National grid transformer won’t support additional solar

Another alternative for some is to self consume power if the rate paid is less than they generate and store it for. It is actually happening in California and Hawaii.
The path of least resistance pretty much means that it will cover all the loads before it backs up through a substation.
You are correct about the design and that is the obstacle. It is not physics that is the limitation and you can understand that as an EE. It is the design of the control systems that cannot control power bidirectionally in a grid that has become increasingly distributed. I place that blame on the utilities who lobbied against and buried their head in the sand about the benefits of a distributed grid. I can cite a case study of a micro grid that actually saved a utility the cost of a major infrastructure upgrade because of the installation of that micro grid. So I disagree with your statement that distributed generation is not a benefit to the grid. Do a little research on distributed generation and form an opinion based on objective information. I do not expect to change you mind. I just want other readers to objectively see the concept and form their own conclusion.
Yes they did and that proves my point that they should have seen the handwriting on the wall long before the substations were at risk.
The right to generate is not a physics issue, it is a legal issue. My research has found no law in Califonia that says it is illegal to generate one's own power as long as it complies with building codes. Just ask any off gridder if he feels the government or a utility can tell him he cannot generate his own power. Yes there are building codes that say we must have a Grid connection if one is provided but there is no statute in California that says when or how much of that power I must must use. It is a fundemental concept of property law going back before we knew there was elecricity.

It is sad to hear someone that is locked into high electric rates because of their political people that likes to complain about how a POCO is stealing from them. If you don't like what is going on with your utilities you can either vote out the people that support them or move to a place that does not restrict solar.

So there might not be a law in CA that states you can't self generate but there are rules about connecting to the grid which is not owned by the public.

Also until you have seen what a large power source that is backfeeding the grid cause issues when it stops and starts again you can't understand the issue of what a POCO is going through to keep the lights on no matter what.

I am done arguing with you about why a POCO can limit the installation of solar in an area. It is their decision and not yours as to who can self generate and where it can happen. If you don't like the rules then change them but until then stop complaining about the poor solar installations being governed by their POCO.

What happened in my area is that because too many people had solar, and the transformer was no longer sized properly, on sunny days when all solar homes were producing at their max, the grid voltage started rising above the limit allowable, I would see voltages over 254 Volt and that in turns can cause issues.

For once, if the grid voltage rises too much, in areas regulated by Rule 21, recent solar installation would start throttling solar production down to avoid causing even more grid voltage rise...

I was lucky, my POCO (PG&E) agreed the transformer was approaching its limit and they changed it.

I just pulled our line voltage stats and we are seeing it go as high as 250v. Interesting, when it went above 250v around 2pm on 12/26, the surge protectors on the overhead lines popped (sounded like a gun shot), and had to replace fuses in all the pad mounted transformers in the neighborhood.