accountant managing all income and payments. Accountants prepare and examine financial records, gather documents for financial audits, track incoming and outgoing funds, and make sure taxes are paid properly. Every business, government entity, or organization that handles money in any way utilizes the services of an accountant if they don’t have one or more on staff. Most accountants have a bachelor’s degree in accounting or a closely related field. A Certified Public Accountant (CPA) is one certification that accountants may earn, but it is not required. A CPA must pass an exam and have one or two years of relevant work experience.

Customer Service Representative If you have ever needed to call a company with a question or a problem, you’ve interacted with a customer service representative (CSR). This person’s responsibilities include solving problems, answering questions, and calming upset customers. They must be patient and professional, be good verbal communicators, know how to find answers quickly, and have good problem-solving skills. In the solar energy industry, customer service representatives may answer questions about solar systems or record customer information for referral to an engineer, marketing specialist, or installer. To become a customer service representative, you will need a high school diploma and will undergo on-the-job training. Excellent communication skills are a must, and being able to work with computers is a plus. A CSR often remains seated at a workstation for the duration of their shift. A good CSR can rise to a supervisory position or move into a researchtype position where more complicated situations needing more time are resolved.

ELECTRICIAN

Image courtesy of Kadmy/Adobe Stock

Drone Pilot Unmanned aerial vehicles (UAVs), or aircraft with no crew or passengers, are frequently used to perform tasks that are difficult or dangerous for people to do. Commonly referred to as drones, UAVs are small, airborne vehicles that are controlled remotely by a person. Like a helicopter, they can hover or fly in almost any direction. Drone pilots must be able to safely operate a drone while adhering to regulations and operating requirements governing their use. In the solar energy industry, drones are used to inspect large solar installations or rooftop systems for physical signs of damage or disrepair. Becoming a drone pilot does not require a specific educational background but does typically involve special training through an accredited institution and passing tests for certification through the Federal Aviation Administration. Being a certified drone pilot while working in the energy industry can keep workers very busy.

Electrician Because electricity can be deadly, proper knowledge of how electrical systems are wired and installed is needed to stay safe. Electricians are people who know how to be safe and how to correctly install or repair high voltage (transmission and distribution) or low-voltage (inside a building) systems. Most electrician programs are apprenticeships, and many are paid positions meaning the apprentice earns a paycheck while learning. Electricians may specialize in areas like utilities, controls, construction, or renewable energy by earning additional certifications beyond their apprenticeship and license. Electrician apprenticeships require a high school diploma and other qualifications like physical capability or prohibited substance testing. They have to haul heavy materials and tools to their worksite and need to be in good physical condition. Electricians have to strictly follow safety standards, and are therefore trained to work safely with electricity and in high places. Depending on the job, electricians may work indoors on a construction site or outdoors on electrical lines.

Image courtesy of David Fuentes/Adobe Stock

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Energy Auditor

Load Forecaster

Energy auditors check buildings for energy use. They inspect things like temperature, humidity, light levels, air flow, and indoor quality while checking equipment, doors, windows, plumbing, and attic spaces for proper functioning and insulation. They collect data about how a building is using energy and report their findings along with recommendations to save energy. One suggestion an auditor may make is to add a solar system to reduce electricity costs or fossil fuel consumption. Some auditor jobs are entry-level and trained on-thejob by utility companies to work with their customers at home. A Certified Energy Auditor must have at least a bachelor’s degree and three years’ work experience. Auditors have to be physically able to climb stairs and ladders and potentially able to fit into tight spaces such as crawl spaces or mechanical rooms.

Suppose you’re in charge of an electric utility. You need to provide enough power to your customers but don’t want to waste energy. How do you know the amount of electricity to put on the grid? Load forecasters predict how much electricity people will use at different times so power companies can generate the right amount of energy. They analyze weather patterns, historical energy use, and market trends to help balance electricity supply and demand. A person needs a bachelor’s degree in engineering, mathematics, economics, or meteorology to work in this field. Load forecasters work in offices using computers and data analysis tools, and they often collaborate with utility companies and energy traders. Strong math skills and attention to detail are important for ensuring a steady power supply while avoiding blackouts or energy shortages.

STUDENTS PARTICIPATING IN AN ENERGY AUDIT

Mechanical Engineer Mechanical engineers design and develop machines, tools, and mechanical systems, including engines, vehicles, robots, and manufacturing equipment. They use physics and math to improve the performance and efficiency of mechanical devices. To work as a mechanical engineer, a person needs a bachelor’s degree in mechanical engineering, and some earn certifications in specialties like aerospace, robotics, or energy systems. Mechanical engineers work in offices designing products, in laboratories testing prototypes, and in factories overseeing production. They need problem-solving skills, creativity, and a strong understanding of physics to develop innovative solutions.

Meteorologist

Image courtesy of NEED

Energy Trader Energy traders buy and sell electricity, natural gas, and other energy sources to make sure homes and businesses have power when they need it. They monitor energy prices, weather patterns, and supply levels to decide when to buy or sell. Most energy traders have a bachelor’s degree in business, finance, or economics and need to understand how energy markets work. They work in offices with computers and data screens, often in fast-paced environments where quick decisions are important. Energy traders must have strong math skills, attention to detail, and the ability to work under pressure as they manage energy deals that can be worth millions of dollars.

Meteorologists study the atmosphere and weather patterns to make forecasts and understand climate changes. Some meteorologists focus on severe weather like hurricanes and tornadoes, while others work in broadcasting, aviation, or environmental research. A person needs a bachelor’s degree in meteorology, atmospheric science, or a related field to enter this career. Meteorologists work in offices analyzing weather models, in television studios presenting forecasts, or in the field gathering climate data. They need a strong understanding of math and physics as well as strong computer, and communication skills to interpret weather data and explain it clearly to the public or other professionals.

Renewable Energy Engineer Renewable energy engineers design and develop systems that generate power from renewable sources like wind, solar, hydropower, and biofuels. They work to improve efficiency, integrate renewable energy into the grid, and create sustainable energy solutions. A person needs a bachelor’s degree in renewable energy, electrical engineering, or mechanical engineering to work in this field. Renewable energy engineers work in offices, laboratories, and field sites where energy projects are being built. Strong problem-solving skills and knowledge of energy technology are essential for creating a cleaner future.

