In addition to this link (Kostal Piko MP plus Werte aus XML auslesen) explaining how to extract live data, I also found a way to extract yield values. (daily and yearly)

Create a Virtual HTTP input with the following URL: 

Create a Virtual HTTP input command with the Following command recognition: \ilabelValueId\i\i= "\i\v

This gives you this year's yield.

The same can be achieved to get the daily yield. Here we use the following URL: and the same command recognition value as in the previous example.

Unfortunately there is only one yield label in the Energy Monitor, so I choose to display the year (eP). 

This is how it looks: