Solar-heated buffer tank?

[ReedRichards]

I already use spare solar power to heat my DHW cylinder but is it worth adding a switch that would enable me to heat the buffer tank also (it's in the same place)?  If so, what temperature should I set it to?  Would the heat pump be confused by return water that is unexpectedly hot?  At present the immersion heater in the buffer tank is not connected at all.  

[PeterW]

What triggers the ASHP to heat ..? Tank stat on the buffer or something else ..?

[ReedRichards]

I have a third party controller.  If a room thermostat on either of my two zones is below the set temperature then the circulation pump on the central heating is activated and the heat pump is powered on.  The water circulates through the heat pump for a few minutes and ordinarily the heat pump will then activate.  But if the return water is too hot then the flow water will be too hot also so nothing will happen externally until my central heating has dissipated enough of the stored heat in the buffer.  I think.  

[HughF]

How big is your buffer tank? You could decouple the supply and demand if the buffer was large enough. Room stats would just draw heat from the buffer as required. The buffer temp sensor would call for the heat pump to recharge the buffer as required. No different to a biomass boiler, just with lower temps involved.

[ReedRichards]

I actually don't know the size of my buffer tank.  It is integrated into the base of my DHW cylinder with no partition visible externally.  Nor does the buffer tank have a temperature sensor, the sensors are on the flow and return pipes on the heat pump.