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Solar Installer

SOLAR INSTALLER

Any solar system with solar panels and related equipment, whether large or small, needs to be installed properly; this is the job of a solar installer. Photovoltaic systems are designed specifically for the location where they are being installed, whether residential, commercial, or utility-scale. The racking, wiring, and special equipment like inverters and charge controllers that go along with the solar panels themselves are all things a solar installer needs to know. They spend time in an office designing the system, and then go to the location where the system will be installed and do the work. Solar installers are often licensed electricians with additional certifications in solar systems. Some solar system companies will train high school graduates in-house to be assistants; someone who designs, sites, and installs a solar system will have completed several years of education after high school. That education can be from an apprenticeship or provided at a community or technical college.

Solar Marketing Specialist Solar marketing specialists promote solar energy products and services to homeowners, businesses, and communities. They develop advertising campaigns, manage social media, and educate potential customers on the benefits of solar power. A person can enter this field with a background in marketing, communications, or environmental studies, often with a bachelor’s degree. Solar marketing specialists work in offices, attend industry events, and sometimes visit project sites. They need creativity, communication skills, and knowledge of renewable energy to effectively connect with customers and expand the use of solar power.

Surveyor Surveyors measure land and create maps used for construction, property boundaries, and infrastructure projects like pipelines. In the solar energy industry, they will mark the boundaries of large solar installations and leave stakes showing important locations. Surveyors use specialized tools like GPS and laser equipment to collect accurate land measurements. A person needs an associate or bachelor’s degree in surveying or a related field to enter this career, along with state licensing. Surveyors work outdoors in all types of weather and spend time in offices analyzing data and creating reports. They need strong attention to detail, mathematical skills, and the ability to work with technology to provide precise measurements for engineers and developers.

Image courtesy of nuiiko/Adobe Stock

Transmission System Operator Transmission system operators control the high-voltage power grid, ensuring electricity flows safely and efficiently from power plants to homes and businesses. They monitor energy demand, adjust power generation, and respond to system disturbances to prevent outages. A person typically needs an associate or bachelor’s degree in electrical engineering, energy management, or a related field, along with specialized training and certification. Transmission system operators work in control centers and must stay alert during long shifts. They need strong decision-making, problem-solving, and technical skills to manage the electrical grid in real time.

Welder Welders use heat and pressure to join metal parts in industries like construction, manufacturing, and energy. They work on everything from pipelines and buildings to power plants and solar racking systems. A person can enter this career with a high school diploma and training from a trade school, apprenticeship, or on-the-job experience. Welders work in workshops, factories, and outdoor job sites, sometimes in extreme weather conditions. They need good hand-eye coordination, attention to detail, and knowledge of different welding techniques to create strong and precise metal structures.

WELDER

SURVEYOR

Image courtesy of Caitlin/Adobe Stock

Image courtesy of Makeev Petr/Adobe Stock

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Solar Industry Career Profile Peyton Arkema

ASSISTANT PROJECT MANAGER, SOLAR DIVISION, NORTHEAST CONSTRUCTION, INC.

Q: What does an Assistant Project Manager do? A: Most of the time, I’m involved in multiple projects that are each in a different stage of construction, so my week often varies. I visit active construction sites to coordinate activities, meet with inspectors, handle material deliveries, and report the progress of construction. I also visit potential sites for future solar installations and use software to design solar arrays that could be built on a particular site. If an installation requires minor maintenance or repairs, I travel to the site and perform those as well. Although it can be busy with traveling, I really enjoy my job and have a lot of fun. Q: How did you train for your current position? A: While a student at Virginia Polytechnic Institute and State University (Virginia Tech) I majored in agribusiness management. I then worked at an agronomy lab as an analyst. Because of my interest in construction I was hired as a survey crew member and briefly was a designer. My interest in renewable energy, particularly solar, grew and I was fortunate enough to find my current position in NCI’s solar division. Although my job at NCI does not align very closely with my college major, I frequently use what I learned in school such as principles of management, economics, and accounting. Q: What special skills or certifications do you need to do your job? A: Besides being interested in construction, I love the outdoors and have a deep interest in renewable energy. I learn best hands-on and enjoy seeing the entire construction process from start to finish. I currently hold Occupational safety and Health Administrators (OSHA) 30 and American Red Cross First Aid and CPR certifications, which are very important in the construction industry. Safety is the top priority on a job site. Many people in the solar industry obtain North American Board of Certified Energy Practitioners (NABCEP) certifications. I have the PV Associate certification and am working toward others. NABCEP certifications are widely recognized and respected in the renewable energy industry. Anyone who wants to work in renewable energy should obtain NABCEP certifications. Q: If a student were interested in project management, what advice would you give? A: The renewable energy industry employs a wide variety of people in many different jobs. Pursue your passion, whether it’s in sales, engineering, technology, construction, education, or many others. If you do, you’ll love what you do. Anyone seeking to get into construction project management could major in construction management at two- and four-year colleges. Some people who have engineering degrees also go into construction project management.

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Review Questions 1.

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

Define renewable energy. Explain why solar energy is considered renewable.

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

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

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

How do new thin-film technologies compare to conventional PV cells?

Explain briefly how a PV cell converts radiant energy into electricity.

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

Define current and voltage and give the unit used to measure each.

10. Which area of the United States would be most advantageous for installing a utility-scale solar system? Use evidence in the text to support your answer.

11. Are photovoltaic systems better or worse for the environment when compared to a thermal power plant using natural gas as the fuel? Justify your answer with evidence from the text.

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Digital Multimeter DISPLAY

V ---

DC VOLTAGE

1000

OFF

200

2000 µ

200 m

20 m

2000 K

200

RESISTANCE

200K B

B E

10 20K

NPN PNP

AC VOLTAGE

200µ

20 2000 m

ROTARY SWITCH

750

200

Ω

hFE 2000

DC CURRENT

200

DIGITAL MULTIMETER

A ---

10A max unfused

10ADC VΩmA 750VAC

10A JACK FOR RED (NOT USED)

1000VDC 200m A max

VΩmA JACK FOR RED

COM

500V max

COM JACK FOR BLACK

Directions DC Voltage (

)

1. Connect RED lead to VΩmA jack and BLACK to COM. 2. Set ROTARY 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 ROTARY SWITCH to lower settings until a satisfactory reading is obtained. 5. With the solar modules or array, the 20 DCV setting usually provides the best reading.

