Melting snow on solar panels

[zac]

Does anyone have experience keeping snow from accumulating on roof mounted solar panels in a mountain climate with heavy snow accumulation (up to 100 pounds/sqft)?  

Since the winter wiped out my solar array and is being replaced by insurance, I'm trying to come up with a way to prevent the snow from sticking or to melt it.  One possibility was with heat tape, but the stuff is expensive and I'm uncertain if sticking on the perimeter aluminum frames of the solar panels would warm the panels enough to prevent snow accumulation.  

https://www.tempco.com/Products/Electric-Heaters-and-Elements/Flexible-Heaters/Adhesive-Backed-Heating-Tape.htm

Or electrical heating cable for radiant floors:

https://www.lowes.com/pd/schluter-systems-0-188-in-x-634-8-in-grey-120-volt-warming-wire/50201647

Another idea is to put flexible pipe underneath the panels to circulate hot water (some kind of liquid like a propylene glycol solution that won't freeze) through.  This would be something similar to the PEX flexible pipes used for plumbing and radiant floor heating and would only be run immediately before and while it is snowing.  it would need to be UV (sunlight) resistant.   I imagine melting a several foot thick accumulation would be very difficult if allowed to accumulate.  

http://www.pexheat.com/Tubing_2

1/2" PEX pipe costs about US$0.24/foot which seems pretty reasonable. With a 24 panel 7.5 kw array (roughly 34' x 13'), 1000' would be enough for 7 passes under each panel which may be more than necessary.  

https://www.amazon.com/1000ft-Tubing-Barrier-Radiant-VIVO/dp/B00HFFCL9Q

https://www.radiantcompany.com/system/closedsystem/

https://www.amazon.com/ECOTOUCH-Electric-Tankless-Digital-Efficiency/dp/B07MDZC6KG

https://www.amazon.com/Rheem-RTEX-13-Heating-Residential-Tankless/dp/B01NAUZJPE

https://www.amazon.com/Grundfos-15-58-Speed-Circulator-Cast/dp/B07DM3B8HD


 

[Tekno1]

A scientific paper posted today @sonsivri, describing a solution that solves snow building on Solar Panels with a good explanation of electrical details, hardware construction and field experiment results. Good part of the idea besides science is; it  triggers an avalanche of  the covering snow rather than melting it (so saving high energy).
   
" Re: IEEE Xplore Requests
« Reply #1123 on: Today at 12:41:05 PM »

Photovoltaic cell electrical heating system for removing snow on panel including verification "

http://www.sonsivri.to/forum/index.php?topic=10773.1100

Good luck.

[towlerg]

Out of the box. Clear snow from panels by tilting them with an actuator when weight increases. Or maybe modified windscreen wipers.

[Parmin]

No snow where I am, but some of my panels are heating up by itself when they are in the shades since the chain generates power and teh one in the shade have slightly lower voltage and thus somehow represent a resistance to the flow.  I might be wrong in my surmision tho but this is actually happening.

So, I just wonder if reversing the flow of the current might actually heat up the panels enough to remove the snow and when the panels are clear you can put back the flow to normal and carry on.

[towlerg]

@Parmin. Do your panels heat up at night?

[Parmin]

@Parmin. Do your panels heat up at night?

No it does not, my system automatically cut out when the sun light goes below a certain level.

The panels that heated up are in chain in series with other panels that were not in the shade.
I conclude that since that shaded panel is not producing as high voltage as the others in the series, it become a resistor to the line and thus heating up when in the shade.

My suggestion is not to use the sun power to heat up the panels, instead to use external power (ie. feed power to the panels) to heat up the panels temporary until the snow melts and then resume the photo voltaic.  My thinking is that when it does snows the light level is too low to produce power anyway, so it might be better to use the time to heat up and clear the panels to prepare for sunny days.
This may or may not work, I never tried this nor do I have any background on being in the snow beside the occasional stolen time holidays to the mountains.

[solutions]

Heating the glass would unfortunately negate a lot of the power you're generating. So, pulling the insulation out of your attic would probably not be a good idea.

Thinking out of the box...what about waxing the glass?

Or some other hydrophillic coating material (silicone oil, whale oil, ...)?

What angle from the horizontal is your array? Are these mono or poly cells? Knowing these might lend to some mechanical solutions.

[zac]

Heating the glass would unfortunately negate a lot of the power you're generating. So, pulling the insulation out of your attic would probably not be a good idea.

Thinking out of the box...what about waxing the glass?

Or some other hydrophillic coating material (silicone oil, whale oil, ...)?

What angle from the horizontal is your array? Are these mono or poly cells? Knowing these might lend to some mechanical solutions.

The array is about 20 degrees from the horizontal and are mono cells.  I've tried rain-x, but it didn't seem to make much difference in helping the snow to slide off the panels.  So far, the most practical cost effective choice appears to be putting uv-stabilized pex pipe underneath the panels and circulating hot water through them to heat the panels when snow is imminent or falling.  I would probably go with a proplylene glycol solution in that case.

I would have to come up with a way to automatically turn on the heater and pump when I'm not home though based on forecast or falling snow. 

[CocaCola]

So far, the most practical cost effective choice appears to be putting uv-stabilized pex pipe underneath the panels and circulating hot water through them to heat the panels when snow is imminent or falling.  I would probably go with a proplylene glycol solution in that case.

