Solar Hot Water. Indispensable Money Saver.

We decided to use a Solahart (now Rheem) system for our domestic

solar hot water

heating because several other people that have built Earthship style homes in the area have used it. It’s a thermal siphon system that requires no pump if have city water. It has some drawbacks in cold climates. For one, the domestic water supply and return pipes run outside and exposed to the cold. They must do this because that is where the 80-gallon heat exchanger/storage tank is.

Solar hot water. Exposed pipes on Solahart.

Exposed pipes on Solahart.

Solar hot water. Exposed pipes on Solahart.

Exposed pipes on Solahart.

The tank must be above the collector panels, and the whole system design is for a roof. It is possible to have the collectors outside and the tank inside and above the collectors. However, this requires the extension of some metric size copper pipes, and possibly some significant architectural changes to the structure.

Our solution, which allowed us to install this system temporarily on a small cabin, was to encase all but the collectors in a big box.

Solar hot water. Covered Solahart tank.

Covered Solahart tank.

The supply and return pipes are further encased in a 2-inch rigid foam box tunnel, inside the big box. A small 12-volt box fan pumps warm air from the cabin through the pipe tunnel. This has kept the pipes from freezing for many years. The fan draws just a little power from our trailer battery and single solar panel.

This system seemed to work fine, and provided us with good hot water in all but the coldest days of winter. However, by 2013 (8 years after the installation of a replacement set of panels) we began to see a decrease in the water temperature we were getting. By late spring 2014, we knew we had a problem.

I checked the glycol in the system and found it was low. I added some glycol I had to the system and it improved for a day. The next morning I noticed a puddle of glycol at the bottom of one collector and knew I had a leak. I pulled the leaking collector out and replaced it with one of the original collectors (I’ll go into why I had 2 sets of collectors shortly). I filled the collectors with water and pressurized it to around 12psi for testing. When I was sure the system was not leaking, I drained the water and installed glycol. The system is now working OK.

Now I come to a big problem with


collectors, corrosion!

When I disassembled the leaking collector, I was amazed at what looked like rust on the black surface of the collector plate. I thought that maybe it was something in the Black Chrome surface paint. I knew copper would not rust like that.

I pulled the plate out of the box structure to find a leak that I determined was on the bottom. What a surprise I got; these plates are made of STEEL , NOT COPPER . My experience goes back to the old days when all collector plates were copper. Back then everyone knew copper was one of the best heat conductors, and that steel would corrode.

And that’s exactly what happened to this collector plate. The bottom pipe of the collector had massive amounts of corrosion on it. It was so bad that it ate a hole through the aluminum outer case, just under a corner plastic piece. When I removed the rust, I ended up with many holes, as you can see from the photos.

Solar hot water. Corroded Solahart panel.

Corroded Solahart panel.

Solar hot water. Holes in bottom manifold.

Holes in bottom manifold.

I’m sure the corrosion was caused by condensation inside the panel collecting in the bottom of the case and causing a reaction between the steel plate and possibly the rock wool insulation. The top pipe on the collector plate is fine.

So now I have to worry about the other 3 collectors and a way to repair this one before another one starts leaking.

Solar hot water. Holes in bottom manifold.

Holes in bottom manifold.

I tried silver soldering with Dynaflow, but the steel is to thin, it just melts. Next, I will try an epoxy and fiberglass mixture. Many fuel tanks are made this way. I’ll let everyone know how it comes out.

In closing, I would like to answer the remarks I made on the Solar Energy Page , and ask for some comments on what is a good collector:

First, on the Solar Energy Page I stated that I would not be using Solahart on my house when it is completed. Now you know why.

Second, I said I had 2 sets of Solahart collectors. I noticed the first set was getting condensation inside after just the first year. It did not worry me to much because I had seen many collectors with condensation in the past. However, I contacted the Solahart rep and he said I should not be getting condensation in my collectors and he would send me 2 new ones right away, I need not return the others. That is why I have 2 sets of Solahart collectors. Do you think the rep knew something? He sure did not want the first set back.

Thirdly, does anyone know if all solar thermal collectors are steel now? Was I stupid for assuming collectors would still be copper? Is anyone else having these problems with Solahart? I have seen a blog where people were taking about some fungus buildup inside of Solahart collectors. Guess what, it’s not fungus, it’s corrosion!

Please send a comment if you can answer any of these questions.

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