Need help with solar panel array design for apartment building

[mikael6]

Just one more idea I thought of that might save me the expense of having a new panel installed. I think that the 30 am double pole breaker goes to an electric dryer (I am going to check that when I have a sec). I could probably replace that dryer with a natural gas fired one as I have a natural gas pipe connection nearby. There woudn't be a cost to me as a company provides me with my coin operated washer and dryer as they get a cut of the money used in it. They said they could provide me a natural gas model free of charge. In that case I could remove that breaker and install a double pole one for the solar panel in its place.

I plan on running 8 gauge wire between the inverter and the panel. I am using a sunnyboy 3800us inverter. My panel array diagram is attached earlier in the post that shows the system I want to install and future additions to it. In that situation, what breaker would make sense? maybe 40 or 45 amp double pole

[Naptown]

40 amps is the generally accepted maximum OCPD for a #8 wire. However that #8 is way overkill for the application.
Your inverter will put out about 16A max. The NEC requires in this case as the load is considered as continuous that the conductors be rated for 125% of the load
In this case 20A or #12 wire. You are wasting your money on the #8 where #12 will work and # 10 would give you a little wiggle room for a long run from inverter to panel box. In your case fuse with 20A and a 20A breaker.

[mikael6]

Ok, got you. I was kind of thinking for the future of having the bigger breaker if I do a 2nd or 3rd string with 12 more panels in the future and maybe doing a bigger inverter to take advantage of the extra output. However, I didn't realize your point about not oversizing the breaker for the current application as the inverter will only put out 16 amps. It sounds like a 40 amp breaker on this would be ok with 8 gauge wire but due to NEC code it would be much higher than the 16 amps the system is putting out. So, it sounds like I should do the 20 amp breaker now (I am assuming 8 gauge wire won't hurt and can only help and I will have extra lying around) and then in future if I upgrade inverter to a sunnyboy maybe 4000 or higher that I at that point upgrade the breaker to a higher amperage, but not before.

Let me know if my logic makes any sense and as always much appreciated

[Naptown]

A 40A breaker feeding a 100A panel will not fly A 20A will The #8 and 40A breaker are fine but it will mean a panel upgrade. (Which you should probably do anyway.

[mikael6]

Ok, if dryer is on the current 30 amp breaker, I will remove it to free up two breaker slots and put a 20 amp breaker there per your recommendation. If and when I upgrade my inverter to a higher capacity I will then pursue the panel upgrade option. Extremely appreciative of all your help.

thanks!

[inetdog]

A 40A breaker feeding a 100A panel will not fly A 20A will The #8 and 40A breaker are fine but it will mean a panel upgrade. (Which you should probably do anyway.

True, but according to the OP the panel is rated for 125A (nameplate), and the main breaker is actually 60A. Lots of headroom!

[Naptown]

True, but according to the OP the panel is rated for 125A (nameplate), and the main breaker is actually 60A. Lots of headroom!

True but in my experience inspectors do not think that way They take one look at the main and go from there.

[bonaire]

You can always have two inverters. So if you have a string of 8 now and one inverter, to expand, just "do it again" and have a second inverter/string wired into another backfeed breaker. Since you bought the inverter used - do you know the # of years it was in-use? They don't last more than maybe 12 years.

The way we have my PV setup now (going live anyday now) it is two Power One Aurura 3.6 inverters - tied together into one small subpanel, then the 240V single-phase goes to the house with a supply-side connection so that there is no backfeeding at all in the house.

Going from the electric dryer to the nat gas dryer is one move in the right direction for planning Solar PV. You want to conserve the electric usage and this is one good way to do it. Should save dozens of kWh per month moving to natgas. And for free too!

[inetdog]

True but in my experience inspectors do not think that way They take one look at the main and go from there.

Can't argue with experience, and you may or may not be able to argue with an inspector. Not a good prospect if you are in a hurry, that's for sure. That is where a plan review in advance may help.

