Hello, I’m planning an off grid cabin installation with panels on a roof. This rural area has no code enforcement, but thankfully I’m picky about trying to do things right the first time and I have some background in electronics and electrical systems.
I’ve been searching the forums and it looks like all the answers to questions I could have for this any install are here, but I’m aware interpreting and applying code to the specific situation can be unclear and products in this industry are changing quickly.
My first concern is planning the DC wire runs and finding the right types of parts to order, so my current design is as follows:
PV wires from string(s) 10ga Cu and #6 Cu bare from rails enter a rain tight metal box through UV rated cable glands. The box is screwed to an adjacent array rail and PV wire is terminated to THHN-2 or equivalent 90C+ rated Cu wires 10ga. RMC or IMC (or LFMC) conduit ½” is run from the box rain tight adapted to LFMC HC 90C+ bends around the gutters and under the eave (drip loop). All above the required 7/8 gap from the roof. The flex gets adapted to another piece of conduit or directly to a metal weather rated box with an SPD and IMO disconnect installed in it. The #6 Cu ground is contiguous from the array. I’m in a humid environment so I think I need to add weep holes, but I’m not 100% sure what is ideal. I’m hoping to cover the ground wire to the rod with some protective tubing as well which may introduce questions and moisture concerns.
I think the area directly below would be ideal for a Cu ground rod for the array. I know it’s best to be contiguous and short. Since it’s a wet region I’m thinking I only need 1 GND rod and could run the EGC from the AIO/equipment under the cabin (in earth) back to the same rod. However, I’ve also read a ground should be in the conduit with the DC lines and that seems safer in case the metal enclosures/tubing bond is poor.
If a 2nd rod is necessary I understand it should be 6ft away and most would suggest bonding them together with Cu contiguously.
The equipment wall is about 10ft inside in a small open hall closet space for ventilation and ease of access. I plan to line it with some leftover cement board for firebreak and I’m thinking of hanging curtains of fiberglass fire/welding blanket in front of it all.
I’m aware once inside I can switch to EMT and THHN, but I certainly don’t want any unnecessary splices or boxes for DC. I think I can run EMT straight horizontally from rigid through the outside wall from the IMO box. At the equipment my concern is many of the cheaper AIO’s don’t appear to be made to connect conduit/tubing directly. I’m hoping I can arrange the AC main box above the AIO and the battery on the floor. But, there may be several runs of tubing in a small area so I’d like to lay it all out in some detail ahead of time since I’m not experienced with EMT. I may also be lazy and adapt flex.
I plan to use EMT inside the cabin because it doesn’t have many wall cavities (it’s a mix of 6x6 oak cants, beams, planks and some earthen walls) and I know critters are inevitably a threat to romex. I’d rather be safe than sorry. In general I’d like every wire in metal, but I do see all the images of people choosing to use plastic boxes and just bond the bare Cu to the conduits. Given the high cost of metal boxes is it worth the it? I'd love to get the total cost for this project to several thousand $ to save for a much bigger solar project, but that seems wishful with the prices I'm seeing for the small components. I've started looking for metal scrap recycling etc., but I'll my the DC conduit new.
I’m not that familiar with conduit and EMT adapters so I’m searching for good sources online. I’m in a rural area that often has poor quality products locally, so I’m expecting to have to order most items. Any source links and advice are much appreciated.
While I don’t think I have many long wire runs there may be some with quite a few turns. So at what lengths and number of turns is stranded wire ideal over solid?
I’ve yet to decide the exact panels and AIO equipment setup, but I’m looking to order from Signature Solar because they’re not too far by freight. I want to put as much PV on the roof as possible, but current estimates are 4-5KW of PV up and a 14KWhr wall mount heated battery would be nice. I was looking at the small EG4 3KW AC/5KW PV 500V max Voc AIO, but now I’m leaning towards one of the growatt 5KW AC/6KW PV units.
The only large loads planned in the cabin will be a small tank water heater ~2KW and a water pump 300-500W. But, from the totals I expect a 40A main breaker in the 120V AC panel will be sufficient.
I checked max Voc cold (0F min here) calcs for 12 solarever 450W/562W panels, but I’m looking for better wind and hail rated panels like the Aptos. The bifacials on a roof throw a bit of uncertainty into the calculations. The roof is green metal, but I doubt it’s worth painting white. The corrugation of the metal also isn’t flat trapezoidal. It’s a style that already has sealing screws in the flats. I need to do more research on mounting rail kits for metal roofing, but it looks limited and companies appear to change systems a lot or go out of business.
From examples I’ve seen I could use some EJOT fasteners rails with T nuts and L brackets. Another possible concern is the metal roof is designed with an air gap. The engineered moisture barrier (felt with mylar) has a grid of wood slats over it to enable hot air flow out from under the metal. I think it’s all well fastened, but may present challenges and require longer fasteners.
I’d like to get the panels as high as possible for bifacial gain, but from what I’ve read, I probably can’t expect 10% so that decision will be mostly about mechanical weather resistance and dimensional fit. I’ve heard there are often fire codes that apply to roof panel layouts, but in my case I think I can do whatever is safe for access. There is an overhang above a wall of south facing windows so I’m planning the array closer to the bottom with an access path above it. To enable thorough safety I’m planning to put safety anchors on the wall above for clipping a safety harness in because the roof angle is ~45 deg. As far as the solar hours calcs the ~45 deg angle helps average seasonal power out to ~4 hrs in winter and ~6 in summer and it’s likely more of a winter use cabin.
