Add 2nd System without impacting 1st?

[britincali]

Hi. I'm in Southern California and I have a 25 panel system installed by SolarCity a couple of years back. It's not big enough for our load and I don't want to give Tesla any more money as they were horrible to deal with and the 25 panels we have perform poorly. However I have 23 years left of their warranty, so don't want to mess that up.

I have a flat garage roof next to the Solarcity inverter and distribution box. I have space for another 8 or so panels.
I've seen that I can DIY for a lot less cash. I'm an Electronics Engineer and I design things a lot smaller than these, but the background is the same. I may also look at a DIY solar battery as part of it too.

The distribution panel is a SC2040M200PF. Looking at the rather sparse data on it I see the smart meter plugs in to the panel and it looks like the inverter output goes right in.
I took a look inside the hatch that the solar power conduit goes into, and it dissapears into the back of the smart meter area.

If I wanted to add a 2nd system with a separate inverter how would I go about connecting it? I'm assuming I can't simply wire it in parallel with the output of the Solarcity inverter box?

Some photos for reference

https://ibb.co/frJb82Z

https://ibb.co/WvyGGsy

https://ibb.co/xDG7bB2

https://ibb.co/fkNz58g

Thanks
Marc

[sdold]

Hi Britincali, welcome to the forum.

I helped a friend do the same thing in Milpitas CA using microinverters. He had an existing Solar City installation that he didn't want to touch for the same reasons as yours. Solar City's inverter fed the service panel through a breaker at the bottom of the bus (opposite end from the main breaker) and we added the new breaker for the microinverters just above it. I wouldn't suggest microinverters unless you need them for shading or to meet rapid shutdown requirements since this is a new installation and may have new requirements. I don't see any reason a simple string inverter couldn't be used the same way. It would only be in "parallel" insofar as having its own breaker feeding the same bus. You need to make sure the new feed doesn't exceed the maximum allowable amperage for the bus rating. Read up on the "120% rule."

It wasn't designed as an addition or expansion to the existing system, it was a separate new system and needed to be engineered and permitted as such. Also check with the power company to make sure there aren't any problems with your plan, like exceeding a certain percentage of the generation in the original NEM agreement and forcing you into a new, less desirable plan for both systems.

[Mike90250]

If the garage is detached, it may not require Rapid Shutdown. Your AHJ may hint at it if you ask nicely.

[britincali]

Thanks for the responses.

So if I understand this correctly I can basically attach a grid-tied inverter straight into the service box, on a separate breaker. I'll have to get the lid off and have a look at the main breaker setup.

The garage is attached. I'm still scoping out the required kit at the moment.

[sdold]

Thanks for the responses.

So if I understand this correctly I can basically attach a grid-tied inverter straight into the service box, on a separate breaker. I'll have to get the lid off and have a look at the main breaker setup.

The garage is attached. I'm still scoping out the required kit at the moment.

NEC 705.12(D) covers this. You should already have a breaker from the Solar City inverter.