Plugging into the Sun®

Solar thermal demonstrator Fully functioning portable rig demonstrating solar water heating systems. The solar water heating demonstration unit shown here was recently developed for the London Borough of Lewisham Sustainable Energy Unit. It has been designed and fabricated by the Schools & Homes Energy Education Project in partnership with Heeley City Farm Energy Project, Carnyx Renovations and I & D Fabrications, Sheffield. Solar radiant energy is captured and converted into thermal energy by the collector. This thermal energy is transferred to water (heating it) in a storage tank. Self-Help solar water heating course syllabus available; please see Course Details

Build a thermo-siphoning solar water heater that uses sunlight to heat water to cover national curriculum outcomes in science, design & technology, materials and their properties, physical properties and sustainable development

AGE RANGE: 11 - 16+

TIME: 2 x 50 minutes to build the water heater, approximately 2 - 3 hours to heat the water. Of course this will be dependent of number of full sunshine hours.

MATERIALS: Divide the class into groups of 4 - 5. For each group you need:

1. Shallow rectangular cardboard box (without flaps) at least 45 x 30 cm, no higher than 10 cm. Cut down and use an empty 4 ream paper box.
2. 3 meters of plastic tubing, approximately 2 mm thick and 1.2 cm in diameter.
3. Matt black paint and a brush.
4. 2 buckets that each hold at least 6 litres of water.
5. 2 thermometers.
6. Food colouring.
7. Aluminium foil, perspex that is the same size as or larger than the box.
8. Extra cardboard.
9. Tape.

PROCEDURE:

1. Ask students how energy from the sun gets to earth. How much solar energy reaches the Earth's surface? Ask about the difference between heat and light energy. Review the basics of solar energy collection, such as storage, reflection, insulation, and heat absorption of different colour and density materials.

2. Have students do a web search on solar thermal systems.

3. Review how thermo-siphoning works. Explain how differences in temperature in water can cause differences in pressure. Explain how this pressure difference can be used to siphon water.

4. Discuss with students about solar thermal systems. Ask them how they think a system for heating water might work and look. Describe a solar hot water heater and a solar thermal power plant. Describe developments in modern technology.

5. Distribute the handout "How to build a solar water heater."

6. Ask students to measure the temperature of the water periodically during the 3 - 4 hours that it is heating. Also ask them to write down the temperatures inside the heater.

How to Build a Solar Water Heater - Student handout

NOTE: Supervise student construction, helping if problems arise and/or students and teachers can email enquiries@pluggingintothesun.org.uk

(Pictures to accompany instructions currently being created.)

1. Poke two holes in the box at opposite ends of one side. Make them the size of the tubing you will use.

2. Paint the box black inside as this will increase the 'absorption' of sunlight.

3. Insert this tubing through one hole and curl it like a snake along and across the bottom of the box. Poke the tubing out the hole at the other end. Leave roughly equal amounts of tubing sticking out of both ends of the box.

4. Pin the tubing to the bottom of the box. Do this by bending a paper clip. Stick it around the tubing through the bottom of the box. Bend the clip ends on the other side, clamping the tubing down.

5. Completly paint the tubing inside the box black.

6. Tape a thermometer to the bottom of the box.

7. Cover the box with clear plastic or Plexiglas. Tape it on so that it is airtight.

8. If the buckets you use do not have lids, make lids out of cardboard. Insulate the buckets by taping sheets of newspaper around them. Poke two holes in the lids of one of the buckets for the tubing. This is your experiment bucket. The other bucket will be your control.

8. Fill both buckets with the same amount of water and at the same temperature. Insert tubing in your experiment bucket. Make sure that one end of the tubing in the experiemnt bucket is near the top and the other end of the tubing is at the bottom. You may need to cut off some tubing in the end that is near the top of the bucket.

9. Prop up the box at a slant so that it is facing the sunlight (its shadow should be directly behind it). Place the experiment bucket on some support (books or another box will work), so that it is completely above the level of the collector. Arrange the control bucket at the same level and facing exaclty the same way.

9. Suck on one end of the tubing in the control bucket to fill the plastic tube with water. Make sure there is no air in the tube when you insert it back in the water.

10. Leave the solar heater and control bucket out in the sun for 1 or 2 hours and measure the temperature of the water periodically, as well as the temperature inside the heater.

FOLLOW-UP:

1. Ask students to name the ways heat was collected and transferred to the water in this activity.

2. Ask students what limitations sunlight might place on solar thermal system use. Factors to discuss are amount of sunlight, cloudiness, angle of sun, seasonal differences, and location.

3. Ask students to test and evaluate their solar water heater and to suggest and implement ways to improve the efficiency of the solar heater. Factors to discuss are amount of sunlight, cloudiness and shade, angle of sun and collector, seasonal differences, and location and orientation of collector.

4. Take the temperatures that students measured and write them on the board. Ask students to draw conclusions about them. You may want to average the temperature readings of the different groups.

5. Ask them how a system would be designed to heat water enough to create steam for electricity. What fluids could be used in place of water?

6. Assign independent science research projects on solar thermal systems. Some possible topics are:

· solar water heaters
· solar thermal generating plants--either parabolic trough, central receiving tower, or parabolic dish collectors
· recent developments in either of the above