Ron's Batch Solar Water
Heater from Stock Tank -- Version 2
This is an update on the
batch solar water heater that Ron did using a livestock tank as the
Ron made several changes to
improve performance and durability.
The original version, which has a lot of the construction detail,
Thanks very much to Ron for
keeping us up to date on changes and improvements!
I designed and built the tank about a year ago. Inevitably there were
lessons to be learned and thus changes to be made.
Version 2 of Ron's batch water heater
1). I have replaced the two pieces of
plexiglas with a single 2í X 8í piece. I didnít like the tape down the
middle of the older pieces or the potential leakage that could occur.
2). I placed another piece of the vinyl weather stripping directly under the
metal bars holding down the plexiglas. This was after the first glass
cracked under one of the bars near the end. No metal in contact with the
plexiglas. Also make sure the screws are tight enough to stop leaking but
not too tight. And make sure to drill the holes larger than the diameter of
the screw to allow for expansion and contraction.
3). The 1í X 8í glass mirror(s) were replaced with a stainless steel mirror,
also 2í X 8í. Technically itís referred to by the steel industry as #8
non-directional mirror finish stainless steel. This was necessary since not
only did the glass mirrors that were on before crack they also tarnished in
places caused, I assume, by moisture and heat. By the way, I did try the
Mylar on the 2í X 8í board, and while it did get hotter, I found the Mylar
to be of a flimsiness I did not like. Further, when I tried to glue it down
it ruined it.
Note: About the stainless steel mirror,
I had quite a difficult time locating this piece of art. Almost none of
the small, local metal shops had any idea where I could find it. Those
who did wanted exorbitant (I thought) amounts of money for it. One place
actually sold me what he told me was mirror finish only to find that
when I got it home and peeled off the protective plastic layer it was
nowhere near reflective enough. It was a #4. When I was about to give up
I learned of a specialty metal outfit in Oxnard, California called ďMirror
MetalsĒ. The price for a 4í X 8í piece is, at the time of this
writing $189.00. Since I only needed half that I found a metal shop that
carries their products about 60 miles from me which allowed be to buy
only half. It cost $125.00 - not cheap, but a lot less expensive than
the prices a couple of others who said they could get it wanted. Call
Mirror Metals for a list of distributors close to you.
4). A side benefit of the doubling of the reflector area is that I can now
completely cover the top at night to hold in heat and during storms. My
thanks to Gary for this idea, it was no small benefit. Iíve also located a
good quality water proof blanket from
blankets. They make high quality blankets that range in price from $30
to $100+. They can custom make it for you. Iím going to lay the blanket down
on top of the tank then lay the mirror lid on top of that. To make sure it
fits right, before attaching the lid to the wood posts behind I first laid
it on top of a blanket of usual thickness then aligned it with the posts and
screwed it on.
Click on pictures for full size
5). The pressure relief valve which I had situated inside the tank with a
pipe going from it to outside the tank was itself moved outside. This was
after I discovered that it would leak a couple of drops at the handle when
the pressure in the line increased. Over time this caused increasing
condensation inside the enclosure which would form on the inside of the
plexiglas when temps outside cooled down. Also the connected plastic PVC
fitting was changed to metal.
6). I added a water pressure regulator to keep pressure down inside the
core. It is placed on the lower incoming water line. Itís set to 30 psi
which Iím told should prevent any other leaking and protect the inside of
the core. The outgoing pressure is fine.
7). I sealed on and around the grommets on the outside of the tank with a
high heat silicone sealant just to add another layer of protection against
rain, I also intend to seal around the underside if the rim of the plexiglas
next to the weatherstripping. Note: Though itís not a big problem I also
plan to more solidly attach the metal washing machine hoses to the tank so
that there is no pushing or pulling on the grommets when the tank is
adjusted in height.
8). I removed the rebar that was holding the tank apart and just attached
the plexiglas supporting bar to the tank with screws, on top of which I put
a couple drops of liquid metal.
9). This one is more hypothesis so I donít really know what the benefit (or
detriment) might be. Rather than having the Reflectex lying flat on the
bottom of the tank I have lifted it off some under the core so as to provide
a pocket under the Reflectex for the cooler air to go. There are small
openings next to the 2 X 4s for air to go.
