Introduction: Homemade Solar Thermal Collector

Solar thermal water heating systems are environmentally friendly alternatives to heating water with electricity. Although solar thermal technology is one of the most affordable renewable energy technologies, the initial price is still too high for many low-income individuals in the United States or in developing countries.

The purpose of this research project was to construct a relatively inexpensive solar thermal water heating system out of readily available and recycled materials. By maximizing the efficiency of the system and minimizing the cost, this system demonstrates that it is possible to design and construct a small-scale solar thermal system for showering or washing dishes for a fraction of the price of conventional systems (4x 6.5 collector is approximately $900 and does not include the rest of the system components).

By measuring the beginning temperature of the water and the temperature after the water has passed through the collector, one can determine the efficiency of the system. This system relies on thermosyphoning and will not require electricity to move the water throughout the system, thus lowering the price of the system even further. Keeping the design simple and the costs as low as possible, the goal of this is to teach and instruct others on how to easily design and build their own small-scale flat plate, solar thermal system.

Step 1: Materials and Tools Needed


-Window frame (23 x 40.5) $40.00
-Metal refrigerator coolant system (with Freon properly removed. If your local dump has white storage, they probably have a number of old refrigerators that have had the Freon removed. - Free
-Duct Insulation  Self Adhesive Foil and Foam (1 roll) - $12.99
-Plywood - $4.45
-2, 2 x 4 footings (13 inch each, 36 degree angle) - $2.15
-1 package steel wire, 22 gauge - $3.99
-5 gallon heat resistant storage - $4.00
-2, Pex Hose Barb Adapter (3/16 Barb x 1/4" MIP) - $4.15
-2, Pex Pipe Reducing Coupling (1/4 FIP x 1/8 FIP) - $4.15
-1 Package Thread Seal Tape - $1.0
-Vinyl Tubing 3/ 16 10 feet - $2.00
-2, 1/2" o-rings - $0.49
-12, wood screws (2 inch) - $1.45
-metal fastening attachments Free, off refrigerator backing

Total System Cost $80.87


-Tape Measurer
- Phillips Head Screw driver
- Protractor
- Saw
- Angle Grinder (optional but made adjusting refrigerator backing MUCH faster)
- Pliers
- Drill, 1/2" bit
- Scissors
- Thermometer

Step 2: Refregerator Backing

Once you have collect all of the necessary tools and materials, the first challenge is to make the refrigerator backing appropriately fit the window frame. As the photograph shows, the refrigerator backing did not originally fit the size of the window. Wanting to have as much collector surface area as possible, I decided that I would modify the refrigerator backing.

The little wires that provided the backing with support had to be removed to make the metal tubing more flexible. This was the most tedious part of the project. If you can find a refrigerator backing that will fit into window frame that would make the project less time consuming but you would not have as much surface area for the water to pass through in the collector.

With an angle grinder I cut each row of the metal pieces. I then used pliers to remove each of the sections. Be careful as the metal pieces are sharp once cut and can easily hurt your hand.

With the package if steel wire, I then condensed the metal tubing to fit in the window frame. Use the steel wire as twist ties to hold the metal together.

Step 3: Window Frame

Next, I had to use the saw to make the plywood fit the back of the window frame. After the back of the collector is adjusted, apply the duct insulation  self adhesive foil and foam to the inside of the window frame and on the back of the collector. Covering the entire backing will help create a good seal when attached to window frame.

Attach the refrigerator metal backing to the back of the solar thermal collector that is covered with insulation. Attach with metal plumbing/fastening attachments. I used two and that securely attached the refrigerator backing sufficiently.

Drill two holes in window frame on opposite ends of the window. Drill a hole where the bottom of the collector is (the cold in) and on the opposite side, drill a hole at the top (the hot out).

Step 4: Attaching the Backing to the Frame

Next it is time to attach the back of the collector to the window frame. Insert one of the ends of the refrigerator backing into the appropriate hole that was drilled into the window frame. Getting each of the ends of the refrigerator backing to fit took careful placement but the flexibility of the metal makes it easier/possible.

When the back of the collector is lined up squarely top the window frame, use 6 screws to seal the collector. Since the window frame was narrow, careful attention is required when tightening.

Once the collector has been sealed, use the 2x4 to make two footings for the collector. The latitude where this system was constructed was 36 degrees so, the angle of the tilt of the collector was made to equal the altitude. Use the protractor, tape measure, and saw to make the footings. Attach to the back with the several wood screws.

Step 5: Water Storage

Once the collector is completed, begin working on the storage. Drilling two, � holes into the 5 gallon bucket is necessary. Similar to the collector, drill one hole toward the bottom. This will be where the cold water is taken from. About two thirds the way up the bucket, drill another whole. This will be the hot water return location.

Attach the 2 Pex fittings to the bucket. In order to get a tight seal, use an o-ring for each fitting. Also use thread seal tape to ensure secure attachments.

Once the fittings have been installed, use the remaining duct insulation to wrap the bucket (side, bottom, and top) to increase insulation and minimize heat loss.

Attach the nylon tubing to the barb fittings and the refrigerator backing ends. The diameter of the tubing created a tight connection to both ends.

You are almost ready to test.

Step 6: Operations

Fill up the bucket of water. You will need to fill the refrigerator backing. This is the rough part. Use gravity to help you out but you will need to suck the water through the cold-in side. Go ahead and attach the nylon tubing to the refrigerator backing that you are going to suck through helps to make this step more enjoyable.

Take the temperature of the water before you set the system in the sun facing south. Each hour, check on the system and record difference in temperatures of the water and ambient air.

Step 7: Testing

The day that this system was originally tested the temperature was 41 degrees F. This system is ideal for a place that doesnt freeze because there is no freeze protection with this system.

The water was originally 58 degrees F. Over the 6 hours of testing, below are the results:

The steady increase in water temperature is encouraging. Given the air temperature and the minimal insulation, the results indicate that through thermosyphoning, the system circulated water through the collector.

For increased performance it is advisable to use in a warmer location and apply insulation to the exposed pipe. It is expected that this water would get very warm/hot in warmer weather.