Solar PV + EV Charging Maths: A UK 2026 Guide

A typical UK domestic solar installation in 2026 is 4-6 kWp of panels, roughly 10-15 panels on a south-ish roof. Annual generation:

• 4 kWp south-facing, unshaded: ~3,400-3,800 kWh/year (Midlands/South); ~3,000-3,400 (Scotland/North).
• 6 kWp south-facing: ~5,000-5,700 kWh/year (Midlands/South).
• East-west split arrays: roughly 85-90% of the equivalent south-facing total, but the generation profile is flatter through the day (more morning + evening, less midday peak).

Seasonal split is heavily summer-weighted: roughly 70% of annual generation lands May-September. In December the same 4 kWp array might generate 90 kWh for the whole month; in June it could generate 500 kWh in a single month.

Annual EV consumption at 3.5 mi/kWh real-world average:

• 5,000 mi/year: ~1,430 kWh
• 8,000 mi/year: ~2,290 kWh
• 12,000 mi/year: ~3,430 kWh
• 15,000 mi/year: ~4,290 kWh

For a 4 kWp array + 8,000 mi/year driver, generation (~3,600 kWh) roughly equals total annual EV demand. But the household uses energy too - lighting, appliances, hot water - so the car competes with the rest of the house for those kWh.

Without a battery, the proportion of solar generation you actually use yourself (rather than export) depends entirely on when you're home + what's drawing power. Typical UK self-consumption rates:

• Family at work, no battery, no EV: 25-35% self-consumed. Most generation happens 10am-3pm when the house is empty.
• Same household + a 10 kWh battery: 60-75% self-consumed. Battery stores daytime surplus for evening use.
• WFH + EV charging on solar during the day: 50-65% self-consumed (no battery). The car becomes the battery for those days you're home.
• WFH + 10 kWh battery + EV daytime charging: 75-90% self-consumed.

This is why the 'EV charges from solar' story only really lands for people who are home during the day (WFH, retired, shift workers with day-off patterns) OR who've got a home battery storing daytime surplus for an evening EV charge.

For a commuting EV driver (out of the house 8am-6pm Mon-Fri), direct solar-to-EV charging realistically only happens on weekends, holidays + WFH days. A typical 4 kWp array on a sunny weekend day delivers 20-25 kWh - enough for 70-90 mi of EV range, plus household use. Across 100 days/year of being home in daylight, that's maybe 1,500 kWh going into the car directly from solar.

The other ~800 kWh of annual EV demand (the rest of 8,000 mi/year) gets imported overnight at off-peak EV-tariff rates (7-8p/kWh in 2026). Without solar, the same overnight import would cover 100% of demand at that rate.

To force-charge on solar with no daytime presence, you need a solar diverter (Eddi, MyEnergi Zappi in 'eco' mode, Easee Pro with solar integration) that throttles the car charger up + down based on real-time export. These work, but only deliver useful EV charging in the strongest 4-6 hours of a sunny day - limiting how much energy you can capture without the car being constantly plugged in.

SEG (Smart Export Guarantee) rates in 2026:

• Octopus Outgoing Fixed: 15p/kWh exported (only available alongside Intelligent Octopus Go or Flux import tariff).
• Octopus Flux: variable, typically 20-30p/kWh in 4-7pm peak window, 5-10p outside.
• British Gas Export: 6.4p/kWh flat.
• EDF / E.ON / Ovo: typically 4-6p/kWh flat.

The choice between self-consume + export is straightforward: if you can use a kWh yourself, you save the import cost (~26p/kWh peak, 7p off-peak). If you can't, you export at the tariff rate. With Octopus 15p export + 7p off-peak import, there's an arbitrage argument for actually exporting daytime solar + importing overnight - the spread is small but positive on the spreadsheet.

Household: 4 kWp solar, no battery, 8,000 mi/year EV, commuting pattern (away 8am-6pm Mon-Fri), Octopus Intelligent Go (7p off-peak, 26p peak) + Outgoing Fixed export 15p.

• Solar generation: 3,600 kWh
• Self-consumed (household, no EV): ~1,000 kWh (saves 1,000 * average 18p = £180)
• EV charged direct from solar (weekends + 30 WFH days): ~700 kWh (saves 700 * 7p off-peak alternative = £49 - but also avoids export at 15p = lost £105 - so net BENEFIT vs exporting: -£56)
• Exported: ~1,900 kWh * 15p = £285
• EV charged from grid off-peak: ~1,590 kWh * 7p = £111 cost

Net household electricity P&L: £180 + £285 - £111 = £354 saving vs grid-only. Without solar, the same household would import 1,000 kWh + 2,290 kWh EV = ~£260 net cost (mix of off-peak + peak). Solar saves roughly £600 annually for this household.

Note the counter-intuitive finding: it's often economically BETTER to export daytime solar at 15p + import overnight at 7p than to force the EV to charge during the day. The Intelligent Octopus algorithm exploits this automatically - you don't need to think about it.

A 10 kWh home battery (typical 2026 install cost ~£5,000 fitted) shifts the maths in a few ways:

• Daytime solar surplus stores for evening household use instead of exporting - higher self-consumption percentage.
• You can ALSO charge the battery from cheap off-peak grid kWh (7p) + discharge it during peak hours (26p) - a ~£1.90/day arbitrage on full cycles.
• Combined with the EV, total annual saving for the worked-example household climbs to ~£900-£1,100 (depending on tariff + battery cycling discipline).
• Payback period on the battery alone is 6-9 years for most UK households - shorter when paired with solar + EV than without.

For most households the order of operations is: solar first (payback 8-12 years), EV next (no payback as such - it's a fuel-cost saving), battery last (payback 6-9 years from tariff arbitrage even without solar).

Solar + EV in the UK 2026 is a clear win on annual fuel + electricity cost, but the romantic 'free charging from the sun' picture only really applies to households who are home during the day OR have a home battery doing the time-shifting for them. For everyone else, solar + a smart EV tariff with decent export rate (Octopus Outgoing) does the same job via the export-then-import-overnight loop - and the maths works out almost identically.

The single biggest cost-effectiveness lever isn't 'force the car to charge from the sun' - it's pairing solar with an export tariff above 10p/kWh + an EV tariff below 10p/kWh off-peak. That spread is where the savings live.