Wednesday, October 10, 2012

Off-The-Shelf DIY solar water heating -- Version 2

I've had a bit of a reset on the Off-The-Shelf solar domestic water heating system.

The idea of this system is to provide a very easy to build DIY solar domestic water heating system that uses off the shelf collector, tank, controls, etc.  -- a system in which you just install the off the shelf components rather than building your own collector and tank.  The objective is to keep the total cost to about $1000 (compared to about $8000 for commercially installed systems).

The first version of this system used plastic mat style pool heating collectors installed in a horizontal format and at a not very steep tilt angle.  I've decided to change to a vertically oriented mat style pool heating collector installed at a steep tilt angle.   The advantages include an easier and cleaner installation, better cold season performance, less susceptibility to summer overheating, and more flexibility in trying a vented glazing system to increase winter performance without overheating.

The new collector
The new collector is a single 4 by 10 ft pool heating collector mounted off my existing Solar Shed.  The vertical mount appears to be more secure and less subject to sags and folds -- it basically hangs from the upper manifold with straps to secure it from winds.  Its easy to install and appears to be quite secure.
More collector area could be provided by going with a 4 by 12 collector and/or adding a 2nd collector.

The same Softank that was used on version 1 is retained.
The plot below shows one sunny days performance.

Sunny day performance
On this sunny October day, the collector heated the 132 gallons of water from 83F to 110F.  It was mostly sunny with an ambient temperature of about 70F -- so, this is quite nice performance.

For later in the season when ambient temperatures are lower, I intend to try some form of vented glazing to see if the winter performance can be improved over that of an unglazed collector -- stay tuned.

All the details on the build and performance to date...

If you have any ideas for improving this design, please let me know.



  1. this sounds like a very good alternative to the commercially installed ones. I hope you'd give us a step by step process on how to create one or install it.

  2. Have been busy on other stuff lately, but just logged a full day yesterday (11/15/12) -- a nice, full sun day with outside temperature in 20'sF and snow on the ground. No glazing on the collector.
    It did surprisingly well taking the tank's 130 gallons up from 73F up to 93F. So, somewhat surprisingly, it can do pretty well on a nice winter day even in MT.
    Hope to get into testing with and without "leaky" glazing soon.


  3. How would you compare the Softank to your plywood tank, in terms of cost, flexibility, durability and so-on? Would there be any issues with storing either one outside? I don't have a lot of space in the garage, so I was thinking about storing it outside on the other side of the wall and running the plumbing through the wall into the normal water heater.

  4. Hi -- I'd rate them both as durable with a good long life. The plywood tank has more flexibility on size and shape, as you choose both. For the size of the Softank, I think the total cost is pretty close -- the plywood tank might be a little cheaper.
    Both would be OK outside, but would need protection from the weather. My Solar Shed tank lives in what is basically a garden shed and works fine -- even with temperatures down to -30F.

    Both good tanks.


  5. Hello Gary

    Just wondering how far you are with the glazing part of this design?

    I think that is the key to improving year round performance for these pool heating collectors and making them viable for domestic hot water heating.


    1. Hi Bruce,
      I have been trying a couple things.

      I should have something up on the results next week. As a rough assessment, the current glazing scheme comes in on efficiency about half way between the no glazing version and a top quality commercial glazed collector.

      There may still be some improvements that can be made to the glazing scheme to do a bit better.



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