DC Current (

Set up

)

1. Connect RED lead to VΩmA jack and BLACK to COM. 2. Set ROTARY 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). 4. With the solar modules or array, the 20mA DC setting usually provides the best reading.

Reading

YOUR MULTIMETER MIGHT BE SLIGHTLY DIFFERENT FROM THE ONE SHOWN. BEFORE USING THE MULTIMETER READ THE OPERATOR’S INSTRUCTION MANUAL INCLUDED IN THE BOX FOR SAFETY INFORMATION AND COMPLETE OPERATING INSTRUCTIONS.

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Simple Solar Circuit & Background A circuit is a pathway for electricity to travel. A simple circuit just has a power source and a load, or device using the power (such as an LED). This activity is designed to introduce you to a simple circuit made with a solar panel acting as the power source. By connecting it, an LED, and a digital multimeter together, you can learn how some factors affect the panel’s electrical output.

? Question  What factors affect a solar panel’s output?

 Hypothesis Develop a hypothesis to address the question.

 Materials Bright light source PV panel 1 Digital multimeter 1 LED 3 Alligator clips Tissue or translucent paper Cardboard or cardstock

Procedure 1.

Plug the red multimeter lead into the port labeled “VΩmA” and the black lead into the port labeled “COM”.

Connect one alligator clip to the red lead and the other end of the alligator clip to the red wire on the solar panel.

Connect a second alligator clip to the black wire on the solar panel and the other end to the short end of the LED.

Connect the third alligator clip to the long end of the LED and the other end to the black lead of the digital multimeter.

Turn the digital multimeter on to measure 2000 microamps (µA) DC.

Turn on the solar panel or place it in direct sunlight. If the LED does not light, try switching it around in the circuit, and make sure all of your connections are secure and the meter is switched on.

Observe the reading on the meter. If it shows a “1” at the far left of the display, turn the switch up one click to the next highest scale for DC current.

Observe the brightness of the LED and the reading on the meter. Record observations.

Block part of the panel with cardboard or something opaque. Observe the brightness of the LED and the reading on the meter. Record observations.

10. Block the entire panel with something opaque. Observe the brightness of the LED and the reading on the meter. Record observations. 11. Repeat steps 9 and 10 using a translucent material. Record observations. 12. Tilt the panel slowly away from the light source, observing the meter reading as well as the LED brightness. Record observations. 13. Disassemble your circuit. Turn off the multimeter and return materials according to your teacher’s instructions.

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 Data & Observations CONDITION

DIGITAL MULTIMETER READING

BRIGHTNESS OF LED

Flat, unshaded, in direct light Partially shaded by opaque material Completely shaded by opaque material Partially shaded by translucent material Completely shaded by opaque material Tilted halfway away from light source Tilted fully away from light source

 Conclusion 1.

Under what circumstances did your solar panel produce the most current? Cite data from your investigation to support your answer.

If you placed a solar system where it would be partially shaded, what would the result be? Use data from your investigation to support your answer.

What does the translucent material simulate? What happens to solar system output on cloudy or rainy days? Use data from your investigation to support your answer.

When installing a solar system, how should the panels be tilted? Use data from your investigation to support your answer.

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Breadboards and How to Use Them What is a Breadboard?

Diagram 1

a b c d e 1 2

Breadboards got their name in the 1970s when engineers and electronics enthusiasts needed a way to easily connect and rearrange electrical components without soldering, so they could be disconnected and rearranged. The first breadboards were made from wooden cutting boards, most often used for bread. Screws or nails were inserted into the boards to create conductive points for wires to wrap and connect.

3 4 5

Modern breadboards conceal the conductive connections inside of a plastic casing. The holes, (also called ports), on the breadboard use friction to hold components in place, connecting them below in specific ways. Breadboards can vary in shape and size, but generally all include the following features and labels.

2 Terminal 3 Strips 4 5 6 7

Simple20 Circuit21 22

Power (+) Rail

Running the length of the breadboard are the power (+) and ground (-) rails. These rails are connected vertically in single columns and align with anode (+) and cathode (-) terminals of the circuit and power source, such as a battery or solar panel. For example, the column of holes in the power (+) rail are connected to one another, but they are not connected to any other holes in the breadboard. Power (+) and ground (-) rails on opposite sides of the board are not connected. These rails allow you to power multiple points within the circuit and even connect multiple power sources. They often follow a red (+)/ black (-) color configuration, like most electrical components.

Power and Ground Rails

f g h

Bridge

Ground (-) Rail

A breadboard is a small, usually plastic, flat box with holes organized into grids and labeled with letters and numbers. Breadboards are used to easily make connections between electronic components while exploring or designing circuits.

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Solar Panel

Terminal Strips The bulk of the breadboard is made up of a grid of holes (ports) arranged in numbered rows and lettered columns. Each of these horizontal rows of holes is called a terminal strip. Mounted inside the breadboard are strips of metal that connect each set of holes in each terminal strip. The terminal strips are not connected to one another, nor to the power (+) and ground (-) rails. There is a gap between the two sets of terminal strips, called the bridge. The terminal strips on either side of the bridge are not connected. For example, any component that is connected to hole 16e is also connected to holes 16a-16d, but not 16f-j. To connect between rails and terminal strips, one needs to use electrical components and/or jumper wires to build a circuit.

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Connecting Components to Make a Circuit

Problem Solving

To build a powered circuit that connects a power source to electrical components, you must build a path from a power (+) rail, through the terminal strips, that ends at a ground (-) rail. You can connect to any power (+) rail or ground (-) rail, as long as your power source (or solar panel) are connected to the same rails. Any connecting components must overlap on the same terminal strip. Electrical components must connect between rails or separate terminal strips. If the component’s anode/cathode are connected to the same terminal strip, the circuit will short circuit and bypass the component.

