Heat pump water heaters already exist. These are hybrid things where a traditional electric water heater is fitted with a heat pump. The heat pump can increase the water temp but cannot deliver enough, so heating elements are still needed to reach a usable temp.
I’m wondering if that design can be improved on this way: instead of powering the heat pump from the wall, the heat pump can be connected directly to a PV. I think that would be more efficient and cheaper because PV output is not normally directly usable. IIUC, it’s variable D/C which must be regulated and/or inverted to A/C involving more hardware, conversion, and waste. But exceptionally, I’ve heard that a PV can directly power a compressor with no middleware. Any reasons this would be infeasible or uninteresting?
Of course the tank still needs wall power for the heating elements, but would use less wall power and entail less conversion loss.
Why not thermal solar panels wired to a water heater? Seems to be the least energy transfers, each of which incurs efficiency loses
Yes, thermal solar panels would be way more appropriate.
While trying to gain a few % through the transformation process OP is not addressing the elephant in the room: PV panels turn around 20% of the sun energy into electricity, thermal panels turn around 80% of the same energy into heat, They are way more efficient.