[RE-wrenches] Shedding ice

boB at midnitesolar.com boB at midnitesolar.com
Tue Jan 17 18:47:30 PST 2012


On 1/17/2012 6:32 PM, Bill Hoffer wrote:
> Bob
>
> Wonder how Module manufacturer warranties will handle applying reverse 
> current to the module , especially if it is more than the power rating 
> of the module???  I would want that one in writing before risking 
> having to write off an array in order to melt a little snow!
>
> Bill
>

Hey Bill !!

Don't worry, I wouldn't dream of doing something that is outside the 
module's specifications.

Most  PV module manufacturers don't quite understand how this works 
either but one particular
manufacturer liked the idea when I brought it up to them a couple years 
ago at SPI.


This mode of operation is also done in part of the UL testing.  There 
are certain rules
that have to be followed for this and luckily, most properly installed 
systems are already protected.

It's actually much easier on the modules than you might think.

boB





> On Tue, Jan 17, 2012 at 4:37 PM, boB at midnitesolar.com 
> <mailto:boB at midnitesolar.com> <boB at midnitesolar.com 
> <mailto:boB at midnitesolar.com>> wrote:
>
>     On 1/17/2012 4:18 PM, benn kilburn wrote:
>>     boB,
>>     If this concept were to become a working option for the Classic,
>>     would the modules have to be modified in any way?  Why are the
>>     diodes not blocking the reverse current?
>>     benn
>>
>>     DayStar Renewable Energy Inc.
>>     benn at daystarsolar.ca <mailto:benn at daystarsolar.ca>
>>     780-906-7807 <tel:780-906-7807>
>>     HAVE A SUNNY DAY
>
>
>
>     No mods.  However, as you can see, if the controller is maxed out
>     as far as
>     array size, that could limit the snow melting effect.   I don't
>     have any hard
>     data as for the minimum power needed to apply to the array for
>     snow melting,
>     but it could be around twice the power to melt snow as the power
>     rating of
>     the array.   Yesterday's experiment was less than 2wice the power
>     rating
>     and it may have been fine with with even less, so that's a very
>     good sign.
>
>     How much power does it take to melt snow off of a car's rear
>     window from
>     the electric defroster ?  It's a similar kind thing.
>
>     Diodes ??  You mean the bypass diodes ??   No problem.  Those don't
>     conduct in this case.
>
>     boB
>
>
>
>
>>
>>
>>
>>     ------------------------------------------------------------------------
>>     Date: Mon, 16 Jan 2012 13:14:36 -0800
>>     From: boB at midnitesolar.com <mailto:boB at midnitesolar.com>
>>     To: re-wrenches at lists.re-wrenches.org
>>     <mailto:re-wrenches at lists.re-wrenches.org>
>>     Subject: Re: [RE-wrenches] Shedding ice
>>
>>     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' <re-wrenches at lists.re-wrenches.org>
>>         <mailto: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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> -- 
> Bill Hoffer PE
> NABCEP Certified Solar PV Installer^(TM)
> Sunergy Engineering Services PLLC
> 2504 Columbia Ave NW
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