Solar Hot water versus Air to Water heat Pump

[Calvin]

Hello everyone..
I'm looking for advice..
I am building a new house and I am planning to install a combi air/water heat pump with integrated hot water tank to heat domestic hot water and underfloor heating. I am aware that these systems have a coefficient of efficiency of about 3:1 but the tank is relatively small at 260 litres.
I will need to install a second hot water tank for the odd day when the 260 litres won't be enough.
Would anyone advise me to install a solar hot water system or just a standby electrical secondary tank.
Does anyone have any other ideas for my system? Would electric under floor heating (expensive to run) and DHW heated only by solar be a better idea?
I would much appreciate your input
Many thanks

[IrinaGrant]

I am not sure you can use solar for heating floor, I think, only for heating water for washing dishes and bathing.