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Solar Energy: Classroom Activities

Solar Water Heating


Goal

To develop a better understanding of how solar radiation can be used as an energy source for heating water.

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Background Information

Active solar heating systems can be used to heat water for hot-water use in homes, buildings, or even swimming pools. These systems have two main parts: a solar collector and a storage tank. The solar energy is collected with 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 solar radiation that strikes the black surface is converted to heat. Cool water is circulated within pipes through the hot collector box and into a storage tank. The water is warmed as it passes through the collector box. The heated water in the storage tank is then used for a variety of purposes, including washing dishes or clothing.

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Activity Overview

Students construct a simple solar water heater.

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Materials and Equipment

15 ft. of flexible plastic tubing, cardboard box or lid trimmed to height of 1 in. (photocopy paper box top or large pizza box works well), black paint or black construction paper, clear plastic wrap or sheet (or sheet of thin clear Plexiglas® cut to box size), ruler, tape, two glass or plastic containers (2-L minimum), Styrofoam® cooler, two thermometers, siphoning bulb, adjustable tubing clamp, stopwatch, funnel

Activity

  1. Tell students that they will be constructing a solar water heating system that will heat water contained within a rubber tubing. Provide students the necessary materials and instruct them to set up the solar water heating system as shown in the following diagram.
    water heater diagram
  2. Provide students the following guidelines for constructing a solar water heating system:
    1. The inside surface of the heater box should be painted black or lined with black construction paper.
    2. Water must be added to your device using a funnel placed at the top and must leave your device and flow into an insulated collecting container.
    3. Put the source container above the level of the heater box so that water will flow through the tubing by gravity. You may need to use chairs, books, or other appropriate items to prop up the device.
    4. The container to collect the water, once it has run through your device, must be placed at the bottom.
    5. The tubing must pass through a box.
    6. You may put holes or openings in the box.
  3. Have students run their solar water heaters on a sunny day. Initially, they should place their devices on a flat, horizontal surface in the sunlight. Instruct them to run 500mL of cool water through theirs devices to cool them off.
  4. Tell students to run another 500mL of cool water through their devices. This time, they should measure and record the initial temperature of the water. After they run the water through the device, they should measure and record its temperature in the insulated collecting container at the bottom.
  5. Have students tilt the heating boxes (using chairs or books for support) so that they face directly toward the Sun. Instruct students to run another 500mL of cool water through the devices, as they did in step 4.
  6. Instruct students to run another 500mL of water through their solar water heaters, as they did in step 4, but this time they should use the tube clamp to keep the water inside the devices for five minutes. Then, they should release the water and measure its temperature.
  7. Have students answer the following:
    1. Describe any changes in the temperature of the water after it passed through the solar water heater.
      Answers will vary. Students should notice an increase in temperature in the third run.
    2. If the water became heated, by how many degrees, or fractions of a degree, did it warm up? What heating mechanism caused the water to heat up?
      In its simplest form, a solar water heater uses the energy of the Sun to increase the temperature of water as the water flows through a coil of tubing.
    3. How could you improve the design of your solar water heater so that it heats water more effectively?
      Answers will vary. Some suggestions might include:
      • insulate the bottom and walls of the heater with good insulation material.
      • insulate the transparent cover of the heater by doubling it with an air space between the layers.
      • paint the tubing a low-gloss black.
    4. How could you adapt the design to heat water in a home?
      Answers will vary.
    5. For what would you use this water?
      Answers will vary. Students might suggest using the warmed water for washing dishes, clothes, or bathing.

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