Panel angle for snow shedding

Rybren · May 2013

I'm getting ready to build a structure to mount my 4 x 210W panels. My plan is to build a small (10'-ish x 8'-ish) shed and mount the panels on the roof and place the battery bank, controller, etc in the shed.

The camp only sees 3 season use, so I won't be there in the winter to keep the panels clear of snow. The camp is located at ~45degrees N and I've been thinking of building the shed with the south facing roof at a 50 degree pitch. For those of you who live in the snow belt, do you think that 50 degrees is steep enough? Could I get away with a shallower angle? I'd prefer not to build a tilting mount.

Thanks.

-Jerry

NorthGuy · May 2013

Re: Panel angle for snow shedding

No.

I have 65 degrees. Mostly it works fine, but sometimes snow melts and freezes, then new snow piles up on top of the ice and ice doesn't let it fall down as it would with the glass. If I clean the snow from the top, the ice usually melts during few hours of sun. If I wanted something self-shedding, I would go at least with 70-75 degrees. That's what I'm planning for my second array.

BB. · May 2013

Re: Panel angle for snow shedding

I don't live in the snow belt--So take my suggestions with a grain of salt.

First there is the question of where the snow will "self clear too" (mounted high enough to slide off to ground, room to move snow from in front of array--if you have enough snow to build up in your area.

Second, will there be snow on the roof structure behind the panel and with the array become a snow/ice dam or be damaged from sliding snow from the rear?

Lastly--How much battery bank do you have and will the camp be occupied when there is snow on the array? If there is no power use during the winter, you probably only need 1% rate of charge (vs 5% to 13% typical) to keep the batteries fully charged (cold batteries have lower self discharge too--So, perhaps even 0.5% would be enough solar power)... If true--Then mount one (or a few) vertical panels on the wall of the building for winter sun (again, if you don't get drifts against the building). And/or only a one or couple panels would need near 90 degree tilt for winter charging.

-Bill

gww1 · May 2013

Re: Panel angle for snow shedding

I have also heard it is better to lay the panels long ways rather then tall. Then if you get some shading from the snow collecting on the edge ridge it doesn't effect all the rows of cells as bad.
cheers
gww

Cariboocoot · May 2013

Re: Panel angle for snow shedding

Vertical works in all but the stickiest snow.

And there is the issue: snow that sticks, sticks. The greater the panel angle the stickier the snow has to be to stick.

Since you won't be using this year-round you only have to be sure that it will shed most of the snow most of the time. The panels warming up in sunshine will clear any small amounts that remain.

Tony (Icarus) lives in your neck of the woods so should know about the Winter characteristics there. Although I know he has some at vertical he probably has a good idea what angle works for "standard".

My panels are at quite a severe slope owing to their being set for Spring/Fall at 52 Lat. But even the roof angle of 37 doesn't accumulate much snow (pain to walk on anything that steep, btw).

Your optimum angle is probably about 42-45 degrees. If you can get the power you need at 50 then all the better for shedding snow.

Rybren · May 2013

Re: Panel angle for snow shedding

Thanks for your thoughts guys.

Once the snow flies, the camp will be unoccupied and all loads will be disconnected, so I'll only need enough juice to offset self-discharge.

Vertical mounting is an option, but seeing as how I really only need power during the non-snow periods, I think that I'd be sacrificing a fair bit when I need it the most.

My three cabins have steel roofs with a standard roof pitch of 20 to 30 degrees. The one time that I hiked into the camp at mid-winter (after a significant thaw) there was still at least a foot of snow on all of the roofs. Not much sliding going on.

icarus · May 2013

Re: Panel angle for snow shedding

Mount your winter panel on the wall, vertically . My wall panels never collect snow over the winter
Mount them on hinges, sooyou can change the angle after snow season. I adjust mine seasonaly.

Tony

NorthGuy · May 2013

Re: Panel angle for snow shedding

Rybren wrote: »

Once the snow flies, the camp will be unoccupied and all loads will be disconnected, so I'll only need enough juice to offset self-discharge.

Panels covered with 2 inches of snow still produce 2-3% of the capacity.

If you turn everything off (inverter, charger etc.), self-dischage during 2-3 months will not be that big. I think many people do that

Cariboocoot · May 2013

Re: Panel angle for snow shedding

NorthGuy wrote: »

Panels covered with 2 inches of snow still produce 2-3% of the capacity.

If you turn everything off (inverter, charger etc.), self-dischage during 2-3 months will not be that big. I think many people do that

I disconnect my inverter. I do not disconnect the charge controller. Nor would I recommend doing so. Batteries fully charged before leaving in late Fall are always fully charged when returning in Spring.

But my panel angle is steep and the snow here is rarely wet enough to stick to them, at least for long.

Rybren · May 2013

Re: Panel angle for snow shedding

icarus wrote: »

Mount your winter panel on the wall, vertically . My wall panels never collect snow over the winter
Mount them on hinges, sooyou can change the angle after snow season. I adjust mine seasonaly.

