Solar Panels & Electric Cars: Complete Guide

Annual driving costs comparison (7,400 miles/year — UK average):

| Fuel Method | Cost per Mile | Annual Cost | |------------|-------------|-------------| | Petrol (£1.40/litre, 40mpg) | 15.9p | £1,176 | | EV — grid rate (24.5p/kWh) | 7.5p | £559 | | EV — Octopus Go overnight (7.5p/kWh) | 2.3p | £171 | | EV — solar charged (free) | 0p | £0 | | EV — solar + Go hybrid | ~1p | £68 |

Savings vs petrol: - EV on grid: saves £617/year - EV on Octopus Go: saves £1,005/year - EV on solar + Go hybrid: saves £1,108/year

Savings vs grid-rate EV charging: - Solar + Go hybrid saves £491/year vs standard grid charging

Adding solar to an EV household effectively eliminates fuel costs. The combination delivers the strongest financial returns of any home energy investment.

Source: DfT average mileage; fuel prices; Ofgem Q1 2026; Octopus Go rates.

The ideal solar + EV configuration:

1. Solar panels: 5–6kW (13–16 panels) - Generates enough for home electricity + significant EV surplus - Cost: £6,500–£11,000

2. Smart EV charger: Zappi (by Myenergi) - Eco mode: charges only from surplus solar - Eco+ mode: solar + configurable grid top-up - Fast mode: full speed from any source - Cost: £800–£1,100 installed

3. Time-of-use tariff: Octopus Go - 7.5p/kWh overnight (00:30–05:30) - Charges EV cheaply when solar is not available - Saves £400+/year vs standard rate charging

4. Optional: 10kWh battery - Stores daytime solar for evening home use - Frees up more solar surplus for EV during the day - Enables Octopus Flux peak export income (16:00–19:00) - Cost: £4,000–£6,000

Total system cost: £7,300–£18,100 Annual savings (home + car): £1,000–£1,450 Payback: 6–12 years

Source: System design; Ofgem; Octopus tariffs.

Your EV electricity needs: - Average UK mileage: 7,400 miles/year - Average EV efficiency: 3.25 miles/kWh - Annual EV electricity: 2,280 kWh

Solar to cover EV charging: - 2,280 kWh ÷ 1,000 kWh/kWp yield = 2.3 kWp of solar for EV alone - But self-consumption is only 30–50% without smart scheduling - With Zappi smart charging: 50–70% of surplus goes to EV - Practical recommendation: add 3–4kW (8–10 panels) for EV charging

Total system for home + EV: - Home: 4kW (10 panels) - EV: 3–4kW (8–10 panels) - Total: 7–8kW (18–20 panels)

This large system generates more than most homes can use — the surplus charges the EV, and any remaining surplus exports for SEG income.

Source: DfT; EV efficiency data; PVGIS.

Zappi (Myenergi) — £800–£1,100 installed: - Best solar integration in the UK market - Eco mode: charges ONLY from surplus solar (zero grid import) - Eco+ mode: solar + minimum grid import (configurable threshold) - Integrates with Eddi hot water diverter for complete surplus management - 7kW (single phase) or 22kW (three phase) - OZEV approved for grant (if still available)

Ohme — £500–£700 installed: - Smart scheduling via app - Integrates with Octopus Energy tariffs - Solar-aware via API (less direct than Zappi's CT clamp) - Good for tariff optimisation, weaker for real-time solar diversion

Hypervolt — £600–£900 installed: - Solar-aware charging - Load balancing (prevents tripping main fuse) - App control with scheduling - Good mid-range option

Standard 7kW charger — £300–£500 installed: - No solar integration - Charges at fixed 7kW whenever plugged in - Can be scheduled via car's own app for off-peak charging - Cheapest option but no solar intelligence

Recommendation: Zappi for solar owners (best solar integration). Ohme for Octopus tariff users without solar. Standard for budget-only installations.

Source: Manufacturer specifications; OZEV approved charger list.

Scenario 1: Work from home (car parked all day) - Solar charges EV directly during daylight - Zappi Eco mode uses all surplus for the car - 5kW system surplus: ~1,500–2,500 kWh/year to EV - Free driving: 5,000–8,000 miles/year - Remaining miles: Octopus Go overnight at 7.5p - Annual EV cost: £30–£80

Scenario 2: Commuter (car away 8am–6pm) - Car is away during peak solar hours - Solar charges battery during the day - Battery charges EV in the evening (if battery is large enough) - OR: Octopus Go charges EV overnight at 7.5p - Weekend solar charging supplements - Annual EV cost: £120–£200

Scenario 3: Part-time home (mix of home and office) - 2–3 days at home: Zappi charges from solar - Office days: Octopus Go overnight - Annual EV cost: £60–£120

All scenarios dramatically cheaper than petrol (£1,176/year) or standard grid EV charging (£559/year).

Source: Usage modelling; tariff calculations.