An electric car is the largest load most houses have ever had

The scale is different from anything else in the house

Household appliances have grown steadily more efficient, and the result is that the individual loads in a modern home are mostly small. Lighting is a fraction of what it was. Televisions and computers draw modest power. Even the largest conventional loads run briefly. Then a car arrives, and the annual consumption of a single household can change by a very large proportion.

How large depends entirely on how far the car is driven, which is why no general figure means much. The useful way to think about it is per kilometre: an electric car consumes a broadly predictable quantity of electricity for each kilometre travelled, so annual charging is that figure multiplied by annual distance. A household driving a long commute daily will see the car dominate the bill.

The reason this matters isn’t the cost in isolation, since the alternative fuel had a cost too. It matters because the shape of the demand changes, and shape is what tariffs, supply capacity and solar systems all react to.

Power and energy are separate questions

The energy the car needs is fixed by the distance driven. The power at which it is delivered is a choice, and it is a choice with consequences. A domestic charger drawing seven kilowatts adds more instantaneous load than most houses ever draw for anything, and a three-phase charger can add several times that.

The constraint is the incoming supply. Every property has a main fuse or breaker with a rating, and everything in the house shares it. Adding a large continuous load on top of an oven, an immersion heater and a shower can approach that limit, which is why load-management devices exist: they monitor the incoming current and throttle the charger when the rest of the house gets busy.

Those devices are usually a far better purchase than a supply upgrade. Upgrading an incoming supply is disruptive, sometimes expensive, and often subject to a queue at the network operator. Simply charging a little more slowly when the oven is on costs nothing, because the car is parked for many more hours than it needs.

Nearly all of it can be moved

The redeeming feature of vehicle charging is that it is the most flexible large load a household is ever likely to own. A car that arrives home in the evening and leaves in the morning has a window many hours long in which to absorb energy it needs for perhaps a couple of those hours. Almost nothing else in a house offers that.

That flexibility is worth real money wherever electricity is priced differently across the day, and it is the reason charging is the single most rewarding load to schedule. It also makes vehicle charging attractive to network operators, which is why arrangements that reward off-peak charging have appeared in a number of markets.

The scheduling can live in the car, in the charger or in the tariff, and the practical advice is to pick one and let it own the decision. Two systems both trying to be clever about when to charge is a common source of the complaint that a car charged at exactly the wrong time.

Charging from the roof is harder than it sounds

The obvious ambition is to charge from solar surplus. The obstacle is that the car is frequently not at home when the surplus exists, and the surplus is variable in a way that ordinary charging equipment handles badly. A charger fixed at seven kilowatts will either import heavily whenever a cloud passes or refuse to run at all.

Surplus-following chargers solve this by modulating current continuously to match whatever the array is exporting, and they need a current sensor at the incoming supply to know what that is. Below a minimum current the car will not accept a charge at all, which is a limitation of the vehicle standard rather than the charger, so very small surpluses can’t be used this way.

Where it works, it works well, because it converts export at a low price into avoided import at a higher one. Whether it works for you is a question about your daily pattern and your latitude, since a household in a cloudy northern winter will find the surplus mostly absent for months.

What to be careful about spending money on

The fastest charger the wiring will support is a common purchase and rarely a useful one. A car parked for twelve hours doesn’t benefit from being filled in three rather than six, and the faster unit is more expensive, is more likely to require a supply assessment, and pushes the household closer to its capacity limit for no practical gain.

The other frequent overspend is a battery bought to charge a car. Storing energy in a home battery and then moving it into a vehicle battery means paying the round-trip conversion loss twice, and the quantities involved dwarf domestic storage anyway. If the goal is cheap charging, the tariff does that job far better than hardware.

What is worth attention is the connection paperwork. Many network operators require notification of a charger installation, and some impose conditions on load management in constrained areas. It is routine, the installer normally handles it, and skipping it can matter later.