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Solar design Challenge - off-grid workshop - Page 3

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Posted by Josepi on November 11, 2009, 3:47 am
Looks very good.

However, this is really climate dependant. In my climate this would be
useful a few months of the year, maybe, way too hot for 3-4 months of the
year and absolutely freezing for 4-5 months. It would extend the summer
months usage but be very unreliable, IMHO.

As I see it, the difference with your passive system is, you cannot ever get
the slab any warmer than the room air temperature. This prevents any large
heat storage for release later by virtue of the higher storage temperature
required. We have days and days of no solar input very frequently during the
year's climate. When I first set my shed solar system up we had about 7
weeks in Dec-Jan with only 6 hours of sun, total. Talk about being
depressed, SADS, dead batteries and frozen parts...LOL Have to get back to
this some year but have too much to finish the rest of my house right now.

Posted by Morris Dovey on November 11, 2009, 4:49 am
Josepi wrote:

Of course it is. Solar heat only works when the sun is above the
horizon, which means that if you're close to (or north of) the Arctic
Circle or you'll need a different method (same deal for people in the
southern hemisphere near or south of the Antarctic Circle).

I have no personal experience at all of the Maritimes (I'm pretty sure
that watching Anne of Green Gables on PBS doesn't count). The
northernmost installation of this panel particular design is in Sarnia,
Ontario (at the southern tip of Lake Huron) - not all that far north.
The customer there was so enthusiastic about his that be became a dealer.

If you're talking about dark overcast (marginal) conditions, then
performance will depend very much on quality of design, which is why I
suggested to the OP that he track down his local solar guy for advice.

I get a kick out of how everyone believes they live in a place with
really terrible winter weather. I thought so myself when I lived in
Minnesota (and had to prop a door open even when the outside temperature
was -30F/-34C, because I'd overdone the solar heating).

Morris Dovey
DeSoto Solar
DeSoto, Iowa USA

Posted by schooner on November 11, 2009, 11:06 am

All depends on your weather, lot of short cloudy days in Maritimes
especially Dec/Jan.  When it is cloudy for days on end you wont get much if
any solar heating and the overall temp would soon drop if that is your only
heat source.  Very cold clear days then solar works great, but less cold
overcast days not so much.

Posted by Morris Dovey on November 12, 2009, 8:03 pm
 schooner wrote:

Because there weren't any new issues or questions raised, I was tempted
to not respond - but I'd like to voice (gentle) disagreement with your

If you experience a rapid temperature drop in any structure, it's an
indication that the structure is either poorly insulated or leaky (or
both), and this has nothing to do with the method of heating.

A _good_ solar heating panel should produce useful amounts of heat on
even cloudy days and, as you mention, should provide excellent
performance during clear days. I suspect that there may be a fairly wide
range of opinion on what constitutes a /good/ solar heating panel.

I have some fairly obvious biases as to what constitutes "good", but I
don't have any qualms about applying Sturgeon's Law to the whole of
solar technology. :)

Morris Dovey
DeSoto Solar
DeSoto, Iowa USA

Posted by schooner on November 12, 2009, 8:18 pm

Don't beleive I said anything about "rapid tempurate drop".  However
overcast/snowy weather for days on end with cold windy nights is going to
reduce the tempurate of any structure with no other heat source but solar
especially in months with short days where the sun is low and posisbly not
hitting panels fully.

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