Roof or not roof? That is the question

BoFuller
BoFuller Solar Expert Posts: 187 ✭✭✭
I am going to build a log cabin and the roof is going to be facing south. I have some people tell me that the roof is the best place to put the panels and I have others say it is not a very good place (leaks, hard to clean). Any input from you experts?
I thought this was close enough to topic not to start a new thread. Sorry if this is considered hijacking.
12 Kyocera 235 panels, 3 Gyll LiFePO4 batteries (previously 16 Trojan L16 RE-B batteries), Outback 3600W 48V system, Generac 11K propane backup generator, NW AZ, off grid, 6,000 ft (system installed in April 2015)

Comments

  • Joe_B
    Joe_B Solar Expert Posts: 318 ✭✭✭✭✭✭
    Re: Roof or not roof? That is the question

    IMHO a south facing roof is the best place. Although accesibility is a concern, as long as the roof is steep enough the panels will self clear of snow and leaves. By putting it on the roof, you are saving the cost of a trench and underground cables as well as it being a pretty good theft deterrent. I have a lot of land and I chose to roof mount my system for these reasons.
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Roof or not roof? That is the question

    I split this off because it is different from the other and a very good topic for discussion:

    Is it better to put the panels on the roof or build a separate support structure such as a mast mount?

    (Besides, it gave me an excuse to make up a bad pun title. :p )

    From my POV it would depend on several things, not the least of which is the orientation of the roof in respect to how good that is for maximum PV production at the site (including roof slant). The age of the roof is a significant factor too: the panels will probably last 25+ years so if a new roof has just been put on there should be no worries about having to re-roof and take the panels down (says the guy who has to re-roof and take the panels down).

    To that end, certain types of roof lend themselves to solar panels better than others. You won't be too happy trying to retrofit mounts to ceramic or concrete tile roofing. Metal can be difficult to work with too. Wood shingles or shakes are problematic. With any type there is the question of if the underlying structure is strong enough to support the additional weight of the panels.

    Access may be an issue, although one generally doesn't have to access the panels much. Cleaning can often be done from the ground or ladder. It all depends on the particular site.

    That's the thing; it isn't a universal yes/no question, but one that is tied to the specific installation.

    I'm sure others will have something to say about this too.
  • BoFuller
    BoFuller Solar Expert Posts: 187 ✭✭✭
    Re: Roof or not roof? That is the question

    It will be a 2 story cabin and the roof is going to be sealed standing seam. The pitch will be 6/12 and I can still tweak the direction the cabin faces up to 15 degrees to the SW or the SE. The roof will be plenty strong enough.
    I don't know how many panels yet. We will be retiring to the cabin fulltime and it is totally off-grid. Nearest wires are 10 miles away. NW Arizona; 6200 feet elevation.
    What else helps?
    12 Kyocera 235 panels, 3 Gyll LiFePO4 batteries (previously 16 Trojan L16 RE-B batteries), Outback 3600W 48V system, Generac 11K propane backup generator, NW AZ, off grid, 6,000 ft (system installed in April 2015)

  • BoFuller
    BoFuller Solar Expert Posts: 187 ✭✭✭
    Re: Roof or not roof? That is the question

    I have 40 acres, so I'm not limited to the roof, but there are trees everywhere and I don't want to cut down any more than I have to.
    I plan on building a shed behind the house (north side) to house the batteries, inverters and such so the panels will be about 45-50 feet (horizontally) and 25 feet vertically for wiring purposes.
    12 Kyocera 235 panels, 3 Gyll LiFePO4 batteries (previously 16 Trojan L16 RE-B batteries), Outback 3600W 48V system, Generac 11K propane backup generator, NW AZ, off grid, 6,000 ft (system installed in April 2015)

  • BoFuller
    BoFuller Solar Expert Posts: 187 ✭✭✭
    Re: Roof or not roof? That is the question

    Harvesting rain water from the roof is highly desireable, but I would guess that the panels wouldn't really make a difference there. The water has to come down to the gutter eventually.
    12 Kyocera 235 panels, 3 Gyll LiFePO4 batteries (previously 16 Trojan L16 RE-B batteries), Outback 3600W 48V system, Generac 11K propane backup generator, NW AZ, off grid, 6,000 ft (system installed in April 2015)

  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Roof or not roof? That is the question
    BoFuller wrote: »
    I have 40 acres, so I'm not limited to the roof, but there are trees everywhere and I don't want to cut down any more than I have to.
    I plan on building a shed behind the house (north side) to house the batteries, inverters and such so the panels will be about 45-50 feet (horizontally) and 25 feet vertically for wiring purposes.

