[RE-wrenches] Shedding ice

Mon Jan 16 15:22:03 PST 2012

Just thinking out loud here, but wondering if it would pay to attach an
insulated back to the panel for the winter months to decrease the
convection.  I may need to set up a lab here and find out. . .

Best regards,

Mark Dickson,

NABCEP Certified Solar PV Installer T

Oasis Montana Inc.

877-627-4768 toll-free

406-777-4309 (0830 fax)

Mark Dickson, Certified Solar PV Installer

 <http://www.oasismontana.com/> http://www.oasismontana.com/

 <http://www.grid-tie.com/> http://www.grid-tie.com/

 <http://www.pvsolarpumps.com/> http://www.pvsolarpumps.com/

  _____  

From: boB at midnitesolar.com [mailto:boB at midnitesolar.com] 
Sent: Monday, January 16, 2012 3:43 PM
To: RE-wrenches
Cc: penobscotsolar at midmaine.com; Mark Dickson
Subject: Re: [RE-wrenches] Shedding ice

On 1/16/2012 1:34 PM, penobscotsolar at midmaine.com wrote: 

Impressive, Bob, but if one 125 watt panel took 1000 watts of power, what
is it going to take to melt my two 1600 watt arrays, pole mounted,
(theoretically, of course, and at a 65 degree tilt)....? Just wondering as
it seems a lot of power to use in the winter for an off grid or solar
reliant system.

Thanks,
Daryl

Yes, it can take a lot of  energy.   How much and how long depends on what
the outside ambient temperature is.  I think it will have a problem in
extreme
cold because it depends on temperature rise of the module to get it above
freezing.
If the sun comes out, that helps a lot so would help to reduce the energy in
melting.

The melting we just now tried here, melted 2 X  200W modules (series)  in 45
minutes with 700 Watts
of power into them (0.7 kW-hour) which is much better than my older
experiment and I believe
being off the ground makes a big difference.  The outside temperature right
now is only 31
degrees F so kind of warm.  The array is sitting at about 25 degree tilt
just above the metal
roof on our building.    It is still snowing here so no sun.

Colder temperatures like the one in my animated gif will take longer but I
am sure that
keeping them off the ground helps a lot.   My 3 year old test was sticking
in the snow
on the ground.

There may be times though where it might be better to run some power into an
array that
has a chance of melting while the generator has to run anyway.  If it didn't
quite work  then
nothing much lost.   Unless it has a chance of working fairly quickly
without too much energy
from the batteries, you'd want to have a generator running.  Todays melting
experiment
was done off the batteries only.

  To have any gains,  you would have to have some sun coming soon
after it was melted off the array before it snowed again.

This isn't a complete fix but something that may be put into the bag of
tricks
when it does work to an advantage.  Here it is still snowing so it wouldn't
make any difference but is sure fun to watch !

PS for Mark Dickson, I don't know what it would take for your 50 watt module
but much
less power than for the 400 watts of PV we just melted snow on in the same
conditions.

boB

On 1/16/2012 11:39 AM, David Katz wrote:

Mark,
I believe the Midnite Classic has this feature built in. Check with
them.
David Katz

It just snowed up here in Arlington, Washington A.C.  and we were just
starting to melt some snow
on a couple of modules on our roof just now with one of our charge
controllers here in the lab.

This feature is not yet in the Classic, BUT, check out this experiment
that I did about 3 years ago
in my front yard with an animated gif time lapse.

One module is being powered and the other is not powered, just sitting
there for comparison.
These are KC125s.

The time involved here was about 3 hours and took about 1 kW-hour of
energy but gives you
an idea of what may be done with this idea.  One thing not in our favor
here is that the module
that is being powered is resting on the ground, in the snow, which would
significantly
hinder snow melting I would think rather than being properly mounted.

Oh what fun it is to melt some PV snow tonight !

http://fusion.midnitesolar.com/PVsnowMelt3.gif

boB

*From*: Mark Dickson [mailto:Mark at OasisMontana.com]
*Sent*: Monday, January 16, 2012 10:00 AM
*To*: 'RE-wrenches'  <mailto:re-wrenches at lists.re-wrenches.org>
<re-wrenches at lists.re-wrenches.org>
*Subject*: [RE-wrenches] Shedding ice

I recall a conversation a while back about the possibility of
"reversing" the current in a solar module to increase the cell temp
enough to shed ice/rime.  To follow-up, has anybody been successful at
this?  I am guessing, if so, it would entail, removal of diodes,
increasing PV and battery capacity and some way to sense the ice at
the very least. . . It sounds good in theory, but I am skeptical as to
whether it will work in reality. . .

Best regards,

Mark Dickson,

NABCEP Certified Solar PV Installer ^(TM)

Oasis Montana Inc.

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