The starting point
Heat loss survey came in at 7.6 kW peak demand on a -3°C day — well within ASHP territory for a property with the existing fabric upgrades. The roof was south-facing with no shading, perfect for solar. The half-hourly smart-meter data the family pulled from Octopus showed evening peak consumption around 4.2 kWh — a 10kWh battery would carry them through the expensive evening window seven days a week.
BUS eligibility was straightforward: valid EPC, no outstanding insulation recommendations, owner-occupied, replacing a gas boiler. The £7,500 grant was applied at the quote stage, deducted from the heat pump invoice before the family ever paid us a penny.
What we installed
Daikin Altherma 3 R 9kW outdoor unit on a noise-rated bracket against the side return, 250L unvented cylinder in the airing cupboard, replaced 4 of the 11 radiators with larger panels to keep flow temperature at a steady 47°C, weather-compensated controls. The MCS commissioning sign-off was issued the same day as install completion.
Solar PV: 12 × Longi 425W panels in a single south-facing array, GivEnergy 5kW hybrid inverter sized for the future battery. G99 application to UKPN approved before install. The battery — GivEnergy Giv-Bat 10.0 — fitted in the garage two weeks later as a single-day add-on.
The outcome
First month of full operation showed the heat pump averaging a SCOP of 3.9 — better than the 3.7 we'd modelled. Switched the family onto Octopus Cosy. Combined gas + electric annual cost projection: £2,160/year vs. the pre-install £3,800/year baseline. £1,640/year saved.
Solar generated 4,800 kWh in year one, of which 71% was self-consumed (battery doing its job). Surplus 1,400 kWh exported at Octopus Outgoing Fixed = £210/year. Combined with the heating saving, the package paid back £1,850/year against a customer contribution (after BUS) of £14,300 — a 7.7-year payback before factoring in any future energy price rises.
“We were dreading the boiler dying in mid-winter. Instead we got a heat pump, panels and a battery all sized to work together. The bills have collapsed and the system is silent — the kids didn't even notice the changeover.”