How does solar-diversion EV charging work?

A Zappi (or similar diversion-capable charger) uses a CT sensor at your meter to detect when your solar panels are producing more than your home is consuming. The surplus is routed to the EV charger instead of being exported to the grid — meaning free charging from sunshine.

Which EV chargers support solar diversion?

Zappi 2.1 from myenergi is the gold standard with built-in solar diversion. Hypervolt supports it via add-on hardware. Some Wallbox commercial models also support it. Ohme, Easee, and Pod Point don't have native solar diversion (though Ohme has solar-aware scheduling).

How many free EV miles can solar diversion give me in Cornwall?

For a typical 6kW Cornwall solar system with a Zappi, around 1,500-2,500 kWh of solar surplus is captured for the EV per year — equating to roughly 6,000-10,000 free miles. Larger solar systems and frequent daytime EV plugging-in give more.

Do I need a home battery for solar-diversion EV charging?

No — solar diversion works without a home battery. You get free miles whenever the EV is plugged in during daytime surplus. A battery stores surplus for evening use; an EV diversion routes surplus to the car immediately. Both can coexist; some chargers (Zappi + libbi) integrate priority management.

Is solar diversion worth it if I have an export tariff?

Almost always yes. Export tariffs (SEG) pay 4-15p/kWh; import electricity costs around 28p/kWh on a default tariff. Diverting to the car saves more than exporting earns. Exception: if you're on Octopus Flux with high peak export rates, the maths can shift — consider battery-first in that case.

Do I need a south-facing roof?

South-facing is optimal but not essential. East or west-facing roofs still produce 75-85% of south-facing output. North-facing significantly reduces output and isn't recommended for any solar install. Cornwall's south coast is excellent for east/south/west facing roofs.

Can I retrofit solar diversion to an existing EV charger?

Only if it's a Zappi or Hypervolt. Most other chargers don't support solar diversion. If you're planning solar PV install on a house that already has a non-Zappi EV charger, you may want to budget for a Zappi upgrade alongside (around £900 fitted).

How much extra does a Zappi cost vs a non-diversion charger?

Around £100-£200 incremental cost vs an Easee or Pod Point. The Zappi fits at £900-£1,000 vs £700-£850 for budget alternatives. For solar PV homes, the incremental cost typically pays back in 12-24 months on diversion savings alone.

Solar-Diversion EV Charging: Free Miles from Your Roof

Combining solar PV and an EV is one of those rare modern setups where the numbers genuinely work out as a free lunch. A Zappi (or similar diversion-capable charger) automatically routes surplus solar energy into your EV when the sun is shining — replacing miles you'd otherwise pay 28p/kWh for. For Cornwall homes with south-facing roofs, this can mean 1,500-2,500 free EV miles per year. Here's the maths, the kit, and the setup.

How it works

A solar-diversion EV charger (most famously the Zappi 2.1 from myenergi) uses a clip-on current transformer (CT sensor) at your incoming meter to monitor your home's electricity flow in real time. When the system detects:

Solar generation greater than home consumption: the surplus is "exported" — the meter would send it back to the grid (for around 4-15p/kWh depending on your SEG export tariff)
The Zappi is plugged into your EV: instead of exporting, the surplus is diverted to charge the car
The charger continuously adjusts: if clouds reduce solar by 30%, the charging rate drops accordingly — never drawing from the grid unnecessarily

The Zappi modes

Fast mode: Use any combination of solar + grid — charge as quickly as possible regardless of source. Useful when you need a top-up now.
Eco mode: Use solar surplus when available; supplement with grid if needed to maintain a minimum charge rate (usually 1.4kW). Balanced approach.
Eco+ mode: Solar only — if clouds reduce surplus below ~1.4kW, pause charging entirely. Maximum free miles but slower overall.

Most Cornwall solar-EV households leave the Zappi on Eco+ during sunny months (April-September) and switch to Eco or Fast for overnight charging on cheap-rate tariffs.

Cornwall is excellent for this

Cornwall has some of the UK's best solar irradiance — the south-facing coast gets more annual sunshine than almost anywhere except parts of Hampshire and Sussex. Typical Cornwall solar output:

4kW south-facing roof system: around 3,800-4,200 kWh/year
6kW system (typical install size in 2026): around 5,700-6,300 kWh/year
8kW system (larger Cornwall installs): around 7,600-8,400 kWh/year

Of this annual output, roughly 50-70% is exported as surplus if you have no diversion — the rest is used directly in the house. Diversion catches that surplus and puts it in your car instead.

