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  • Heat tape on the back of the panel to melt snow?

    Hi everyone, I hope you guys don't mind me registering to ask some questions...

    To give you a little background - I'm off the grid in north-central CO full time. I have a 2800 rated watt PV array running through a trace and a couple of outbacks, charging a 16 battery bank made up of Rolls 530 amp hour lead acid batteries. As you'd probably guess, the system runs great.

    Only issue we have is in December when the temp drops to about -20 overnight and hovers around -5 during the day. When it's that cold, even 2" of snow on the solar panels isn't going anywhere, even in bright sunshine at 9600'.

    Since I have a bit of a panel access issue, I've been kicking around various ideas about how to deal with the snow besides climbing up and brooming it off. One thing that came to mind was that since the panels are so thin in most places, I might be able to run heat tape along the back of the panels with the idea that I could even run the tape off my generator. I'm concerned that this approach will either generate too much heat and damage the panels, or not enough heat and will have no effect on the snow load.

    Anyone here play around with this idea at all?

    Thanks guys!

  • #2
    Generally, the panels will heat up even with snow, and self-shed in a day. But maybe it's too cold. How hot does the tape get ? I wonder if putting it on the alum frame would be enough, I'd be very careful about applying heat to the backside sealing layer..

    What about windshield de-icer ? Or a good coat of wax before snow season ? This is the first I've heard of panels not clearing. Maybe a sheet of styrofoam cut to fit backside to retain heat, and allow to thaw. Remove before warm weather.
    spreadsheet based voltage drop calculator:
    http://www.solar-guppy.com/download/...calculator.zip
    http://www.solarpaneltalk.com/showth...oss-calculator

    http://www.mike-burgess.org/PVinfo_2.html

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,
    battery lugs http://tinyurl.com/LMR-BigLug
    Setting up batteries http://tinyurl.com/LMR-NiFe

    gear :
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||

    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||

    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    Comment


    • #3
      Originally posted by Mike90250 View Post
      Generally, the panels will heat up even with snow, and self-shed in a day. But maybe it's too cold. How hot does the tape get ? I wonder if putting it on the alum frame would be enough, I'd be very careful about applying heat to the backside sealing layer..

      What about windshield de-icer ? Or a good coat of wax before snow season ? This is the first I've heard of panels not clearing. Maybe a sheet of styrofoam cut to fit backside to retain heat, and allow to thaw. Remove before warm weather.
      Hi Mike, thanks for the reply. Lots of days, the sun does melt the snow off, but even in many of those instances it would be very helpful to be able to do it on command. Frequently, snow comes over a 3 or 4 day period and we'll be doing a regular generator cycle to keep the batteries at a good voltage. When the sun comes out, losing several hours of it to snow melt just means I've got another day of generator. Not to mention that that generator doesn't really get the batteries all the way full. You can really tell after a good storm when we'll make ~23 kw in the next two good sun days. A normal daily recharge is about 6kw.

      I thought about doing the frame as well but was concerned it wouldn't have enough effect - it's an easy way to do it, but I've never heard a success story. The problem I see with the styrofoam is that it insulates against heat as well as cold. When the sun comes out, the glare up on the snow covered roof is ridiculous and when there's no wind, the temp rises very quickly. And unfortunately, since we live near the tree line, there's always a decent amount of dust and pollen blowing around and anything you spray on the panel collects the dirt like a sunuvubich.

      I think I'm just going to pass on trying to modify the panels... I just added some stairs and am building a walkway above the panels. I already have a rig to tie into and will just continue going up there and clearing the panels off with a broom. If anyone else has any thoughts, it'd be great to read them. Thanks guys!

      Comment


      • #4
        9600 feet. Wow. Electrical resistance heating is so ineffiecent I'd seek another solution. I'd suggest using the winter solar horizon to your advange and build a cantalivered roof to cover them. Cantaliver it so you won't lose any summer watts after you remove the actual roofing material.

        We sweep.

        Comment


        • #5
          One member, Mountain, placed his panels vertical under an overhang to get around this problem.

          He lives at a ski resort some place way up North.

          Loses production in the summer but not too much in the winter he said.
          sigpic

          Comment


          • #6
            dear jmf,

            ever thought of mounting the panels on a rack that could be ajusted in two different angles. One low one to get the maximum output in the summer and a steeper one to ommit the snow problem in winter and get a higher output for the lower sun in winter.

            Solarc

            Comment


            • #7
              The fellow I mentioned, Mountain, also said he placed his panels under the eve of the house - protecting it from snow buildup. He was at one of the ski areas in Western Canada.
              sigpic

              Comment


              • #8
                Thanks for the replies!