10). I had to remove the liquid filled thermometer after it not only turned
black but broke and leaked fluid. No liquid filled thermometers.
11). Of no importance other than looks, I painted the wood border light
green and added some glitter around the mirror. The latter might not have
been a great idea :-/ .
So far. Last year we had to switch back to
gas in November when it started getting really cold. Though on occasional
warm, cloudless days we switched back and got hot water (we could actually
take hot showers in January). This could be remedied some by having a
convenient, indoors way to turn the water going to the gas heater off and
the solar on and visa versa when needed rather than having to go outside and
freeze to do it each time. The other option would be to purchase a tankless
water heater to pick up the slack when the heat from the solar heater begins
to flag. But that would be an additional costly expense. It goes without
saying of course, but Iíll say it anyway, that the moment that clouds or
shade come between the sun and a solar heater it stops heating. If the shade
lingers the temps begin to drop.
I noticed happily that the board holding the mirror has curved a bit from
gravity due to its angle in relation to the tank so as to take on a slightly
concave shape which should focus the light more directly at the core.
Unhappily however, the curvature placed extra pressure on the ends of the
Plexiglas. This caused a small hairline crack in it. Thus I had to cut the
Plexiglas at the ends closer to the tank, about 1 inch away. In researching
repairs it is recommended by others that a tiny, 1/16th inch hole be drilled
at the end of cracks which stops them from just continuing on. Then an epoxy
resin or solvent is carefully filled in the hole and along the hairline.
Weld-On brand or TAP acrylic cement has been suggested. Iíd use some kind of
tape, perhaps rubber electrical tape, and lay it right up to the edge of the
crack while gluing to stop the epoxy from going where you donít want it.
The updates I made as described above are too recent to have any real
performance information but in general the water is getting hotter, though
not as hot as had I thought it might. Still when you can take a hot shower
the next morning (after a hot day previous) thatís pretty good in my book. I
checked the water temp coming out of the pressure relief valve with a candy
thermometer. When the internal air temp was about 200 F or maybe a bit more
the water was about 150 F, though itís probable that by the time the
thermometer had reached that reading the water had cooled off. Iím thinking
about a way to screw in an automobile water temperature gauge to directly
read the water temperature since the thermometer I have sitting on the tank
now only reads the air temperature.
Update from Ron May, 2011:
I've been wanting to mention that I figured out the benefit of
doubling of the mirror size on my solar batch water heater. While it
did increase the actual average temperature somewhat, about 5 +
degrees, the real benefit is that MORE water in the tank is getting
heated. That means that I've been able to turn off the gas and use
solely solar two months earlier than when the mirror was half the
size. So for the past two years I been using it from the first of
April until the first of November rather than the June to November
period it was before.
Other ideas. I have wondered about the feasibility of attaching a heating
element to the inside of the tank to aid in heating during the winter. Itíd
have to be solar powered though or any advantage gained in heat would be
lost in cost.
During the course of the year someone sent
me an idea for a solar powered device that would lift and lower the lid
automatically in response light. While it sounds great itíll have to be one
for the back burner (for now)
Note: I think that
this may not be a good idea unless the insulation around the batch
tank is very good -- Gary
Ron October 2009
Solar tank wildlife
A couple further notes from Ron:
A couple of other notes. I've heard that Lexan polycarbonate would have
been a stronger alternative to the acrylic plexiglas I used. Live and
This is true -- polycarbonate is both more
impact resistant more temperature resistant that acrylic (Plexiglass)
It is also important to get the type of glazing with a UV filtering
coating on it to prevent yellowing. -- Gary
By the way, about two weeks ago we had very strong winds accompanied by
about six inches of rain here, 65 mph winds all day and into the evening
that knocked down some of our tree branches and tore tiles off the
roof. They were so strong that at one point, after I had put a 35 lb (I
weighed it) concrete block on top of a heavy board to try to hold the
tiles on over the porch, while we were sitting in the house feeling it
shake around us suddenly we heard a loud booming above us. The concrete
block was being pushed up the roof! It came down the other side
and crashed a hole in the back porch smashing two boards. The board that
it had been holding down we found in the field next door. We were also
without power for 34 hours. Yet the solar water heater came through
unscathed -- Yea!
Gary October 28, 2009