To check that your circuit is connected, run your finger or pencil from the power (+) rail to the ground (-) rail through the whole circuit path. If the circuit does not light up:

The Simple Circuit example in Diagram 1 highlights a common way to wire an LED and resistor in a circuit powered by a solar panel. The power source, a solar panel, is connected via the power (+) rail and ground (-) rail. The power (+) rail is then connected to a terminal strip by a resistor, which slows the current in the circuit to prevent the LED from burning out if the power source should provide too much current. The LED’s long leg (anode) is connected to the same terminal strip as the resistor, connecting the LED to the power (+) rail. The LED’s shorter leg (cathode) is connected to a separate terminal strip. This separate terminal strip is connected to the ground (-) rail through a wire. Circuits will vary, but this example starts at the power (+) rail and ends at the ground (-) rail through one continuous path. Each component bridges between a rail or a terminal strip, with the terminal strips connecting the components.

Resistors do not have direction and can be connected in the circuit at any point.

Circuit Examples The top two circuits in Diagram 2 are examples of circuits connected in series. In each example, the circuit is connected to a power (+) rail and ground (-) rail that is connected to a solar panel. There is a single path between the rails, connected by electrical components, wires, and terminal strips. Example A is powered by the left rails via Solar Panel 1 and Example B is powered by Solar Panel 2 via rails on opposite sides of the breadboard. Circuits will vary, but both examples start at a power (+) rail and end at a ground (-) rail. You can follow a single path as components connect between terminal strips and rails. The LED’s long leg is always aimed toward the power (+) rail, and the circuit always includes a resistor to limit the current.

Check that the power (+) and ground (-) rail are connected to both the circuit and solar panel (power source). LEDs have 2 legs. The long anode (+) should connect to the power (+) rail. The short cathode (-) should connect to the ground (-) rail).

Electrical components should only connect between rails and terminal strips. They should never be connected to the same terminal strip. Terminal strips should be used like wires to connect between components. If a component is connected to the same terminal strip in 2 places, the component will be bypassed, and the circuit will be shorted.

Diagram 2

Solar Panel 1 +

a b c d e

f g h

9 10

13 14

18 19 20

22 Parallel 23 Circuit 24

22 23

Series 7 8 Circuit 9

j 1

The circuits at the bottom of Diagram 2 are examples of circuits connected in parallel. The current creates a single powered and ground path, connected by LEDs that create multiple paths through the circuit. Example C is powered by the left rails via Solar Panel 1 and Example D is powered by Solar Panel 2 via rails on opposite sides. Circuits will vary, but both examples start at a power (+) rail and end at a ground (-) rail. You can follow the paths as components connect between terminal strips and rails. The LED’s long leg is always aimed toward the power (+) rail, and the circuit always includes a resistor to limit the current. The LEDs are parallel to one another in both examples.

30 a b c d e

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Solar Panel 2 26

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Connecting and Using a Solar Panel Cells, Modules, and Arrays The image to the right is representative of the PV panel included in the curriculum kit. The term “array” represents the whole PV panel, which is made of two modules. Each module is made of multiple cells. Both modules each have their own set of red (+) anode and black (-) cathode wires. Designate the left as Module 1, and the right as Module 2 for your work with this kit.

Voltage is always measured in parallel to the solar panel and a load, like the resistors and LEDs in the circuit. The breadboard’s power (+) rail and ground(-) rail make a parallel path with your circuit. To measure voltage, connect a multimeter’s black probe to the breadboard’s ground (-) rail and the red probe to the breadboard’s power (+) rail. The schematic diagram to the right shows the multimeter measuring voltage in its own path compared to the LEDs and resistors.

Direction Matters A photovoltaic cell is like a really flat battery. It produces electric current that flows in only one direction, known as a direct current (DC), just like a battery. The direction of this current, from anode (red wire) to cathode (black wire), describes the polarity of the PV panel.

Module 1

Module 2

Light emitting diodes, or LEDs, only function when the current flows in one direction (see How Light Emitting Diodes (LEDs) Work, on page 28). If an LED’s polarity does not match the polarity of the solar panel used to power it, it will not light up. The long leg of the LED should always connect to the power (+) rail and the short leg of the LED should connect to the ground (-) rail of the breadboard. If an LED does not light up, flip the LED around.

Connecting a Solar Panel in Series Series circuits provide only one pathway for electricity to flow, with all components in a single path or loop. To wire a solar panel in series, you need to create a single path through both Module 1 and Module 2, via their red (+) and black (-) wires. Connect Module 1’s red (+) wire to Module 2’s black (-) wire. The remaining wires (Module 1’s black (-) wire and Module 2’s red (+) wire) connect to the breadboard to provide power the circuit. Most activities in this guide will utilize the series orientation for the PV panel. Current is always measured in series in a solar panel, through the load of the resistors and LEDs within the circuit. To measure current, you must connect a digital multimeter directly into the path of the circuit. This requires you to disconnect a component from the power (+) rail and bridge that gap with the multimeter. The schematic diagram to the right shows the solar panel, LEDs, resistors, and multimeter measuring current in a single series path.

Connecting a Solar Panel in Parallel Parallel circuits have two or more pathways for electricity to flow. The circuit splits into branches, giving the current options as it flows through the electrical components. All branches should meet together at each end. To wire the PV panel in parallel, connect both Module 1 and Module 2’s red (+) wires to the power (+) rail of the breadboard. Connect both Module 1 and Module 2’s black (-) wire to the ground (-) rail of the breadboard.

LED SOLAR PANEL

LED

RESISTOR

100Ω

RESISTOR

68Ω

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MULTIMETER MEASURING VOLTAGE

Circuit Schematic

MULTIMETER MEASURING CURRENT

How Light Emitting Diodes (LEDs) Work When you were reading about solar cells and learning how radiant energy is transformed into electrical energy inside of one, you saw that electrons are able to absorb energy. However, they do not want to stay energized, or in an energized state, for long. We use the energy they absorb from sunlight to do useful work, like turn a motor or light a flashlight. A light emitting diode, or LED, could be considered a sort of “solar cell in reverse.” Like a solar cell, they are made of semiconductors and are doped. However, instead of transforming radiant energy into electrical energy, an LED transforms electrical energy into radiant energy – light – that we use. LED lighting is the most efficient lighting available on the market today, producing 80-100 lumens of light for every watt of electricity used. Compared to old-fashioned incandescent lights, at 12-15 lumens/watt, you can see why LEDs are rapidly becoming the most common form of lighting used in homes and many commercial buildings.

