Will your grid connection take a charging fleet?

Whether your grid connection takes a charging fleet of electric vehicles depends on the highest half hour of combined demand, the peak the chargers add to the site's existing load, measured against the maximum import capacity the site already holds. The extra energy an EV fleet draws over the year is a separate question. A connection with headroom above its current peak can absorb a good deal of charging; a connection already close to its agreed ceiling can be pushed past it when the fleet charges at the wrong time. What makes fleet charging different from most new loads is that vehicles sit for hours while they charge, so when the draw lands is partly a choice.

Why the peak decides it

A grid connection is rated for power, the rate at which energy flows at a given moment, recorded in kVA. The level a site is contracted to draw is its maximum import capacity, and the bill carries a daily charge for each kVA of it whether the site uses it or not. Drawing above that level brings an excess capacity charge, and a site that does so repeatedly can be required to raise its agreed capacity before the network operator will allow the extra draw. A charger is rated in kW, the real power it delivers, while the capacity is set in kVA, so reading a charging peak against the capacity assumes the site runs at a power factor near one; at a lower power factor the real-power headroom is smaller than the kVA figure alone suggests. DC rapid chargers can run below unity, so this matters most for a fleet on fast chargers.

This is why the total energy a fleet adds over a year is the wrong thing to watch. A depot can charge a large number of vehicles overnight and add a great deal of energy, yet move its peak very little if that charging is spread across the hours the vehicles are parked. The same vehicles plugged in together the moment they return, all drawing full power at once, can take the connection past its ceiling while adding the very same energy. What the connection is rated for is the instantaneous power at the worst half hour, so how the charging is arranged in time matters more than how much energy it needs.

How an EV charging fleet loads the connection

A charger's rated power sets how hard a single vehicle can draw: a depot of overnight AC chargers draws modestly per socket, while rapid DC chargers for quick turnarounds draw many times more each. The peak at the connection is not the sum of every charger's rating, because vehicles rarely all draw full power at the same instant. Some have nearly finished and tapered off, some are not plugged in, and a vehicle draws its highest power only over part of its charge. This shortfall between the realistic simultaneous draw and the sum of the ratings is the diversity of the fleet: the larger and slower the fleet, the greater the shortfall, so its coincident peak becomes a smaller fraction of the installed total. A small fleet on fast chargers shows little diversity, so its peak sits close to the installed capacity; a large depot charging slowly overnight shows a great deal, so its peak is only a fraction of the connected total.

When the charging peak lands

Whether that peak stacks on the site's existing one depends on the fleet's pattern. A back-to-base depot, where vans or trucks return in the evening and leave in the morning, charges through the night, which on most commercial sites sits well below the daytime working peak, so there can be real headroom to use before the combined demand reaches the agreed capacity. Opportunity charging through the day, where vehicles top up between runs, lands inside working hours and adds directly to the existing peak. A customer-facing or shared charging point draws whenever a driver arrives, which is the least predictable pattern of the three. Where the site also runs electrified heat or process load, the charging stacks on top of whatever those draw, so it is the combined demand that has to be planned for; our guide to electrification and grid capacity covers that combined picture.

What managed charging changes

Because a parked vehicle does not need its energy until it leaves, the timing of fleet charging can be chosen within the hours the vehicles are plugged in. Managed charging, sometimes called smart charging, uses a controller that measures the site's live demand and the chargers together and holds the total import below a set limit by slowing or staggering vehicles rather than letting them all draw at once. An overnight depot has many hours in which to deliver each vehicle's energy, so the controller can flatten the charging into a long, low plateau that fits under the agreed capacity, as long as every vehicle still reaches the charge it needs by the time it departs.

The headroom test for a fleet is therefore as much about the control strategy as about the chargers. The same installed charger capacity can produce a peak that pushes the import past the agreed capacity or one that sits comfortably within it, depending on how the charging is managed. This is the main thing that sets fleet charging apart from other electrification loads: much of the peak follows the control strategy, so it can be changed.

Working it out from the site's own data

The combined peak is only knowable from the site's half-hourly import data, which records demand in every half hour of the year and shows when the site is already busiest. Our guide to reading half-hourly data covers what that record holds and how to read a load profile from it.

The method is to build a half-hourly charging profile from the fleet: the number of vehicles, the energy each needs, when they arrive and depart, and the charging strategy that places that energy across the available hours. Adding that profile to the site's measured demand half hour by half hour gives the new annual peak and how many half hours a year the site would sit close to its agreed capacity. A peak reached only on the busiest evenings is a different proposition from one reached on most working days, and the two point to different answers on whether the connection needs changing at all.

If the combined peak exceeds the agreed capacity

Where the modelled peak sits above the maximum import capacity even after the charging is managed, the site has two routes. It can hold the peak down further with on-site generation and storage. Or it can apply to the distribution network operator to raise the agreed capacity.

Raising the capacity depends on the headroom on the local network. Where the network has room, the change is a contractual one and raises the daily capacity charge from the date it takes effect. Where the network is constrained, the operator can quote for the work needed to carry the extra import, and that reinforcement can carry a material cost and a long lead time. Our guide to grid connection reinforcement costs covers what drives that charge and how to tell whether the project still holds up once it is included.

How solar and storage hold the peak down

Because the connection is rated for instantaneous power, anything that lowers the import at the worst half hours lowers what the connection has to carry. A battery charged at other times and discharged across the charging peak shaves that peak, which can keep the combined demand under the agreed capacity and so avoid a capacity increase or reinforcement. A battery sized for this work has a connection question of its own: under the Energy Networks Association's Engineering Recommendation G99, electricity storage rated above 16 A per phase, about 3.68 kW on a single 230 V phase, needs an application to the distribution network operator before it is connected, so a commercial battery is approved alongside the rest of the import rather than after it. For an overnight depot the battery has to hold its output across the whole charging window, which is a long plateau, so it is sized for both the power it must cover and the energy it must deliver over those hours.

Solar helps where the charging happens in daylight. A fleet that opportunity-charges through the day can take that draw partly from the site's own generation, which lowers the daytime import directly; our guide to solar self-consumption covers how much of its own generation a site tends to use. An overnight depot gains less from solar, since the charging runs when there is no generation, though a battery can move daytime solar into the night. The connection, the chargers, the charging strategy and any generation and storage are therefore worth sizing together rather than one at a time.

Working it out for a specific site

Lupa models a site's own half-hourly demand with the fleet's charging load added, then tests each combination of solar and battery against it, and gives the import capacity the site would need under each one. That shows whether the existing connection covers the fleet, how much managed charging or a battery would have to shave to keep the site within its agreed capacity, and what that does to the return. One caution applies to any such model: dispatch worked out with perfect knowledge of future prices overstates what a real controller can capture, so a realism discount is applied and the peak-shaving benefit should be read as the discounted figure.