Tools required
Saw or jigsaw with appropriate blades for cutting wood / metal / plastics
Screwdriver - pozidrive No.2
Drill with 2.5mm bit
Stanley-type knife
Sandpaper/emery paper for metalworking
Pipe cutter

Procedure for making the box
1) Cut out plywood side panels
2) Cut out hardboard base - use a jigsaw or a Stanley knife
3) Assemble sides and base in jig and check fit
4) drill a 25mm deep hole for each screw (2 per corner) at least 1cm from the top or bottom edge of the wood. You may need to turn the box over in the jig to drill the lower holes
5) Use 2 x 25mm screws to join each corner. You may need to turn the box over in the jig for some screws
6) Turn the box upside down - choose the neatest edge for the top
7) Use 2 x 20mm screws along each side to fasten the hardboard to the box sides
8) Turn the box the right way up
9) Paint the inside of the box black if possible. The outside can be decorated in any way
10) Cut the plastic lid to size. Use a Stanley type knife to score and snap the sheet, or use a hacksaw.
11) Lay the lid on the box. Check that it is square
12) Put a strip of tape along the lid so that the tape is approximately 12mm onto the plastic
13) Holding the lid in place, tape the top edge of the lid to the top side of the box. The tape can be tacked on to the box if you like.

Procedure for making the absorber panel
14) Turn the clip fin upside down and draw a pencil line across the width of the clip fin, half way along (190mm)
15) Carefully cut the clip fin in half
16) Round the sharp corners of the fin with emery paper
17) Find a well ventilated space and paint or spray the TOP of the fin with the matt black paint.
18) Allow to dry
19) Clip the fin to the 190mm length of copper pipe so that the ends are level with the fin
20) Put a No.13 stopper in each end of the copper tube.

Procedure for using the water heater
a) Open the lid
b) Pupils lay insulation in the bottom of the box, maximum 25mm thick
c) With a stopper in one end of the copper tube, fill the tube with cold water
d) Put a stopper in the other end of the tube
e) Put the fin on top of the insulation, black surface on top
f) Close the lid. If the lid doesn't stay down, tape it down.
g) Put the Solar Water Heater in direct sunlight, facing towards the sun
h) Wait ten minutes
i) Take the fin out of the box and carry it to a sink
j) Take out one stopper and test the water temperature.

Questions
1) What is the insulation for?
2) What is the box for?
3) What is the transparent lid for?
4) What does the black fin do?
5) Describe the temperature of the water at the start and after ten minutes in the sun.
6) How much did the energy used to heat the water actually cost?
7) What do you think is the main cost involved in solar water heating?

Teachers notes : constructing and using the model solar water heater

Clipfins are available from
FilSol Solar Ltd.15 Ponthenri Industrial Estate, Ponthenri, Llanelli, Carmarthenshire, SA15 5RA Telephone 01269 860229. Website: www.filsol.co.uk

Solar water heating seems to be counter intuitive. Pupils will not necessarily expect it to work, so it is important to prove to them that it does at a physical level. The best way I have found to do this is by pupils feeling the temperature of the water before and after, and being in control of the heater in the meantime - there can be no tricks. Subject to safety considerations, I would hope that the pupils do just about everything for themselves when using these heaters.

In step (j), the intention is to give pupils direct experience, so get them to pour the water onto their hands. Obviously this needs to be safe. Ten minutes usually means that the water temperature will not exceed 60°C even in Summer. On a really, really sunny day you may wish to reduce this to 5 minutes to be absolutely safe, but it is advisable to check with a thermometer until you have some experience of the capability of the panel.

The wooden sides need to be cut accurately and neatly.

If you are going to make a set of panels. It may well be worth making up your own jig to drop the wood into for screwing - this ensures that the corners are right angles!

If the screws are too close to the end of the plywood, it is more likely to split.

An automatic pipe slicer makes light work of cutting copper pipe and doesn't leave a jagged edge.

If you would prefer to measure the temperature of the water, do so before and after. Bear in mind that the amount of water in the tube is quite small - only 24-25cm3.

If you wish to make this an investigative activity, try comparing the water from the solar water heater with water from:
a) An unpainted fin in the solar water heater
b) A painted or unpainted fin in the sun without the box
c) An painted or unpainted fin in the box without the insulation
d) An painted or unpainted fin in the box with the lid left open
e) An painted or unpainted fin in the box with half the fin shaded from direct sunlight