# Solar Storage Tank



## Kevingr (Mar 10, 2006)

Hopefully this won't be a politically charged topic, as we've been seeing here lately .

I need to build a storage tank, I'm still working on the details of it's size as I read through Solar Gary's info, Solar Water Heating by Bob Ramlow and Solar Water Heating Systems by Bill Keisling. But, I am thinking about materials for the tank. 

My tank will not be in the ground, it will be in my basement, heavily insulated. Instead of building a wooden box and using some kind of liner, why not just use a Cattle trough? A cattle trough is only about 2' deep though, but they are relatively cheap. Or is there a benefit to being deeper and not having so much surface area?


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## wy_white_wolf (Oct 14, 2004)

They do have oval troughs that are about 3' deep. You could find 2 of them (one larger than the other) and place one inside the other and fill the gap with foam. Couldn't find one on the web quickly for an example. I have one up at that ranch that we plan on using with a rain catchment system.

Wonder if you sealed up an old chest freezer if it would handle the weight of being filled with water?


Edited to add:

P.S. How dare you try and start a thread that isn't politically motivated!


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## WisJim (Jan 14, 2004)

The advantage of a cattle tank is that they are made to hold water. The plastic ones wouldn't corrode, and would be a little insulation, too. That would work if it stored enough volume of water for your purposes. Build a well insulated cover for it, and you would be all set. Runn all the piping in through the cover so you have no places for it to leak water.


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## Jim-mi (May 15, 2002)

scratching my head as to your worrying about a tank of water becoming a political thing.


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## Kevingr (Mar 10, 2006)

I was following the Abc and the Volt thread, 'tis a bit political, but interesting. I don't normally see such threads here in this forum.


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## SolarGary (Sep 8, 2005)

Hi Kevin,

I thought about the galvanized stock tanks. I ended up building the wood one with the EPDM lining mostly because the shapes they offered did not work out well for my space. But, I did wonder how the galvanized tanks hold up to hot water over the long term?

I would not use a plastic tank that is made of polyethylene. They start to lose strength around 130F, and that seems to low to me. They might work if you can give the walls some support, but the seem doubtful to me.


Did you see this one?
http://www.builditsolar.com/Projects/SpaceHeating/AlanTank.htm

Gary


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## Kevingr (Mar 10, 2006)

Yep, I saw that one, and it's a nice one. Smells like money!

Right now I'm not ruling out anything, just trying to narrow the field down to a few choices and cost is a huge factor.


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## Windy in Kansas (Jun 16, 2002)

Just one question about using a stock tank for storage--can you get it into your basement?

I don't remember the width of the oval tanks but the galvanized would be uniform sized whereas the poly tank would be tapered, if like most I've seen. I would sure want to take doorway and stairway measurements before making a purchase.


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## Kevingr (Mar 10, 2006)

I've got lot's of flexibility there, I have a trap door that goes down into the "dungeon" as my wife calls it. I can easily get a 96" oval stock tank down there, even if it was 4' deep. The house was built in 1895 and the basement was originally a cellar. After the cement floor was added we only have a 5'10" ceiling height, so the entire basement is truly a utility room which gives me lot's of options for equipment in the basement.


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## fishhead (Jul 19, 2006)

I bought some 500 gallon poly tanks from Litchfield. They cost about $450 each. Even if they deformed a bit they are circular so it shouldn't matter. They are open topped so probably isn't the best choice. Another option would be a plastic chemical sprayer tank. They're self supporting with ribs built in for strength.

It sounds as if your 5' 10" ceiling will limit the size unless your door is wide enough to accomodate a 8' tank lying down.


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## Kevingr (Mar 10, 2006)

Yep, an 8' high tank would be a problem, but an 8' diameter stock tank I can get down there. As I go into the basement through the trap door I can lay it down. 

An open top tank is fine, I'd just need to make an insulated top and run my lines through the top.

Sounds like a bit more research into temperature are in order.


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## SolarGary (Sep 8, 2005)

Hi,
Before buying a plastic tank, I would at least email the manufacturer and see what they think of the idea, and what they set as the max service temperature.

Its important that the lid seal to the tank well. My first one did not, and you get a lot of water vapor leaks, which tend to be messy and also reduce the effectiveness of the insulation. You do want a very small vent hole so that the tank does no pressurize.

Gary


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## Windy in Kansas (Jun 16, 2002)

I would think you would need a top on the tank to keep basement humidity down to prevent decay, insects, and fungal growth.


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## Kevingr (Mar 10, 2006)

Most definetly. You would need to make one and insulate it, and as Gary points out, ensure that it can withstand the heat.


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## PyroDon (Jul 30, 2006)

Ok a likely foolish question .
if you are planning to make this a perminent part of your heating ,why not section off an area drill the concrete floor and build a re-enforced block wall.
insulate the inside with 3-4" of rdgid foam then line with EPDM.
Now as for watter storage i have a question . which stores heat better water or stone? somewhere I could have sworn I read stone stored longer or more because its denser . If that is the case ? wouldnt it make sense to place drainage type piping in the top and bottom and allow the water to flow through stones $


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## Kevingr (Mar 10, 2006)

The concrete tank would certainly work and be permanent, but would be costly. I don't know about the rock storage though, sounds like it would work.

I did a little more research and pricing and bottom line I think the cheapest alternative is something similar to Gary's tank, so I'm going to go that route. There's not a lot of question regarding heat and the break down of the tank and it offers many options regarding heat exchangers within the box. 

Now I just need to size it and get on with the other components. I'm thinking full sheets of plywood to make a 700 gallon tank.


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## fishhead (Jul 19, 2006)

I've got some experience building water tanks from plywood. Be sure to really beef up the supports on the side. I've seen tanks build from 6"x6" landscape timbers that should work.

You could always fill the tank with large rocks and water to increase your storage mass.


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## SolarGary (Sep 8, 2005)

Hi,
I think you are better off with just water and no stones for heat storage.

I'm going by memory here, but I think that the heat capacity of rock is about 0.22 BTU/lb-F, and water stores 1 BTU/lb-F. So, water is about 4 times better per lb for storage. This is partly offset by the fact that stone is more dense that water, but its not enough to offset the 4 times higher heat capacity.

Gary


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## fishhead (Jul 19, 2006)

What about using saltwater?


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