Commercial Solar EV Charging: How It Works in Practice

Most businesses meet solar and EV charging as two separate purchases, often years apart, each carrying its own consultants, its own grid application and its own invoice for trenching the same stretch of car park. The better-run projects of the last few years have demonstrated the alternative: treat generation and vehicle charging as one electrical system, and both halves get cheaper and more valuable.

The architecture, demystified

There is no special cable from panel to plug. A combined system is ordinary AC engineering: the solar array feeds the site’s distribution through its inverters; the chargers draw from the same distribution; the grid makes up shortfalls and takes surpluses. What makes it a system rather than two coincidences is the control layer — metering at the supply intake and on the generation feed, plus a load-management controller speaking OCPP to every socket.

That controller does three jobs at once. It keeps total site demand under the supply capacity, which is what lets ten sockets live on a supply that naïve arithmetic says supports four. It schedules vehicle energy across each vehicle’s parked hours, because a van that sits from 9am to 4pm does not need — and should not get — full power at 9:01. And it biases charging into measured solar surplus, which is where the money is made.

Where the money is made

UK commercial electricity rates in 2026 sit around 24–30p/kWh. Export earns 4–12p. Public rapid charging costs 60–85p. Those three numbers explain the whole business case.

A solar array on a five-day business typically exports 20–40% of its generation at the lowest of those rates. Add vehicles and the controller converts that export into displaced fuel at the highest one: every kilowatt-hour steered from the export meter into a van battery that would otherwise have rapid-charged in public is worth 55p or more. Self-consumption climbs past 90%; the array’s effective return improves without a single extra panel; and the fleet’s energy lands at the lifetime solar cost of roughly 5–8p/kWh.

On the cost side, the combination saves again. One DNO engagement covers the G99 generation application and the new charging load. One groundworks package serves canopy bases, charger plinths and cable routes. One design fee, one mobilisation, one commissioning visit. Delivered combined projects routinely come in 10–20% under the sum of their separated parts.

A worked sketch

Take a 30-staff services firm planning eight electric vans. An 80kW rooftop array yields about 70,000kWh a year. The building takes 38,000 of those directly; smart-scheduled van charging absorbs another 26,000; 6,000 export. The vans cover 144,000 miles annually on roughly 41,000kWh — so the array covers around 63% of fleet energy, with the grid (cheap, overnight, load-managed) covering the rest.

Value: about £9,900 of building displacement, £14,300 of avoided public charging versus the rapid-network alternative, £400 of export. Call it £24,600 a year against a combined install in the low £90,000s — before the Workplace Charging Scheme contributes £350 per socket and the Annual Investment Allowance removes the project from taxable profits in year one. Net payback lands under three years. The same maths at fleet-depot scale gets more dramatic, not less.

The mistakes to skip

Sizing the array to the chargers’ nameplate. Eight 22kW sockets do not draw 176kW; they average a fraction of it. Size generation to annual energy (building plus vehicles), size the control system to worst-case simultaneity.

Buying proprietary chargers. If the hardware doesn’t speak OCPP, your site belongs to one vendor’s software pricing for fifteen years. Open protocol is a one-line specification that preserves competition forever.

Trenching twice. Duct for the end-state socket count on day one, even if phase one is four sockets. Empty duct costs pounds; reopened tarmac costs thousands.

Treating the DNO as an afterthought. The combined application is genuinely easier — a flattened, managed demand profile with on-site generation is a friendlier proposition than either project alone — but only if it goes in early, with the design stable.

Believing “free fuel from the sun”. Solar shifts the average cost of fleet energy decisively; it does not abolish the grid. Overnight charging, dark Decembers and rapid turnarounds all still draw from the network. The honest pitch — 30–60% solar-powered fleet energy on a daytime-dwell operation — is impressive enough without the fiction.

Where to start

Not with hardware. Start with twelve months of half-hourly meter data, your vehicle schedules and mileages, and the site address. That is enough to model the energy budget, the power budget, the grant position and the cash flow — the document a board can actually approve. The hardware list falls out of the model, and never the other way round.