Harnessing direct solar energy – a progress report
Activity 6
Making a solar water heater
In this activity, we can see how solar water heaters take advantage of the fact that hot water rises.
Materials (for small group)
large cardboard tray, approximately 60 × 30 × 15 centimetres (made by cutting down a cardboard carton)
sheet of glass, larger than 60 × 30 centimetres
6 metres of plastic tubing or garden hose
2-litre plastic bottle
cardboard carton (big enough to hold the plastic bottle)
thermometer
scissors with pointed ends
plasticine
sticky tape
water
black and white poster paints
sheet of clear plastic, larger than 60 × 30 centimetres
a variety of insulating materials (eg, old clothing, sawdust, plastic foam, crumpled newspapers)
Set up the model solar water heater (as shown in the diagram) and place it in a sunny position.
Fill the bottle and the plastic tubing with water.
Record the temperature of the water after the solar water heater has been in sunlight for 20 minutes.
Test for the effect on the temperature of altering variables (eg, clear plastic versus glass covering the box; various insulating materials around the bottle; the colour of the bottom of the cardboard box; the angle at which the box is tilted).
Questions
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Why was it important to have one end of the plastic hose entering at the top of the bottle and the other end entering at the bottom?
- Why did the model solar water heater have a long length of the plastic hose positioned in the bottom of the tray?
Teachers notes
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One of the holes should be at the top of the bottle and the other
at the bottom to ensure that circulation and mixing occurs as the water is heated.
- Positioning as much of the tubing as possible across the bottom of the box ensures that the maximum area of tubing is exposed to the sun.
Posted February 1997.