Terrace property in Bristol

Our heating and hot water is supplied by an air-source heat pump, and by PV solar collectors feeding in electricity to our immersion heater in our tank.  We also have a 'solar switch' which diverts our 'surplus' PV-generated electricity to our tank, maximising its use for us. Unused electricity is exported to the grid. The house is a large mid-terrace from 1870, solid wall construction (stone and brick). We have some (modest?) energy saving measures, such as full double-glazing, full standard loft insulation and some internal insulation. We do not have any external wall insulation, heat recovery etc. Our cooking and appliances are all electric, as a result we have been able to remove the gas supply to the house, thus saving on the standing charge. Our main motivation in installing a heat pump was to replace an ageing gas boiler with a non-carbon power source.