I procrastinated a long time over our heating hot water requirements and considered what you are also considering. Our situation was that the thermal store was at the same level as the wood burner boiler but the pipework situation meant that we needed a pressurised system with the inherent inclusion of the safety inclusion of water quenching and yearly testing. (This would be a solution for your arrangement I think.)We continued with wood burners and have 2 but no back boilers. We have MVHR so the heat from the wood burners will eventually circulate through the house. On the heat pump situation we considered both ground source and air source and discounted both because in terms of cost, maintenance and repairs in the future it would work out too costly. Due to the amount of insulation and solar gain from the design we would not qualify for much RHI (perverse really you get paid for what the size of the unit is not how little energy one would use.) Have solar thermal panels feeding the TS (350L) and u/f heating. Hot water comes from an external heat exchanger fed from the top of the store and returns into the bottom providing hot water at a controlled temperature without recourse to mixing valves. There is a gas LPG boiler installed but not connected to the supply yet will happen next week. Supply will be from bottles as at the moment we think that will be the cheaper option as we do not expect to use much. I know not very green but we reckon our demand will be low and our green credentials are otherwise pretty sound. The cost of the gas we are likely to use over the rest of our years dwarfs the cost of heat pump installation. Quite pleased with the performance so far with the solar thermal it has off course been a good time of the year, and have been using the source to commission the u/f heating. The next bit of development is to install solar PV and feed a storage battery and the immersion of the TS.

Depends on how much heat the solar thermal panels provide. If they completely heat the thermal store for say eight or nine months a year, then it may well be a lot simpler and cheaper to use an immersion heater to supplement during the other few months. Perhaps extend the solar thermal or add some PV if either of those look sensible.

Wot GreenPaddy said +1

If you are running a wood burning stove to heat a TS (or provide CH then unless it is on gravity you should have a laddomat or similar to maintain the stove temp. to avoid over cooling the stove and chimney. The Laddomat has a pump (and will shut off when the stove runs out of fuel) so having the TS below the stove is no issue. Combining DHW and space heating with a back burner wood stove is always a compromise where IMO both DHW and CH suffer - along with the occupants. If you have the space then I would suggest a TS and back burner stove for space heating with a separate DHW tank heated by solar thermal or PV with an immersion to cover when the sun don't shine.

Thank you so much for the input it is very appreciated - going to fully get my head round the responses and then come back to this thread - - GreenPaddy and Peter in Hungary you have managed to get the grey matter working like what you are saying. The Laddomat sounds like a great piece of kit, reading to do - Thanks all