Solar heat for the shop. ^5's Morris!

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dpb wrote:

A really accurate answer would involve more waffling than I can tolerate (weather patterns, geographic location, snowfall, whatever's in front of the panel, ad nauseum) so I'll give you the short, over-simplified (and somewhat conservative) answer that each two-foot section delivers heat comparable to a milk-house heater on "High" when there's no snow on the ground. If there's clean snow between the panel and the sun, then add 75-90% to account for reflected energy.

Although there isn't one, the panel /acts/ as if it had a moderately hefty blower. For really good heat distribution, it's difficult to beat a ceiling-hugging variable speed ceiling fan turning slowly to prevent heat stratification near the ceiling. On my web page with the shop photos, you can see the ceiling fan right in the middle of the shop - it's used to both prevent stratification and to push warm air down to warm the floor, which is what keeps the shop warm overnight. Without the fan, it'd still be warm during the day (but less evenly so) and it'd be probably 5-10F cooler overnight.
As summer approaches, the vertical panel shuts itself off by reflecting more and more of the sunlight to the ground in front of the panel (DAGS "critical angle" for a technical explanation).
To shut the panels completely off, you could install a cover over the glazing - but none of my customers have yet done this (and they all asked the same question <g>).

They replace all but the inner surface (drywall or paneling) of the wall. The barn would need to be reasonably "tight" and "well-insulated" for /any/ kind of heating to be worth the money - and you're right about adding a "high tech" look to historical structures...
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Morris Dovey
DeSoto Solar
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Morris Dovey wrote:

More on this at http://www.iedu.com/DeSoto/Astro/Seasons.html
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Morris Dovey
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Soooo.. if I were to put a 4x8 sheet of something...like white melamine in front of this panel, on the ground.......
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Soooo.. if I were to put a 4x8 sheet of something...like white melamine in front of this panel, on the ground....... *************************
An interesting idea. The material would need to be stable, durable and highly reflective. It would probably need to be washed now and then too. I don't think birds could resist using such a bright surface as a target.
Still....., if this works, it would just improve the numbers on payback, etc.
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Robatoy wrote:

By George, I think he's got it!
Heh - how about a little spray adhesive and some aluminum foil on that melamine if you're going to be /really/ greedy?
Or... You could get a dozen 4x8 sheets of rear-silvered polycarbonate mirror material and make your shop really toasty. :-)
See photos at http://www.iedu.com/DeSoto/Projects/Stirling/Heat.html to see how to produce serious warmth...
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Morris Dovey
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Morris Dovey wrote:

Do you watch Mythbusters? :-)
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-MIKE-

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-MIKE- wrote:

I've heard of but never seen (no cable TV). What did they do?
This heat, BTW, is used to run an engine whose only moving parts are air and water (in keeping with my fondness for keeping things as simple as possible).
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Morris Dovey wrote:

They did an episode on Archimedes' Death Ray, which purportedly was used to burn up attacking ships out in the sea. Thousands of solders holding mirrors pointing at a ship.... phhhhhew, it bursts into flames.... so legend has it.
Some of their "experiments" closly resembled your parabolic. I'm guessing a youtube search could yield both episodes in their entirety. Although I'm guessing there would be a lot of, "Nooooooo," and "That's not how you do it," coming from your lips. :-)

I'm really enjoying reading your info. Ever work with geothermal? Not volcanic steam they get in Greenland, but piping buried underground to get the constant 55 degree temp.
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-MIKE-

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-MIKE- wrote:

Yuppers, I'd read about that. I've heard that references have been found to a description of a steam engine in the Library at Al Iskanderia.

Yeah, I'll admit to being at least that much a geek. Isn't it amazing just how little of all this technology is actually /new/?

I haven't, but here's a bit of native Iowa geothermal technology:
http://www.cobett.com /
The gentleman whose shop you looked at has one of these and added horizontal plastic pipe runs at the bottom for a bit of added heat. He introduced me to the guy who came up with the stock waterers, and I can vouch for him being a good guy to do business with (blatant plug).
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Morris Dovey wrote: ...

