Lab Manual : Do-it-Yourself Solar LED Lantern Kit
Lab Manual : Do-it-Yourself Solar LED Lantern Kit(For use with Sundance Solar item No. 900-10017-35)Welcome to the kit that will help you store sunshine in a jar! You are also helpingthe earth by reusing a glass or plastic jar, which could take hundreds to millions ofyears to decompose if it were thrown away. This solar lantern kit also helps tosupport the creation of solar lanterns to help those who live without electricity(more on that later).Your first task is to find a container with a wide lid, such as a peanut butter ormayonnaise jar. If you want, you could even get more creative: what otherobjects would you want to glow at night? Ask your parents for permission first!The solar lantern you create will charge itself during the day, and will light up atnight. The next day, the lantern will charge itself again. This is because energycan be changed from one form to another. The sun’s energy (which comes fromthe fusion or combining of atoms) releases light energy, which is turned intoelectrical energy in the solar panel. The electrical energy from the solar panel isstored in the batteries in the form of chemical energy. At night, the chemicalenergy in the batteries is changed back into electrical energy, which feeds into theLEDs, causing them to release light energy.DAYTIMENIGHTIMElightSUNSOLAR PANELsunlightBATTERYelectricityLEDelectricity1
Table of ContentsHow it Works: Solar Cells .page 3Intro to Circuits . page 4Giving the LEDs More Power: Adding Solar Panels . .page 6Putting it All Together . .page 7Assembly Instructions and Pictures .page 8Solar Insolation Maps and Recharge Times page 9Challenge: Developing Solar Lanterns for South Africans . page 11Glossary .page 12Solar Jar Light Kit Materials ListIn each of the 15 solar jar kits:1 - 3V 70mA polycrystalline solar panel with wires1 - Circuit board (pcb) with dusk/dawn operation with 2 LED’s1 – Battery holder for 2 AAA batteries2 – AAA NiMH rechargeable batteries4 – Grey wire nutsRequired for the Optional “Time Out and Try Its”: plastic combs,balloons, aluminum soda cans, red LEDs, 3V coin cell batteries, extracopper wire, earphones, pennies, aluminum foil, a small cup (like amedicine cup), and warm salt water.Not included: Mason jars or other “containers” for your solar lantern, electric drill and drill bits,silicon adhesive and/or hot glue gun (use adult supervision)2
How it Works: Solar CellsPhotovoltaic (fo-to-vol-ta-ik) panels are solar panels that produce electricity directly fromsunlight. The term "photo" means “light”. "Voltaic" is named after Alessandro Volta (17451827), a pioneer in the study of electricity. Photovoltaics, then, means "light electricity."Photovoltaic panels produce clean, reliable electricity without consuming any fossil fuels. Theyare being used in a wide variety of applications, from providing power for watches, highwaysigns, and space stations, to providing for a household's electrical needs.How Does a Solar Cell Work?An atom (the smallest unit of matter) has three atomic particles: the proton (red in thediagram below) with a positive charge, the neutron (green in the diagram below) with nocharge, and the electron (yellow in the diagram below). Atoms have the capability to loseelectrons, which can flow from atom to atom in the form of electricity. Some types of atoms‘give up’ their electrons easily, while other atoms tend to ‘hold on’ to their electrons. Theatoms that make up solar panels are made of mostly silicon, but have other atoms (such asboron and phosphorus) which are set up in a way so that an electric field is created that‘pushes’ the electrons to the bottom of the solar panel.electronsA photon (a unit of light coming from the sun) can strike an electron at the bottom of the solarpanel, giving it enough energy to ‘boost’ it back up to the top of the solar panel. The electronsflowing to the top of the panel are collected in a wire called a terminal. Since electrons have anegative charge, the terminal at the top of the panel is the negative terminal. In electronics,the black wire is usually connected to the negative terminal, and the red wire is connected tothe positive terminal.The electrons at the negative terminal, however, cannot create a current (or get the electronsto ‘flow’) unless they are hooked to a ‘loop’ which feeds back to the positive end of a solarpanel. The closed loop through which electricity flows is called a circuit.3
