Destination charging: how much power do you need for a short or long stay?

An electric car might spend half an hour in a supermarket car park, a couple of hours outside a restaurant or an entire night at a hotel. If the driver plugs in while shopping, dining or staying overnight, that’s destination charging. For the business running the car park, the question is how much energy each customer needs before they leave.

How does destination charging work?

On a long journey, drivers may make a dedicated charging stop and leave as soon as they have enough energy to continue. With destination charging, the length of the stay depends on what the driver is doing while the car is parked. A hotel guest who arrives at 8 pm and leaves at 8 am can keep the car plugged in for up to 12 hours. As long as the car has enough charge by morning, finishing at 9 pm may offer little extra benefit to the guest. For the hotel, those extra hours give it more flexibility to share the available power across the cars plugged in overnight.

How much energy can an electric car gain while it’s parked?

To estimate the energy delivered in kWh, multiply the average charging power in kW by the time spent charging in hours. Delivering 30 kWh in half an hour would take an average of 60 kW. With six hours available, the same amount would take an average of 5 kW.

At a steady 11 kW, a half-hour supermarket visit is enough to deliver around 5.5 kWh, while a two-hour dinner gives you 22 kWh. Over an eight-hour overnight stay, an average of 4 kW can deliver around 32 kWh. How much energy you need to offer depends on what customers typically need for their next journey.

These figures are estimates of the energy delivered by the charge point. Some energy is lost during charging, so less reaches the battery. The car may also spend only part of the visit plugged in. With AC charging, the vehicle’s onboard charger is another factor that affects electric car charging times. A car that accepts up to 11 kW on AC will still be limited to 11 kW when plugged into a 22 kW AC charge point.

When does charging speed matter more than the number of charge points?

At a supermarket where customers tend to park briefly, higher charging power can help them gain more energy before they return to the car, provided the vehicle can accept it. At a restaurant, a two-hour stay can give customers a useful top-up at a lower AC charging power. For hotel EV charging, the priority may be giving more guests a place to plug in when they arrive and enough charge to set off in the morning.

The choice between AC and DC charging depends on how much energy drivers need and how long they stay. If many customers are passing through and need a substantial top-up before continuing their journey, DC charging may make sense. Where cars tend to stay parked for several hours, there is more scope to share the available power across several vehicles at once.

How quickly do charging bays become available?

Consider a restaurant with four charge points and two dinner sittings. If diners from the first sitting move their cars before the next group arrives, the same four points can serve up to eight cars in one evening. If the sittings overlap, arriving customers may find all the charging bays occupied even if some cars have finished charging.

The effect is especially noticeable at hotels. If four guests plug in at 9 pm and leave their cars parked until morning, a fifth guest arriving at 11 pm may find every charging bay taken. Increasing the charging power can help sessions finish earlier, but a bay only becomes available when the car is moved. When deciding how many points to install, allow for the time vehicles spend in the bay after charging has finished.

How to share 44 kW across four electric cars

Imagine a car park with 44 kW available for EV charging. With four AC charge points and four compatible cars, each vehicle can charge at up to 11 kW while the full 44 kW is available. Over two hours, each point could deliver up to 22 kWh. All four drivers can plug in as soon as they arrive.

Available power can vary during the day. If the charge points share an electrical supply with a restaurant, the kitchen may leave less capacity for charging during dinner service. A Power Meter measures power flows at the meter, giving the dynamic load balancing system the data it needs to adjust the total power allocated to charging. Power sharing then distributes that allowance across the active charge points. When the kitchen’s demand falls or one car finishes charging, more power can be made available to the remaining vehicles, within the limits of the installation, the charge points and the cars.

A site can therefore operate four 11 kW charge points with less than 44 kW available to them if the system manages the combined load. To judge whether that setup meets customers’ needs, work out how much energy each car can receive while it is plugged in.

How much energy can you deliver at peak times?

Suppose four diners leave their cars plugged in for two hours. For the first hour, the kitchen’s demand leaves 22 kW available for EV charging. In the second hour, the full 44 kW is available again. The charge points can deliver 66 kWh across the two hours, or 16.5 kWh per car if power is shared equally and each car can accept its share.

That would cover a target of 15 kWh per car during dinner. A target of 20 kWh per car would leave the restaurant 14 kWh short across the four vehicles. Measuring electricity demand during dinner service helps you see how long the peak lasts and how much it overlaps with the time customers are plugged in.

What to check before sizing a destination charging installation

If you’re assessing EV charging solutions for your business, start with four figures.

• Typical parking duration. Look at how long customers stay and how that varies by day and time.

• Energy required per session. Estimate how much customers typically need to continue their journeys.

• Number of cars plugged in at once. Ten charging sessions spread across the day can require fewer charge points than ten cars arriving together.

• Power available at busy times. Check how much capacity is left for charging when customers are on site and the business is already drawing power.

Taken together, these figures help you decide whether your car park needs faster individual sessions or more places to plug in. The aim is to give as many customers as possible the energy they need by the time they’re ready to leave.