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.

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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.

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    19 Discussions


    10 months ago

    Hello! Please help. Can this Instructable be connected to a turbine or dynamo of sorts to generate electricity? I think it's possible, but I'm having a hard time connecting the two.


    6 years ago on Introduction

    "The water was originally 58 degrees F. Over the 6 hours of testing, below are the results:"
    Okay, I give up. Where are the results? Don't see them.


    6 years ago on Introduction

    Great experiment. I wanna know how hot it gets in the snow!

    This unit would be more efficient if the water pipes were insulated, the water bucket was placed in sunlight and all was contained in a closed box.

    My brother built a similar solar water heater for my mom's pool in california only there were differences like he built it on her roof, used pvc pipe, a long concave mirror underneath the pipes and a convex plexiglass cover. It heated her pool to 89 degrees F. She said that was too hot and had to take off the pool blanket. lol


    7 years ago on Step 2

    "The little wires that provided the backing with support had to be removed to make the metal tubing more flexible."

    Those little wires are not for support (sure, they have that effect) but to improve heat exchange capabilities by increasing the surface. When used as a refrigarator backing, to loose heat more efficiently.

    I'm willing to bet that removing them actually reduced the heat absortion efficiency of the tubing when installed in the thermal collector. So it would be interesting to test (when you run accros another refrigerator backing) with not removing the wires except maybe in the middle to be able to fold the whole thing double to make it fit in the housing... And see if that gets you a better result, or not ;)


    9 years ago on Step 6

    Hey, can you drink this water? I've just finished making a similar on to this with a freon-removed fridge condenser, and it heats water like a charm, but at first the water came out oily. Now it's coming out cleaner but a bit brownish, like maybe the pipes are corroding. I'd like to use this to make coffee but I don't want to kill anyone. Anyone have ideas on cleaning/testing for chemical content? Thanks!

    1 reply

    Reply 7 years ago on Introduction

    As a guy that has spent almost 40 years working on refrigeration systems all I can say is I WOULD NOT DRINK WATER COMING OUT OF THIS unless I was dying in the desert. One of the byproducts of a refrigeration system can be hydrochloric acid not to mention the oil that circulates in the tubing along with the refrigerant. Can be some pretty nasty stuff, my opinion is wash your hands thoroughly and keep all the inside stuff (brown water,oil) out of your diet and out of the coffee. Why spoil good coffee?


    8 years ago on Introduction

    i would like to point at some mistakes you did which gravely affected your heating.

    1) NEVER cut away those wires connecting the tubes! they are called PIN/NEEDLE FINS. they increase exposure area to exchange heat. in your case, absorb heat.
    2) reflective surface under the tubes will "send away" any heat falling on the surface. so the only heat absorbed in your case is the one falling directly on the tubes. which is VERY little compared to the amount 'sent away'. ( its the surface area ratio.)
    next time keep the wires and cover them with blackened foil. see the difference!!


    9 years ago on Introduction

    Would it be feasible to replace the storage tank with a car radiator and car expansion tank, and the water with antifreeze? I would roof mount the collector over a small south-facing shop space, with the radiator inside the shop. Likely put a small fan behind the radiator. I could even put a small fountain pump inline to recirculate the coolant. Think it might produce enough day-time heat to keep an 80 square foot space warm in 20 degree weather?

    1 reply

    Reply 8 years ago on Introduction

    will work fine.
    to minimise costs and complexity, try the "hot fluid rises up" concept. try putting the radiator at a lower level(below knee height) you will eliminate the use of a fan behind it.
    but first find out how much solar heat energy is falling over a unit area and how much heat is needed to warm your shop space. (space=volume. not floor area!!)
    IF the heat is less than 20% then the project is of no good. its like lighting up your house using a single LED bulb!


    9 years ago on Introduction

    The idea of a thermosyphon is to have the colder water gravity fed from an outlet in the bottom of a storage tank to the bottom of the collector. It is then heated and rises to an inlet at the top of the storage tank. In that case you wouldn't need a pump. You should lift that bucket so the bottom is a few inches above the collector and make sure the both inlet and outlet are submerged. I bet you could get the temperature up higher than you are getting it.


    10 years ago on Introduction

    Nicely done. I WOULD advise, however, to NOT remove the "support wires". They add a significant heat exchange surface. Also, there are built-in standoffs.. holding the radiator a short distance from the reflector...for better secondary heating(reflected). If you can't find(or it's too expensive) the ducting insulation... Pink foam insulation and a $1 space blanket work admirably. be careful though, as even in the winter, these rigs can heat cold water to scalding temps. I had one, a few years ago, made almost the exact same way... hooked to a table fountain pump, mounted inside the toilet tank. Kept that whole toilet nice and toasty during the winter. Tank, pedestal, and even the seat were warm to the touch. Along with the water line(insulated copper) I also ran an electric cable. On one end was the pump, the outside end mated to a solar panel. During Daylight hours, the panel pumped the water up to the "Thermal Collector" continusouly. When the sun set, the solar cell stopped powering the pump, and the water drained out of the collector, preventing freezing problems. Material cost were about $5 from the junkyard(where they safely recycled the refridgerant) and $20 for the solar cell(I think it was an automotive battery tender). As an added bonus, the bathroom stayed nice and toasty too, from the free radiant heat.

    2 replies

    Reply 10 years ago on Introduction

    Hey, ironsmiter will ya do an instructable for it??????? I need something like that.


    Reply 10 years ago on Introduction

    hmm, sorry. I've got a metal roof now...so it's a bad thing to drill random holes, to experiment :-( If you need something like that... begin by using this ible(and possibly those in the related section at the bottom of the page) to create your heater box. With that done, put your pump into a bucket of water, and hook it up. Give it a go, and see how hot it gets. It really is just basic plumbing. To answer the question simply, NO. I won't make that instructable. If, however, you want my help/guidance/advise in making your own, and want to give me a little credit when you write up YOUR instructable, I'd be glad to accept :-) One serious drawback is, during the summer, you have to unhook the system. Also, in houses with good climate control, it's fairly unnecessary. That setup is really only good for old, drafty, cold houses. I had convection radiators on the first floor, and NOTHING on the second, so the upstairs bathroom got a bit chilly (electric heaters supplied what upstairs heat was needed, for most rooms). I suppose, in a hunters cabin, it might work fairly well. Second drawback was, I had hard water. this required bi-annual maintenance on the rig. I'd have to sit the pump in a bucket of lime-away mix to clean the system out, otherwise it'd clog up :-(


    10 years ago on Introduction

    Good instructable. I'm a little confused about the placement of the inlet/outlet hoses, and can't figure it out from your photos - maybe a diagram or more photos would help? I have all the materials for this, having meant to build one from an earlier instructable. I have a pump, but I'd prefer to use the siphon method as yours does, but again, I can't see or figure out where the hoses go, and it seems that's critical to making this work. Also - and this is minor - you noted that you had results from your testing, but aside from noting the temp that day was 41 degrees, there aren't any notes about the water temp - how hot did you get it, and how long did it take? Once I've built mine, I'm hoping to show this as an experiment to my children's classes, both as a green way to heat water and as an exercise in recycling. Thanks!

    1 reply

    10 years ago on Introduction

    one could use this on a large scale and heat their house using pipes under the tile floor very similar to the copper cricket except the copper cricket uses methonal heated then heats water with that that water is potable they are out of business now most water heaters use pumps and that takes energy so not very efficient

    1 reply

    10 years ago on Introduction

    use 2-3 magnifying glasses and concentrate their heat on copper pipes!


    10 years ago on Introduction

    I hope that no one misconstrues this Instructable for heating potable water.