I would have to come up with a way to automatically turn on the heater and pump when I'm not home though based on forecast or falling snow. 

On that thought, and thinking out of the box my stepfather who loves to tinker built himself two 4 foot by 8 foot fixed position solar hot water collectors, I don't know where he got the plans but they were similar to this design ( https://www.instructables.com/id/Solar-Water-Heater-Part-1-The-Collector/ ) but he took it a step further and using a hole saw cut out the bottoms of a few hundred soda cans into disc, slide them over the pipe turning the copper pipe into a DIY fin tube, and instead of glass he just used a 4x8 Lexan greenhouse panel for the front...  Anyway inside he also built a highly insulated 4 foot square plywood box, and they stuffed that box with multiple coils of PEX tubing and more insulation to act as a holding tank... I think he told me the capacity is several hundreds of gallons of hot water stored it the coils of pex tubing...  I don't have much input on the automated cycle on/of system he used to move the hot water from the outside to the inside (the collectors will boil water even in the winter, so it has to constantly move and I would guess have a pressure blow of safety feature) but I know he found a DIY article on moving the water around using some real small pumps 12V that he also runs by solar...  Anyway, he runs that water through radiators in the house and it's stupid amazing how much heat he gets off them even in the dead of winter, he had plans to integrate the system to heat hot water for showers as well but I don't know if he got that far...  Using the same type of hot water solar collectors you could likely build a pretty darn efficient hot liquid system to defrost the regular solar panels, worst case you may have to supplement the heating of the water sometimes if the capacity of your holding tank isn't enough...

The nice thing about using solar heated water is that you are not paying to heat the water, just a little bit to circulate it...  Plenty of wifi enabled switches on the market that could allow you to remotely turn on/off the pump with ease...

[solutions]

The array is about 20 degrees from the horizontal and are mono cells. 

Thinking waaay out of the box - tilt the panels to 60-90degrees during snow season. You're going to lose power heating them, anyway, and mono will make power even if vertical.

[rtm]

There is a crazy idea. Why not use an ultrasonic device? Do you know that melting by an ultrasonic wave takes 32 times less energy than melting by heat?

Look to this video about an ultrasonic snowmelter:
https://www.youtube.com/watch?v=6_qvv8Yhe9Y

There is an article on an ultrasonic system for solar panel cleaning:
https://www.researchgate.net/publication/256549072_Ultrasonic_system_for_solar_panel_cleaning

[zac]

Thinking waaay out of the box - tilt the panels to 60-90degrees during snow season. You're going to lose power heating them, anyway, and mono will make power even if vertical.

This is the array before it was damaged last winter:



That is an interesting idea to tilt the panels, but wouldn't be practical for my situation. Aside from the difficulty with climbing on the roof to do that, snow would be trapped behind the panels and cause a problem.  

[solutions]

Put the panels on an overhead garage door track with a counterweight so they position where they are or slide down to vertical at the ground, or slightly above, level.

Bring them down to vertical for bad weather (as I said, they'll still make some power when vertical) and cleaning.

[CocaCola]

Bring them down to vertical for bad weather (as I said, they'll still make some power when vertical) and cleaning.

On that topic, during the winter months the sun's arch is much lower in the sky, raising the panels more verticle during the winter will increase their production over the very low angle you have now, and should be done regardless of snow build up if you want to optimize the system...

This website has a quick calculator http://www.solarelectricityhandbook.com/solar-angle-calculator.html

For my area it specs 24 degrees from verticle or about 66 degrees from horizontal, that angle alone should self remove most snow build up...

[zac]

Keep in mind that each panel weighs about 40 pounds.  I'm not very keen on using the panels as heating elements since there may be hot spots that could cause damage.  I'm planning to use ironridge XR1000 (or XR100) rails for the replacement.   Passing a PEX pipe through the middle seems like reasonable option and there would be 3 or 4 of the rails under each solar panel.  The larger XR1000 could easily fit a 5/8" PEX pipe (0.75" O.D.) and the smaller XR100 maybe a 1/2" pipe.  I wounder how hard it would be to thread a pipe through those extrusions.    

https://www.ironridge.com/pitched-roof-mounting/features/

[LabVIEWguru]

How about 1, 2 or 4 pulleys near the center of the roof and the same number of pulleys aligned on the eves (or lower). The rope (or whatever) runs under and over the solar panels forming a loop. Aluminum tubing has "something" to offset it from the face of the panels and the rope runs through the cross-section of the tubing and is affixed there. Plexiglas and a bunch of self-taping screws and you have a squeegee. You could run another loop down (or bicycle chain) to a crank near the door to run the squeegee "down," then back "up" to the stops at the top. If you have much snow at all, once you get it moving it's going to slide off the panels. If you have a small motor around, you could use something with teeth to pull the chain... then you could add microswitches... or a microcontroller to count revolutions and return it to the top... and an IR sensor so you just point your remote out your window to activate it...

sorry.. maybe I was getting carried away...

How about, I think it's called "cove base" or "cove molding" for the blade of your squeegee? I think it's 4 or 6 inches high and made from some type of heavy rubber. it would actually wipe snow and moisture from the face of your array. Your wife will adore you for your ingenuity.

[Checksum8]

Take advantage of the snow.

https://newsroom.ucla.edu/releases/best-in-snow-new-scientific-device-creates-electricity-from-snowfall