Solar Hot Water Storage Tank


Well I started designing the storage tank last weekend.  I stuck with my original
plan except that I am going to make my first tank with a 55 gallon food storage
drum a friend at work had. 

Here is a picture of the barrel. It has two access ports on the top.  I put some
of my left over PEX inside to see if I could spool it thru for a heat exchanger.

I don't really want to cut the drums top off, so for now I think I will just use this
as a test storage tank to check on the collector and insulated wall solar performance.

I built some wood frames out of 1x6x6 fence pickets I got at home
depot for $1.19 each.  I also bought a roll of R-19 insulation to
put inside the frames.  Here are some of the frames.  I can do this
since the box isn't going to required to hold back the water since I
am using the barrel.  It just has to hold up the insulation.

Next I put the barrel inside my frame to check for fit.  Each wood frame
connects at right angles to the next frame.  I just put a couple of wood
screws between each frame to hold them together.  It ended up being pretty
rigid considering it is made of just 8 pickets...

Next I stapled some roofing felt I had to the backside of each frame to give
each wood frame a back wall to hold the insulation in place.  I trimmed
back the insulation off the wide edge so as not to provide an air gap
between the 1x6 and the felt for heat to escape.  Here's a view inside the
frame where the barrel will reside.

Next I just cut my insulation and stapled it into each frame.  The frame size
ended up being just right for the two strips of insulation (30 inches wide).
Here is a picture of the 4 walls with insulation stapled in.

I had to take this apart and reassemble outside before mounting the
insulation in since the box was bigger than the door to the basement....

Next I built a floor wall out of some old 2x4s and R-13 insulation I had left
over.  I put some OSP for the flooring and tried to cheat my outside walls
in a bit to get them close to the edges of the barrel.  The flooring needs to
be strong since the barrel filled with water will weight around 450 lbs.

Next I just need to finish the top cover out of my last two 1x6 planks and
R-19 insulation and then plumb it with an inlet, outlet, pump and connect
to the pump controller I built.  But that will need to wait till I get my pump

So far here is how much this storage tank has cost.

Storage Tank ‎‎‎(55 Gallon)‎‎‎ Cost


I decided to abandon the enclosure idea above because I became worried that the loose insulation would get wet due to the high humidity of the hot water.  The other problem is the other encluse got really big due to the 6 inch walls. A buddy at work had some 3 inch styrofoam he wanted to get rid of that he was taking out of an old hunting cabin.  So I got some of it and decided to make my enclosure out of it. 

Here is a picture of a piece of it as I'm getting ready to cut some wall pieces out.  It cut easily with a kitchen knife.

Here are 4 walls cut and you can see the base piece under the barrel.

Next I got the jig saw out and cut out a big hole in the top of the barrel to get the heat exchanger and pump in and out easily.  I drilled 4 cornet holes with a 1/2 inch drill and then used a jig saw to cut it out.

I decided to wash out the barrel good and took it outside to clean it up.  At this point I needed to wire up my water pump to the myDTC temperature controller.  I am going to use the controller to turn the pump on when the solar collector is hotter than the water in the tank.  I am using 3 or the 4 temperature inputs on the myDTC:

T1 - This is measuring the solar collector panel temperature
T2 - This is measuring the temperature of the water in my storage tank.
T3 - This is measuring the ambient temperature

Here is a picture of the temperature controller and a AC plug wired into the temperature controller relay output.  The water pump is plugged into the plug which will get power when the solar collector temp is hotter than the water.

Here's a link to my website I use to sell these little differential temperature controllers with logging capability

Here is the temperature sensor for the water.  I took the sensor and put a big piece of aluminum tape on it and hung the sensor in the barrel until the aluminum tape was submerged.  Eventually I will waterproof the temperature sensor, but for now this will work...

Here is a picture of barrel showing the water pump at the bottom of the barrel.

I lashed the styrofoam walls together with some rope for now to do some outside testing.  Eventually the tank will be inside the laundry room next to the hot water heater.  The enclosure isn't perfectly air sealed since I want to be able to take it back inside and its too big to fit thru the door all put together.

In the picture you can see the PEX tubing coming in and out of the tank and the lashed together tank.  I ended up cutting some little tunnels at the top edge to fit the PEX under the cover piece.

I put the top on and started the temperature controller and programmed it to log temperatures every 15 minutes.  I will check back in a couple of days and provide the logging data so we can see how well it worked.