[RE-wrenches] Snow Removal Strategies (was PV Reference System)

[Rob Harlan]

We can set modules at 68 degrees (latitude + 15) and it increases (but does
not completely takes care of) snow shedding. Although the winters here are
typically sunny, temperatures below 0F are common through the winter with
dips as low -40F. There are approx. 86 days of snow cover.  In Edmonton on a
6in12 pitch (27 degrees) roof, snow on modules doesn't shed until the
ambient rises to 28F on a sunny day. With no manual snow removal an array at
6in12 takes about a 14% annual performance hit.

A lot of the city dwellers here set their arrays flush with the roof for
aesthetic reasons so we are hoping to develop a reference system that
provides data from various angles with and without snow removal.

A tracker on each reference module that dumps periodically would certainly
aid snow shedding but probably wouldn't address ice build up.  A little
"heating pad" to periodically bring the module up to 28F when there is snow
cover + sun would probably do it but it would have to be designed to not
insulate the modules when the pad is not needed.

Elevating the rack to allow for snow build up is important - also
engineering for the accumulated dead load at the base of the "snow fence".

Thanks for your thoughts. I am hoping that the wheel has already been
invented and tested.  Interesting challenge...
Rob
Rob Harlan
Executive Director
Solar Energy Society of Alberta
www.solaralberta.ca
office at solaralberta.ca
(780) 439-5608

Message: 10
Date: Mon, 3 Jan 2011 21:52:32 -0700
From: jason pozner <zzyyzzx11 at gmail.com>
To: RE-wrenches <re-wrenches at lists.re-wrenches.org>
Subject: Re: [RE-wrenches] Reference PV System
Message-ID:
    <AANLkTikFwGb8WNvgUy5sFgWXcd=vK_tREn7zLR-VZgaO at mail.gmail.com>
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Rob,

I think much of your snow removal will be at your lesser test angles.  4:12
might be a problem, but here in Western Colorado we are seeing 10:12 pitch
(40 deg) shed quite easily after a storm (would be curious about the 6:12(we
don't see too much here)).   I think, although we don't share similar
latitudes, we do share similar snowpack.   Colorado, and I believe Edmonton
have a Continental snowpack which tend to have lower moisture content
(colder dryer snow).  Usually we don't see the rhyming issues that a Costal
or even Intermountain experience, so the "tackiness" of the snow is less of
a problem.  Usually with the first sun after a storm, we see a pretty good
shed of the array.  I agree with Todd in that raising the array will give
the snow a place to accumulate.  I am curious about an automated snow
removal.  Whats that like, can it be done without heat?  Thinking about the
steep pitched array, I always wonder if just a bit of heat to melt and
lubricate the glass sliding surface would be enough of a boost to clear snow
earlier.  I have had the conversation a few times with an off grid client,
and convinced him it wasn't the best use of his energy harvest, but for
science....

Jay Pozner
Nunatak AES
Crested Butte, CO


>> Sent: Monday, January 03, 2011 1:25 AM
>> To: re-wrenches at lists.re-wrenches.org
>> Subject: [RE-wrenches] Reference PV System

>> I am working with the City of Edmonton, Alberta to develop a reference
system.  The intent is to provide accurate data for owners of systems within the
city limits to use to verify their system performance.  It is seen as a great
way to insure quality installations under their municipal grant program, as well
as a way to provide some real life performance data for system sizing and
installation recommendations. The City is considering tying the dispersal of
system grants to  verified performance.  (We are hoping to eventually have a
municipal performanced-based FIT,  but until then...)
>> 
>> At this point the plan is to permanently install modules at eight different
orientations to imitate common installations:
>> 
>> True South 18.4 degrees ( Equivalent to a 4 in 12 pitch roof)
>> True South 26.6 degrees (Equivalent to a 6 in 12 pitch roof)
>> True South 45.0 degrees (Equivalent to a 12 in 12 pitch roof)
>> True South 53.0 degrees (Latitude)
>> True South 70.0 degree pitch (the estimated best angle for year round
performance in Edmonton when snow is not removed)
>> True south 90 degree pitch (Equivalent to a vertical wall installation)
>> SE 18.4 degrees ( Equivalent to a 4 in 12 pitch roof)
>> SW 18.4 degrees ( Equivalent to a 4 in 12 pitch roof)
>> 
>> We will probably install two modules at each orientation to provide
redundancy to back up possible equipment malfunction. Each module will have its
own micro-inverter uploading data to a website.  The system will be installed on
a municipal building, probably a firehouse.
>> 
>> We are also considering installing a second, identical system which would
have snow removed once a day (at daybreak).  This would provide owners
considering snow removal with comparative  data.  The challenge here is how to
consistently remove accumulated snow.  We probably will not be able to get
municipal staff to carry this out so we are looking into automated systems.
>> 
>> So gentlemen I would love to get your thoughts:
>> 
>> Anybody familiar with PV reference systems developed by other municipalities?
Have they been successful?
>> Have you found the Enphase Envoy to be consistently accurate?
>> 
>> Does anyone have a reliable automatic snow removal scheme with a track
record?  We are putting it out to the University of Alberta mechanical
engineering department to see what they come up with but I know this has been
grappled with many times before.
>> 
>> Thanks much in advance for your input.
>> Rob
>> Rob Harlan
>> Executive Director
>> Solar Energy Society of Alberta
>> www.solaralberta.ca
>> office at solaralberta.ca
>> (780) 439-5608