[RE-wrenches] Reference PV System / snow removal

Tue Jan 4 14:17:51 PST 2011

Rob, Its great to see that the city is looking to come up with some local production 'standards' for PV system owners to gauge their own system production.  
To answer your direct questions... no, i'm not familiar with other PV reference systems, but i'll be on the look-out.... and i haven't installed an additional output monitor on any Enphase systems yet, so i can't comment on the Envoy's accuracy.  I have suggested this to a few clients, but no takers, yet.
For each micro-inverter branch circuit, i'd second the suggestion of having the circuit's output monitored by dedicated "utility grade kWh meter" to compare to the micro-inverter data against.
Snow build-up/removal ... In and around the Edmonton area, i've seen snow stick and stay on array's tilted up to 70deg.  A very sunny and not too cold day will certainly help the melt-off process, but typically a bit of help (quick sweep, if accessible and safe) is necessary if any reasonable amount of energy production is expected for the day.  The reason for this being that for our 4 coldest winter months (nov-feb) the avg temp is about -10 deg C and we are lucky if we get 2-2.5 decent hours of sun each clear day (clear days are few and far between).  If snow build-up is not swept off the array asap, what typically happens is the sun (when it does comes out) will start melting the snow and before it has cleared off the modules, the sun is gone, it gets colder (quite quickly) and the melted snow then freezes into ice, which takes even longer to melt off on its own or remove manually.
I have equipped some of my clients with telescopic snow brushes, and recommend clearing the snow as soon as possible after a snow fall.  This is only recommended if the roof is easily accessible and it is safe to do so.  I do not recommend to my clients to get up on their roofs or ladders to do this.  
The above comments are generally for flush-mounted roof arrays.  For angled, tilt-able and pole mounted arrays i suggest/design for up to 70 deg tilt for a winter angle and at least 3 feet from the bottom of the array to the ground when at this angle to allow for the snow to pile up.
I would think that before too much effort is put into designing an automated snow removal system that what needs to be looked at is...-given our short sun-hr days (and energy production) during the snow season, how much potential energy loss can be calculated for the "array snow-covered" days and what the cost of this potential energy production would be.  ... when figuring this out, remember that not all "array snow-cover days" are "energy production loss days" because the sun won't be out every day that the array is snow-covered.
.......... actually just got off the phone with a local client with an array on a 45 deg roof and he agreed 100% with what i said above about the days not being long/sunny enuf to clear the snow with out some help.  he can reach his array with a long roof rake and he notices that there is ice build-up on the lower part of the array if the sun was out the day before and it (or he) didn't clear all the snow off the modules beforehand.  He also suggested a "heated" snow removal system, fair suggestion, i've heard it many many times, these are just not feasible IMO..............
back to what i was saying....we need to figure out the cost of the "energy production loss" so that we have this in mind when designing a snow removal system.  Otherwise we will have a (hundreds of) dollars snow removal system that helps produce $5-10 of energy a year.  I believe that to be feasible, any snow removal system would have to be manual. (gasp!)It may just be that for an array that is not accessible or unsafe to reach, that is is best to just wait till the snow melts off on its own.
I hope to read some other great feed back on this, especially answering Rob's questions on ...Anybody familiar with PV reference systems developed by other municipalities?   Have they been successful?Have you found the Enphase Envoy to be consistently accurate?
Well, its snowing out.  I've got to go do some shoveling....
benn
DayStar Renewable Energy Inc. benn at daystarsolar.ca780-906-7807 HAVE A SUNNY DAY

Date: Sun, 2 Jan 2011 23:24:30 -0700
From: mendosol at mcn.org
To: re-wrenches at lists.re-wrenches.org
Subject: [RE-wrenches] Reference PV System

Message body

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

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