Optional “Time Out and Try It”: Electric FieldsCharged objects create an invisible electric force field around themselves. Theseelectric fields are essential to solar cells. One of the simplest ways to show the forces ofelectric fields is with static electricity. For the following activities, you’ll need a dryplastic comb, a faucet, balloons, and an aluminum soda can.“Bending” Water with a Comb1. Turn on a faucet and slowly turn down the water until you have a VERY thinstream of water flowing.2. Take the plastic comb and brush it through your hair ten times.3. Now slowly bring the comb close the flowing water, (without actually touching thewater). If all goes well, the stream of water should bend towards the comb! That’sbecause the comb collects electrons from the hair, and the trickle of water has amore positive charge.“Rolling” a Can:1. Place the can on its side on a flat smooth surface like a table or a smooth floor.2. Rub the blown up balloon back and forth through your hair really fast.3. Now the fun part: Hold the balloon close to the can without actually touching thecan. The can will start to roll towards the balloon without you even touching it!That’s because when you rub the balloon through your hair, invisible electrons buildup on the surface of the balloon. The electrons have the power to pull very lightobjects (with a positive charge) toward them - like the soda can.Intro to BatteriesThe energy from the solar panels needs to be ‘stored’ in the batteries so that the energy can beused to create light at night. The chemical reactions in the battery causes a buildup ofelectrons at one end (making it negatively charged), and a loss of electrons at the other end(making it positively charged). A fluid inside the battery allows the electrons to flow from itsnegative to its positive end. But the electrons in the negative end of battery will not ‘flow out’of the battery unless they are connected by a wire which touches the positive end of thebattery. This wire ‘loop’ will allow for the electrons to flow in a circuit.4
Optional “Time Out and Try It”: Making a Simple Coin BatteryWith a little time and preparation, you can make your own battery and ‘hear’ theelectricity coming out of it! You will need a small medicine cup, warm salt water, copper coins,aluminum foil, two copper wires, and an earphone.1.Tape one copper wire to a coin, and place the coin wire side down in a small cup. Make sure thecopper wire is leading out of the cup. Then layer a piece of paper towel (the size of the penny) on topof the coin. Then put a piece of aluminum foil (the size of the coin) on top of the paper towel.2.Layer the coins, paper towel circles, and aluminum foil circles in the same repeating order until youget at least 5 layers. The more layers the better!3.Tape another copper wire onto the topmost layer (which should be a foil circle). The top copper wireshould also lead out of the cup. Then cover the coin/paper/foil stacks in the cup with warm saltwater.4.Wrap one of the copper wires leading outside the cup around an earpiece or earphone. Scrape theother copper wire leading outside the cup against the first. Did you hear a ‘static’ sound? Then youmade electricity with your ‘battery’!Intro to CircuitsElectricity flows in circuits: closed paths through which electrons flow. Within these circuits or“loops” in which the electricity travels, one needs to incorporate an energy source, switches,and loads (something that the current feeds into - in this case, it is the LEDs). The solar panelprovides the energy, and the battery stores the energy. Switches will allow one to disconnectthe circuit at will. The LEDs (which stands for Light Emitting Diodes) will emit light. In the caseof solar panels, the electricity flows in only one direction, which is called direct current. All theexperiments we are doing in this kit involve direct current. But the electricity used in ourhouses runs on alternating current, which regularly changes its forward and backward directionin the circuit many times a second. So if you hook solar panels up to a house, you will need touse a special device called an inverter to change the energy from direct current to alternatingcurrent.Optional “Time Out and Try It”: Making a Circuit with a Batteryand an LEDGet a 3 volt coin battery and an LED from your instructor. Your first “challenge” will be tolight up the LED using only the coin battery.The reason why the LED works in only one direction is because it is a diode (it only works inone direction only). Which end of the LED is positive? Which end of the LED is negative?Label on the picture to the right.5
Giving the LEDs More Power: Adding Solar PanelsSolar panels can be connected in order to produce more voltage (the ‘push’ of electrons in acircuit) or more current (the amount of electrons ‘flowing’ through a circuit). The unit forvoltage is the volt, and the unit for current is the amp. If you multiply voltage times current,you get power (in units called watts). You can increase the power of multiple solar panels byconnecting them in certain ways. Connecting solar panels ‘end to end’ will increase the voltageof the circuit. Connecting solar panels ‘side by side’ will increase the current in a circuit. Thisway, you can ‘step up’ the current or voltage to what is needed.Optional “Time Out and Try It”: Making a Two Panel CircuitLet’s try hooking up two solar panels ‘end to end’. In electronics, this is called aseries circuit. Get together with another group and connect your two solar panelstogether using wire nuts, like the picture below:Now shine a light on both solar panels, and connect an LED to the leftover black andred wires. Does the LED light up when the solar panels are lit? Does it stay lit if thesolar panels are taken away?Disconnect the two solar panels and connect an LED to a single panel. Again, shinea light on the panel. Does the LED light up? How bright is it compared to beingconnected to two solar panels?6
