As I previously said, I’m not that clued up with the EVSE stuff so I do not know for sure. But I’m guessing his suggestion is essentially to change the source of the value that the EVSE uses to track your energy “available for EV charging”.
When you tell your EV to track export (which I guess would be the default) you will end up with the EV and the “MartinR” diverters battling for the excess and due to the way the “MartinR” diverter works i thinjk that might prevail so only once your DHW tank is up to temp or whatever dump loads you have, are finished would the EV be charged.
If I understand correctly, Glyn’s suggestion is to tell the EVSE to track your PV rather than the export. The result there, if I’m not mistaken would be that the EV could consume all of your PV leaving you to import for essential consumers.
If the EV is to have top priority over excess PV before the MartinR diverter gets at it, but without costing you import. I think you need to create a “available_excess” feed which is pretty much PV minus regular non-diverter consumption. and “publish to mqtt” that value for the EVSE to use. Then whatever the EV doesn’t use is “mopped up” by the diverter by closely tracking the grid import/export.
Which ever feed you chose to use, you need to navigate to the EVSE settings and add the MQTT topic details there. I’m not yet sure that my assumptions above are correct and I’m really unsure about the polarity/signage of the feed you need to track because ordinarily when monitoring a grid cable, export is negative, conversely PV is a positive so I’m a tad confused about whether you need to track a positive or negative value. It’s easy to change sign, I just don’t know which it is you need.
I hope at least some of that make some sense to you. You were warned EV isn’t my strong suite 