Air to Water heat pumps are a great way to heat your home and water from solar PV. The heat pump moves heat from the surrounding air into the water, it uses around 20-25% of the energy than if you were heating the water directly. So a 5Kw heat pump is using only 1.1Kw of power to get 5Kw of heat. These units can be easily installed inside or outside instead of using a boiler. The water can be used for radiators, underfloor heating, hot water etc, and in summer you can switch it to reverse to use for cooling instead. If you were after an air to air heat pump for hot air then you can connect these to an air blower heat exchanger.
Efficiency of Solar Thermal vs Solar PV with a Heat Pump.
Solar Thermal is around 70%-90% efficient so with 1000W of sun you would get around 700W-900W of energy captured.
Solar PV is 15%-20% efficient and a heat pump generates about 4.5 times more heat energy than electricity used. So with 1000W of sun you would get around 675W-900W of heat energy making PV with a heat pump a viable alternative to solar thermal in terms of efficiency.
If your using a heat pump to replace your boiler or as your only heat source then you can use a standard single coil water tank.