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$300 Homemade Solar Water Heater - Made with Florescent Bulbs

How Do I...

How do I build a cheap solar water heater large enough to provide hot water for my house?

How to Find the best Angle and Location to Install your Solar Water Heater
Why I Built my Solar Water Heater using Florescent Light Bulbs.
How to Puncture Florescent Bulbs
Tags: Solar, Water Heater, Passive, PVC, Thermosyphon, Florescent, Green

How To

Summary: This how to will help you build a solar water heater that can heat 80 gallons (310 liters) of water to 135 F or 55 C.

Before I get started here is some basic info about this solar water heater:  it uses PVC instead of copper (to reduce cost), to increase efficiency I sheathed the pipes in the collector with glass tubes made from old florecent bulbs (Click here to see why I used Florecent Light bulbs), the solar collector is approximately 27ft2 (2.5 m2), it includes a $30 backup heater for cloudy days, it is a passive solar heater, so there are no moving parts - it relies on a thermosyphon to circulate the water. Heating water requires a lot of energy. For example here in Brazil we use instant water heaters that are built into the shower head. To raise water by 45F degrees (from 60F to 105F) about 5,000 to 7,500 watts are required. That is equivalent to heating your shower water with four or five microwaves on at the same time! In America typical water heaters have 4,500 watt heating elements (think 45 100 watt light bulbs on at the same time). Needless to say with electricity costing 0.22 cents USD per kilowatt hour here in Brazil, there is a financial incentive to find an alternative way to heat water.

Step 1 - Find the location

For more help, check out: How to Find the best Angle and Location to Install your Solar Water Heater 

 First you need to find the location for your solar water heater.  Since this system relies on a thermosyphon to circulate the water, location is important.  Here is how a thermosyphon works: as the water in the collector warms up it becomes less dense and moves upward, pulling cold water into the collector.  For this to work the collector needs to be lower than the hot water tank so that the hot water can rise into it.

My tank ended up in my attic and the collector is attached to the soffit.

Step 2 - Building the Panel

Collector in the Box

PVC parts put together

The Ts and Bulbs

After I found my location I started building the solar collector.

The solar collector is made up of 1/2 inch and 3/4 inch PVC pipe and florescent light bulbs. The collector is encased in an insulated box with glass on one side. To make the plumbing part of the heater I bought 64 T fittings and with them made 2 pipes, 32 T's each with the T's butt up against each other. Then between the two I put a pipe that was just a bit longer than a florescent bulb. To prepare the bulbs (THE BULB ARE ONLY USED AS A SLEEVE, no water runs through them) I tore off the metal parts on each end, then poked a large hole in both ends so that a 1/2 inch pipe could fit through.  (How to prepare the florescent bulbs)  Then I pushed a piece of a sponge through a couple of times to clean out the powder. When I was done I had a long clear glass tube. While I was taking apart the bulbs I used a mask and was sure to wash my hands and cloths afterwards, since they contain mercury.

The bulbs were painted black on the back side, and the pipes were completely painted black. Then I closed off the ends of the bulbs with tin foil and a bit of spray foam, since they are just used as a basic insulator its not that important that they be air tight. The solar collector was lined with black plastic, underneath were some Styrofoam sheets to help insulate the heater.

The solar collector is approximately 2.5 m2 (27 ft2), the pipes that are exposed to the sun have a total volume of about 18.5 liters (5 gallons), which is equivalent to 6% of the volume of the hot water tank. (Meaning that if the water circulates 16-17 times all the water in the tank will have been heated once, in theory).

Step 3 - Installing the panel

35 degree angle

For more help finding your latitude and the proper angle for your collector, follow this guide.

My panel was installed at a 35 degree angle and about 1 foot below the bottom of the water tank. It is below the tank so that it does not act as a water cooler at night. Basically, the cold water is already at the bottom, so it should not circulate with the water in the hot water tank.

To install your panel you need to first figure out at what angle to install it since this will vary depending on how far you are from the equator.  I am 25 degrees from the equator. That means that on an average day (ie, during a equinox) if my panel is at 25 degrees the sun will hit it directly during the noon hour.  By offsetting it by 10 degrees it extends the time period in which the sun has good coverage of the panel.

Step 4 - The hot water tank

I used a 80 gallon (310 liter) water tank that is made for cold water.  But after some foam insulation I was able to make it into a hot water tank.  Then I had to add some holes.  Here they are listed from top to bottom:

-Over flow - just a pipe that carries water out of the tank if the float were to malfunction and it were to over fill. -Water Intake Valve. Just a pipe and float that fills up the tank with more water as we use it, similar to what is used in a toilet tank. -Hot water pipe. This feeds the house with hot water. It is above the two pipes that feed the solar heater so that there is always water in the solar heater. This protects it from over heating if our water pump shuts off and no water comes into the tank to replace the water we have used.

-Return from Solar Heater. This pipe connects to the top of the solar heater, and to the top of the tank, just below the pipes above. As the water is heated it becomes less dense and rises. As it rises cold water takes its place. So the hot water flows slowly through the return to the top of the tank.

-Supply to the Solar Heater. This pipe connects to the bottom of the solar heater, it also connects to the bottom of the tank. It supplies the solar heater with the cooler water that settles to the bottom of the water tank.

Step 5 - Backup Heater

While I was installing the tank I added a $30 backup heater.

On mostly cloudy days the heater reaches about 90 degrees, on very cloudy and windy days it wont get above 80 and may only reach 70. So I came up with a backup. (Note: while I have this tested and installed, I actually have it unplugged to save electricity). I bought a 'Bucket Heater' that automatically turns on at 80 degrees and turns off at 110. I suspended it inside the water tank so that it only heats the upper portion of the water. I assume that if it were resting on the bottom that the hot water would rise. By the time the hot thermostat measured 110, the water at the top of the tank would be well over that.

Step 6 - Make a Solar Water Heater that Pays You

This solar water heater is paying itself off faster in ad revenue than it is in energy savings.

This site,, is a revenue sharing site.  If you build a solar water heater, or really anything else, sign up (its free) and post your instructions. With a little luck your invention may start making you money.

Additional Resources

... ... - Solar Water Heating Projects and Plans

The most comprehensive list of DIY solar water heaters.  A great place to go for ideas and information.

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General Comments

2010-12-26 09:38:57franjavbier comments:
hey, great question is if have used just PVC or CPVC??...thanks. Francisco, Chile

2010-12-26 10:27:42jake comments:
I used PVC. I do not have access to CPVC, otherwise I probably would have used it.

2011-01-30 22:33:28ajfranks comments:
nice work. one question: did you use pvc or cpvc glue?

2012-04-24 03:06:49specterdetector comments:
Super cool idea. One thing to look into, you can get Legionaire's Disease from standing warm water.. This aquatic bacteria thrives in temperatures between 25 and 45 °C (77 and 113 °F), with an optimum temperature of 35 °C (95 °F). You should try to keep your hot water above 120° all the time.

2012-04-24 03:10:25specterdetector comments:
..sorry, that's 140 degrees F.

2012-09-10 06:20:25ldebernardi comments:
Could you post a parts list?

2012-10-16 20:47:09mikorians comments:
120F they start to die real slow. How about experimenting for us using a silver ion spa device (instead of a really really expensive ionizer) like: Freshwater AG+ Continuous Silver Ion Purifier for $25 Meant to hang in your pool drain, lasts 4 months. This way, perhaps tepid water wouldn't be so evil. Experiment:REQUIRED before use. It says certified for drinking water...

2012-10-18 17:24:26mikorians comments:
Try using a spa ionizer module if you're worried about contamination. They're only $25