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...
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,
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...
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
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
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.
"Playing is not something I do at night, it's my function in life"
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:
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).
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...
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.
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. :)
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.
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...
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.
If you're going to be dumb, you better be tough
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...
If you can get the efficiency up there and turn an alternator, you may
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.
If you're going to be dumb, you better be tough
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
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