The solar water heater consists of two basic parts, the hot water tank and the solar collector. The tank is 310 liters (80 gallons), it sits in the attic and is insulated with spray foam insulation.

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.

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).

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 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. (Click Here to read more about this step) 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 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.

Close up of the bulbs and pipes, The entire array, The solar collector in the insulated box.
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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 Heater installed (before glass I tried transparent plastic sheeting but it wilted in the heat), Installing the Water tank
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The 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. Click here for more on how to connect it to the water tank.

On sunny days when the outside temperature is in the mid 80's the water heats up to about 135 or more. Even on cloudy days the water heats up to the 90's.

How to prepare the florescent bulbs

There are two ways to break open the ends.

Method #1:

The simple, but tedious way is to puncture them with a screw driver. Here's how I did it:
First I tore off the metal caps, then I put a screw driver in the end and wrapped a rag around. The rag is dual purpose. One, it helped protect me from the mercury inside (I also wore a mask and did it in a ventilated area), the rag also helped slow down the air as it flowed into the bulb. The bulbs seem to have a near vacuum inside them, so when they are punctured the air enters pretty quickly, and can propel some of the debris from the puncturing into the other end and break it. The rag helps slow the air down. After the bulb was broken on both ends I tapped out just enough glass so that a ½ inch pipe could fit in I found G.E. bulbs to be the easiest to work with. Afterwards be sure to wash your hands.

In the end the bulbs are just for insulation so they don’t have to be perfect. They just keep the hot air around the pipe, and the ends are sealed off with foil, which covers up a lot of the imperfections. Of the bulbs in my collector about ½ of them have breaks or small imperfections. But it doesn’t seem to matter, it still increases efficiency.

Method #2:

Here is a link to the other way to break open the ends. It isn’t nearly as simple. I haven’t tried it, but it was published in a magazine so I am sure it works. I found it with an article about a florescent bulb solar air heater. It uses common items to build a glass cutter. From what the site says, it should make nice looking cuts. Link to cutter instructions

Connecting it to the water tank - I put 5 holes into the tank. They are listed here from highest to lowest.

Cheap $30 Backup System for Cloudy Days:

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.

Why I built the solar water heater this way

After doing a lot of research on the internet, and a couple experiments I came to a few conclusions.

With this in mind I set out to design a solar collector. I priced copper but found it to be very expensive. PVC was much cheaper, but it does not withstand more that 135 degrees. This I found out not to be entirely true.

After some tests I found that the PVC pipe itself will withstand higher temperatures without losing rigidity, however I assume that the fittings would begin to fail at lower, but still hot, temperatures. I should also note that the water pressure in the collector is very low, just as much pressure as is created by about 2-4 feet of fall, others who had failures in their PVC fittings had put their heater inline before their water heater, as a primer. Unlike houses in the USA where the water enters the house already pressurized, houses in rural Brazil have water tanks in their attics to create pressure. So I figured that the max temp for my PVC would be higher than the standard since I have sub standard pressure and will subject the pipes to much less stress.

So decided to go with PVC and to insulate the fittings from the temperature inside the collector and protect them from sunlight. That way only the pipe itself would be exposed to the sun light and the highest temperatures.

Since I wanted to try to keep the heat close to the pipes I decided to use old florescent bulbs to act as a second glazing. The wind will cool the glass panels that cover the solar collector, which in turn cools the air inside the collector. The florescent bulbs act as another barrier. The trap in the hotter air around the pipes and keep it from circulating with the cooler air outside of the bulbs. In tests the pipes with bulbs heated up faster and to a higher temperature than those without.