                I haven't looked into an eve or replacing the racks, only because of the difficulty of the project. The panels are on the drop side of a modified a-frame, about 45' off the ground. At some point in the future, I'll need to replace the roof on the house, and I'll be looking at those options at that time. I'm hoping to get them off the roof all together, but we're on a north facing ridge... Being up on the roof gives us excellent sun. Far better actually than most of our neighbors on the south facing slope. Even in december/january, we're making power by 9am and then do so until sun set. But 10' off the ground, the sun coverage is lousy in most places, except for one spot that's about 600' from the house. So, it's a bit of a wash in the end. I haven't gotten the walkway built yet, but we're having a nice indian summer here and it could still happen. This time last year, we had 3' of snow in two days...

                Comment


                • #9
                  Melting Snow off solar panels

                  I saw on you tub a guy selling Midnite controllers and he talked about with his controller you could thru the internet tell your panels to melt the snow...
                  Just a note .. interesting.. maybe the Midnite people know how too....
                  Something about working in reverse..?
                  Ernie

                  Comment


                  • #10
                    Hi Ernie - No doubt it can be done but just not efficiently.

                    Russ
                    sigpic

                    Comment


                    • #11
                      Originally posted by Eherst98 View Post
                      I saw on you tub a guy selling Midnite controllers and he talked about with his controller you could thru the internet tell your panels to melt the snow...
                      Yep, take out the blocking diode, and at nighttime, your batteries discharge thru the panels, making them warm.

                      But, not awfully effective, and it drains your batteries.
                      spreadsheet based voltage drop calculator:
                      http://www.solar-guppy.com/download/...calculator.zip
                      http://www.solarpaneltalk.com/showth...oss-calculator

                      http://www.mike-burgess.org/PVinfo_2.html

                      solar: http://tinyurl.com/LMR-Solar
                      gen: http://tinyurl.com/LMR-Lister ,
                      battery lugs http://tinyurl.com/LMR-BigLug
                      Setting up batteries http://tinyurl.com/LMR-NiFe

                      gear :
                      Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||

                      || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||

                      || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

                      Comment


                      • #12
                        For an idea of how much energy is required to melt snow please see the following link - http://withouthotair.blogspot.com/20...alination.html

                        In short - Quote - The latent heat of melting of ice is 6 kJ/mol, or 333 kJ per kg, a quantity I have never been able to memorise... until now! Using the same trick as above, we can convert this into an equivalent temperature rise, by dividing by the heat capacity. The answer is "the latent heat of melting of ice 'is' 80 degrees C".
                        I don't think I'll forget that number! It really brings home why mountaineers spend so much time melting snow. The energy to melt the snow is roughly the same as the energy to bring the melted snow up to boiling point!
                        sigpic

                        Comment


                        • #13
                          If you're panels are off of the roof a few inches why not block off two of the sides and 'seal' them to the roof temporarily for winter and blow warm\hot air under them this way the panels heat up in a more natural way?
                          But what if you use 12% and only get 8% energy return not filling a battery completely off the solar array- is this considered a cycle? Mmmmmmm mauh brain's sizzling
                          [/QUOTE]
                          If a pigeon had his brains it would fly sideways

                          Comment


                          • #14
                            Originally posted by russ View Post
                            For an idea of how much energy is required to melt snow please see the following link - http://withouthotair.blogspot.com/20...alination.html

                            In short - Quote - The latent heat of melting of ice is 6 kJ/mol, or 333 kJ per kg, a quantity I have never been able to memorise... until now! Using the same trick as above, we can convert this into an equivalent temperature rise, by dividing by the heat capacity. The answer is "the latent heat of melting of ice 'is' 80 degrees C".
                            I don't think I'll forget that number! It really brings home why mountaineers spend so much time melting snow. The energy to melt the snow is roughly the same as the energy to bring the melted snow up to boiling point!
                            Ah, but you don't need to melt all the snow, just a very thin layer to allow the rest to slide off, like butter off a hot knife
                            spreadsheet based voltage drop calculator:
                            http://www.solar-guppy.com/download/...calculator.zip
                            http://www.solarpaneltalk.com/showth...oss-calculator

                            http://www.mike-burgess.org/PVinfo_2.html

                            solar: http://tinyurl.com/LMR-Solar
                            gen: http://tinyurl.com/LMR-Lister ,
                            battery lugs http://tinyurl.com/LMR-BigLug
                            Setting up batteries http://tinyurl.com/LMR-NiFe

                            gear :
                            Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||

                            || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||

                            || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

                            Comment


                            • #15
                              Originally posted by Mike90250 View Post
                              Ah, but you don't need to melt all the snow, just a very thin layer to allow the rest to slide off, like butter off a hot knife
                              this.

                              Butter and knives go together like bacon and turkey!
                              You only need to create a small layer of melted snow to 'lubricate' the rest so the angle and gravity takes care of the rest.
                              But what if you use 12% and only get 8% energy return not filling a battery completely off the solar array- is this considered a cycle? Mmmmmmm mauh brain's sizzling
                              [/QUOTE]
                              If a pigeon had his brains it would fly sideways

                              Comment

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