Adding a microinverter system to a house with an existing string inverter setup

[sdold]

A friend has a home system installed and owned by Solar City. He now wants to add his own ten-panel microinverter system in a different location (over the garage, away from the current install) since he's anticipating more energy use and doesn't want to have Solar City add to their system. I just finished installing my own system and will be helping him with the drawings, calcs, permits etc.

He has a 200A panel with a 150A main breaker, so I think the panel bus capacity is OK.
Is there any technical reason a string inverter and a string of microinverters can't "share" the bus in the main panel, and not interact in some way? They would both have their own breakers.

I realize the power company would need a new net metering agreement. He pays the power bill and has the account, not Solar City, so I assume it will be an amendment or new agreement.

I know this is pretty unusual, and wondered if there are any obvious problems we hadn't thought of.

Steve

[inetdog]

From the purely technical point of view, there is nothing inherently incompatible between microinverters and string inverters on the same AC system.
There may be some issues with panel bus size if you are on earlier than 2014 NEC, since you will have to add up the breaker ratings rather than the actual production amps to apply the 120% rule.
Also make sure that there is room for the additional PV breaker(s) at the opposite end of the bus from the main with no load breakers in between.

[SunEagle]

Since the first system is owned by Solar City it must be a leased project where they have a "production meter" to determine the amount it generates.

Is it even possible to add a second system to this house and not look like it is competing with the Solar City system?

[inetdog]

Since the first system is owned by Solar City it must be a leased project where they have a "production meter" to determine the amount it generates.

Is it even possible to add a second system to this house and not look like it is competing with the Solar City system?

There are actually at least three options in which Solar City retains ownership of the hardware:
1. Straight lease.
2. Prepaid lease.
3. Power Purchase Agreement (PPA).

Only in case 3 would there be any potential for legal problems. And if the PPA uses a production meter connected to the Solar City system, their revenue will still not be affected by adding additional PV that does not shade their panels.

[sdold]

Thank you for the replies. Fortunately he's case #2 (a prepaid lease). Next is sorting out the panel situation.

[sdold]

Just a followup, my friend's additional system has been permitted, signed off and turned on and has been working well. The only inspection hitch was a slight modification to the grounding system and he wanted better securing of the wiring along the rails. The inspector climbed on the roof and looked at everything with an inspection mirror and magnifying glass, practically. Nothing wrong with that, he simply held us to the code and my friend ended up with a safe system that should last many years.

This was in Milpitas CA. They were also good about allowing a reasonable variance to the fire setbacks.

Inetdog and SunEagle, thanks for your help and ideas.

Steve

[SunEagle]

Just a followup, my friend's additional system has been permitted, signed off and turned on and has been working well. The only inspection hitch was a slight modification to the grounding system and he wanted better securing of the wiring along the rails. The inspector climbed on the roof and looked at everything with an inspection mirror and magnifying glass, practically. Nothing wrong with that, he simply held us to the code and my friend ended up with a safe system that should last many years.

This was in Milpitas CA. They were also good about allowing a reasonable variance to the fire setbacks.

Inetdog and SunEagle, thanks for your help and ideas.

Steve

I'm glad everything worked out for your friend.