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 outer shell.

Ron made several changes to improve performance and durability.

The original version, which has a lot of the construction detail, is here...

Thanks very much to Ron for keeping us up to date on changes and improvements!

Version 2

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 2’ X 8’ piece. I didn’t 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 1’ X 8’ glass mirror(s) were replaced with a stainless steel mirror, also 2’ X 8’. Technically it’s 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 2’ X 8’ 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 “Mirror Metals”. The price for a 4’ X 8’ 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. I’ve also located a good quality water proof blanket from Mambe waterproof blankets. They make high quality blankets that range in price from $30 to $100+. They can custom make it for you. I’m 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. It’s set to 30 psi which I’m 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 it’s 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 don’t 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 :-/ .

Performance

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 I’ll 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. I’d 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 don’t 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) that’s 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 it’s probable that by the time the thermometer had reached that reading the water had cooled off. I’m 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.

Best regards,

Ron

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. It’d have to be solar powered though or any advantage gained in heat would be lost in cost.

Note: I think that this may not be a good idea unless the insulation around the batch tank is very good -- Gary

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 it’ll have to be one for the back burner (for now)

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 learn...

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