Off grid 19kWp system

[jeffroboto]

Hi-
I'm new around here. I've been on an internet solar power crash course on the last 48 hours and most roads lead here. So here I am. I've already learned a lot from y'all and expect that will continue.

I'm a solar newby so we should probably start with the big picture. I'm in the planning stages of a permitted (NEC 2020) off-grid system. I'll try to attach a diagram. Am I going down the any wrong roads or walking into traps? Am I missing any major components in my system? I haven't drilled down into the details on everything (e.g I haven't sized breakers, conduit, conductors, etc.). The equipment on the left side of the diagram has largely been purchased used. This drove some of the design decisions.

My intent is to maximize length in the day that solar is collected. I'm accomplishing this by facing strings SSE (-30°) and SSW (+30°). The hope is to minimize batteries. They sure are expensive! I'm currently under paneled but plan to add more. I've got space so I can use some less efficient (cheaper) ones if I find a deal.

If (BIG if) I pass the first test of a somewhat reasonable plan then I've got some questions. These may be "stupid" because I'm no electrical engineer.

1. How to size breakers? Is it just base on wire protection? Do I need to ensure the power source (inverters) have enough capacity to trip? Or is that not a concern because the inverters can supply much larger wattage for short periods?
2. Can I add batteries later? I here conflicting opinions on mixing battery age and manufacturers. I'd prefer to start with fewer and add more down the line if that is possible.
3. Do I bond neutral and ground on load center shown, or on the house's load center? My lack of working NEC knowledge shows here.
4. Should I run RS-485 to the Sunny Boys? Or rely on the Sunny Island to frequency shift and shutdown the PV? I don't see many examples of people using RS485. The Sunny Boys would need an additional RS485 module and hopefully it would work....
5. SMA calls for at least 100ah of battery per 1000W of "nominal AC power from the AC sources in the stand alone grid." Is that only my PV sources (not the Sunny Island 12000W)? I assume this is to provide a place for the energy to go (the batteries) while the PV is shutdown if the system demand falls rapidly. Is this the case?
6. I imagined mounting the gear on a strut rack with roof for shade and moisture protection. I'd place the battery rack into a NEMA enclosure and insulate it. NEC2020 Section 690 likely precludes that because the energy storage system (ESS) needs to be UL. Now I'm thinking I should install in a small shed?

My end goal is a set of drawings that I can pull a permit with. I know I'm a long ways from that but hopefully I'm moving in the right direction. Thank you again for your help. edit: I couldn't figure out how to attach a .pdf so I took a screen shot.

-Jeff

 

[jeffroboto]

If I'm off my rocker you can tell me and I won't be hurt. Maybe my questions do not make sense. I looked into greenlancer to help with NEC calcs. Everyone seems to recommend them but they seem setup for business to business? https://www.greenlancer.com/solar-permits asks for a company name.

I noticed an error on my drawing; the two Sunny Islands should be on different phases.

 

[pvgirl]

How to size breakers? Is it just base on wire protection? Do I need to ensure the power source (inverters) have enough capacity to trip? Or is that not a concern because the inverters can supply much larger wattage for short periods?

Breakers will be sized to 125% of the continuous output current of the inverter.

Do I bond neutral and ground on load center shown, or on the house's load center? My lack of working NEC knowledge shows here.

There should be only one neutral ground bond in the system, the location would normally be at the service disconnect for your grid connection.

SMA calls for at least 100ah of battery per 1000W of "nominal AC power from the AC sources in the stand alone grid." Is that only my PV sources (not the Sunny Island 12000W)? I assume this is to provide a place for the energy to go (the batteries) while the PV is shutdown if the system demand falls rapidly. Is this the case?

This is to insure there is a place for the power to go when the grid is off, if you are grid connected you will need a SMA microgrid isolation device to disconnect the grid feed when it goes down, and isolate your system to allow it to power the home, when the grid is down

I imagined mounting the gear on a strut rack with roof for shade and moisture protection. I'd place the battery rack into a NEMA enclosure and insulate it. NEC2020 Section 690 likely precludes that because the energy storage system (ESS) needs to be UL. Now I'm thinking I should install in a small shed?

Shouldn't be a major issue as long as the enclosure will keep the equipment within it's operating conditions.

Depending on local requirements you most likely will need to use a UL9540 listed ESS system, many of these are listed combinations of batteries and inverters.

 

[jeffroboto]

Thank pvgirl.

I understand that there can only be one Ground-Neutral bond. This is a 100% off grid system so I think there is flexibility and I could bond at the inverter, solar combiner panel, or load panel. I think I prefer to do it at the solar combiner panel. If the inspector wants it in the load panel I can move it there too. I'll probably make both panels service entrance rated so that the bond could be made at either place (but not both!).

I was not aware of the requirement for a listed combo of batteries + inverters. When I dig in it appears to be driven by 2021 IRC? The AHJ is on NEC 2020 but IRC 2015. I think this would indicate only my battery needs to be UL9540 but correct me if I'm wrong. I want to submit a package that will pull a permit without many changes. AHJ might have their own ideas too.

 

[pvgirl]

UL9540 is required in IRC 2018 and later, but IRC 2015 predates UL9540 so it isn't required.