The Age of Electric Vehicles

[dyqik]

https://jech.bmj.com/content/early/2024 ... 024-221902

During 2013–2017, casualty rates per 100 million miles were 5.16 (95% CI 4.92 to 5.42) for E-HE vehicles and 2.40 (95%CI 2.38 to 2.41) for ICE vehicles, indicating that collisions were twice as likely (RR 2.15; 95% CI 2.05 to 2.26) with E-HE vehicles.

Looks like they need to be made noisier - to protect pedestrians.

Another factor is that EV/HEs might be that they have longer braking distances. I've been unable to find out whether this is in fact the case, there seems to be some disagreement about it.

They shouldn't have worse braking distance than the highway code etc. suggests. Separately, emergency braking distance is a function of tires and suspension, and driver alertness, not drive train type. Weight only comes into it if the tires and brakes don't match up to vehicle weight.

The use of high efficiency tires might increase stopping distances, but so does worn tires, etc.. Against this, most EVs include collision avoidance driver assistance features that older ICE vehicles don't. And noise from passenger vehicles doing 30 mph is at least as much road noise of tires on road as engine noise. It's only at low speed that engine noise is important - when fatalities are much less likely.

But for older electric hybrid vehicles in the 2013-2017 time frame, I suspect that there's a confounding factor of the kind of people who drove those vehicles vs the general driving population. Priuses, etc. have a particular image and market segment they includes quite a few older people, as well as taxi usage.

[Woodchopper]

https://jech.bmj.com/content/early/2024 ... 024-221902



Looks like they need to be made noisier - to protect pedestrians.

Another factor is that EV/HEs might be that they have longer braking distances. I've been unable to find out whether this is in fact the case, there seems to be some disagreement about it.

They shouldn't have worse braking distance than the highway code etc. suggests. Separately, emergency braking distance is a function of tires and suspension, and driver alertness, not drive train type. Weight only comes into it if the tires and brakes don't match up to vehicle weight.

The use of high efficiency tires might increase stopping distances, but so does worn tires, etc.. Against this, most EVs include collision avoidance driver assistance features that older ICE vehicles don't. And noise from passenger vehicles doing 30 mph is at least as much road noise of tires on road as engine noise. It's only at low speed that engine noise is important - when fatalities are much less likely.

But for older electric hybrid vehicles in the 2013-2017 time frame, I suspect that there's a confounding factor of the kind of people who drove those vehicles vs the general driving population. Priuses, etc. have a particular image and market segment they includes quite a few older people, as well as taxi usage.

I suspect that typical usage patterns maybe part of the explanation. The study compared accidents per million miles of driving. During the period being studied range anxiety meant that electric cars were more likely to be used on short urban journeys whereas ICE cars were more likely to be used on long cross country journeys. Most accidents are in urban areas where people live, and not on motorways etc used for long distance driving, and engine noise will also affect accidents at low speeds, but not motorway accidents. The difference between electric and fossil fuel cars may reduce over time as electric cars are now used more frequently for long distance journeys.

[dyqik]

The range part wouldn't apply to hybrids though (my 2010 Prius gets 450-500 miles range on highways).

[FlammableFlower]

New EVs definitely have to have a sound emitted if the vehicle is going slowly - although interestingly, the government regulations around this state:

From 1 July 2019, all manufacturers must install a system in new types of quiet electric and hybrid electric vehicles. Sound generators will produce a specified level of noise when they are reversing or running below 20 km/h (about 12mph). The sound generated will be similar to that made by a conventional engine and can be temporarily deactivated by the driver if judged necessary.

Mine kicks in below 19 mph. Above that the road noise is pretty much equal to any other ICE vehicle. I can't switch it off temporarily, but in my previous, 2018 Zoe, I could.

Just conjecturing, there are two possible issues, both around problems with familiarity with ICE vehicles not translating to EV - one being the speed of acceleration; I generally keep mine in Eco mode as I've found it's otherwise ridiculously easy to spin the wheels pulling away, but even then with Eco, the 0-30 acceleration is much better than most ICE vehicles. So yes, people do underestimate the time they have to pop across a road, for example.

The other issue is with familiarity with engine noise. We've had so much exposure to ICE vehicles that the sound of an engine is very familiar to people and so hearing that sound automatically gives a subconscious indication of a vehicle in proximity and taken into account. Whereas with EVs, even with the emitted noise, there's a lack of familiarity that might not necessarily have the same effect. My car has the "choir of damned" sound (as some have termed it, being choral and quite eerie) and it's pretty loud (my kids have complained about how it sounds from outside - e.g. when I'm arriving at home), but I definitely notice that if I'm approaching pedestrians from behind, and it's narrow/lot's of parked cars etc, then they often don't appear to take any notice until I'm in their peripheral vision. Seeing as it's definitely audible, I'm putting it down to a lack of association with proximity to a car.