    It's good that this is a new build; you will know what's holding the roof up!

    But this one is a bit of a problem: you've got roughly 75 feet from panels to controller, which is a fair amount of wire (i.e. Voltage drop potential). Have you run any numbers on this with a V-drop calculator to see what would be needed? Maybe panels on the power shed roof would work out better all 'round, since it's going to be built anyway.
  • BoFuller
    BoFuller Solar Expert Posts: 187 ✭✭✭
    Re: Roof or not roof? That is the question
    It's good that this is a new build; you will know what's holding the roof up!

    But this one is a bit of a problem: you've got roughly 75 feet from panels to controller, which is a fair amount of wire (i.e. Voltage drop potential). Have you run any numbers on this with a V-drop calculator to see what would be needed? Maybe panels on the power shed roof would work out better all 'round, since it's going to be built anyway.

    I have not run any numbers. You are over my head there. This solar thing is new to me.

    The plan was for the shed roof to face East/West instead of N/S. I could rethink that. I'll have to wait until I go there next time and see how that would fit. Since the cabin is two story, it may shade the shed in the winter. It would shade it if I moved it to the east side or the west side also. Can't put it on the south side as that is the drive and the front porch and view. A shed there would NOT get the approval of the boss. ;)
    12 Kyocera 235 panels, 3 Gyll LiFePO4 batteries (previously 16 Trojan L16 RE-B batteries), Outback 3600W 48V system, Generac 11K propane backup generator, NW AZ, off grid, 6,000 ft (system installed in April 2015)

  • Peter_V
    Peter_V Solar Expert Posts: 226 ✭✭✭
    Re: Roof or not roof? That is the question
    BoFuller wrote: »
    I have not run any numbers. You are over my head there. This solar thing is new to me.

    The plan was for the shed roof to face East/West instead of N/S. I could rethink that. I'll have to wait until I go there next time and see how that would fit. Since the cabin is two story, it may shade the shed in the winter. It would shade it if I moved it to the east side or the west side also. Can't put it on the south side as that is the drive and the front porch and view. A shed there would NOT get the approval of the boss. ;)


    You want to keep your DC cables as short as possible. You can make up for extra length by using large cables, but that get's expensive fast. Basically the cable cost goes up as the square of the distance (a cable that is twice as long and twice as thick costs 4x as much, 4x as long ends up costing 16x as much, etc.)

    Might be better to build a battery "room" on to the house. Maybe even on the second story? Or at the very least attached to the side of the house.

    You could even get by with a battery "box" built into a utility room, maybe with the washer and dryer. The box has specific requirements: has to be ventilated to the outside, needs to be lockable or in a lockable room, etc.

    I can't remember if you're allowed to have the box in a closet or not.

    As an extra advantage having a battery room in the house will keep temperature would be more stable (not get as hot or as cold) than an external shed.
    Hot batteries don't live as long and cold batteries don't produce as much power. Ideal battery temperature is around 65-70 degrees.
  • BoFuller
    BoFuller Solar Expert Posts: 187 ✭✭✭
    Re: Roof or not roof? That is the question
    Peter_V wrote: »
    You want to keep your DC cables as short as possible. You can make up for extra length by using large cables, but that get's expensive fast. Basically the cable cost goes up as the square of the distance (a cable that is twice as long and twice as thick costs 4x as much, 4x as long ends up costing 16x as much, etc.)

    Might be better to build a battery "room" on to the house. Maybe even on the second story? Or at the very least attached to the side of the house.

    You could even get by with a battery "box" built into a utility room, maybe with the washer and dryer. The box has specific requirements: has to be ventilated to the outside, needs to be lockable or in a lockable room, etc.

    I can't remember if you're allowed to have the box in a closet or not.

    As an extra advantage having a battery room in the house will keep temperature would be more stable (not get as hot or as cold) than an external shed.
    Hot batteries don't live as long and cold batteries don't produce as much power. Ideal battery temperature is around 65-70 degrees.

