Adding the second PV system to a sub-panel and not main panel

[bhakan]

I have a 5.4kW system for 10yrs in my main electric panel that also has my Tesla EVSE 60 amp circuit. I also have a 200 amp subpanel that was upgraded before all the first PV system and my TEsla EVSE was added to the main panel. I also have a Generac backup. All these have approval stickers.

I had asked Tesla for a second solar panels and I went thro Tesla's home assessment where a guy came and took all the pics of my panels, my electric load to the main and sub panels. He mentioned that I have a lot of spares on my sub panel and should not be a problem. I went thro Tesla's design review which they submitted to my utility and it was approved by my utility also.

Tesla scheduled my install for Feb 7th ( yesterday) and even had the materials delivered last week and the crew was there yesterday morning. However, someone from Tesla ( possibly the electric guy) went and looked at the panels and he was looking at the main panel and I showed him the main and sub panel. He told me that he was talking to my project advisor and I need an upgrade of the main panel. So after about two hrs all the trucks and everyone left and they did not shut all the materials they opened and left. I was asking my project advisor for updates in the mean time.

This evening Tesla sent me a redesign and said they have to upgrade my main panel for $4590 and after that is done they can install this 5.2kW system.

My question is do I really need an upgrade of my main panel? Why can't Tesla feed the 5.2kW system to my sub-panel? Will there be a problem? I thought it is all electricity going in to a bucket. I don't have any powerwall.
I have attached some pics of my main panel, sub-panel, and my Generac backup (partial as it is a 17kW system) with circuits.

TIA. I greatly appreciate it.

 

[arnolddeleon]

My guess that's because you can theoretically feed your main panel more than 240A, 120% of your bus bar ratings (I'm also guessing there). In the old days you could argue that the subpanel being completely unloaded and the solar production at maximum and the load in the main panel being at 240A or greater was practically impossible so it would be safe to do so.

Hmm, I wonder if adding a Powerwall would solve the problem (it can limit PV exports). You would need to spend more but at least you get something useful for it.

Could you put 20A breaker on your existing PV system? Don't know that would be allowed. Basically, if both your PV systems were on 20A breakers then it might be ok.

I'm complete amateur here, I suspect @Vines @wwhitney can cite chapter and verse of what code is being violated here.