I'd be most interested in that, too, Morris...
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dpb wrote:

Here it comes 'round again:
http://www.cobett.com /
:)
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Morris Dovey wrote:

Oh, sorry...I thought that was an indirect connection referred to.
I'm on way out of town; will check at some more length later on.
Am still curious about the approximate Btu panel output, though...
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wrote:

There was an interesting article in the Nov PM mag about an Arizona company named Stirling Energy Systems. They're testing a 38' wide dish powering a 25KW Stirling engine that heats and cools hydrogen gas. They claim to have set an efficiency record for a commercial solar device at 31.25 %.
After reading that, I'm wondering how many mirrors I can glue to my neighbor's old 6' satellite dish.
Mike O.
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Mike O. wrote:

Unless you're looking for a new hobby (or have bottomless pockets) don't get caught in the efficiency trap. An increase in efficiency allows you to get a little more out of an improved engine, usually at a greater cost. Each increment of additional efficiency is likely to cost appreciably more than the previous.
With this technology you can almost always arrive at the output you need by scaling up an appropriate amount and using a bit more of that free sunshine - without having to pay the penalty for bleeding-edge efficiency.
Methinks their efficiency record won't stand long. :)
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Morris Dovey wrote:

We're beef not, dairy so I don't have a clue of what you think a milk-house heater on "High" BTU output is... :)
I don't give a patootie about really accurate, I was just looking for ballpark sizing guesstimates.
So, iiuc, this is relying on ground reflection not direct solar? The thoughts I had were more for hayloft.
The point about tight is a good one--that's a real issue for the barn which is why the free fuel source is attractive--if it could at least knock of the worst in an area w/ some internal baffling to reduce the draft it would be more than have presently.
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dpb wrote:

Oops - sorry. Usually 1300 - 1500 Watts.

Ballpark without reflection as above. Reflected energy is a variable bonus in addition to that.

The panels will certainly add heat, but warm air rises and is guaranteed to find any upward path to the outdoors. If you have a specific area you'd like to heat, then a bit of framing to support insulation and some plastic film might provide a way to retain much of the heat...
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Morris Dovey wrote:

That looks like a winning cost trade. Thus far, all of the other alternatives like solar electric don't come even close. I did a trade earlier this year and couldn't get the system to even pay for itself over the advertised 25 year life span. That took into account any credits and rebates available and included paying cash for the system (i.e., no interest cost) and not assuming any lost investment value on the cash. What was really ironic was that the company selling the solar system was willing to issue a 30 year note on a system for which they were advertising a 25 year life.
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Mark & Juanita wrote:

Solar thermal can be awesomely efficient and solar photovoltaics offered on the consumer market (as opposed to those made for aerospace applications) have energy conversion efficiencies of only 10-15%.
I've been working to develop a couple of fluidynes (Stirling cycle heat engines) capable of converting sunlight directly to mechanical energy. These have a theoretical maximum efficiency of only about 55% - and I don't expect to do better than 25-30% with my design but, still, they'll be a lot more efficient than using PV panel to charge a battery which is then used to run a motor (with losses at each conversion).
OTOH, direct solar doesn't work very well at night...
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Morris Dovey wrote:

If you can get the efficiency up there and turn an alternator, you may have something

No, but if you can get the effiecencies a bit above what you are thinking, one can either charge batteries or sell back to the electric company. Right now, a lot of places they do 1 for 1, in the future I would expect that to change to more like 2 for 1 cost to buy-back ratio. Still that might be a good trade for having to buy and replace a battery farm.
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Mark & Juanita wrote:

I figure I'll have something as soon as I can get these things to irrigate the first million acres of marginal cropland through a dry season.

My first priority is availability, rather than efficiency. As with many engines and motors, the first increment of efficiency is almost free and the final increment defines unaffordability.
I'm taking the lazy man's way out by trying to solve the easy problem first... :)
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