Any comments will be appreciated, especially criticism.
I’ve been searching the forums and it looks like all the answers to questions I could have for this any install are here, but I’m aware interpreting and applying code to the specific situation can be unclear and products in this industry are changing quickly.
My first concern is planning the DC wire runs and finding the right types of parts to order, so my current design is as follows:
PV wires from string(s) 10ga Cu and #6 Cu bare from rails enter a rain tight metal box through UV rated cable glands. The box is screwed to an adjacent array rail and PV wire is terminated to THHN-2 or equivalent 90C+ rated Cu wires 10ga. RMC or IMC (or LFMC) conduit ½” is run from the box rain tight adapted to LFMC HC 90C+ bends around the gutters and under the eave (drip loop). All above the required 7/8 gap from the roof. The flex gets adapted to another piece of conduit or directly to a metal weather rated box with an SPD and IMO disconnect installed in it. The #6 Cu ground is contiguous from the array. I’m in a humid environment so I think I need to add weep holes, but I’m not 100% sure what is ideal. I’m hoping to cover the ground wire to the rod with some protective tubing as well which may introduce questions and moisture concerns.
I think the area directly below would be ideal for a Cu ground rod for the array. I know it’s best to be contiguous and short. Since it’s a wet region I’m thinking I only need 1 GND rod and could run the EGC from the AIO/equipment under the cabin (in earth) back to the same rod. However, I’ve also read a ground should be in the conduit with the DC lines and that seems safer in case the metal enclosures/tubing bond is poor.
If a 2nd rod is necessary I understand it should be 6ft away and most would suggest bonding them together with Cu contiguously.
The equipment wall is about 10ft inside in a small open hall closet space for ventilation and ease of access. I plan to line it with some leftover cement board for firebreak and I’m thinking of hanging curtains of fiberglass fire/welding blanket in front of it all.
I’m aware once inside I can switch to EMT and THHN, but I certainly don’t want any unnecessary splices or boxes for DC. I think I can run EMT straight horizontally from rigid through the outside wall from the IMO box. At the equipment my concern is many of the cheaper AIO’s don’t appear to be made to connect conduit/tubing directly. I’m hoping I can arrange the AC main box above the AIO and the battery on the floor. But, there may be several runs of tubing in a small area so I’d like to lay it all out in some detail ahead of time since I’m not experienced with EMT. I may also be lazy and adapt flex.
I plan to use EMT inside the cabin because it doesn’t have many wall cavities (it’s a mix of 6x6 oak cants, beams, planks and some earthen walls) and I know critters are inevitably a threat to romex. I’d rather be safe than sorry. In general I’d like every wire in metal, but I do see all the images of people choosing to use plastic boxes and just bond the bare Cu to the conduits. Given the high cost of metal boxes is it worth the it? I'd love to get the total cost for this project to several thousand $ to save for a much bigger solar project, but that seems wishful with the prices I'm seeing for the small components. I've started looking for metal scrap recycling etc., but I'll my the DC conduit new.
I’m not that familiar with conduit and EMT adapters so I’m searching for good sources online. I’m in a rural area that often has poor quality products locally, so I’m expecting to have to order most items. Any source links and advice are much appreciated.
While I don’t think I have many long wire runs there may be some with quite a few turns. So at what lengths and number of turns is stranded wire ideal over solid?
I’ve yet to decide the exact panels and AIO equipment setup, but I’m looking to order from Signature Solar because they’re not too far by freight. I want to put as much PV on the roof as possible, but current estimates are 4-5KW of PV up and a 14KWhr wall mount heated battery would be nice. I was looking at the small EG4 3KW AC/5KW PV 500V max Voc AIO, but now I’m leaning towards one of the growatt 5KW AC/6KW PV units.
The only large loads planned in the cabin will be a small tank water heater ~2KW and a water pump 300-500W. But, from the totals I expect a 40A main breaker in the 120V AC panel will be sufficient.
I checked max Voc cold (0F min here) calcs for 12 solarever 450W/562W panels, but I’m looking for better wind and hail rated panels like the Aptos. The bifacials on a roof throw a bit of uncertainty into the calculations. The roof is green metal, but I doubt it’s worth painting white. The corrugation of the metal also isn’t flat trapezoidal. It’s a style that already has sealing screws in the flats. I need to do more research on mounting rail kits for metal roofing, but it looks limited and companies appear to change systems a lot or go out of business.
From examples I’ve seen I could use some EJOT fasteners rails with T nuts and L brackets. Another possible concern is the metal roof is designed with an air gap. The engineered moisture barrier (felt with mylar) has a grid of wood slats over it to enable hot air flow out from under the metal. I think it’s all well fastened, but may present challenges and require longer fasteners.
I’d like to get the panels as high as possible for bifacial gain, but from what I’ve read, I probably can’t expect 10% so that decision will be mostly about mechanical weather resistance and dimensional fit. I’ve heard there are often fire codes that apply to roof panel layouts, but in my case I think I can do whatever is safe for access. There is an overhang above a wall of south facing windows so I’m planning the array closer to the bottom with an access path above it. To enable thorough safety I’m planning to put safety anchors on the wall above for clipping a safety harness in because the roof angle is ~45 deg. As far as the solar hours calcs the ~45 deg angle helps average seasonal power out to ~4 hrs in winter and ~6 in summer and it’s likely more of a winter use cabin.
Any comments will be appreciated, especially criticism.
