How does temperature affect EV performance?

All cars are affected by temperature. Cold weather increases air resistance because cold air is denser than warm air.  Cold weather also makes the tires loose pressure and thus increases the rolling resistance. However cold air but also raises slightly the performance of some combustion engines.

Most importantly people tend to drive slower in winter traffic due to reduced grip and visibility. This means that ordinary petrol cars often maintain roughly the same fuel economy summer and winter. However in Nordic countries diesel fuel is always diluted in the winter time so diesel drivers could experience a small drop in power and range. All in all the changing seasons are not a big worry for conventional cars.

Battery electric cars carry only a small amount of energy equivalent to 2-3 liters of petrol. This is enough for driving 110 - 160km because the EV drive train is hugely effective. However there is little excess heat available for cabin heating. Therefore cabin heating can take up to 25 % of the battery energy.

The battery itself is also sensitive to temperatures. As illustrated below the capacity of a battery cell is reduced by 30 - 40% at -20°C. These are quite extreme temperatures which are rarely experienced except for the north most areas like Finland and Lapland.

Even though the outside temperatures should reach -20°C the battery will gradually heat itself during operation. So the loss of capacity will not be that drastic in real life. Many EVs have preheating of the battery which ensures that the battery never falls below the ideal temperature range.



Figure 29: Battery capacity decreases with temperature


High temperatures could also be a problem for some EV batteries. Some EV batteries have no active cooling at all while others have fan assisted air cooling and yet some have liquid cooling. Early reports from the USA have indicated that EV's with no battery cooling could suffer from degradation in the extreme heat of Arizona. Choosing an EV with active battery cooling should definitely reduce that problem significantly. Technically speaking liquid cooling should be the most effective means.

The driving performance (speed and acceleration) is largely unaffected by temperature.