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Temperature and EVs, does it matter?

Fortunately for most Kiwis, we live in a pretty temperate climate.

Most of the year our temperatures are between 10 degrees and 30 degrees -- hardly extreme.

Such conditions are ideal for electric vehicles so today's column is probably not a subject that will be worrying many inhabitants of Godzone.

However, those in other countries might not be so lucky. In parts of Europe and the UK right now, a heatwave is driving daily temperatures to well over 40 degrees and in many Northern countries, winter lows are the stuff of legend.

So just how effective are EVs in these extremes of temperature?

Well interestingly, the country with the most EVs per capita, Norway, is also one of those cold Northern nations.

In fact, the top three countries for uptake of EVs (Norway, Iceland and Sweden) are all ice-bound in winter. (cite).

This would clearly indicate that cold temperatures do not make EVs impractical at all.

However, it is acknowledged that EVs do lose (sometimes significant) range in very cold temperatures, for a number of reasons.

Firstly, the batteries themselves perform far less efficiently at low temperatures and this is why "better" EVs have built-in battery "preconditioners" (aka: heaters) to ensure they are closer to optimum temperature.

The other range-killer in winter is the need to provide heating for the passengers. In very simple systems this can be little more than a fan and a resistive heater. Unfortunately such a set-up is far from efficient so some manufacturers are now switching to heat-pumps which also act as air conditioning in summer. Even these however, can suck significant amounts of energy from that valuable energy stored in the battery.

It's worth noting also that in the Nordic countries, infrastructure seems to be well set up for cold weather operations. Most dwellings have plenty of insulation and perhaps even some heating in their garages so that vehicles don't get that cold overnight. Urban parking is also more likely to be a whole lot warmer than the Wilson's Parking garages we live with here in NZ.

So what about heat?

Well cold temperatures may hamper a battery's efficiency but high temperatures can kill those batteries.

It's also a whole lot easier to heat a cold battery than it is to cool a hot one.

For this reason, I expect that making an EV your daily driver will be far more problematic in extremely hot countries than in the colder ones. Perhaps this is one of the reasons we don't see a huge uptake of EVs in such places yet.

The effect of temperature on battery longevity became very apparent when some versions of Nissan's Leaf started seeing battery failures long before their anticipated working life was over. Unlike most modern EVs, these Nissans relied solely on air to cool their battery packs and in some cases, overheating shortened the battery life significantly.

Most modern EVs have quite sophisticated and effective battery cooling solutions, usually reliant on liquid coolant and radiators to get rid of excess heat. However, this can only work well when the outside temperature is lower than that of the battery and on a very hot day, driving on black tarmac, this might not be the case.

Even on days when the measured temperature might be around 40 degrees, the air immediately above a hot road surface can be significantly higher than that. If an EV's radiators are being blasted with 55-60 degree air then they can't bring the battery temperature any lower than that. This can mean reduced power, reduced range and a risk of battery damage.

Of course ICEs can also suffer in extreme heat and cold. Extreme cold risks freezing the coolant in the engine and thus cracking the radiator or block whilst extreme heat can cause the coolant to boil. The latter is even more likely in turbo-charged vehicles that may be driven hard for extended periods and then caught in slow moving traffic.

The general rule of thumb is that vehicles and electronics are most happy at temperatures where you're most happy. With climate change well under way, this could mean that those designing EVs and electronic devices such as smartphones, computers etc, will have to give far more consideration to cooling solutions. Unless this is done, reliability and longevity may be compromised.

Carpe Diem folks!

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