If I understand it well I can use Modbus to make a connection with my Solar system from SMA 5000TL over TCP. The Modbus binding shows that the SMA is online.
How can I receive the values from the SMA and make them visible?
You create poller bridge things to read groups of modbus registers. You create data things to interpret those registers into channels suitable for openHAB Items, and you create Items to link those channels to. The you can configure a sitemap to display Item states in one of the UIs.
You’ll need an understanding of the format and role of the devices registers. You’ll need to understand the fairly detailed Modbus binding docs.
You might look and see if anyone has done this before
https://community.openhab.org/search?q=sma%20modbus