Possible to add a secondary solar system to property on new ADU (unpermitted)?

[EnergyEfficientFiend]

I currently have a 7.48kW Tesla panel system with 2 powerwalls, and will have my first true-up in April after almost 2 years (original install happened just after the annual true-up date). It looks like it will be close to even, possibly I will owe some. Right now it is powering my house (2300sf, 2 story, no heat pumps, electric dryer, EV charging, tankless gas water heater, plus my old, poorly constructed rental unit (350sf, gas water heater, gas stove, electric cove heater).

I am in the process of designing a new (detached) ADU to replace the old crumbling one and trying to be as smart about energy efficiency as possible. Looking at building with SIPs, heat pump water heater, mini-split heat pump for heat/AC, induction stove, heat pump washer/dryer combo, etc., so while it will be more energy efficient overall, I think the electric demands will increase. I would love to add a bit more solar, but won't be able to do that before NEM3 hits, so am getting creative in my mind and wondering if this great community could help me figure something out:
Could I DIY put solar panels on the new ADU (after final is signed off) so that it is covering the bulk of the ADU's electrical needs, and I assume will feed back through my main system any excess, to be captured either by my Powerwalls, or to go back to the grid? I checked my interconnect agreement and it shows they see me as having a 6.926kW CEC-AC rating. I'm wondering if a solar system can be put on the ADU (again, I am assuming panels and their own inverter) connected to the ADU sub panel, which then feeds back to my main panel, which is all tied in with the Tesla system. Would this cause problems (safety, or otherwise with the electrical systems, the Tesla system, etc.)? And given I have seen my system output over 8kW at a given moment, I also assume there is some flex in the max output going back to PG&E, so as long as I'm correct and the new ADU will pull more power, it likely won't be sending a ton more (or maybe even less) than it's been sending back to the grid for 2 years now. So, I guess what I'm saying with that is it *seems* like it's not super likely PG&E would notice a dramatic change and freak out, inspect, and force me to NEM3 (but obviously no guarantees on that), hence I'm mostly concerned about whether it is possible to technically design and implement it properly.

Thanks!

 

[SolarRich]

What's an ADU?

 

[EnergyEfficientFiend]

Sorry, accessory, dwelling unit. Its acronym used commonly at least in California to refer to a separate living unit that you can rent out.

 

[Ampster]

Yes it is also possible. An unpermitted Accessory Dwelling Unit (ADU) won't care but most likely getting a Net Energy Metering arrangement is not going to be easy. There may be a grandfather provision that might allow you to get a permit for the replacement of the old ADU. Your local planning ordinance might be a clue. If asking the building department it may be wise to say you are asking for a friend.

 

[EnergyEfficientFiend]

Sorry, I probably garbled the heck out of my original post! I will be building a new permitted ADU, and existing solar on the main house will get me through permitting requirements to have solar. I am hoping to add some solar to the roof of the ADU after the building is signed off, and doing the solar addition “under the radar.”

 

[Ampster]

I am hoping to add some solar to the roof of the ADU after the building is signed off, and doing the solar addition “under the radar.”

It is probably too late to get it in under NEM 2.0 so depending if you have a separate meter for the ADU you could AC couple it to your existing system. I have a similar situation and I am careful to control my total export so that I do not go over the 1kW or 10 percent allowance under my existing NEM agreement. Your energy efficient design elements will have a complementary impact. With some of those new loads it may be optimal to schedule them when solar peaks so that the solar production is netted out.