Follow the Lead • Can you think of any other small-scale tasks you could do or things you could make by focusing sunlight in this way? • What other safe, useful things could you do by focusing the Sun’s energy with a magnifying glass? • Now, think big. How could the Sun’s energy be focused on a larger scale to create electricity? Keep in mind that enough heat would have to be gathered to boil water and turn the blades of a turbine that is connected to an electrical genera- tor. Draw a diagram of how you could accomplish this by designing a solar electrical generator.
• Once you’ve drawn your design, go online and search under “solar power plant” to see if the designs of real power sta- tions are anything like the one that you imagined.
Activity: Solar Heat by the Gallon
Water is the best common substance to use for storing heat. It takes a lot of heat to warm up water, but it loses that heat very slowly. A container of water that heats up in the sunlight continues to give off that heat well into the night. Follow the steps in this activity to create a small passive capture solar heater for your school or home.
Materials: • Dish soap • Dish drainer • Four (or more) 2-liter-size beverage bottles with screw-on lids • Drop cloth • Paintbrush • Can of flat black interior latex paint (any flat, dark color will do) • Clean, quart-size (about a liter) can or plastic container full of water for cleaning the paintbrush • Water for filling bottles • Bookshelf
Do the Deed Passive solar heat is easy to catch. All you need is something dark that absorbs the Sun’s heat during the day and then radiates it back into the room at night. 1. Use the dish soap to thoroughly clean at least four 2-liter plastic beverage containers. Save the caps. Remove labels from the outside of the containers, and wash the outside well so the surface is clean and paint will stick to it. Rinse the inside of each container well, and put it upside down in the dish drain to dry.
2. Once the beverage containers are dry, place them on the drop cloth and use the brush to paint them with the flat black paint. It is best to do this outside or in an open garage or other space that is well ventilated.
3. Use the container of water for cleaning the paintbrush, then set the brush aside to dry. 4. Once the paint is dry, fill each container with water and cap it off snugly. Leave about an inch of air on top to allow space for the water to expand as it warms up. Be sure not to crush or bend the containers while handling them or the paint might crack off.
5. Place the black jugs full of water on the top of a bookshelf in a sunny window or on a windowsill to create a simple solar heat collector.
Follow the Lead • Add more shelves and “Solar Heat by the Gallon” jugs to your homemade heat collector to increase its storage capacity. • Experiment by placing other kinds of dark-colored containers full of water in the Sun to see which one holds the heat longest once the Sun goes down. Try using containers made from glass, ceramic, metal, or thicker plastic. Which kind of container works best? Why?
• On a sunny day: Open one of the bottles in the morning, and lower inside it the long, thin sensor end of a cooking ther- mometer or a science-class dial thermometer. If the bottle is deeper than the thermometer is long, you may need to tie a string around the top of the thermometer. Make a graph showing temperature along the left-hand side and time along the bottom. Read the thermometer every half hour, capping the container after each reading. Use a dot to record the temperature at each half-hour time mark. Once the Sun goes down, observe how the temperature rose and fell during the day. When was the “heat of the day?” Was it exactly in the middle of the day? Why, or why not?
• Try this same experiment by recording and graphing the water temperature on a cloudy day. How does that temperature pattern compare with the results from the sunny day?
• Repeat the previous experiment using two bottles: one that sits in direct sunlight, and one that rests in the shade. Using a different colored marker for each bottle, chart the temperature of both bottles on your graph throughout the day. Compare the temperature changes that occurred in each bottle. Why do you think you got that result? Is it what you expected?
• How does the temperature chart from the bottle that sat in the shade in this experiment compare with the graph you made earlier of the bottle kept exposed to the sky on a cloudy day?
©2011 Michael J. Caduto, All Rights Reserved Page 42 GREEN TEACHER 93
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