Revive solar thermal – GreenBuildingAdvisor

About the only thing solar thermal might make some sense for is heating a pool. Outside of that, add more PV panels. Even if those panels are driving resistive heaters, it will still be cheaper for the same BTU output as thermal panels plus all the bits to get it to work.

Since you have a heat pump and if you want to take this on as engineering project, you can size a buffer tank that will be filled by the AWHP to shift some excess daytime PV into night time heat. You can control the speed of the pump feeding the buffer tank to adjust heat pump output to match excess solar. You might also be able to hijack the DHW mode to get extra hot water for this without effecting the operation for the rest.

Same as thermal PV, the cost of this means ROI is pretty much never, but would be fun to play with.