    A second floor balconey would be a possibility - on the east end. There will be a balconey on the west side but that will be for the views of the valley and the mountains beyond.
    12 Kyocera 235 panels, 3 Gyll LiFePO4 batteries (previously 16 Trojan L16 RE-B batteries), Outback 3600W 48V system, Generac 11K propane backup generator, NW AZ, off grid, 6,000 ft (system installed in April 2015)

  • solarix
    solarix Solar Expert Posts: 713 ✭✭
    Re: Roof or not roof? That is the question

    The specific answer depends on your site, but the general answer i say is roof.
    Ground mounts are easier to clean but get dirtier easier too (In dusty Arizona for sure). Use S-5! clamps on your standing seam roof for an easy no penetration solution.
  • Vic
    Vic Solar Expert Posts: 3,208 ✭✭✭✭
    Re: Roof or not roof? That is the question

    Batteries like moderate temperatures. The Root Cellar concept is great for batteries. Somethng closely coupled to the ground, and shaded/insulated by the rest of the structure.

    I have not yet been able to do this, but it seems to be a great concept, especially when it is considered as a part of new construction. I wind up running A/C for power rooms to keep the electronics and batteries happier in the summer.
    Sounds like a fun project. Have Fun, Vic
    Off Grid - Two systems -- 4 SW+ 5548 Inverters, Surrette 4KS25 1280 AH X2@48V, 11.1 KW STC PV, 4X MidNite Classic 150 w/ WBjrs, Beta KID on S-530s, MX-60s, MN Bkrs/Boxes.  25 KVA Polyphase Kubota diesel,  Honda Eu6500isa,  Eu3000is-es, Eu2000,  Eu1000 gensets.  Thanks Wind-Sun for this great Forum.
  • BilljustBill
    BilljustBill Solar Expert Posts: 219 ✭✭✭
    Re: Roof or not roof? That is the question

    Attachment not found.
    Peter_V wrote: »
    You want to keep your DC cables as short as possible. You can make up for extra length by using large cables, but that get's expensive fast. Basically the cable cost goes up as the square of the distance (a cable that is twice as long and twice as thick costs 4x as much, 4x as long ends up costing 16x as much, etc.)

    Might be better to build a battery "room" on to the house. Maybe even on the second story? Or at the very least attached to the side of the house.

    You could even get by with a battery "box" built into a utility room, maybe with the washer and dryer. The box has specific requirements: has to be ventilated to the outside, needs to be lockable or in a lockable room, etc.

    I can't remember if you're allowed to have the box in a closet or not.

    As an extra advantage having a battery room in the house will keep temperature would be more stable (not get as hot or as cold) than an external shed.
    Hot batteries don't live as long and cold batteries don't produce as much power. Ideal battery temperature is around 65-70 degrees.

    I've found a way to get around the costs of heavy copper wiring. In getting my supplies together before I begin my solar off grid project, I'm always looking for supplies I need. With my odd assortment of panels, the majority will be on a 10' high by 40' long ground mount. I have shade issues for the house roof. On the one South facing shed roof, the back side where the panels would be nicely out of sight is within easy theft-reach with a ladder from a cleared 30' wide utility easement.

    This might seem like a rarity, but I've found multi-strand #6, #8, #10 within flexible conduit, and both #2/0 and #4/0 at both flea markets and garage sales. Two summers ago I found what appears to be a non-oxidizing # 6 copper wire used for railroad signal needs. It's not supposed to turn into that infamous black dust like some low voltage/high amp solar guys are finding. I paid $5 for a long roll of it. Then, Last summer, I bought a 90' length of 2/0 and 4/0 copper wire; each cost $45. Just last month at the monthly flea market, I bought approx. 1,500 ft. of single run #8 copper, one full reel and one about half full, and paid $90 for both.

    Inspecting the wire to be sure it's not junk or faulty and if it will be long enough for my needs are the first order of business; then price. The one draw back when buying wiring this way is having a receipt needed if ever there was an IRS audit on the 30% tax credit. With the prices I'm finding, just leaving out those low costs in the final tally is something I can live with...;)

    The only other drawback I found was some of the "conditions" in which one runs across good buys like these. At the garage sale selling the $5 "railroad wire", pickers and diggers were going though boxes and perimeter shelving in a large metal shop building. After being there 20 minutes or so, the lady running the sale said: "May I have your attention? May...I...Have...Your...ATTENTION??" After things quieted down, she continued: "I just wanted to say that yesterday while my husband and I were getting this sale ready, inside here, he killed a large COPPER HEAD !!!"