How Light Emitting Diodes Work 1. Diodes are made of semiconductors and conducting materials that need to be added to the semiconductor. In an LED the most common conductor added is aluminum-gallium-arsenide (AlGaAs). The AlGaAs is “doped” by adding small amounts of another material. One material will have more valence electrons than AlGaAs, and another doping material will have fewer electrons. The two doped materials are put together in a crystal. The material with more electrons is the “n-type” (n for negative) and the material with fewer electrons is the “p-type” (p for positive). When these materials are sandwiched together, the electrons move to balance themselves out. The area between the materials, called the p-n junction, is also called the “depletion zone.” 2. Connecting a power source to the diode, such as a battery, provides electric current that carries electrical energy. The electrons in the n-type are repelled by the electric current, and move through the depletion zone to the p-type. They are energized, and will want to return to their original, unenergized state in the n-type.

Inside an LED emitted light epoxy case

reflecting cup photons p-type layer p-n type junction n-type layer cathode lead

anode lead

How Light Emitting Diodes Work p-type

n-type

Current Flow

n-type

p-type

Battery Current Flow

p-type

n-type

3. When the electrons move back through the depletion zone to the n-type, they release energy as light. This is the light that we see from the LED. This process continues over and over again–electrons absorbing energy, moving, then moving back and releasing the energy, until the power supply is disconnected or depleted. 4. Connecting the power supply in the wrong orientation does not allow the LED to work. Instead, it merely increases the size of the depletion zone. Therefore, it is important that LEDs be wired to their power supply in the correct orientation.

LED chip

Battery

No Current Flows

n-type

p-type Increased Depletion Zone

Battery

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Planning Your Breadboard Circuit The drawing to the right is a schematic diagram that represents the circuit you will be powering with photovoltaic (PV) cells. These components represent the load in your solar panel system, which allow you to measure voltage and current in the circuit.

LED

Your circuit must include two LEDs and two resistors, wired in a series configuration. The two resistors (100Ω and 68 Ω) are represented by zigzag lines. The two LEDs are represented by triangles with two arrows. The direction of the arrow indicates the direction of the current as it flows from the power (+) rail to the ground (-) rail.

SOLAR PANEL

Schematic diagrams are a representation of a physical circuit, but you still need to plan how the schematic fits onto a breadboard. Draw the locations and connecting points between all four components on the breadboard below. Each component stretches six ports vertically, horizontally, or on an angle amongst the terminal strips. The center and rail bridge gaps count as two ports. Your breadboard plan should include the following:

LED

RESISTOR

100Ω

Electrical components represented by the proper schematic symbols. RESISTOR

Connected ports represented by both a circled port and a line connecting the component to the port.

68Ω

The circuit starting on a (+) power rail and ending on a (-) ground rail on the opposite side.

A layout that follows the breadboard’s internal wiring organization rules.

MULTIMETER MEASURING CURRENT

Your Breadboard Circuit Plan +

a b c d e

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j 1

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Build & Test Your Circuit: Parallel ? Questions  Does your breadboard circuit layout work to provide power from the solar panel to the bulbs? How will wiring the components in parallel compare to wiring them in series?

 Hypothesis Develop a hypothesis to address the questions.

 Materials PV panel 2 LEDs 100Ω Resistor 68Ω Resistor Breadboard Light source

Procedure 1.

Build the circuit that you planned in the Planning Your Breadboard Circuit activity.

Your solar panel has two modules made of PV cells. Each has its own red (+) anode and black (-) cathode wire. Make sure to double check that you do not cross the wires as you power your circuit.

Place both red (+) anode wires from Module #1 and Module #2 into the (+) power rail that is connected to your circuit.

Place both black (-) cathode wires from Module #1 and Module #2 into the (-) ground rail that is connected to your circuit.

Hold your PV panel in the light. If your circuit’s LEDs do not light, you may need to problem solve. Check the connections, amount of sunlight, and the polarization (direction) of the LEDs themselves.

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Build & Test Your Circuit: Series ? Questions  Does your breadboard circuit layout work to provide power from the solar panel to the bulbs? How will wiring the components in parallel compare to wiring them in series?

 Hypothesis Develop a hypothesis to address the questions.

 Materials PV panel 2 LEDs 100Ω Resistor 68Ω Resistor Breadboard Light source

Procedure 1.

Build the circuit that you planned in the Planning Your Breadboard Circuit activity.

Your solar panel has two modules made from individual photovoltaic cells. Each has its own red (+) anode and black (-) cathode wire. Make sure to double check that you do not cross the wires as you power your circuit.

Place the red (+) anode wire from Module #1 into the (+) power rail that is connected to your circuit.

Using any terminal strip, insert the black (-) cathode from Module #1.

Connect the red (+) anode of Module #2 to the same terminal strip so that it is connected to Module #1’s black (-) cathode.

Place the black (-) cathode wire from Module #2 into the (-) ground rail that is connected to your circuit.

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Set Up Multimeter 1: Voltage & Background In a photovoltaic system, voltage is measured in parallel because it represents the potential difference, or “pressure,” between two points in the circuit. Connecting a voltmeter or multimeter in parallel allows it to measure the voltage across a component without disrupting the flow of current through it. When wired in parallel, the multimeter is connected to the circuit and the solar panel itself. The voltmeter or multimeter itself has a very high internal resistance, so it draws minimal current, ensuring it doesn’t significantly alter the circuit’s behavior, and provides an accurate reading. Connecting the multimeter to the same power (+) rail and ground (-) rail is the simplest way to connect the multimeter in parallel.

 Materials PV panel 2 LEDs 100Ω Resistor 68Ω Resistor Breadboard Light source 1 Digital multimeter 2 Alligator clip jumper wires

Figure 1: Close-up view of breadboard circuit with multimeter connections.

Procedure 1.

Clip an alligator jumper wire to the black (-) probe of the multimeter by using the alligator clip end of the wire and clipping it onto the conductive surface of the black (-) probe.

Plug the jumper wire’s prong end (male end) into a port on the ground (-) rail of the breadboard. This should connect the multimeter’s black (-) probe to your circuit’s ground (-) rail.

Clip an alligator jumper wire to the red (+) probe of the multimeter by using the alligator clip end of the wire and clipping it onto the conductive surface of the red (+) probe.

Plug the jumper wire’s prong end (male end) into a port on the power (+) rail of the breadboard. This should connect the multimeter’s red (+) probe to your circuit’s power (+) rail.