Real-world savings

For a typical Cornwall home with a 6kW solar system and a 7kW Zappi:

Annual solar surplus (the bit that would otherwise be exported): around 3,000-4,500 kWh
Realistic captured by Zappi (depends on when you're plugged in): around 1,500-2,500 kWh
EV miles per kWh: around 4 miles
Free EV miles per year: around 6,000-10,000

Compared to charging on Intelligent Octopus Go at 7p/kWh, the saving is around £100-£175/year. Compared to public rapid charging at 65p/kWh, the saving is around £975-£1,625/year. Compared to ICE petrol at 13-15p/mile, the saving is around £780-£1,500/year.

What you need

The setup:

Solar PV system — any size; bigger is better but even 4kW works. Most Cornwall homes choose 4-8kW. Our partner site Solar Panel Installation Cornwall covers solar PV install.
Zappi 2.1 (or equivalent diversion-capable charger) — Zappi is the gold standard for solar-diversion; Hypervolt with add-on, and some Wallbox models also support it.
CT sensor / "harvi" — clipped to your incoming meter cable. Sometimes the CT sensor is hard-wired; sometimes wireless via the myenergi "harvi" sender.
An EV with the right port — Type 2 (universal in 2026 UK market).

Cost

Zappi 2.1 fitted: around £900-£1,000
Harvi sender (if needed): around £80-£120
Total incremental over a non-diversion charger: ~£100-£200

For a £100-£200 incremental cost, you get £100-£175/year saving on tariff alone (potentially much more if you'd otherwise use rapid chargers). Payback is 12-24 months; lifetime ROI is excellent.

What about home batteries?

If you have (or plan) a home battery, the diversion question gets nuanced:

Home battery stores excess solar; releases it later (often evening)
EV diversion takes excess solar; puts it in the car
Both compete for the same surplus

The right priority depends on your usage: if you use EV daily, EV-diversion-first usually wins. If you're rarely at home during daylight (commuter), battery-first may win because the battery shifts solar to your evening usage.

The Zappi family integrates with myenergi's libbi home battery, allowing intelligent priority between car and battery. Other battery brands (Tesla Powerwall, Givenergy, etc.) work alongside Zappi via the CT-sensor logic, though without the same integrated priority control.

Stacking with EV tariffs

The premium setup for Cornwall solar-EV households:

Daytime (sunny): Zappi solar diversion — free miles
Daytime (cloudy): minimal grid use; defer charging to night
Overnight (23:00-05:30): Intelligent Octopus Go at around 7p/kWh — cheap miles
Net annual cost per mile: typically 1-2p/mile (vs 13-15p for petrol)

The overall household electricity bill often goes DOWN after fitting solar + EV + Zappi, even allowing for the EV's electricity use. Counterintuitive but real.

Considerations

Solar export tariff (SEG). Diverting to the car instead of exporting means foregoing export income. With export rates around 4-15p/kWh and electricity import rates around 28p/kWh, diversion almost always wins financially — but check your specific SEG rate.
Octopus Flux. Octopus's solar/battery tariff offers higher export rates at peak times — sometimes 25p+ per kWh. If you're on Flux, the trade-off shifts; consider battery-first.
Schedule. You need the EV plugged in during daylight to capture solar. If your EV is at work all day, you can't divert. Weekend / holiday charging is when diversion shines.
System size mismatch. A small solar system (2-3kW) generates less surplus; diversion benefit is smaller. Bigger solar systems (6-8kW) generate more surplus during daylight; diversion benefit scales.

Cornwall examples

Truro semi, 4kW south-facing solar, Zappi: around 1,200 free EV miles/year, saving around £85/year on tariff or £750/year vs rapid
Falmouth detached, 6kW south-facing solar, Zappi + libbi: around 2,000 free EV miles/year, saving around £140/year on tariff or £1,300/year vs rapid
Penzance bungalow, 8kW south-east solar, Zappi (weekends only): around 1,500 free EV miles/year, saving around £105/year on tariff or £975/year vs rapid (more if EV used more weekdays)

Got solar PV (or planning it) and considering EV charging? Submit your postcode for a Zappi-capable Cornwall installer quote, or check our partner Solar Panel Installation Cornwall for a solar-and-EV combined quote.

Disclosure

EV Charger Cornwall is a lead-gen service connecting customers with vetted local OZEV-approved installers. Solar savings depend on system size, orientation, and use patterns; figures above are typical, not guaranteed.