Hi All,
I'm designing an off-grid solar system. Neither the electrician or the inspector are really familiar with solar, so I'm doing the heavy-lifting. I'm a software engineer by trade, not an electrician, hence I came to this forum looking for advise from the experts. I've sent my design to SMA, but they've been a bit slow to respond to my questions. I'll update this post if/when they get back to me.
I think I've read all the available SMA Sunny Island and Sunny Boy documentation and watched every video and webinar available online. I also attended a couple free webinars recently. After all of that material though, I have some questions that need answering.
Thanks in advance!
High-level project overview
To review my wire diagram, see https://drive.google.com/file/d/19cFPZQCwli-pH73-9VSAv5qRtN3G4nfW/view. Don't assume I know what I'm doing. If something looks silly, tell me
My outstanding questions/concerns are:
1. The bonding of the neutral. Is bonding the neutral in a breaker panel like this advisable with an off-grid SMA system? The panel will sit near the Sunny Islands, in a basement.
2. The Sunny Boy manual (refer to https://files.sma.de/downloads/SBxx-1SP-US-41-IA-xx_12.pdf ), on page 48 has a notice that says the inverter is not protected from ground faults during operation. On page 72, section 10.7 lists an "All-pole sensitive residual-current monitoring unit", which I'm pretty sure is a feature of the Sunny Boy. This RCD was said to monitor and handle detected ground-faults safely in tech tips on older models (refer to
,
,
), so I'm a bit confused. Do I need a separate ground fault protection device or not? To be clear, my concern is on the DC side. I cannot find a device that will work at the ~400 volts the PV strings will be operating at, that doesn't require a separate power source. I was also told by someone at a major online solar retailer that they sell hundreds of Sunny Boys a year, and no one installs ground-fault protection devices and they have never heard of inspector-related issues. I'm still waiting on SMA for a definitive answer on this, so hopefully someone here can clear this up for me. I'm more concerned about safety than passing inspection anyway, so just because others are getting away with it, doesn't mean I'll just blindly follow the crowd.
3. Section 6.3.2 of the Sunny Island manual (refer to https://files.sma.de/downloads/SI4548-6048-US-BE-en-21W.pdf) seems to suggest that a breaker less than 56A be used when connecting AC1. 56A x 120V = 6720 watts, which is quite a bit less than the surge rating of 11,000 watts. I need clarification on this, as I've seen a number of references online suggesting to use a 70 AMP single pole breaker (e.g.
). I've seen some comments elsewhere that seem to imply that the Sunny Island AC1 to AC2 relay is limited to 56A, which seems more correct. What say the experts?
4. What load contactors are being used with the Sunny Islands? I've identified TeSys LC1D80ED, LC1D95ED, and LC1D115ED as potential candidates. Will these work with SI? If not, what models can you recommend? On a related note, got any recommendation for an enclosure that supports a DIN rail? I assume you're not just mounting these contactors on the wall.
5. My wire diagram shows Relay 1 and Relay 2 being used for load shedding. When both relays are being used, it's on unclear from the manual how to wire the relays, as there's only one BatVtgOut+ and BatVtgOut- available. In my diagram, I show both relay 1 and relay 2 C terminals connected to the single BatVtgOut+ and a single conductor connected to the BatVtgOut- terminal. The later terminates on a busbar in the contactor enclosure, and splits to each contactor's A2 terminal. Is this right?
6. In section "15 Relays" of the SI manual, the description of relay function AutoLodSoc1 and AutoLodSoc2 refer to Lod1Soc and Lod2Soc limits. Are Lod1Soc and Lod2Soc editable system properties? I don't see them in the manual.
7. While I don't have surge protection devices in the current diagram, I'm under the impression that these should be installed in each panel, since the panels are either outside (at the arrays) or being fed by wires from outside the building. Thoughts?
8. I don't have formal plans to ground the array itself, since I was planning on using a steel frame, bonded to the PV panel frames. In affect, this would create a bunch of earth electrodes on the DC side, at the array, so I'm in doubt that running copper ground rods would be necessary. And yes, I watched Mike Holt's discussion on grounding. The grounding in my diagram simply assumes all the PV modules are ground by the ground mount hardware and the ground mount hardware will have a ground conductor running to the Sunny Boy DC ground terminal. My diagram shows each string with a separate ground conductor, but in practice, I doubt that will happen, as the strings will share the same mount. I was even considering having all six strings on a single mount, meaning both inverters will be attached to the same DC ground conductor, but I suppose that will disable both inverters in the event of a ground fault, so maybe two arrays would be the better option. Thoughts?
9. What battery switches are being used for systems like this? The ABB S6N (refer to https://www.ebay.com/itm/273640129655 ) but I don't need something complicated, unless it's also acting as a fuse. Will something like a basic switch pass code (refer to https://www.camperid.com/parkpower/...onnect-switch-mpn-720rv.html#specifications)? Please note, that my current design is using LiFePO4 batteries, which can run higher than 48vdc.
10. What fuses are recommended for a system of this size? I was thinking of using Little Fuse model 0CNN800.V and LFFB0003Z (or something similar). 22,000 sunny island split-phase surge watts / 48V = ~460A. In section 6/2/2, the SMA math suggests I should plan for ~480A with 22k surge watts. Since the battery cables will be short, I don't mind going big on cables and fuses. I'm open to other suggestions.
If you read this far, thank you! I appreciate your help.
I'm designing an off-grid solar system. Neither the electrician or the inspector are really familiar with solar, so I'm doing the heavy-lifting. I'm a software engineer by trade, not an electrician, hence I came to this forum looking for advise from the experts. I've sent my design to SMA, but they've been a bit slow to respond to my questions. I'll update this post if/when they get back to me.