Tony

Tony,

Would you happen to have any pics of your wall-mount setup?

FWIW, my camp was unoccupied for 5 months this winter. There's no way that I'd let the batteries self-discharge for that long.

BB. · May 2013

Re: Panel angle for snow shedding

If your batteries "get cold"--They do not need much charging current...

More or less, a good engineering rule of thumb is for every 10C change in temperature, life (and many other paramters) change by a factor of 2x or 1/2...

If your batteries are at 0C, then that is -20C or they should last 2x as long (aging) and probably self discharge 1/2 as fast (i.e., instead of 1 month between recharging, you could go 2 months)...

However, 5 months is probably pushing it.

One advantage to a couple small panels on the side is less obvious stuff to tempt thieves and vandals (thinking like a city fella again

).

-Bill

Cariboocoot · May 2013

Re: Panel angle for snow shedding

Rybren wrote: »

Tony,

Would you happen to have any pics of your wall-mount setup?

FWIW, my camp was unoccupied for 5 months this winter. There's no way that I'd let the batteries self-discharge for that long.

It would be more accurate to say that cold batteries do not self-discharge at the same rate as warm ones: the lower temperature slows the chemical process. In six months you'd lose about 6%, which is really barely noticeable. It does not dip below the SOC where sulphation becomes an issue. Some might even argue that charging them in that time could be worse because of the risk of water loss, et cetera. But batteries left on panels & controller all Winter come out just fine; no worries!

vtmaps · May 2013

Re: Panel angle for snow shedding

NorthGuy wrote: »

I have 65 degrees. Mostly it works fine, but sometimes snow melts and freezes, then new snow piles up on top of the ice and ice doesn't let it fall down as it would with the glass. If I clean the snow from the top, the ice usually melts during few hours of sun. If I wanted something self-shedding, I would go at least with 70-75 degrees.

Same here. I have a DPW top of pole mount and it only tilts to 65° (25° from vertical). That is NOT enough to shed snow... I scrape it clean many times per winter.

NorthGuy wrote:

Panels covered with 2 inches of snow still produce 2-3% of the capacity.

If you turn everything off (inverter, charger etc.), self-discharge during 2-3 months will not be that big. I think many people do that

Good point! Of course, there could be a bit more than 2 inches. I've seen 6 inches on my panels at 65° (and then I scraped it off). If Rybren puts his panels at 50° he may not count on that 2-3% of capacity.

--vtMaps

rich · May 2013

Re: Panel angle for snow shedding

Short of using a windshield wiper ..lol... has anybody ever tried to wipe down their panels with Teflon fortified windshield wash fluid?...on the car the snow just rolls off this stuff...im not sure if im posting a question or a solution, any ideas?

Cariboocoot · May 2013

Re: Panel angle for snow shedding

If you can get at the panels to clear them it doesn't matter much how you clear them. But if you're not there over Winter ... Things like RainX or Teflon fluid don't do much. May work for a while, but inevitably needs to be renewed.

icarus · May 2013

Re: Panel angle for snow shedding

Rybren wrote: »

Tony,

Would you happen to have any pics of your wall-mount setup?

FWIW, my camp was unoccupied for 5 months this winter. There's no way that I'd let the batteries self-discharge for that long.

I don't have a picture handy, but it is pretty simple. I have a pair of older Siemens 40 watt panels that are only ~q12" wide. They simply hang from a "T" hinge on the top. They are held to the wall at the bottom with a roller screen door latch to keep the wind from getting under them. When I am away I simply lock them against the wall and walk away.

When I return, I can prop the bottom off the wall with diffent length 2x2 sticks to get them at the proper angle depending on the the time of year. I have left some of my systems for as long as 9 months and the batteries are always at 100% when I return. Just make sure you top up the water before you leave.

Tony

As an alternative you could ring the PV with semi conductor heat tape so that runs just for a few minutes ithe edge of the panel. (maybe coupled with a photo cell) on a sunny day, almost regardless of the temp, (certainly as low as 0f) just a little window of melt, and panels will clear themselves pretty quickly. If all you are trying to do is keep up with self discharge that might. A reasonable solution.

T

peakbagger · May 2013

Re: Panel angle for snow shedding

I have a wall mount array with a top pivot. I am at 44 degrees north in a high snow load location for the east (white mtns in NH). I can adjust the angle with a 2x6 and a floor jack. Its over an angle bay window so I cant run it down totally vertical but I do have high wind mode where I park it at about 15 degrees. In the winter I set them at 30 degrees and they do retain snow during and after a storm. Usually once the sun comes out, light reflects off the snow and the front of the house under the panels and the snow slips off. I can clean them with a roof rake and gain about a days worth of generation. The frame is made out of gold unistrut and is mounted off the house with Stainless standoffs as I have cedar siding which can attack unistrut. The array size is 660 watts. My adjustment technique would need a modification if the panels were completely vertical as

westbranch · May 2013

Re: Panel angle for snow shedding

Ryben, if the batteries are fully charged when you close up all you need is one or 2 panels to keep the batteries topped off , so take an old single bed metal frame, cut it down and re-weld to fit 2 panels, mount 2 medium door hinges on the top edge and screw it to the side of the sunniest building low enough to catch the sun & Bobs your uncle!