Ensure the multimeter’s probes are in the correct banana jacks and turn on the multimeter. Follow the settings guidelines below.

Hold your PV panel in the light. Measure the voltage across the circuit when the solar panel is covered and uncovered. Record your data in the table below. If you are unable to read accurate measurements, check your connections.

Multimeter Settings Black banana jack: COM Port Red banana jack: VΩmA Voltage range: 2-20 Volts

 Data COVERED

UNCOVERED

VOLTAGE

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Set Up Multimeter 2: Current & Background In a photovoltaic system, current is measured in series because the digital multimeter must be placed directly in the path of the current you want to measure. Essentially, to measure the current in a solar panel system the multimeter must be part of the circuit itself. You should be able to track the path of electricity’s flow from the power (+) rail to the ground (-) rail via the multimeter and circuit. Digital multimeters have a very low internal resistance to ensure that they don’t significantly change the current in the circuit when they are connected. The most effective way to connect your circuit in series is to remove the component connected to power (+) rail, and reconnect it to the power (+) rail via the multimeter.

 Materials PV panel 2 LEDs

100Ω Resistor 68Ω Resistor

Breadboard Light source

2 Digital multimeters 4 Alligator clip jumper wires

Procedure 1.

Disconnect the component that is connected to the power (+) rail from the power (+) rail. The other end of the component should still be connected to the circuit.

Connect the disconnected end of the component into an unused terminal strip.

Clip an alligator jumper wire to the black (-) probe of the multimeter by using the alligator clip end of the wire and clipping it onto the conductive surface of the black (-) probe.

Plug the jumper wire’s prong end (male end) into a port on the same terminal strip as the disconnected component. This should connect the multimeter’s black (-) probe to your circuit.

Clip an alligator jumper wire to the red (+) probe of the multimeter by using the alligator clip end of the wire and clipping it onto the conductive surface of the red (+) probe.

Plug the jumper wire’s prong end (male end) into a port on the power (+) rail of the breadboard. This will complete the connection from the power (+) rail, through the multimeter, and back into the circuit.

See the image and Figure 1 below to ensure your circuit is set up correctly. Ensure the multimeters’ probes are properly connected to the jacks and turn on the multimeters. Follow the settings guidelines below.

Hold your PV panel in the light. Measure the current through the circuit when the solar panel is covered and uncovered. Record your data in the table below. If you are unable to read accurate measurements, check your connections.

Multimeter Settings

Figure 1: Three Step Diagram STEP 1 Complete the circuit so that it connects from one power (+) rail to a ground (-) rail.

Black banana jack: COM Port Red banana jack: VΩmA Voltage range: 2-20 Volts

STEP 2 Turn the electrical component that is connected to the power (+) rail 90˚. STEP 3 Connect the multimeter’s red probe to the power (+) rail and black probe to the ground (-) rail. Once the 2nd multimeter is turned on, the circuit will turn back on.

 Data COVERED

UNCOVERED

VOLTAGE

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PV Variables: Verify Solar Module Similarity ? Question  Should similar PV modules within an array (panel) vary significantly in electrical output under similar conditions?

 Hypothesis Develop a hypothesis to address the question.

 Materials Bright light source PV panel 2 Digital Multimeters 2 LEDs 100Ω Resistor 68Ω Resistor Breadboard 6 Alligator clip jumper wires

Procedure 1.

Continue with your layout from the multimeter activities.

Turn the current meter on to measure 20 mA DC. Turn the voltage meter on to measure 20 V DC.

Turn on your light source and shine it on the PV panel. If everything is connected properly, the LEDs should light, even a small amount, and you should be able to read current and voltage values.

If the LEDs do not light, reverse the current flow by reversing the connection points of the black and red wires from the PV panel in the breadboard. If either meter is displaying a negative value, reverse the connection points of the leads in the breadboard. If the LEDs still do not light, continue checking connections, insert points on the breadboard, and direction of the LEDs with respect to the solar panel and each other until you have everything properly connected and aligned. The most common problem is having the LEDs and solar panel wired opposite to each other.

Record the current in mA and the voltage in V for side A.

Keeping track of which clip is connected to which wire, disconnect the alligator clips from the red and black wires of Module 1 and connect them to Module 2.

Turn the meters on if necessary, turn on the light source if necessary, and record current and voltage for Module 2.

Turn off the meters and light source, answer the questions in the Conclusion Section, and continue with additional activities according to your teacher’s instructions.

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 Data CURRENT (mA)

VOLTAGE (V)

MODULE 1 MODULE 2

Observations

 Conclusion Were the current and voltage outputs of both modules similar? What else can you conclude about the two modules within the panel?

Were there any other experimental factors that could have influenced your results?

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PV Variables: Light Intensity ? Question  How does light intensity affect the electrical output of a PV panel wired in series?

 Hypothesis Develop a hypothesis to address the question in an “If ___ then ___ because ____” format.

 Materials At least three light sources: bright (high lumen), moderate (medium lumen), and dim (low lumen) PV panel 2 Digital multimeters 2 LEDs 100Ω Resistor 68Ω Resistor Breadboard Ruler 6 Alligator clip jumper wires 1 Allicator clip

Procedure 1.

Continue with the 1 layout from Verify Solar Module Similarity.

Turn the current meter on to measure 20 mA DC. Turn the voltage meter on to measure 20 V DC.

Start with the brightest, or most intense, light source you have. Hold it 5 cm from the panel.

Turn on your light source and shine it on the PV panel. If everything is connected properly, the LEDs should light, even a small amount, and you should be able to read current and voltage values.

Record the current in mA and the voltage in V.

Turn off the light, carefully remove the bright light and replace it with a less bright light, using the lumen rating of the light as your guide.

Holding the light 5 cm from the panel, turn the light on and record current in mA and voltage in V.

Repeat steps 12 and 13 for all remaining light sources.

10. Turn off the meters and light source, answer the questions in the Conclusion and Reflections sections, and continue with additional activities according to your teacher’s instructions. If this is your last activity for the day, disassemble your circuit and return items as instructed by your teacher.

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 Data LIGHT INTENSITY (LUMENS) BRIGHTEST

CURRENT (mA)

VOLTAGE (V)

LUMENS LUMENS LUMENS LUMENS

MOST DIM

LUMENS

 Observations

 Conclusion Will you accept or reject your hypothesis? Use the data you collected to justify your answer.

