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 this energy. 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 but I doubt it will be very practical. The material cost for an all weather 4x8 collectors will cost more than $200. The fiberglass reinforced plastic glazing accounts for more than half the expense, but not to worry we'll be using an inexpensive piece of plastic for this test project.
MATERIAL for a cheapo serpentine collector...
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 small. 1'x2' or 2'x4' would be nice. Remember this is just an experimental collector. It would not last long when exposed to the elements. It's only purpose is to illustrate some fundamental solar heat collecting principles.
LET'S GET STARTED
First you'll need to build a bending jig for 1/4 "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. A little help from a friend would be useful for this bending project..
NEXT : make the collector body frame with the 1x4's. The backing can be made with layers of cardboard. Next glue about five layers of cardboard inside the collector body for insulation on the bottom and and sides. You may also use duct tape to hold the collector body together. 1x4 boards with a plywood back may be used to build this experimental collector, but than the materials and tools to build the collector would be more expensive. You have the freedom to experiment and spend as much or as much money on this project as you wish.
Next you should press 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. Paint the flow tube with a mix of mineral spirits and tar. Add additional layers of foil on top and press them into the tar and tightly against the flow tube. Paint the top layer of foil with the tar/mineral spirit mix. ting. Allow the final colt to 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.
When water flows through the collectors the temperature drops rapidly. That's why the size of the collector is so important.
EXPERIMENTAL PART. Get out your digital thermometer
1. Aim the collector at the sun on a clear, sunny day.
2. Get two one quart containers and fill one with water of a known temperature.
3. Slowly pour water through the funnel at the top of the collector. After all the water flows through the flow tube into the other container take a temp reading and record the time. Repeat the process for about 10 minutes.
4. Plat a graph of temperature vs time from the data you have collected.
5. Calculate the amount of heat that you have collected. Heat = (T1-T2)x mass. The mass of a qt of water is about 2 pounds. If you measure a temperature difference of 20 degrees F you have collected 40 BTU's of heat.
6. Estimate the heat that could be collected with a square meter of surface area over the period of one hour from the data you collected.
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