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Solar Energy: Classroom Activities

Solar Collectors


Goal

To develop a better understanding of how solar radiation can be collected and converted to usable heat energy.

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Background Information

Home and building heating is one of the main uses of solar energy. In an active solar heating system, special equipment, in the form of a solar collector, is used to collect and distribute the solar energy. In a passive solar heating system, a home or building is designed to let in large amounts of sunlight. The heat produced from the light is trapped inside.

The collectors used in active solar heating systems absorb solar radiation and convert the energy to heat. Typically, a collector is a thin, flat, rectangular box with a transparent cover. The bottom of the collector box is a plate that is coated black on the upper surface and insulated on the lower surface. The collector is mounted on the roof of a building, facing the Sun. While the Sun is shining, the solar radiation that strikes the black surface is converted to heat. Air or a liquid is pumped into the collector through a series of pipes. As the air or liquid passes through the collector, it is warmed. The warmed air or liquid is then distributed throughout a house or building through more pipes and heats the house or building directly. Alternatively, the liquid and or air and the heat it contains can be stored for later use in insulated

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Activity Overview

Students construct a simple solar collector.

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Materials and Equipment

Large cardboard box (into which a pizza box will fit), cardboard pizza box, newspaper, cardboard pieces, aluminum foil, glue, black construction paper, two thermometers (that will fit inside pizza boxes), plastic wrap, straw

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Activity

  1. Ask students to build a solar collector according to the following directions:
    1. Line the bottom of a large box with insulating materials like crumpled newspapers.
    2. Set a cardboard pizza box inside the big box.
    3. Fill the space between the sides of the two boxes with crumpled newspaper.
    4. Fold cardboard pieces over the insulated space between boxes, and secure tightly.
    5. Line the sides of the inner box with aluminum foil adhered with nontoxic glue.
    6. Line the bottom of the inner box with black construction paper.
    7. On the top cover of the small pizza box, draw a square 3 cm from all the sides.
    8. Cut along three of the lines, but leave the fourth line near the hinge of the box uncut.
    9. Carefully unfold the flap.
    10. Wrap a piece of aluminum foil around the flap, smooth wrinkles, and secure with glue.
    11. Place a thermometer inside the pizza box.
    12. Stretch plastic wrap tightly over the inside top of the box. Smooth the plastic and secure it around the sides with glue or tape so that no air can escape.
    13. Use straws or another device to prop open the flap and allow aluminum lining to reflect the maximum sunlight.
      diagram of insulated box
  2. Ask students place the solar collectors in sunlight. Have them measure the temperature in the solar collector every minute for at least 25 minutes. Be sure that they record their data.
  3. Have students graph their data.
  4. Ask students to answer the following:
    1. Describe any trends in the data.
      Answers will vary.
    2. What heating mechanism caused the solar collector to heat up?
      Solar radiation causes the solar collector to heat up.
    3. What are the different heat transfer mechanisms that are taking place in the collectors?
      Radiant energy enters the box through the transparent top and heats the opaque solid inner surfaces of the box; the air inside the box that is in contact with the solid surface is heated by conduction from the hot surfaces; the heated air circulates inside the box by convection.
    4. What mechanism keeps the heat from escaping?
      The temperature builds up in the collector for two reasons: the space is closed, thereby keeping the heated air from rising convectively out of the collector; and the walls are insulated, to impede heat conduction from inside the box to the ambient air outside the box.
    5. What improvements could be made to the collector if you had to do it over again?
      Answers will vary. Two suggestions:
      • Use two layers of transparent material for the top of the collector, with a thin air space between. This reduces heat loss through the top by providing an insulating air layer, without reducing the transparency very much. Air is a relatively poor conductor of heat.
      • Add more insulation to the walls and bottom of the collector, to cut down heat loss by conduction.

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