    With the prices of scrap copper going down recently, the odds of finding heavy copper wiring for solar needs should improve!

    Attachment not found.Attachment not found.
    Bill
  • BoFuller
    BoFuller Solar Expert Posts: 187 ✭✭✭
    Re: Roof or not roof? That is the question

    Attachment not found.Well, I'm going with the roof mount. My basic roof over living area is 24 X 32 on each side. I also have 8 foot overhangs that I didn't insulate, so I plan on putting 9 panels on each South facing overhang, then run the wires to a shed attached to the NE corner of the house.
    12 Kyocera 235 panels, 3 Gyll LiFePO4 batteries (previously 16 Trojan L16 RE-B batteries), Outback 3600W 48V system, Generac 11K propane backup generator, NW AZ, off grid, 6,000 ft (system installed in April 2015)

  • ILFE
    ILFE Solar Expert Posts: 364 ✭✭
    Re: Roof or not roof? That is the question

    We have a farm and a rental home here in Cambodia. We could live at the farm, I'm just too hard headed to make the move because it is 100% off grid there, and we rely partially on the grid, here in town. Okay. I give up. It's because of the much faster, much more reliable internet connection that I have here. ;)

    Anyway, I recently installed a solar array on a vacant lot adjacent to the house. I had a pole mount constructed 2 meters above the ground. Because of this, I don't have to concern myself with getting anyone else to work on the panels. I don't have to worry about having to get someone else to clean them or to even inspect them. I can do it all myself, as necessary.

    Not to mention, the roof faces East - West. I would have to have two arrays, each on opposite sides of the roof, to get full sun throughout the day. On top of it being a rental home - well, it just isn't worth it to me to go through all of that.

    If you haven't gone with the roof mount yet, as far as the installation goes, you may still wish to reconsider. Life is a lot easier, especially if you have the available real estate to put them on, concerning maintaining your panels. Not to mention, if you put them on a pole mount, for example, you can adjust them through the seasons, earning yourself some extra power along the way. That is something that static mounted panels cannot give you.

    I wish I had done the same concerning the panels at the farm. They are all on top of the house. As soon as I get an opportunity to build a couple of pole mounts out there, they will be taken off the roof.
    Paul
  • BoFuller
    BoFuller Solar Expert Posts: 187 ✭✭✭
    Re: Roof or not roof? That is the question

    I'm planning on 18 panels, and the top of is already South facing, at 6/12 pitch I already have a universal angle (more or less), I would have to take down a lot more trees for a pole mount while the roof is already 25 feet off the ground. It just doesn't make sense to me to not mount them on the roof. Different people have good reasons but so far I see nothing to make me want to switch from roof mount.
    Thanks for all the input.
    12 Kyocera 235 panels, 3 Gyll LiFePO4 batteries (previously 16 Trojan L16 RE-B batteries), Outback 3600W 48V system, Generac 11K propane backup generator, NW AZ, off grid, 6,000 ft (system installed in April 2015)

  • ILFE
    ILFE Solar Expert Posts: 364 ✭✭
    Re: Roof or not roof? That is the question
    BoFuller wrote: »
    I'm planning on 18 panels, ...

    Wow! Okay. I guess when someone mentions a "cabin", I am not thinking of them installing an array that size. I see what you mean, now. Good luck with it.


    Not sure what you decided to do regarding rainwater harvesting. But, this video may give you some ideas. Billy Kniffen and his wife live entirely off rainwater harvesting.
    Paul
  • BoFuller
    BoFuller Solar Expert Posts: 187 ✭✭✭
    Re: Roof or not roof? That is the question
    ILFE wrote: »
    Wow! Okay. I guess when someone mentions a "cabin", I am not thinking of them installing an array that size. I see what you mean, now. Good luck with it.


    Not sure what you decided to do regarding rainwater harvesting. But, this video may give you some ideas. Billy Kniffen and his wife live entirely off rainwater harvesting.

    Yes, we plan to eventually be totally relying on rainwater. It will probably be another year, but we'll get there.
    12 Kyocera 235 panels, 3 Gyll LiFePO4 batteries (previously 16 Trojan L16 RE-B batteries), Outback 3600W 48V system, Generac 11K propane backup generator, NW AZ, off grid, 6,000 ft (system installed in April 2015)