Solar panels not available - surcharge / cancellation possible?

[A friendly phone call with the construction company, asking if they would cover the remaining 50% alongside the solar installer, is something I would make if you want to continue having everything from a single source.] That sounds good and gives a good feeling, but he will just add the money again at the next selection or additional service...

quite possible, but sometimes you just need a Pyrrhic victory - just for the good feeling

That's how I would do it too. Yes, he ripped you off with the photovoltaics, but that was your own fault in the beginning, but getting angry about it for a long time now... It's not worth it. Try to negotiate the 300 euros from the construction company... He will also know that he made a decent margin with the photovoltaics, the chance is very high that he will agree.

I also think we’ll just go with the 300€, and I’ll have another chat with the construction company after the company holiday. But here I can somewhat understand paying the extra charge. It’s not much, but we do get quite a bit more kWp on the roof. After all, I get something out of it.

I don’t really feel ripped off with the photovoltaic system either. It wasn’t very wise that we didn’t dare to contract the trade ourselves. Back then, we had so little knowledge about house construction and technology. That the construction company doesn’t act as the middleman without adding a margin is quite normal. And judging by the price comparisons of what one pays per 1 kWp nowadays, I hear ranges from-to. Sometimes I think net and gross prices get mixed up, and I’ve also heard claims (1000€ per kWp for our system size?!), which is all well and good if somewhere on the Internet it says it should be that cheap, but it never really says WHERE that is, what is installed there, who installs it, and how well they do it.

He wants to install now (new): Jinko Half-Cell Solar Module 325Wp Full Black Cheetah HC 60M-B Is that any good? It doesn't tell me much.

I have Jinko Solar 330 on the roof and can't say anything bad.... the system runs and produces

I don't know the modules. But there are plenty of them like sand by the sea, at least I know a few manufacturers who are more "renowned".

Jinko Solar is the world's largest manufacturer of solar modules. What makes a manufacturer reputable for you?