Using switching to control load sharing of DC?
Can you detect Solar relative power levels with a PD or pulse off the PV to measure change of Voc with solar input, then Vmpt changes 82%+/-8% for most PV's , but you indicated Vmpt=75/80.2=93.2% which is higher than most. 

Pls show PV specs.

This can be done several ways with a hunting algorithm power controller or a "feedforward" compensated shunt switching regulator regulates the input rather than the output voltage based on a PD solar level.  This assumes neither PD and PV are blocked by shadows or dirt so several cheap $.50 Vishay PD sensors may be used in parallel to get a logical "high man wins" current source into a fixed resistive load. The load can be a TIA or simply an Op Amp buffer or an inexpensive buffered PD Light sensor from Panasonic that runs of an LDO of say 5V (p/n AM103). 







simulate this circuit &ndash; Schematic created using CircuitLab

Food for thought. Comments?