 Reflections Choose a light source with an intensity you did not use. For example, if your lights were rated for 500, 750, and 1000 lumens, you could choose 600 lumens. What do you predict the current and voltage output of your panel would be if you used this light? How could you figure it out without testing?

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PV Variables: Angle of Incidence ? Question  How does the angle of incidence of the light source affect the electrical output of a PV panel?

 Hypothesis Develop a hypothesis to address the question in an “If ___ then ___ because ____” format.

 Materials Bright light PV panel 2 Digital multimeters 2 LEDs 100Ω Resistor 68Ω Resistor Breadboard 1 Alligator clip 6 Alligator clip jumper wires Protractor Ruler

x˚

Procedure 1. Use the same circuit wiring scheme you used in Light Intensity. 2. Start with the brightest, or most intense, light source you have. Hold it 5 cm from the panel. 3. Using the light source indicated by your teacher, hold it 5 cm from the panel. Have the light shining directly on the panel. This will be an angle of 0°. 4. Turn on the light and record the current in mA and the voltage in V. 5. Using a protractor, tilt the light away from the panel about 15°. 6. Turn on the light and record the current in mA and the voltage in V. 7. Continue tilting the light in 15-degree increments until the light source is perpendicular to the panel. 8. Turn off the meters and light source, answer the questions in the Conclusion and Reflections sections, and continue with additional activities according to your teacher’s instructions. If this is your last activity for the day, disassemble your circuit and return items as instructed by your teacher.

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 Data LIGHT ANGLE

CURRENT (mA)

VOLTAGE (V)

0° 15° 30° 45° 60° 75° Plot your data, with angle on the x-axis, current on the left y-axis, and voltage on the right y-axis.

 Observations

 Conclusion Will you accept or reject your hypothesis? Use the data you collected to justify your answer.

 Reflections What was the most affected by the angle of incidence of the light? Use your data to support your answer.

If the angle of incidence of the light was 25°, what do you predict the current and voltage outputs would be?

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PV Variables: Shading a PV Panel ? Question  How does covering different parts of a PV panel affect its electrical output? How does the opacity of a material covering a PV panel affect its output? How does the amount of the PV panel being covered affect its output?

 Hypothesis Develop a hypothesis to address each question above in an “If ___ then ___ because ____” format.

 Materials Bright light source Pieces of cardboard or thick paper Pieces of tissue paper or another thin, somewhat translucent material PV panel 2 Digital multimeters 2 LEDs 100Ω Resistor 68Ω Resistor Breadboard 1 Alligator clip 6 Alligator clip jumper wires

Procedure 1. Use the same circuit wiring scheme you used in Light Intensity. 2. Hold the light 5 cm from the PV panel and turn it on. Record the current in mA and the voltage in V. 3. Cover about half the PV panel with a piece of cardboard or thick paper, in the horizontal configuration shown in the diagram. Record the current in mA and the voltage in V. 4. Cover about half the PV panel with a piece of cardboard or thick paper in the vertical configuration shown in the diagram. Record the current in mA and the voltage in V. 5. Cover the entire panel with the cardboard. Record the current in mA and the voltage in V. 6. Switch to the tissue paper and repeat steps 3, 4, and 5. 7. Lay a pencil across the panel vertically, horizontally, and diagonally, measuring the current in mA and the voltage in V each time. 8. Turn off the meters and light source, answer the questions in the Conclusion and Reflections sections, and continue with additional activities according to your teacher’s instructions. If this is your last activity for the day, disassemble your circuit and return items as instructed by your teacher.

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 Data MATERIAL

ORIENTATION

CARDBOARD

HORIZONTAL

CARDBOARD

VERTICAL

CARDBOARD

COMPLETELY COVERED

TISSUE PAPER

HORIZONTAL

TISSUE PAPER

VERTICAL

TISSUE PAPER

COMPLETELY COVERED

PENCIL

HORIZONTAL

PENCIL

VERTICAL

PENCIL

DIAGONAL

CURRENT (mA)

VOLTAGE (V)

Observations

 Conclusion Will you accept or reject each your hypotheses? Use the data you collected to justify your answer.

 Reflections Each material was intended to simulate various installation or weather conditions. Identify what the cardboard, tissue paper, and pencil were designed to represent, and explain how each of these real-world scenarios might impact the output of a full-sized residential or commercial solar system. Use your data to support your discussion.

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PV Variables: Surface Temperature ? Question  How does surface temperature affect the electrical output of a PV panel?

 Hypothesis Develop a hypothesis to address the question in an “If ___ then ___ because ____” format.

 Materials Bright light source Ice water bath Watertight, clear plastic bag Hair dryer Thermometer PV panel 2 Digital multimeters 2 LEDs 100Ω Resistor 68Ω Resistor Breadboard Ruler 1 Alligator clip 6 Alligator clip jumper wires

Procedure 1.

Use the same circuit wiring scheme you used in Light Intensity.

Use the thermometer to record the temperature of the room. Record it in the data table.

Slip the PV panel in the plastic bag.

Hold the light 5 cm from the PV panel and turn it on. Record the current in mA and the voltage in V.

Put the bagged panel into the ice water bath. NOTE: Be careful not to get water inside the bag.

Immerse the thermometer in the ice water bath and record the temperature.

Hold the light 5 cm from the water surface and turn it on. Record the current in mA and the voltage in V.

Lay the bagged panel on your lab table. Lay the thermometer beside it.

Turn on the hair dryer and warm the panel and thermometer up until the thermometer reads 50° Celsius.

10. Hold the light 5 cm from the panel and turn it on. Record the current in mA and the voltage in V. 11. Turn off the meters and light source, answer the questions in the Conclusion and Reflections sections, and continue with additional activities according to your teacher’s instructions. If this is your last activity for the day, disassemble your circuit and return items as instructed by your teacher.

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 Data DESCRIPTION

TEMPERATURE (°C )

CURRENT (mA)

VOLTAGE (V)

TABLETOP (ROOM TEMPERATURE) ICE BATH HEATED

Observations

 Conclusion Will you accept or reject your hypothesis? Use the data you collected to justify your answer.

