My brother has a 10 kVA PV installation on his shop.
He bought the neighbouring house which is not suited for PV panels. The intention is to share part of his energy production between the two buildings.
The idea is to install a normal grid-tied inverter in the new house and connect it as a load to the three-phase installation on the shop via a bridge-rectifier. The resulting DC voltage is around 540 VDC which falls within the limits of the inverter MPPT.
The house inverter I have in mind can be equipped with a control feature that avoids injection in the grid. This way only the needed energy is taken from the shop.
Is this a good set-up?
One of my questions is if some form of current limiting needs to be foreseen. The three-phase installation can provide much higher current than the upper limit of the small inverter. If so, how can I do that? A simple MOSFET current source circuit or something else.

 

If you need to ask questions like that (current limiting by some simple circuit) then you need a locally qualified solar energy electrician and/or installer to answer your questions.
Possible, yes, possibility very dangerous and in violation of local electrical codes, yes.

If you want an honest evaluation (that won't be free most likely) you need to provide exact wring and model details about the entire existing PV installation and the exact details, equipment models for a possible extension including exactly how the 3-phase tap will be configured and monitored and how the power feed into the house will be handled in the main and sub panels.

 

Welcome to AAC!

Is this a good set-up?

You don't mention where this would be done, but it sounds like a very bad idea.

 

Forget it.
Sometimes it helps to put things in writing to realise it is a bad idea

 

My first questions are what is the purpose of this proposed arrangement? What is it supposed to achieve??

And a big safety issue is that 540 volts DC connection, which will be able to provide quite a few amps of high voltage fault current if anything goes wrong. It does not appear that any who would be involved with this project have the experience to put it together so that it would be safe. Understand that DC at that voltage is totally unforgiving of any mistakes. And while it might not evaporate a wrench out of your hand it can certainly deliver a rather lethal shock.