Green Home Technology UK — Solar, Heat Pumps and Battery StorageSolar Panels, Battery Storage, and EV Charging — Combined Home Energy Guide
How to combine solar panels, home battery storage, and EV charging to maximise savings. Costs, payback, smart tariffs, and how the systems work together.
Solar panels, home batteries, and electric vehicles are increasingly being installed together as a complete home energy system. When combined intelligently, they can dramatically reduce your energy costs and carbon footprint.
How the Three Systems Work Together
| Time of day | What happens |
|---|
| Morning (sunrise) | Solar panels start generating. Powers your home |
| Midday (peak sun) | Excess solar charges your home battery AND/OR your EV |
| Afternoon | Solar still generating. Battery may be full — excess exported |
| Evening | Battery powers your home. No solar generation |
| Overnight | If on a smart tariff, cheap electricity charges EV and tops up battery |
Costs at a Glance
| Component | Typical cost | Annual saving | Payback |
|---|
| Solar panels (4kW) | £5,000 – £7,000 | £400 – £700 | 8–12 years |
| Home battery (5–10kWh) | £3,000 – £7,000 | £200 – £500 | 8–15 years |
| EV charger (7kW) | £500 – £1,000 | N/A (needed to charge efficiently) | — |
| Combined system | £8,500 – £15,000 | £800 – £1,500+ | 7–12 years |
Solar Panels
System Sizes and Output
| System size | Number of panels | Annual generation (UK) | Roof space needed |
|---|
| 3kW | 8–10 | 2,500 – 3,000 kWh | ~18 m² |
| 4kW | 10–12 | 3,400 – 4,000 kWh | ~24 m² |
| 5kW | 12–15 | 4,200 – 5,000 kWh | ~30 m² |
| 6kW | 15–18 | 5,000 – 6,000 kWh | ~36 m² |
Solar Income and Savings
| Source of saving | How it works | Value per kWh |
|---|
| Self-consumption | Using solar directly instead of buying from grid | 24–30p/kWh saved |
| Battery storage | Storing excess for evening use | 24–30p/kWh saved |
| Smart Export Guarantee (SEG) | Selling excess to the grid | 3–15p/kWh |
| EV charging | Charging your car from solar | Saves 10–14p/mile vs petrol |
Home Battery Storage
Popular Home Batteries
| Battery | Capacity | Usable capacity | Cost |
|---|
| Tesla Powerwall 2 | 13.5 kWh | 13.5 kWh | £8,000 – £10,000 |
| GivEnergy 5.2 | 5.2 kWh | 5.2 kWh | £2,500 – £3,500 |
| GivEnergy 9.5 | 9.5 kWh | 9.5 kWh | £4,000 – £5,500 |
| Pylontech US3000C | 3.6 kWh | 3.6 kWh | £1,500 – £2,000 |
| Fox ESS | 5.12 kWh | 5.12 kWh | £2,500 – £3,500 |
| SolaX | 5.8 kWh | 5.8 kWh | £2,500 – £3,500 |
What Size Battery?
| Household type | Evening consumption | Recommended battery |
|---|
| 1–2 people | 5–8 kWh | 5 kWh |
| 3–4 people | 8–12 kWh | 5–10 kWh |
| 4+ people or EV | 12–20 kWh | 10–13.5 kWh |
Battery Benefits
| Benefit | Detail |
|---|
| More self-consumption | Use 60%–80% of solar vs 30%–50% without battery |
| Evening power | Use stored solar instead of buying grid electricity |
| Smart tariff arbitrage | Charge on cheap overnight rate (5–10p), use during peak (24–30p) |
| Backup power | Some batteries provide emergency backup during power cuts |
| Reduce peak demand | Less strain on the grid |
EV Charging from Solar
Charging Costs Compared
| Charging method | Cost per kWh | Cost per mile | Annual cost (8,000 miles) |
|---|
| Solar (free) | 0p | ~0p | £0 |
| Smart tariff overnight | 7–10p | ~2p | £160 |
| Standard tariff (home) | 24–30p | ~6–8p | £500–£640 |
| Public charger | 40–85p | ~10–21p | £800–£1,700 |
| Petrol car | — | 12–16p | £960–£1,280 |
Solar EV Charging Maths
| Detail | Value |
|---|
| Average EV efficiency | 3.5 miles per kWh |
| Annual mileage (average) | 8,000 miles |
| Electricity needed | ~2,300 kWh |
| 4kW solar generates | ~3,500 kWh/year |
| Percentage needed for EV | ~65% of solar output |
In practice, you won’t always be charging when the sun shines. A battery helps — or charge at work, and use solar for your home.
Smart EV Chargers
| Feature | Why it matters |
|---|
| Solar diversion | Automatically uses excess solar to charge your EV |
| Scheduled charging | Set charging for overnight cheap-rate periods |
| App control | Monitor and control remotely |
| Smart tariff integration | Automatically charges during cheapest periods |
Popular options: Zappi (solar diversion built in), Ohme, Pod Point, Wallbox.
Smart Tariffs — The Missing Piece
Smart energy tariffs supercharge your savings:
| Tariff | Peak rate | Off-peak rate | Best for |
|---|
| Octopus Go | 24–30p | 7.5p (12:30am–4:30am) | EV owners |
| Octopus Intelligent Go | 24–30p | 7.5p (extended overnight window) | EV owners with compatible car/charger |
| Octopus Agile | Variable | Sometimes negative (get paid!) | Battery owners who can automate |
| Octopus Flux | 24–30p | Export: 20.3p (peak) | Solar + battery owners |
| Smart Export Guarantee | N/A | Export: 3–15p | All solar owners |
How to Maximise Savings
| Strategy | How |
|---|
| Solar + battery + Octopus Flux | Export at 20.3p in peak, charge battery at 14.3p overnight |
| Solar + EV + Intelligent Go | Charge EV at 7.5p overnight, use solar for home in day |
| Solar + battery + Agile | Charge battery when prices are lowest/negative, use when highest |
Grants and Incentives
| Incentive | Detail |
|---|
| 0% VAT on solar panels | No VAT on solar panels, batteries, and installation |
| 0% VAT on EV chargers | No VAT when installed with solar panels |
| Smart Export Guarantee | Get paid for exported solar electricity |
| BUS grant | £7,500 for heat pumps (not solar, but combines well) |
| OZEV EV charger grant | Now only for tenants and landlords (£350) |
Total Annual Savings
| Setup | Estimated annual saving vs grid power + petrol |
|---|
| Solar only | £400 – £700 |
| Solar + battery | £600 – £1,200 |
| Solar + EV (no battery) | £800 – £1,400 |
| Solar + battery + EV | £1,200 – £2,500+ |
| Solar + battery + EV + smart tariff | £1,500 – £3,000+ |
Summary
| Component | Cost | Key benefit |
|---|
| Solar panels (4kW) | £5,000–£7,000 | Free electricity during the day |
| Home battery (5–10kWh) | £3,000–£7,000 | Use solar energy in the evening |
| EV charger | £500–£1,000 | Charge car from solar or cheap overnight rate |
| Smart tariff | Free to switch | Dramatically reduces electricity costs |
| Combined payback | 7–12 years | Savings of £1,500–£3,000+/year |
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