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On cold mornings, many people preheat their EVs by connecting them to the mains. But this doesn’t necessarily save them money. SINTEF researcher Åse Lekang Sørensen has been measuring levels of energy consumption during the preheating for different makes of electric car.

(Photo: Bjørn Ludvigsen / SINTEF)

What’s the best way of warming up your electric car?

A warm car is both safer and more comfortable.

Ida Rambæk COMMUNICATIONS ADVISER

Presented by: SINTEF

Published 19 November 2023 - 04:30

Up until now, car manufacturers and others have recommended using electricity from the grid to warm your car on cold winter mornings because this will save the battery and ensure maximum range.

But research shows that this isn’t always necessary. Nor does it save you money.

“We don’t need a fully-charged battery for most car journeys, so preheating in this way puts an unnecessary strain on both the electricity grid and our wallets,” researcher Åse Lekang Sørensen at SINTEF says.

She and her colleagues at NTNU have calculated how much mains electricity is being used to preheat electric cars and how this impacts the supply grid.

Smart people charge at night

Our increasing use of electric cars means that preheating is putting a significant strain on the electricity grid. This makes it important to know how our use of electric cars impacts total electricity consumption and raises issues about the smartest ways of using electricity.

After parking their electric cars at home in the afternoon, many people wait until nightfall before charging them. This is smart because capacity in the grid is greater at night and electricity is cheapest then.

However, preheating takes place mostly in the morning on the coldest winter days, when the total load on the grid is at its highest and the electricity at its most expensive.

“The amount of electricity we use to preheat electric cars is small in comparison with the big picture, but it nevertheless impacts consumption when the load on the grid is greatest," Sørensen says.

For a single household, this will often lead to higher electricity bills because the spot price is normally highest in the mornings. In some cases, it may also result in a higher grid tariff, if the electricity you use for preheating means that you end up in a higher standing charge band. The standing charge band is a part of the electricity bill calculated based on the highest daily peaks each month.

Many types of electric cars can choose to use power from the battery for preheating. The researcher's advice is to charge smartly at night, as many already do, and then preheat the car with the battery, without the car being connected to the grid. She only recommends preheating from the mains if you are starting out on a long journey in cold weather.

Calculating energy consumption during charging

At the research centre Zero Emission Neighbourhoods in Smart Cities (ZEN), researchers from SINTEF and NTNU tested the preheating of some standard electric cars in various weather conditions.

Five of the most common electric cars sold in Norway were part of the experiment: BMW i3, Jaguar I-PACE, Nissan Leaf, Tesla Model 3, and VW eGolf. Together, these make up 38 per cent of the electric cars currently on Norwegian roads.

The results were as follows:

Most of the electrc cars consumed between 3 and 8 kW electricity at the start, which was later reduced to about 2 to 4 kW after 10 to 20 minutes.
The preheating process lasted between 15 and 45 minutes.
Energy consumption during preheating was up to 2 kWh for the majority of electric cars, with a maximum value of 5 kWh.

The researchers also calculated how a number of different variables impacted on energy use.

“We measured how the electricity consumed in the preheating of electric car cabins is influenced by the car itself, the charging point, the time it takes to warm the car, the exterior and interior air temperatures, as well as charging habits. Charging habits refer to when, how long, and how often we connect to the charger,” Sørensen says.

Finally, the energy use for preheating electric car cabins was compared with other energy use in a typical apartment block.

“This is relevant because it tells us how great a proportion of the total electricity consumed by a household goes towards preheating the car, and thus how the preheating process impacts on electricity bills,” she says.

Reference:

Sørensen et al. Grid-connected cabin preheating of Electric Vehicles in cold climates – A non-flexible share of the EV energy use, Applied Energy, 2023. DOI: 10.1016/j.apenergy.2023.121054