Making Solar Hot Water with a Box

Heating water with the sun's power is free and doesn't add pollution to the environment. Heating small batches of water with a do-it-yourself solar water heater lets you use less alternate fuels and when done on a regular basis can help reduce expenses on utility bills. You can build this particular solar water heater with items you may have on hand or that you can buy inexpensively at a grocery or hardware store.

For this project you'll need: box, sturdy with lid; ruler, pen, box knife, aluminum foil, scissors, laminating plastic, clear tape, construction paper, black, 8 ½-inch-by-11-inch; flat black spray paint, 2 Jars, quart size with lids; pot holders (optional), oven mitts (optional), thermometer (optional) and sunglasses.

Instructions
Place the cardboard box on a sturdy work surface. Measure with the ruler approximately two inches in from the outer edges of the lid and draw a line on all sides except the top. Cut the section along the three lines with the box cutter to allow the new flap to fold back along the top of the box lid.

Fold the flap back and line the flap with aluminum foil to cover it entirely. Tape it into place with clear tape so it doesn't move. Remove the lid from the box and place it aside. Line the entire inside of the box with aluminum foil and tape it down so none of it moves. Tape a black piece of 8 1/2-inch-by-11-inch construction paper to the center of the inside bottom of the box.

Put the lids on the jars and place one piece of tape along the entire vertical height of the jar from top to bottom. Spray paint both jars on all sides except the bottom. Allow the jars to fully dry.

Put the box lid back onto the work surface placing it upside down. Cut a piece of laminating plastic to completely cover the hole you cut in the cardboard. Make sure the plastic is as tight as possible and tape it down along the cardboard edges so that no air can escape from the edges of the plastic.

Put the lid back on the box. Place the solar water heater outside facing the sun so that the shadow that is cast behind the box is almost directly behind the box. Flip back the reflector flap.

Remove the lids from the jars and remove the strip of tape from each jar. Fill the jars with water so that there is approximately one to inches of air at the top and replace the lids. Place the jars inside the solar water heater box on top of the black construction paper. Put the lid back on the box with the reflector flap up. Your water should be hot in approximately four hours.

Important
Keep the aluminum foil as smooth as possible as it helps to focus the sun's rays more intently to the center of the solar water heater. Move the box with the direction of the sun every hour to maximize the temperature of the water throughout the day. The strips you placed in the jars allow you to see the contents of the jar boil and can come in handy when seeing if water or food is boiling.

Use pot holders or oven mitts when carefully removing the jars from the solar water heater to avoid possible burns. Test the temperature of the water with a thermometer prior to sticking a finger in it. According the US Consumer Product Safety Commission, a person can receive third degree burn injuries in as little as two seconds with water that reaches 150 degrees.

References:

United States Department of Energy, Solar Energy Technology, Eere.energy.gov

US Consumer Product Safety Commission, Top Water Scalds, Cpsc.gov

Public Broadcasting System, Make a Solar Water Heater, PBS.org

David A. Bainbridge, The Integral Passive Solar Water Heater Book, BuilditSolar.com