I think I've read all the available SMA Sunny Island and Sunny Boy documentation and watched every video and webinar available online. I also attended a couple free webinars recently. After all of that material though, I have some questions that need answering.
Thanks in advance!
High-level project overview
- Two Sunny Island 6048US battery inverters connected to a 200A Stand-Alone Grid Breaker Panel in split-phase.
- Neutral will be bonded in this single location.
- The breaker panel will be connected to a single ground electrode.
- Each Sunny Island will be connected to the panel via a 70A single-pole breaker
- Two Sunny Boy SB7.7-1SP-US-41 PV inverters in off-grid mode, installed at ground mount arrays.
- Sunny Boys are both connected to an outdoor breaker panel installed at the ground mount, using 35A breakers (max AC output of the SB7.7 is listed as 32A). A single AC circuit will connect this with the stand-alone grid panel, separated by a manual PV system disconnect.
- Solar modules will be wired in series (not parallel). There will be six series of panels at ~10A and ~400vdc for 4000 watt nominal PV module output, each connected to an MPPT on the Sunny Boys.
- Two 100A sub panels branch off the stand-alone grid panel, each separated by manual disconnect switches and load-shedding contactors.
- There will be three 100A disconnect switches outside, one to disconnect from the PV inverters, and the other two to disconnect form the sub panels. The stand-alone grid panel will need to be disconnected by shutting off the Sunny Islands. The battery will need to be disconnected using a separate battery disconnect switch.
To review my wire diagram, see https://drive.google.com/file/d/19cFPZQCwli-pH73-9VSAv5qRtN3G4nfW/view. Don't assume I know what I'm doing. If something looks silly, tell me
My outstanding questions/concerns are:
1. The bonding of the neutral. Is bonding the neutral in a breaker panel like this advisable with an off-grid SMA system? The panel will sit near the Sunny Islands, in a basement.
2. The Sunny Boy manual (refer to https://files.sma.de/downloads/SBxx-1SP-US-41-IA-xx_12.pdf ), on page 48 has a notice that says the inverter is not protected from ground faults during operation. On page 72, section 10.7 lists an "All-pole sensitive residual-current monitoring unit", which I'm pretty sure is a feature of the Sunny Boy. This RCD was said to monitor and handle detected ground-faults safely in tech tips on older models (refer to
3. Section 6.3.2 of the Sunny Island manual (refer to https://files.sma.de/downloads/SI4548-6048-US-BE-en-21W.pdf) seems to suggest that a breaker less than 56A be used when connecting AC1. 56A x 120V = 6720 watts, which is quite a bit less than the surge rating of 11,000 watts. I need clarification on this, as I've seen a number of references online suggesting to use a 70 AMP single pole breaker (e.g.
4. What load contactors are being used with the Sunny Islands? I've identified TeSys LC1D80ED, LC1D95ED, and LC1D115ED as potential candidates. Will these work with SI? If not, what models can you recommend? On a related note, got any recommendation for an enclosure that supports a DIN rail? I assume you're not just mounting these contactors on the wall.
5. My wire diagram shows Relay 1 and Relay 2 being used for load shedding. When both relays are being used, it's on unclear from the manual how to wire the relays, as there's only one BatVtgOut+ and BatVtgOut- available. In my diagram, I show both relay 1 and relay 2 C terminals connected to the single BatVtgOut+ and a single conductor connected to the BatVtgOut- terminal. The later terminates on a busbar in the contactor enclosure, and splits to each contactor's A2 terminal. Is this right?
6. In section "15 Relays" of the SI manual, the description of relay function AutoLodSoc1 and AutoLodSoc2 refer to Lod1Soc and Lod2Soc limits. Are Lod1Soc and Lod2Soc editable system properties? I don't see them in the manual.
7. While I don't have surge protection devices in the current diagram, I'm under the impression that these should be installed in each panel, since the panels are either outside (at the arrays) or being fed by wires from outside the building. Thoughts?
8. I don't have formal plans to ground the array itself, since I was planning on using a steel frame, bonded to the PV panel frames. In affect, this would create a bunch of earth electrodes on the DC side, at the array, so I'm in doubt that running copper ground rods would be necessary. And yes, I watched Mike Holt's discussion on grounding. The grounding in my diagram simply assumes all the PV modules are ground by the ground mount hardware and the ground mount hardware will have a ground conductor running to the Sunny Boy DC ground terminal. My diagram shows each string with a separate ground conductor, but in practice, I doubt that will happen, as the strings will share the same mount. I was even considering having all six strings on a single mount, meaning both inverters will be attached to the same DC ground conductor, but I suppose that will disable both inverters in the event of a ground fault, so maybe two arrays would be the better option. Thoughts?
9. What battery switches are being used for systems like this? The ABB S6N (refer to https://www.ebay.com/itm/273640129655 ) but I don't need something complicated, unless it's also acting as a fuse. Will something like a basic switch pass code (refer to https://www.camperid.com/parkpower/...onnect-switch-mpn-720rv.html#specifications)? Please note, that my current design is using LiFePO4 batteries, which can run higher than 48vdc.
10. What fuses are recommended for a system of this size? I was thinking of using Little Fuse model 0CNN800.V and LFFB0003Z (or something similar). 22,000 sunny island split-phase surge watts / 48V = ~460A. In section 6/2/2, the SMA math suggests I should plan for ~480A with 22k surge watts. Since the battery cables will be short, I don't mind going big on cables and fuses. I'm open to other suggestions.
If you read this far, thank you! I appreciate your help.