Rybren · May 2013

Re: Panel angle for snow shedding

Lots of great ideas and comments. Thank you.

I'll have to see what I can come with that will be functional and still pass the SWMBO test. I've found that the latter is often the most challenging.

westbranch · May 2013

Re: Panel angle for snow shedding

First step is to get her to 'HATE' the genny sound and to 'LOVE' the silence of solar power that you get from having the panels in the 'optimum' spot.:roll:

Rybren · May 2013

Re: Panel angle for snow shedding

Unfortunately - or fortunately, we've never had a genny running at the camp. The silence is already golden 8)

westbranch · May 2013

Re: Panel angle for snow shedding

they call that Double Jeopardy, damned if you do and damned if you don't!

DanS26 · May 2013

Re: Panel angle for snow shedding

Check these panels out:

http://www.szna-usa.com/product-portfolio.html

You can reverse the flow of coolant/heated medium and thus keep your panels snow free. You just have to think out of the box!

Rybren · May 2013

Re: Panel angle for snow shedding

Interesting concept. Wonder how well they work.

waynefromnscanada · May 2013

Re: Panel angle for snow shedding

Rybren wrote: »

Tony,

Would you happen to have any pics of your wall-mount setup?

If you PM me your email address, I'll send you photos of my set up. Panels vertical in winter, angled up in Summer. Snow problems are totally non-extent, except for the sun reflecting off the snow covered ground in Winter. Before i started angling them vertical for Winter, snow was a constant problem, even when they were only slightly tipped back from vertical, but no more, that's all in the past.

Rybren · May 2013

Re: Panel angle for snow shedding

PM sent. Thanks Wayne

Organic Farmer · May 2013

Re: Panel angle for snow shedding

DanS26 wrote: »

Check these panels out:

http://www.szna-usa.com/product-portfolio.html

You can reverse the flow of coolant/heated medium and thus keep your panels snow free. You just have to think out of the box!

That is a neat idea

Thank you.

Cariboocoot · May 2013

Re: Panel angle for snow shedding

Ah, the ol' "water cooled (heated) panels" idea.
And the energy to move the coolant up to the panels and back comes from where exactly?

The "dual purposing" of panels has been discussed before, and the deficit energy gain as well. To say nothing of the popular notion of heating water while cooling panels. Unfortunately panels don't radiate or conduct heat well so transfer to the medium is poor, and the thermal difference between a well-running solar panel at 25C and a well-running water heater at 60C+ is sufficient to prevent any advantage for either.

Go ahead and try it if you like: it's not my money you're spending.

MidNite had plans to implement a reverse current flow to panels to melt snow from them, but so far they haven't pursued executing this. It would be more practical than other such concepts as it only requires some switching at the controller rather than a lot of extra equipment installed. I believe the hang up was the infinite variety of panel arrangements possible making it difficult to implement in all potential designs.

westbranch · May 2013

Re: Panel angle for snow shedding

From memory, IIRC it would use about 1Kwh to melt on the test panels they used, cant remember how many...

icarus · May 2013

Re: Panel angle for snow shedding

It also sort of depends on the type, depth and duration of hve rage snowfall. A few Cm of light fluff every few day followed by sun, even roof panels will probably clear themselves often enough to keep the batteries topped up. On the other hand, if you get snow very regularly all want, or your snow tends to be closer to the freezing point you may have your panels covered more than not. Finally, if you lie in the Cascades or Sierra where you could get a meter or more on any given night, (often heavy, high water content snow) they will e covered for the winter.

My roof panels are always covered under ~ a meter of snow when I go away for a month in in the winter. Between actual snow fall, coupled with wind they get coverd pretty quick. Once I get them clear,, it only takes a second to keep them so, but it does tak a trip to the roof. Given a choice I would ground mount them, but I don't have any place that has that exposure.

T

DanS26 · May 2013

Re: Panel angle for snow shedding

Cariboocoot wrote: »

Ah, the ol' "water cooled (heated) panels" idea.
And the energy to move the coolant up to the panels and back comes from where exactly?

The "dual purposing" of panels has been discussed before, and the deficit energy gain as well. To say nothing of the popular notion of heating water while cooling panels. Unfortunately panels don't radiate or conduct heat well so transfer to the medium is poor, and the thermal difference between a well-running solar panel at 25C and a well-running water heater at 60C+ is sufficient to prevent any advantage for either.

Go ahead and try it if you like: it's not my money you're spending.

No argument that these panels are not very efficient. But for solar enthusiasts in snow prone areas who are either unable or unwilling to climb up on their roof to clean snow in the winter, this product may be the answer. Lots of people for health or safety reasons do not want to climb roofs, but they want their batteries to stay charged in winter.

Panel angle for snow shedding

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