thanks again for the link and advice.
Our system is very home made and 'trial & error' to keep the costs down. (so I could afford this terribly expensive rMB...).
We have never experienced any trouble with our devices in the last 15-20 years. The only exception is the cheap inverter itself.
The main problem is the distance (150meter from the inverter to our place) which causes some of the voltage differences, I think (but I am definitely no expert). But it works so I won't fix it...until I'll have to.
"Hold the post" have read that inverters & surge suppressors are not mutually compatible, so best to research more.
Q-6