I started down this road couple years ago. Lets do some math:
100watt load to run for the night = 12 hr.
Assumption: you can superheat the water 10 deg. Low temperature heat engines may achieve 10% efficiency.
3.4BTU/watt-hr * 12 * 100w = 4,080BTU * 10 / 10 = 4,080BTU needed. Water has 1 BTU per deg per lbm or 4,080 lbm / 8.35lb/gal = 488.6 gallons
Two golf cart batteries supply more power discharging to 50%.
You can build a larger cheap tank, the other equipment cost are higher than the equivalent solar electric would be? I decided to cool the solar panels to improve their efficiency for the best bang for the buck.
Use the waste heat to melt the snow on my drive way and side walk. Assuming the homes heating needs are met.
Have fun, Scott.
100W of Seebeck devices at ~5% efficiency didn't look like being horribly expensive from the first Chinese site I ran across...
So I guess the nearest obvious apples-to-crabapples comparison is whether the extra water tank capacity that I might put in to support slow energy release overnight is more expensive than the batteries that I might use instead, but the value of that excess capacity in winter is storage of heat for dull days and the generation side-benefit is a lucky bonus.
(Oh and heat leakage from the tank in winter might help take the edge off space-heating requirements.)
So really the point is if the Seebeck devices and supporting nonsense cost more than batteries. Which is I think the analysis that I shall attempt to apply.
Thanks for your pointer!
Rgds
Damon[ Parent ]
Have you looked at PEX for the tubing?
I have designed a zero energy home with the solar features built into the structure, cost adder is 10% above standard construction. No energy bills. Looking for someone with a workshop to test it out. don't want to build a complete home without testing the ideas.
Have fun, Scott.[ Parent ]
I only just saw this post: sorry to miss it.
I can't seem to get any consistency in U-value for papercrete. Do you think it would be better or worse than foam?
Check out http://www.livinginpaper.com/index.htm
Papercrete R2 to R3 per inch, depends on the mix. (how much sand, concrete etc) Foam is R5 to R7 per inch, with a cost of $4 to $6 per cubic foot. I can get 5 tons of paper for free, the Portland cement will cost (?), I saw a 80lb bag for $6 last year.
The papercrete is so much cheaper, use twice the thickness to get the same value or more. A local recycle center will not take foams without a recycle label on it. You could request some and grind it up adding it to the mix for greater R value if important to keep walls below a certain thickness. Many things you can do, let us know what you have in mind. Glad to help.
Thanks for the link! Will read shortly.
Space is a huge constraint for me, but I know that I'm going to need a mix of materials in any case if I do it.
The thing is, by my estimate, I need amazing insulation since I would need to try to keep losses from the tank at or below ~10W (yes, ten Watts, not W/K or kW or 'what'ever) even with an outside temperature of ~10C to retain most of the heat between seasons.
Digging a cellar under our porch at the front of the house is looking like one solution providing that the local maze of drains/sewers doesn't pass under it.
To hit 10w for any tank of size is impractical. Vacuum insulating panes might do it. Very costly.
Retaining heat between seasons look into ground source storage. Dry well, store the heat in the ground, large area can store huge amounts of energy. This is my plan for driveway heating, store the heat below. Bring heat up when it snows.
In another area store the cold from winter for use in summer cooling. Or do like the pioneers did, ICE house, even thin insulation in ground a large block if ICE can run your fridge and AC all summer long.
However, I had a slight brainwave. Instead of a 5t tank losing 10W (10% loss of stored heat over 6 months), why not use a 10t tank losing ~100W (~50% loss of stored heat over 6 months)? The extra energy to put in the tank is readily available in the summer, and I need only ~10% of the insulation, ie something like 50cm instead of 5m+.
The downside is that we'd definitely need to dig down to accommodate a large enough tank as we just don't have lots of ground space. But we might not have to dig much.
