After a lot of searching in the internet, I bought 4 "Apollo 27" panels in landscape orientation. It took a lot of calculation to find panels that would fit nicely at the free space on the wall. These panels are, as far as I now, made in Austria by SUN MASTER and come with a 10-year warranty. SUN MASTER calls them "SUK27L". Another name (given by "sunfiction", where I bought them, is "SFK 270 Q"). Name confusion whereever I look.

Technical details about the panels and the mounting instructions can be found here (in German) - my panels are of the horizontal type.

A detailed desciption of the mounting triangles is here (also German).

Due to my nonstandard angle, and very high costs of the commercially available mounting angles, I chose to make them myself. I learned: with a hand saw, it's a lot of work cutting 4mm aluminum profile!

Things I forgot