Solar Collector 

Science Fair Project

This Science fair project has to do with solar heating water. If you can build this solar collector and understand the parts that make it work you will not only understand the basic principles behind solar thermal heating but you will also have some hands on experience.  Solar energy is diffuse (spread out over a large area). To make good use of the suns energy we must find a practical, inexpensive way to harvest sunlight over a large area. The size of your collector is very important. The larger you make it the better it will work.  You'll need sunlight or it's equivalent in sunlamps to do this. It's possible to build a functional solar collector for under $20. The material cost for the all weather 4x8 collectors that I build cost $200 and I sell them for $500. The most expensive part of my collector is the fiberglass reinforced plastic glazing, but not to worry we'll be using an inexpensive plastic drop cloth in this project.

MATERIAL

1. Lots of cardboard boxes
2. One quart Elmer's glue
3. One hundred square feet of tin foil
4.  Fifty feet of  1/4 inch copper tubing
5. One gallon of tar
6. 1x4 boards
7. a funnel and some plastic tubing to join the funnel to the copper tubing.
8. duct tape.

The actual quantity and quality of materials are up to you. You may have some of these common materials around your house so you won't have to buy them. The suggested size of the collector in these plans is very small (5'x3')

LET'S GET STARTED

First you'll need to build a bending jig for the copper tube. To do this you'll need a nice flat surface to work on like a garage floor. Draw a box on the floor with chalk that's the same size as the inside of your collector. Be sure the box is square.

Now cut a piece of 1x4  three feet long. Use this to mark lines about 4 inches apart as in the picture below.  One end of the 1x4 will need to be rounded so that the copper tube may be bent around this bend as shown in the illustration below. Bend the copper tube carefully. Kinks interfere with the flow of water. 

You'll only need one rounded 1x4 to do the job. If you tape the copper tube to the floor as you go it will make the tube bending easier.

Now you can make the collector body frame with the 1x4's. The backing can be made with layers of cardboard but it would be better with a 1/4" plywood back. Next glue about five layers of cardboard inside the collector body for insulation on the bottom and and sides. 

Next you should glue several layers of aluminum foil to the bottom of your collector body. This will be the bottom part of the absorber plate where heat from the sun is transferred to the flow tube. Before inserting the pre bent  flow tube into the collector body you must drill some holes in the sides of your collector at the appropriate places to accommodate the flow tube.

Press the bends of the flow tube under the cardboard insulation on the sides of the collector. This will keep the flow tube tight inside the collector. After this is done paint the flow tubes and foil with a 50/50 mix of tar and mineral spirits. Apply several more layers of aluminum foil. Paint each layer of foil with the 50/50 mix before applying the next layer of foil.  Paint thin coats. Apply a final colt to the last layer and let the collector dry out in bright sunlight.

After the collector has had time to dry out you could stretch a sheet of clear plastic over the top. The plastic glazing is used to slow down heat loss. Glass or fiberglass reinforced plastic works better than than plastic, but you can still build this project without them.

Congratulations! You have just built a solar collector capable of converting sunlight into heat. Now we need a way to get that heat out of the collector. That's what the funnel at the cold water inlet is for. You'll need to figure out a way to connect the funnel to the copper tube. A 3/8" plastic tube might work, but funnels come in different sizes. I'm sure you'll figure out a way to make it work.

Once your done you could pour cold water into the funnel at the top and collect hot water at the flow tube output at the bottom. Of course you'll need some sunlight. The brighter and more direct the better.

My collectors reach temperatures in excess of 240 degrees Fahrenheit. With the proper glazing and insulation you could also achieve these temperatures. When water flows through the collectors the temperature drops rapidly. That's why it's important to have enough collectors to keep the temperature up. For more information about solar thermal energy feel free to explore any of these topics.

Strawberry Fields Solar Book Store
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