How Solar EV Charging Actually Works

The architecture in one paragraph

Solar panels feed inverters; the inverters feed the site’s AC distribution; EV chargers draw from that same distribution; the grid covers any shortfall and absorbs any surplus. A metering layer watches generation and consumption in real time, and a load-management controller — talking OCPP to the chargers — decides how much power each socket gets and when. That is the entire trick: one electrical system, one set of measurements, one piece of software steering vehicle load into the hours when the roof is producing.

How much of the charging can solar cover? It depends on when the vehicles are parked

An array’s output peaks around midday and in summer; a vehicle can only charge while it is plugged in. An hour-by-hour simulation using PVGIS data for 2005–2023 shows what that means for a London array at a 10° pitch, when the chargers follow the sun and the array is sized against the vehicles’ yearly energy demand:

For a workplace where cars are parked 09:00–17:00 on weekdays, about 60% of the array’s yearly output is produced while they are there, so an array half the size of their yearly demand supplies about 30% of it and an array equal to their demand about 56%. For vehicles parked only overnight, only about 3% of the output falls in the window: even an array as large as their yearly demand supplies about 3%. A battery could move daytime output into the evening; the model does not include one. Parking hours matter far more than the city: across eight British cities the workplace figure at an array equal to yearly demand ranges only from 53% to 56%. The calculator runs your own vehicles, array and prices through the same model.

Solar-following charging: what the controller changes

Charging that simply starts at full power when a vehicle plugs in — usually at arrival, usually all at once — spends the morning’s weak sun and then stops. Solar-following charging does three better things: it spreads charging across the parked hours (a van parked 09:00–16:00 needs only a fraction of its socket rating to leave full), it takes each hour’s charging from the array first, and it caps total site demand below the supply limit. In the model the difference is large:

At an array half the size of yearly demand, a workplace fleet’s solar share is 30% with solar-following control and between 7% and 20% when charging starts on arrival, depending on how much energy each vehicle needs a day. The same controller logic is covered from the compliance side in the load management guide.

The 6 A minimum, and why phase switching matters

The charging standard IEC 61851 specifies a minimum charging current of 6 A per phase, which the open-source evcc documentation turns into 1.4 kW on a single phase and 4.1 kW on three. A charger therefore cannot follow a surplus that falls below those figures. A fleet with many chargers can concentrate a small surplus on one vehicle at a time, which the model assumes; a small site with one or two chargers and a modest array will use less solar than shown unless its charger can switch between single- and three-phase charging, which evcc describes as letting charging start at about 1.4 kW instead of 4.1 kW. Specify the minimum current and phase switching when you buy.

AC, DC and what fleet operators need

Workplace and depot charging is overwhelmingly AC at 7–22 kW: simple sockets, gentle on the supply, well matched to vehicles that sit parked for hours. DC rapid units earn their place for mid-shift turnarounds and heavy vehicles, but they are grid-led by nature — a rooftop array does not sustain a 150 kW charge on a winter afternoon. The design rule that follows: AC for dwell time, DC for turnaround, and solar offsetting the yearly energy of both rather than the instantaneous power of either. At 7 kW a nominal hour adds about 24 miles to a car using 0.294 kWh a mile (3.4 miles per kWh) and about 17.5 miles to a van using 0.40; 22 kW adds about 75 miles an hour to the same car if its on-board charger accepts that rate. Hardware selection is a separate decision — the charger guide covers it. Why the two halves belong in one design is the core idea of commercial solar EV charging.

Sizing: energy first, power second

Two budgets must close. The energy budget sets the array size: the vehicles’ yearly kWh (miles × kWh per mile) divided by the array’s yearly output (759–951 kWh per kW across the eight cities) gives the array that would match their demand; a smaller array covers a smaller share, by the table above. The power budget — the worst-case demand of all vehicles at once against the supply capacity — sets the load management requirement and the DNO conversation.

The two budgets are often wildly different. Twenty vans doing 18,000 miles a year at 0.40 kWh a mile use 144,000 kWh, an average of only 16 kW across the year; delivered in a 12-hour overnight window they need about 46 kW, against 140 kW if every 7 kW socket ran at once. Where the power budget genuinely cannot close, the options run in cost order: smarter scheduling, battery buffering, then a supply upgrade. The grid connection guide covers the DNO side.

The DNO treatment

Generation needs a G99 application unless it is small enough for G98 notification; new charging load goes through the network operator’s own process, and a combined project can put both to the operator together. One quiet advantage of designing the two halves together is that load management flattens the demand profile the operator sees, which makes the demand side easier to accept. Canopy projects add structural and metering specifics, covered in the canopy guide; whole-depot conversions get their own treatment in fleet depot charging.

Monitoring: the system that proves itself

A combined system should report three numbers each month without anyone asking: the solar share of vehicle energy, building self-consumption, and effective pence per mile by vehicle. Those are the numbers the business case depends on, and handover is not complete until the dashboard shows them. Under-performance visible in week two is a warranty conversation; discovered at year-end it is a write-off.

Sources

• EU Joint Research Centre, PVGIS 5.3 hourly series (SARAH3 radiation, ERA5 meteorology), 2005–2023; the model assumptions are set out on the calculator page.
• evcc documentation, “Solar surplus charging” — docs.evcc.io (IEC 61851 6 A minimum; 1.4 kW single-phase and 4.1 kW three-phase; phase switching).
• Zapmap Price Index, August 2026 (the 3.4 miles per kWh implied by its per-mile figures).
• The Electricity (Plug-in Microgenerators) rules referred to in the FAQ: The Plugs and Sockets etc. (Safety) Regulations 1994 and Electricity Safety, Quality and Continuity Regulations 2002 (Amendment) Regulations 2026, S.I. 2026/848 — legislation.gov.uk.

Checked 14 October 2026.