Putting it All Together So why are we using LEDs, and not a different kind of bulb? That’s becauseLEDs don't get especially hot, and they are much more energy efficient thanany other commonly used light bulb. They can be made to be quite smalland bright. They are also frequently used in all kinds of devices, includingremote controls, digital clocks, traffic lights, watches, and ‘on’ lights onappliances and electronics. They are the base of the thinnest flat screentelevisions and computer monitors on the market today.So how is a rechargeable battery different from the non-rechargeable kind,and why do we need to use a rechargeable one? Either type of battery createsa voltage by introducing two chemical reactions which create separatenegative and positive terminals. In a standard battery, the chemical reactionwill eventually reach a limit where no more electrons can be produced, andthe battery is dead. In a rechargeable battery like the one in this kit, thechemical reaction is reversible, so that electrical energy from the solar panelcan recharge the battery, and the battery will refill itself if it gets enoughsunlight.Making a working ‘dusk to dawn’ lantern is more complicated than just connecting the solarpanel to the batteries and the LEDs. The electricity has to be blocked from leaving the batterieswhen they are charging, and an automatic switch needs to turn the LEDs ‘off’ during the dayand ‘on’ at night. Each of these jobs requires a separate component on the circuit board: The printed circuit board (pcb) contains all the circuits that makes thelantern work, and acts like the ‘brain’ of the lantern Diodes are used in the circuit board to make ‘one way streets’, so theelectricity only travels in one direction A transistor helps to ‘direct traffic’ like a traffic signal. During the day,they give the ‘green light’ for electricity from the solar panels to fill thebatteries. At night, they give the ‘green light’ for the electricitygenerated by the batteries to light the batteries.7
Assembly Instructions1. Using a grey wire nut, connect the two red wirestogether from the battery holder to the circuit board(marked BATTERY on the circuit board in small whiteletters). Repeat with 2 black wires from the batteryholder to the circuit board.2. Using a grey wire nut, connect the two red wirestogether from the solar panel to the circuit board(marked SOLAR on the circuit board in small whiteletters). Repeat with the two black wires from the solarpanel to the circuit board.3. You can now test your light. If the LEDs do not turn on,check the switches for the battery pack and the LEDs(the ‘on’ position for the LEDs is toward the center ofthe green ‘chip’ called the printed circuit board or PCB).Now check to see how the LEDs respond when in brightor dark light. The LEDs should light when the solar panelis not in bright light and should turn off automaticallywhen it is in bright light.4. You can now install your LED light in a wide-mouthedcanning jar or a recycled jar (peanut butter ormayonnaise jars work well – you need a rather wide lid).Disconnect the wire nuts connecting the wires to thesolar panel. Drill 2 holes in the top of your jar and leadthe wires through with the solar panel on top of the lid.If you have a metal lid, use electrical tape to make surethat the solder contacts do not touch the lid, causingyour solar panel to ‘short out’. You may want to wrap ortidy up the wires with electrical tape. Use hot glue orsilicon sealant to adhere the solar panel above andbattery pack/PCB/LED complex under the lid.OPERATION The solar garden light should get as much sun as possible. When the solar panel iscovered or when it is dark, turn on inner switches for the LEDs until they light. If you take thelantern back out into the sun, the LEDs will go off. At night, the LEDs will turn back onautomatically. Have fun! 8
Solar Insolation Maps and Recharge TimesSo if you place your solar lantern outside in direct sun, how long will it take to fully charge thebatteries, if they were empty? To do this, follow the steps below:A. Find the total number of peak sun hours per day at your location: peaksun hours per dayB. Find the maximum current that the solar module will produce during these peak sunhours: mA (which stands for milliamps – the number is printed on a label on theback of the solar panel)C. Multiply your answer in A times your answer in B: mAh/day (whichstands for milliamp hours per day)D. Find the capacity of the rechargeable battery: mAh (which standsfor milliamp hours – it’s written on the side of the rechargeable battery)E. Divide your answer in D by your answer in C, and you will get the number of daysneeded to fully charge the rechargeable batteries if they started out empty. Youmay get a decimal Write your answer in the line below –days to fully recharge the empty batteries9