I'm not convinced just being noisier will help.

However, there are other issues around noise - first, older EVs often don't have fitted noise generators and even those with them can be inconsistent. My neighbour's Tesla has no forward noise (it may be pre-2019), but will generate a sound when reversing. Whereas, my newer Zoe is the opposite - oddly it's silent in reverse, which I think is daft.

Overall, it seems like the government regulations and guidance aren't much cop.

[Gfamily]

The data is relatively old, and from a time when EVs were very much a minority, and with it based on casualties per 100k km, it's hard to know how they ensure that the km metrics are comparable.
For example, the 98% of the casualties were from ICE vehicles rather than EVs, so the EV casualty rate would come with higher uncertainty.
In the 'confounding factors' it suggests that young drivers (who present a higher risk of being involved in collisions) are more likely to drive EVs than the average driver, but that is based on 2023 data (regardless of the fact that asserting that over 40% of young drivers have EVs, seems improbable to me at least).

[bob sterman]

I suspect that typical usage patterns maybe part of the explanation. The study compared accidents per million miles of driving. During the period being studied range anxiety meant that electric cars were more likely to be used on short urban journeys whereas ICE cars were more likely to be used on long cross country journeys. Most accidents are in urban areas where people live, and not on motorways etc used for long distance driving, and engine noise will also affect accidents at low speeds, but not motorway accidents. The difference between electric and fossil fuel cars may reduce over time as electric cars are now used more frequently for long distance journeys.

The study looked at urban and rural driving separately.

E-HE vehicles were three times more dangerous than ICE vehicles in urban environments (RR 2.97; 95% CI 2.41 to 3.7).

[Woodchopper]

I suspect that typical usage patterns maybe part of the explanation. The study compared accidents per million miles of driving. During the period being studied range anxiety meant that electric cars were more likely to be used on short urban journeys whereas ICE cars were more likely to be used on long cross country journeys. Most accidents are in urban areas where people live, and not on motorways etc used for long distance driving, and engine noise will also affect accidents at low speeds, but not motorway accidents. The difference between electric and fossil fuel cars may reduce over time as electric cars are now used more frequently for long distance journeys.

The study looked at urban and rural driving separately.

E-HE vehicles were three times more dangerous than ICE vehicles in urban environments (RR 2.97; 95% CI 2.41 to 3.7).

Well that should teach me not to idly speculate

[TopBadger]

So - what does the hivemind / BEV owners think of heat pumps?

I'm looking at buying (well, PCP'ing) a new BEV as our second car and one of the options is a heat pump for £1100. I'm not sure the additional efficiency is worth £1100 given we'll likely precondition the cabin whilst plugged in and won't be using the car for long runs (we'll stick to the diesel for that).

What say you, good folks?

[Grumble]

So - what does the hivemind / BEV owners think of heat pumps?

I'm looking at buying (well, PCP'ing) a new BEV as our second car and one of the options is a heat pump for £1100. I'm not sure the additional efficiency is worth £1100 given we'll likely precondition the cabin whilst plugged in and won't be using the car for long runs (we'll stick to the diesel for that).

What say you, good folks?

I have a heat pump, it wasn’t a primary reason for choosing the car and it came as standard so I’m not sure I have an opinion. It might help the car hold its value though, it’s definitely a useful option.
Why would you precondition the car while plugged in? If you can charge using an off-peak tariff the battery is filled with cheap electricity - so use that, not the expensive peak rate that’s likely to apply at the time you want to precondition.

[IvanV]

So - what does the hivemind / BEV owners think of heat pumps?

Many vehicles have heat pumps, and have done for many years. The more common name for them is air conditioners.

But typically they can operate in both directions either to heat or cool the vehicle interior.

[lpm]

Complete waste of money in England.

Adds a trivial amount to winter range. But how often will you ve going beyond range in the winter?

The improvement in efficiency isn't worth much. It takes a lot of 7p kWhs to repay £1,000.

[TopBadger]

Why would you precondition the car while plugged in? If you can charge using an off-peak tariff the battery is filled with cheap electricity - so use that, not the expensive peak rate that’s likely to apply at the time you want to precondition.

I have Solar which I export to the grid so am on a tariff that doesn't have off-peak. I don't know of any tariffs that allow both cheaper off-peak usage and export... it seems to be they offer one or the other. Or it was last time I looked.

