Simplistic view but true. But you can not compute the mppt point from the actual current and cell voltage. It is a max power point tracking not computing 
I have one of my inverters do grid limiting, And I looked back a few days at the voltage (DC) graph.
10 panels in a string, Recom 390w, Voc of 49v, Max power voltage of 40.8
Whenever the export limit kicks in, the Mppt is pushed off its “maximum power point” from a string voltage of 408ish to 490ish volts, Possibly that could be something that you could work up from and keep increasing the amount of power the openevse draws.
Hello everyone, thanks for all your inputs.
Since yesterday, my new supplier contract is activated and the new grid limit is 6 KVA.
I setup my Fronius accordingly this morning and the PV-divert feature seems to work (more or less, I have another issue with the i3, I’ll open another thread).