This calculation is just an estimate, because the true number of peak sun hours of an area varyby month, the batteries are usually not empty at the start, the sun is not always directly overtop of the panels, and the weather may not be clear and sunny.In practice, we found out that the solar lanterns work more dependably when left out in the sun tocharge for 1 or 2 full days BEFORE turning the LED lights on. This seems to match with the numbers thatwe calculated above.Solar insolation maps can be found online on different web sites, but the most common site ishttp://www.nrel.gov/gis/solar.html.10
Developing Solar Lanterns for South AfricansExcerpt from Pamela Ulicny, Biology and Environmental Science teacher in Tri-Valley Jr/Sr High School inHegins, Pennsylvania:“The inspiration for developing this solar-powered lantern was originally sarted by MarkGamble, CEO of Educo Africa. I was lucky enough to be granted a educational trip to SouthAfrica through the Toyota International Teacher Program, funded by Toyota Motor Sales and theInstitute for International Education. The trip was the experience of a lifetime and a wonderfulexperience to share with my students. But I was also saddened to see so much poverty there.Mark Gamble explained how his organization called Educo Africa helps South African youth fromdisadvantaged communities. The solar-powered lanterns were designed with the eventualpurpose of teaching South Africans science, technology, math, sustainability, and job skills asthey are trained to build their own solar-powered lanterns. Educo Africa would help their youthbuild and sell solar lanterns to those who do not have electricity in their homes. This would helpfamilies in poverty who currently use kerosene lanterns. Kerosene lanterns are a fire hazard andhave already resulted in severe burns, fatalities, and the destruction of many homes. The costof buying kerosene over a long time is more expensive than the cost of a solar-powered lantern.Additionally, the kerosene lanterns create as much smoke as two packs of cigarettes a day.Kerosene smoke also increases the chance of cataracts, respiratory infections, tuberculosis orlung and throat cancers.”11
Glossary:alternating current - An electric current that reverses its direction many times a second at regularintervals, typically used in power supplies.atom – the smallest part of matter.current – A flow of electric charge. It is how ‘crowded’ the electrons are as they flow in a circuit. Theunit that measures the amount of current or ‘electrical flow’ going through a material is called an amp(ampere, Amp or I).diode – A semiconductor device with two terminals, typically allowing the flow of current in onedirection only.direct current - An electric current flowing in one direction only.electron – a negatively charged particle in an atom. Electricity is caused by the flow of electrons.LED – Light Emitting Diode - A semiconductor diode that converts applied voltage to light and is used inlamps and digital displays.neutron – an uncharged charged particle in an atom; it is neither negatively or positively charged.parallel circuit - a closed circuit in which the current divides into two or more paths before recombiningto complete the circuit. This type of circuit adds current but does not add voltages.photon - A particle representing a unit of light or other electromagnetic radiation, also defined as a“packet” of solar energy of a particular wavelength.photovoltaic effect – the creation of voltage or electric current in a material upon exposure to light.power - is the rate of doing work, measured in watts, and represented by the letter P. It is the productof voltage times current.proton – a positively charged particle in an atom.series circuit - An electric circuit connected so that current passes through each circuit element in turnwithout branching. This type of circuit adds voltages but does not add current.transistor - A small electronic device containing a semiconductor and having at least three electricalcontacts, used in a circuit as an amplifier, detector, or switch.voltage - electric potential or potential difference expressed in volts. A volt (V) is a unit that measuresthe amount of ‘push’ that moves the electrons in a circuit.watt – the standard unit for measuring power (P).12
References and Further ce-at-nasa/2002/solarcells/ - How Do Photovolt
Optional “Time Out and Try It”: Making a Circuit with a Battery and an LED Get a 3 volt coin battery and an LED from your instructor. Your first “challenge” will be to light up the LED using only the coin battery. The reason why the LED works in only one direction is because it is a diode (it only works in one direction only).
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