[mikael6]

One more question, my ac disconnect needs to go outdoors per utility company. I bought one that is rated for outdoors but it is not fusible. In other words, I cannot add fuses to it. Is that ok, or do I need an ac disconnect which I can add fuses to to connect my inverter to the electric service panel?

[inetdog]

One more question, my ac disconnect needs to go outdoors per utility company. I bought one that is rated for outdoors but it is not fusible. In other words, I cannot add fuses to it. Is that ok, or do I need an ac disconnect which I can add fuses to to connect my inverter to the electric service panel?

If you are connecting your inverter output to a backfed breaker in your inside panel, that will be the overcurrent device for the circuit. The current that the inverter itself produces is already limited by the size of the panels and so does not need protection from that end. The AC disconnect outside will serve the purpose of keeping the POCO happy and does not need fuse or breaker located there.

[mikael6]

question about neutral wire

I based my design upon another design I saw of an array that a friend had installed. Anyway, if you look at the design I uploaded, there is no neutral wire running from inverter to AC disconnect and no neutral wire from AC disconnect to the panel. Should I have be running a neutral wire from AC output on inverter to AC disconnect and then neutral wire from AC disconnect to service panel? Please advise. thx!

[inetdog]

I based my design upon another design I saw of an array that a friend had installed. Anyway, if you look at the design I uploaded, there is no neutral wire running from inverter to AC disconnect and no neutral wire from AC disconnect to the panel. Should I have be running a neutral wire from AC output on inverter to AC disconnect and then neutral wire from AC disconnect to service panel? Please advise. thx!

If the inverter output is 240 volt and the inverter manufacturer's instructions do not direct you to connect a neutral, then you do not need to run one. But you must have an grounding conductor (EGC) unless the conduit meets that requirement.

What you cannot do is run a required neutral the short way instead of running it out to a disconnect and back.

[mikael6]

neutral wire or not

I looked in manual for the sunny boy 3800u inverter that I have and it states:

Utility Configuration Jumpers
The SB3800U comes from the factory pre-configured for utility interconnection with
neutral. The SB3800U may be reconfigured for grids without neutral by setting the
jumpers on the board of the SB3800U.
The utility configuration jumpers allow the SB3800U to be connected to transformers
where the neutral is not present, such as the 208V and 240V Delta, shown in Figure 4-
3. Refer to the figure below for a description of jumper settings.



There is a connection on the inverter for a neutral wire but I am not sure if I should use it to connect the inverter to the ac disconnect and then to the panel. From reading the manual it states that the sunnyboy may be reconfigured for grids without neutral. I am not sure if my grid has a neutral or not. Should I look at the service lines coming into my panel to see if there is a neutral wire coming in? I am not very familiar with this. Any help would be appreciated. thx!

[inetdog]

I looked in manual for the sunny boy 3800u inverter that I have and it states:

Utility Configuration Jumpers
The SB3800U comes from the factory pre-configured for utility interconnection with
neutral. The SB3800U may be reconfigured for grids without neutral by setting the
jumpers on the board of the SB3800U.
The utility configuration jumpers allow the SB3800U to be connected to transformers
where the neutral is not present, such as the 208V and 240V Delta, shown in Figure 4-
3. Refer to the figure below for a description of jumper settings.



There is a connection on the inverter for a neutral wire but I am not sure if I should use it to connect the inverter to the ac disconnect and then to the panel. From reading the manual it states that the sunnyboy may be reconfigured for grids without neutral. I am not sure if my grid has a neutral or not. Should I look at the service lines coming into my panel to see if there is a neutral wire coming in? I am not very familiar with this. Any help would be appreciated. thx!

Since you are in the US, there will be a neutral wire at your service entrance whether it is 240/120 split-phase or something else.
The UL approval for the inverter requires that it test that the two sides of the 240 service are approximately equal in voltage to neutral before starting up, so you will have to connect the neutral.
The rule that then comes into play is that the neutral has to follow the same path as the two hot wires. Although you must not actually set up the switch to disconnect it.