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If you have ever had a sunburn, hung clothes on a line to dry or watched a plant grow, you recognize the power of the sun. Luckily, the sun is also an inexhaustible and clean source of energy. In fact, life on earth couldn’t exist without it.

To use the sun’s energy, solar cells (also called photo-voltaic or PV cells) convert sunlight directly into elec-tricity. “Photo” means “light” and “volt” is a measure of electricity. To use the sun’s energy, light energy must be converted to electricity. The photovoltaic effect refers to the process of turning the energy of the sun directly into electrical current through PV cells.

For the process to work, PV cells are made of two thin pieces of silicon, which is the material that makes up sand. Amazingly, silicon is the second most abundant ele-ment on earth. One piece of silicon has a small amount of phosphorous added to it, which gives it an excess of free electrons. It is called the “n-layer” because it tends to give up electrons. The other piece of silicon has a small amount of boron added to it, which gives it a tendency to attract electrons. This layer is called the “p-layer” because of its positive tendency. When a photon of light from the sun hits the PV cells, the radiant energy energizes

SUN = ENERGYthe free electrons. The charges on the two layers make the electrons move. If a circuit is made connecting the two layers, electrons flow through the n-layer through a wire to the p-layer, producing electricity.

There are many advantages of using solar to generate electricity. It is a renewable resource that is silent and produces no air pollution or hazardous waste. Once installed, the panels are free to run and require little maintenance because there aren’t mechanical parts that wear out. Not only can solar panels be used for generating electricity, but they can also be used for water heating. The best part is that the environmental impact is minimal.

So why doesn’t every house have solar panels? Unfortu-nately solar panels are expensive so they have a large up-front cost. Even though silicon is abundant, making solar panels is difficult because the silicon has to be heated to super-high temperatures to be formed into very thin wa-fers. Solar technology is also difficult because the amount of sunlight is not constant and its successful use depends on location, time of day, time of year and weather condi-tions. But fortunately, over time solar panels are becom-ing more affordable and available. b

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ART

SolAR beAdS

UV-sensitive beads contain pigments that change color when exposed to the sun.

w create a color pattern bracelet with the beads and then take them outside to check their pattern in the sun-light.

w measure the UV light emitted from the sun at different times of the day or during different weather conditions. b

SolAR PAPeR

Nature Print Paper (also called Sunprint Paper) has been coated with two compounds that make it sunlight-sensitive. When struck by ultra-violet light, these compounds undergo a reaction, creating white and blue prints.

w Place objects on paper in an area where there is no sun-light. Then lay the arrangement in a sunny place for the length of time indicated on the paper directions. To fin-ish, remove the paper from the sun and soak it in water for 5 minutes. Once the images have darkened on the wet paper, remove the paper from the water and place it on a flat place to dry. Challenge: In general, what other things does sunlight alter?

Solar Beads and Paper can be found at: Education Innova-tions, www.teachersource.com. b

ExpErimEnts

Solar CirCuitsMaterials: photovoltaic (PV) cells, motors and

propellers (Note: The PUD loans these materials to teachers for free)

Attach the propeller to the motor and then attach the motor to the PV cell. On a sunny day,

take the solar-energy system outside. Questions to explore: What happens when the solar panel

is turned away from the sun light at different angles? When part of the solar cell is covered with your hand, how does

the rate of the propeller’s spin change? What happens to the propeller when the wires are attached to the op-

posite poles? What happens if several cells are hooked together? Inside a room: Does the propeller spin when an artificial light source, such as an overhead projector, is used? b

WhiCh Material stores solar energy the Best?Materials: cardboard box, black paint, 4 small cans, 4 small thermometers, sand, salt, water and torn-up paper

Fill one can with sand, one with salt, one with water and one with torn-up paper. Place a thermometer in each can. Paint the box black and put the cans in the box. Place the closed box in the sun for 30 minutes. Remove the cans and watch the temperatures fall. Stir occasionally. Which temperature falls the slowest? Which stores heat the best? b

monitor a school’s solar-ElEctric systEm

1. Go to the S4RS Web site at http://solar4rschools.org.2. Locate a school in the Choose a School in Your Program

menu. (There are several schools that are Snohomish PUD grant recipients.)

3. You have the option of viewing information in three tabs: Production, Specs and Photos.

4. To the left of these three tabs is a Search Data magnifying glass that allows you to search and download information from any school in the program. The Search Data page will ask you to set the parameters for three fields: period, data, and site. b

learn in the sun With these sunsational Experiments & activities