Thanks for your replies!
Yes, it has a web UI to configure it and reading data.
Could you please elaborate which component you mean? I only see following Brdiges in OpenEMS UI: M-Bus, Modbus/RTU Serial, Modbus/TCP, OneWire. Searching for HTTP only leads to “Controller Api Websocket” (and Apache Felix Jetty Based Http Service).
No, we are using a Fronius Smart Meter TS 5kA-3, which I also have trouble with reading.
Not sure if I understand you correctly. You mean, to attach a Shelly meter to the inverter cables and read the Shelly values? Would prefer to read the values directly (and maybe later also be able to control the inverter).
Yes, I tried with and without active portal connection – unfortunately didn’t make any difference. I also had the impression, that it looked like Modbus, thus my question. 
Result is a blank page with the message: Sorry, the requested file does not exist on this server. It stays the same if I remove one parameter after the other and finally removing the file and path.