Note: All of these activities need a sunny day with little or no cloud cover.

The sun is our greatest natural source of heat. Energy from the sun heats the land, the oceans, and the air.

Hot water has many uses in the home. Most water heaters use electricity or they burn natural gas, heating oil, or coal. Unfortunately, it takes a lot of energy to heat water even a few degrees. This is why heating water is so expensive.

But what about the sun? Can the sun’s energy be used for heating the water in our homes? Since the 1950s, architects and engineers have been investigating how to do this efficiently and effectively.

Many designs for solar water heaters circulate water through a series of coiled or looped tubes in a collector box with a transparent cover facing the sun. In this activity, you will find out if such a design really works.

Tools and Materials

You will need the following from the Solar Energy SEEDPACK or from sources such as those listed in our Materials List.

• Flat box 20.3 cm by 30.5 cm by 1.9 cm (8 inches by 12 inches by three-fourths inch) with fastener straps attached and two 6 mm (one-fourth inch) holes punched on opposite sides

• Aluminum foil 15 cm by 27 cm (6 inches by 11 inches)

• One five-meter (16.5 feet) length of tubing 6mm (one-fourth inch) outside diameter

• Plexiglas sheet 20.3 cm by 30.5 cm (8 inches by 12 inches)

• Two one-meter lengths of tubing 10 mm (three-eighths inch) outside diameter

• Optional equipment for automated solar tracker (not included): GoGo board Serial cable Two temperature sensors Connecting posts Alligator clip leads GoGo Monitor (software available as a free download)

  Collapsible funnel  

• Plastic beaker 400 ml (13 oz)

• Two bulb thermometers

• Two spring-loaded clothespins

• Transparent tape

• Solar Energy SEEDPACK component box

• Submersible water pump

• Coaxial adapter

• Coaxial DC power jack

• Solar cell backpack with two attached solar cells connected to junction box and Power Out cable

• One pair of alligator clip leads

What To Do

Hot Water—Just a Little Let’s find out how well the solar water heater works with water stored in the tubing
1. The first thing to do is to assemble the solar water heater panel. Spread out the aluminum foil so that it covers the bottom of the flat box. Insert one end of the 6 mm (one-fourth inch) outside diameter tubing into one of the holes in the side of the box, threading about 30 cm (about 12 inches) of tubing from the inside to the outside. Coil the remainder of the tubing into the flat box, and thread about 30 cm (about 12 inches) of the other end of the tubing out through the hole in the opposite side. Arrange fastener straps on top of the coiled tubing. Place a small thermometer on top of the coiled tubing so that you can read the temperature inside of the case once it is enclosed.
2. Place the sheet of Plexiglas on top of the assembled case. Tape the Plexiglas to the case to make an enclosed space containing the aluminum foil, coiled tubing, and thermometer. This completes the assembly of the solar water heater panel.
3. The next step will be to fill the tubing in the panel with water. First, fill the plastic beaker with water and insert a bulb thermometer. Wait a few minutes and then read the temperature of the water. Record this initial water temperature value in the table below.
4. Stand the panel upright on its long edge. Insert the 6 mm tubing coming out of the top of the panel into one of the pieces of 10 mm (three-eighths inch) outside diameter tubing. Tape the funnel to the other end of the 10 mm tubing.
5. Place two spring-loaded clothespins nearby. Slowly pour water from the beaker into the funnel so that the water flows into the tubing.
6. As soon as water begins coming out of the bottom end of the 6 mm tubing, bend the tubing sharply and fasten it with a clothespin to create a seal. With the panel still upright, remove the 10 mm tubing from the 6 mm tubing. Seal off the top end of the 6 mm tubing with the other clothespin. Now the tubing in the panel is filled with water.
Read the thermometer inside the panel and record this initial panel temperature value in the table below.
7. Place the panel outside so that the transparent top faces the sun as directly as possible. Read the thermometer inside the panel at regular intervals and record the values in the panel temperature column of the table. (The grayed cells in the table will not be used.)
Time of reading Water temperature Panel temperature Initial:                       Final:       After at least an hour in the sun, take your final panel temperature reading and retrieve your panel.
8. Stand the panel upright as before and place an empty beaker beneath the tubing at the bottom. Place a thermometer in the beaker. Release the two clothespins so that the water begins to drain from the panel into the beaker. If all of the water does not drain from the tubing, blow gently but firmly through the end of the top tubing to force the remaining water out of the panel and into the beaker. Wrap the end of the tubing in clean tissue paper before inserting it into your mouth.
Stir the water in the beaker gently with the thermometer to distribute the heat evenly. Read the thermometer and record this final water temperature value in the table. When we did this activity, the initial temperature of our water was 30ºC, and the initial panel temperature was 30ºC. During the hour in the sun, the panel temperature rose steadily, reaching a value of slightly over 60ºC. The final temperature of the water that we drained from the panel was 56ºC. You will probably get temperatures different from these. However, the main effect is that your water should certainly have a higher temperature after spending time in the solar water heater panel. Extension Try this same experiment at different times of day. Also try it on a cloudy day. What would happen if a circulation pump was added to your invention? Let's see…

…more Science Lab projects about…
Air & Space
Earth Science
Electricity & Magnetism
Properties of Liquids

…try some interactive experiments in our…
Virtual Lab

…or test your skills at our…
Math Puzzle of the Month
Engineering Challenge