This page serves as the definitive reference for our complete transition from a traditional gas-heated 1980s detached house in the South West of the UK to a fully all-electric, efficient home. All figures are our actual out-of-pocket costs after grants and offers.
We keep the house at a steady 20°C year-round with no more gas bills, thanks to smart automation via Home Assistant that shifts almost everything (heat pump, hot water, and EV charging) to cheap off-peak electricity.
House & Original Heating (Pre-2025)
- Property: 1980s 4-bed detached house, South West UK
- Previous system: Traditional gas central heating boiler with gravity-fed hot water
- Replaced: October 2025 (gas boiler removed – was at end of serviceable life)
Solar PV & Battery System (Installed mid-July 2021)
- Solar array: 4.5 kWp (12 × 375 W Longi Black panels)
- Inverters: 12 × Enphase IQ7+ microinverters (helps with shading)
- Hybrid inverter: 3 kW AC
- Batteries: 2 × 8.2 kWh GivEnergy (total 16.4 kWh)
- EV charger: Myenergi Zappi (supports solar diversion)
- Total cost: £14,000 (all-inclusive)
- 2024 performance: 3,200 kWh generated, 1,851 kWh exported
Air-Source Heat Pump System (Installed October 2025)
- Heat pump: Daikin Altherma 3 Monobloc 8 kW (with Blygold corrosion protection)
- Hot water cylinder: Joule 200 L slimline
- Radiators: 11 new low-temperature radiators
- Installer: Octopus Energy
- Original quote: £13,881
- Government grant: £7,500
- Additional 15% offer discount
- Final amount paid to Octopus: £5,424 (net cost)
- Install date: 12 October 2025 (live and heating from mid-October 2025)
- Design specs: 50°C flow temperature at -1.3°C outdoor design temperature
Current Electricity Tariff (Intelligent Octopus Go)
- Off-peak (23:30–05:30): 5.2p/kWh (as of 1 April 2026)
- Day rate: 27.757p/kWh
- Standing charge: 56.337p/day
- Our usage: 99.5% off-peak thanks to batteries and Home Assistant automation (we charge the batteries and run the heat pump/EVs during the cheap window)
Electric Vehicles (Included for completeness – excluded from ROI)
We now run three EVs, but these are not included in any ROI or payback calculations for the energy tech (solar, batteries, heat pump, etc.). We have always bought second-hand cars in this price range (£10k–£20k, 2–5 years old, 25–50k miles). With EV/ICE price parity now very close for similar age/mileage vehicles, the switch makes no material difference to the energy-system ROI.
- Tesla Model 3 Dual Motor (with acceleration boost): Purchased January 2025 for £19,000 (50,000 miles at purchase) – ~11,000 miles/year, average 3.6 mi/kWh
- 2021 Hyundai Kona Ultimate 64 kWh: Purchased for £15,000 (~29,000 miles at purchase) – ~8,000 miles/year, average 3.9 mi/kWh (3.6 winter / 4.2 summer)
- 2020 VW e-Golf: Purchased ~18 months ago for £10,000 (25,000 miles at purchase) – this is our daughters car.
Previous ICE cars (for reference only):
- 2012 BMW X3 diesel (~37–40 mpg real-world)
- 2014 VW Up petrol (~48 mpg)
Total Investment in Energy Tech (ROI Basis Only)
- Solar PV + batteries + Zappi charger: £14,000
- Daikin heat pump + cylinder + 11 radiators: £5,424
- Grand total: £19,424
This figure excludes the EVs, as explained above. All savings and payback calculations on the blog use only this £19,424 as the investment.
Smart Controls & Automation
A big part of making the whole system work efficiently is our use of Home Assistant combined with GivTCP, running on a Raspberry Pi.
Before we set this up, whenever we plugged the cars in to charge, the house batteries would often discharge at the same time — which completely defeated the point of using cheap off-peak electricity and solar.
Now, Home Assistant and GivTCP work together to ensure the house batteries are charged during the off-peak tariff window at the same time as the cars. This maximises the benefit of the low 5.2p/kWh night rate and any other smart slot allocations, making the entire setup far more effective.
A great example of how this helps us is plugging the cars in during mid-morning. This captures any available smart slot allocations and tops up the house battery before the roof shading hits around 10am–1pm. Once the batteries are full, any excess solar energy (that isn’t needed by the house) gets exported to the grid at 12p/kWh instead of being wasted or used inefficiently in the afternoon.
These automations allow us to achieve ~99% off-peak usage across the heat pump, hot water, and EV charging — turning what used to be conflicting systems into a smart, coordinated setup that works in our favour every single day.
Notes
- All costs are exact out-of-pocket amounts paid.
- Performance data (COP, generation, etc.) is tracked separately in the monthly posts and Modoka spreadsheet.
- Last updated: April 2026
- No finance used for any purchases