 Reflections Why was it important to keep the plastic bag on the panel for all three temperatures, even though it was really only needed in the ice bath?

Of the three temperatures, which was best for maximizing electrical output? Use the data you collected to support your answer.

What does your data tell you about solar system performance in different seasons or weather conditions?

Considering all of the variables you have tested – light intensity, angle of incidence of light, shading, and temperature – what does the data you collected tell you about how solar systems should be installed?

Keeping all of your collected data in mind, evaluate each of the following conditions or considerations when installing a solar system and rank them 1-9 for impact on electrical output, with 1 being the greatest impact. _____

High smoke from a distant forest fire

_____

Dirt and debris from a local empty field

_____

Installing utility poles next to the system

_____

Temperature outdoors

_____

Planting a tree 10 feet from the system

_____

Thin, wispy clouds

_____

Rainy day

_____

Time on the clock (am / pm)

_____

Snowy day

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A Step Further Solar systems do not have just one panel, nor do they power just one item. Most solar systems consist of multiple panels in an array that are providing electricity for several devices. To successfully complete this extension, you’ll need to combine materials with another group of students. Read the question, and as a group discuss the best way to use your materials to produce the highest current and/or voltage you can. Then develop a procedure for testing your ideas.

? Question  How can multiple PV panels be connected to power multiple loads?

 Hypothesis Develop a hypothesis to address the question in an “If ___ then ___ because ____” format.

 Materials Use the materials provided for your combined lab group. You might not need to use all the materials to test your hypothesis. 1 Bright light source 2 PV panels 4 Digital multimeters 4 LEDs 2 100Ω Resistors

2 68Ω Resistors 2 Breadboards 12 Alligator clip jumper wires Alligator clips

Procedure In the space below, write your procedure:

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Data

 Observations

 Conclusion

 Reflections How is this exercise similar to designing, installing, and powering up a full-scale solar system for a home or commercial building? How is it different?

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Can Solar Energy Meet Your Electricity Demands? 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

What is your daily electricity use in kWh? _____________ kWh

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 hours

How much energy will one 250-watt solar module generate on the average day? 250 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 250-watt solar modules would you need to produce enough electricity for your home? Answer: _______modules

If each module costs $775.00 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).

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

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 the total system cost (Part 3, Step 2) by your annual cost for electricity (Part 4, Step 2B). Answer:_______________ years

Part Five: Reflect 1.

What are the different factors that impact payback period?

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

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

Image Credit: Kristian/Adobe Stock

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U.S. Solar Resource Map Annual Average Solar Concentration

Note: Alaska and Hawaii not shown to scale Data: NREL

5 to 6

4 to 5

3 to 4

Less than 3

LOW

Annual Average Solar Concentration (KILOWATT-HOURS PER SQUARE METER PER DAY) HIGH

More than 6

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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 the cabin has no electricity. Uncle Ed believes in hard work and he’s specified one condition—if you are to take possession of this prime parcel, you must plan and install a PV system to support the following four specifications: 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 Ed’s 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!

Extension When you finish your plan, design a battery system to store the electrical energy generated for use at night or during storms.

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Solar-Powered Cabin Planning Page Description of Modules:

Diagram of Design:

Budget Information:

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Glossary

albedo

the amount of solar energy reflected back from the Earth’s surface; different surfaces have different levels of reflectivity

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 AC

amorphous

lacking shape or form

ampere (A)

a unit of measure for an electric current; the amount of current that flows in a circuit at an electromotive force of one volt and at a resistance of one ohm; abbreviated as amp

array

a systematic arrangement, in rows, of photovoltaic cells

baseload power

the minimum amount of electricity a utility must have available to its customers, at all times

breadboard

a board used to connect electronic components including wires, resistors, loads, and coils

charge controller

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

circuit

a conductor or a system of conductors through which electric current flows

concentrated solar power (CSP)

technologies that focus the energy from the sun onto one smaller area creating high temperatures that can 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 flows in only one direction through a circuit, as from a battery; typically abbreviated as DC

dopant

an element that is inserted into a substance to alter the conductivity or electrical properties

energy efficiency

the ratio of useful energy delivered compared to energy supplied

electric current (I)

the flow 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 a measurement of capacity

gamma rays

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

grid

the layout of an electrical distribution system

Ground (GND)

a common reference point for electrical potential, often the physical earth or a circuit’s zero voltage point

heliostat

a sun-tracking or seeking mirror

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

Law of Conservation of Energy

the law governing energy transformations and thermodynamics; energy may not be created or destroyed, it simply changes form, and thus the sum of all energies in the system remains constant

light emitting diode (LED)

energy saving light bulb that generates light through the use of a semiconductor

load

the power and energy requirements of users on the electric power system in a certain area or the amount of power delivered to a certain point; the amount of power drawn by a device

module

multiple PV cells connected together in larger units

multimeter

an instrument designed to measure electric current, voltage, and usually resistance, typically over several ranges of value.

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n-type silicon

layer of silicon in a solar cell that has been doped with phosphorus to have a negative character and repel electrons

nuclear fusion

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

ohm (Ω)

the unit of resistance to the flow of an electric current

Ohm’s Law

a mathematical relationship between voltage (V), current (I), and resistance (R) in a circuit; Ohm’s Law states the voltage across a load is equal to the current flowing through the load times the resistance of the load (V = I x R)

parallel circuit

an electrical circuit with multiple independent paths for electric current to flow through, allowing the current to divide and flow through different components before recombining

p-type silicon

layer of silicon in a solar cell that has been doped with boron to have a positive character and attract electrons

peak load power

amount of power needed to supply consumers during times of high demand

photons

particles that 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) into electrical energy; another name for a solar cell

photovoltaic effect

creating electric current through exposure of a material to light; excited electrons become free, eventually being converted into electrical 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 (P)

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

secondary source of energy

also known as energy carriers, these sources require another source of energy to be created;electricity is an example of a secondary source of energy

semiconductor

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

series circuit

an electrical circuit where components are connected end-to-end in a single, continuous path, creating one route for current to flow

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 and molecules 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 the formation 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 of one ohm when a current of one ampere flows 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 electrical energy per electron that electrons can acquire and/or give up as they move between the two conductors

watt (W)

a metric unit of power, usually used in electric measurements, which gives the rate at which work is done or energy is used

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