EV Charging With Solar Panels

There are two genuinely different ways to put sunshine into your car, and the one that suits you depends on the charger you fit and whether you own a battery. The first is real-time surplus divert. A charger such as the myenergi Zappi uses a CT clamp fitted around your incoming supply cable to measure, second by second, exactly how much solar your panels are sending to the grid. In its Eco+ mode the Zappi diverts only that surplus into the car, ramping charge power up and down from as little as 1.4kW as clouds pass over Wiltshire, and pausing altogether the moment a kettle or oven claims the spare generation. Nothing is drawn from the grid, so those miles are genuinely free rather than simply cheap.

The second method is scheduled charging. A smart charger such as the Ohme Home Pro fills the car during a cheap overnight window on a tariff like Octopus Intelligent Go, typically around 7p/kWh. The Ohme uses app-based Solar Match rather than a Zappi-style CT clamp, so it does not divert your surplus second by second — on a cheap overnight tariff it is mainly buying low-cost grid power on a timer, which for many drivers works out cheaper still. Both approaches are valid; they simply solve different problems.

In practice most of the homes we fit across Wiltshire use both. On a bright day the Zappi's Eco+ mode tops the car up for nothing; on a dull winter evening the same charger (or a scheduled one) pulls low-rate overnight power instead. On a standard 7.4kW single-phase supply a Zappi will charge at up to 7.4kW in fast mode, or trickle down to surplus-only in Eco+; on a three-phase supply it can deliver up to 22kW. Because we handle the EV charger installation at the same time as the array, the CT clamp, consumer-unit tails and app set-up are commissioned as one job rather than two separate visits with two separate certificates. If you want the fullest use of your generation, a battery changes the picture entirely — more on pairing solar and battery below.

The maths is more encouraging than most people expect. A modern EV averages around 3.3 miles per kWh, or roughly 0.3kWh per mile. The average UK driver covers about 7,000 miles a year, so the car itself needs in the region of 2,100kWh of electricity annually. A typical 4kWp array — nine 450W panels — generates around 3,900kWh in a Wiltshire year, comfortably more than the car alone requires on paper.

The real limit is not the size of the roof, it is timing. Your panels produce most of their output between roughly 10am and 4pm, which is exactly when the car is usually parked at your workplace rather than on the drive. Without storage, only the surplus that happens to occur while the car is actually plugged in goes straight into the battery. For a 4kWp system used with a diverting charger at weekends and on home-working days, that realistically delivers 2,000 to 2,500 free solar miles a year — a useful chunk of most people's mileage, but not the whole lot.

To push more of your driving onto sunshine you have two levers: add panels, or add a battery. Higher-mileage households covering 12,000 miles or more often step up to a 5–6kWp array, while anyone who charges mainly overnight will get far more from storage (covered next). Roof orientation, pitch and shading set the ceiling on what any array can produce, which is why we always survey before quoting rather than working from a postcode estimate. If you are weighing up array size against budget, our guide to solar panel costs in Wiltshire breaks down system sizes and prices, and every job is designed and commissioned by our own MCS-certified team as a proper solar panel installation rather than a subcontracted fit. We cover the full 30-mile radius, so whether you need solar panels in Chippenham or solar panels in Melksham, the same team designs the array around your actual driving pattern.

If solar EV charging has one obvious weak point — the car is out during peak generation — a home battery is the fix. Because your panels produce at midday and your car usually charges after dark, a battery bridges that gap: it soaks up the day's surplus and releases it in the evening, either into the house or, through a diverting charger, into the car. It also lets you fill the battery from a cheap overnight tariff on gloomy winter days and still run both the home and the EV from stored energy the following morning.

The 2026 batteries we most often specify all suit an EV household. The Sigenergy SigenStor stacks in 5kWh and 9.5kWh modules up to 54kWh, offers an integrated DC EV-charging option and vehicle-to-grid capability, and carries a 10-year warranty extendable to 15. The Tesla Powerwall 3 gives 13.5kWh with around 11kW of continuous output — enough to run heavy loads and a charger simultaneously — on a 10-year warranty. The GivEnergy All-in-One also offers 13.5kWh in a modular unit with up to a 12-year warranty and a strong UK support network. For most Wiltshire homes adding an EV, a 9.5–13.5kWh battery paired with a 4–5kWp array is the sweet spot; heavier drivers or all-electric homes may stack higher.

Crucially, the 0% VAT on domestic battery storage and solar runs until 31 March 2027, so buying panels and a battery together is materially cheaper than adding storage later. That said, if you already have panels you are not locked out — we can retrofit battery storage to existing solar and wire in a diverting charger at the same time. For a full model-by-model breakdown, our best home batteries UK 2026 guide compares Sigenergy, Tesla and GivEnergy side by side, and we fit all three across Devizes and the wider county — ask about solar panels in Devizes if that is your area.

The reason solar EV charging is so compelling comes down to cost per mile. At 0.3kWh per mile, the fuel behind every mile is tiny, so the price of that electricity dominates everything. Charge from your own solar surplus and the direct fuel cost is effectively zero; the only 'cost' is the export income you forgo, at a good Smart Export Guarantee rate of around 10.8p/kWh — about 3p per mile of opportunity cost, and nothing leaves your pocket. Charge overnight on a dedicated EV tariff near 7p/kWh and you are at roughly 2p per mile. Fall back to a standard import rate around 27p/kWh and it climbs to about 8p per mile, while a public rapid charger at roughly 79p/kWh works out near 24p per mile — and a comparable 40mpg petrol car sits around 16p per mile. The table below sets these out in full.

The wider household economics stack up too. A 4kWp array typically saves £950–£1,100 a year on electricity bills before you count a penny of EV savings, with payback in the region of 7–9 years; the surplus you do not use is paid for through the Smart Export Guarantee. Add a few thousand free solar miles a year on top of that and the case strengthens considerably against public rapid charging and petrol.

On funding, the headline is the 0% VAT on domestic solar and battery until 31 March 2027, which knocks a fifth off equipment costs outright. Beyond that, spreading the cost is straightforward: our solar finance options let many households cover the monthly repayment largely from the bill savings and avoided fuel, so the system part-funds itself from day one. If you are still deciding whether storage earns its keep, weigh it up with our note on whether battery storage is worth it, then read our solar panels plus EV charger guide for a full worked example. Matt Butler and the team will size the whole package — array, battery and charger — around your real mileage before you commit.