I found a stat somewhere that suggests heat pumps increase range from 2.9km/kWh to 3.2km/kWh on average. I.e. about a 10% gain in range (or reduction in charging cost - depending on how you want to look at it).

If we travel 8,000 miles or ~13,000km / yr that give a saving of around £110/yr with the heat pump vs without - assuming it's needed all the time. So, the real saving is less than that.

I.e. the payback time is over 10 years on a car whose battery is warrantied for less than that.

Therefore I'm not convinced spending £1100 is worth it, and I've no idea how much it helps the residual value.

[TopBadger]

Complete waste of money in England.

Adds a trivial amount to winter range. But how often will you ve going beyond range in the winter?

The improvement in efficiency isn't worth much. It takes a lot of 7p kWhs to repay £1,000.

Right - that's where I'm leaning...

[IvanV]

Complete waste of money in England.

Adds a trivial amount to winter range. But how often will you ve going beyond range in the winter?

The improvement in efficiency isn't worth much. It takes a lot of 7p kWhs to repay £1,000.

Right - that's where I'm leaning...

That's fair enough in terms of heating the vehicle.

But do you want chilling in the summer? That's the main reason air conditioners, I mean heat pumps, are fitted.

I do wonder whether this is some marketing bollox. Does the car supplier offer some different price for an "air conditioner" as opposed to a "heat pump", without telling you they are same thing?

[Grumble]

An air conditioner is not the same thing as a heat pump, not in these terms anyway. A heat pump in this sense means one that can take out or add heat to the vehicle, so it can run in both “directions”. AC only takes heat out.

[Martin Y]

Honestly, my main use for air conditioning is demisting the windows on rainy days when we get in the car wearing wet coats and everything instantly fogs up.

[TopBadger]

An air conditioner is not the same thing as a heat pump, not in these terms anyway. A heat pump in this sense means one that can take out or add heat to the vehicle, so it can run in both “directions”. AC only takes heat out.

Right - the car comes with A/C for cooling (which is a heat pump), but needs a separate heat pump for heating. Why they don't use a reversible one is beyond me (or perhaps that's what the £1100 is for, upgrading the unit to a reversible one).

[IvanV]

An air conditioner is not the same thing as a heat pump, not in these terms anyway. A heat pump in this sense means one that can take out or add heat to the vehicle, so it can run in both “directions”. AC only takes heat out.

Right - the car comes with A/C for cooling (which is a heat pump), but needs a separate heat pump for heating. Why they don't use a reversible one is beyond me (or perhaps that's what the £1100 is for, upgrading the unit to a reversible one).

My 20-yr-old Citroen Berlingo TDi, which I paid £10k for new in 2005, hardly a posh car, has a bidirectional A/C for both heating and cooling. So I assumed that was just normal. Unfortunately it did stop working about 3 years ago, but for most people that would be a long enough accessory life.

[Opti]

An air conditioner is not the same thing as a heat pump, not in these terms anyway. A heat pump in this sense means one that can take out or add heat to the vehicle, so it can run in both “directions”. AC only takes heat out.

I have dual inverter air conditioners in my house. I've been pretty impressed by how inexpensive it is to run. Particularly on the heating front.

Mains gas is pretty much unheard of here, it's generally supplied in (subsidised) bottles.
Quite a few people here use bottled gas portable heaters in winter. It works out pretty cheaply, but my word those things are ugly. Then there's the ridiculous condensation they cause unless you have good ventilation. Most Spanish houses don't have adequate ventilation for the winter.

My A/C also functions as a pretty good dehumidifier.

I wish the Spanish government would massively increase their solar generation - but Nimbyism is a thing everywhere.

[shpalman]

An air conditioner is not the same thing as a heat pump, not in these terms anyway. A heat pump in this sense means one that can take out or add heat to the vehicle, so it can run in both “directions”. AC only takes heat out.

Right - the car comes with A/C for cooling (which is a heat pump), but needs a separate heat pump for heating. Why they don't use a reversible one is beyond me (or perhaps that's what the £1100 is for, upgrading the unit to a reversible one).

My 20-yr-old Citroen Berlingo TDi, which I paid £10k for new in 2005, hardly a posh car, has a bidirectional A/C for both heating and cooling. So I assumed that was just normal. Unfortunately it did stop working about 3 years ago, but for most people that would be a long enough accessory life.

My >20-yr-old Mazda MX-5 has a heater driven by the engine's cooling water, and an airconditioning compressor, so that I can have hot dry air for demisting the windows if I switch on the aircon with the heater turned up. The air is definitely less hot, though, as well as being drier, so it's not actually a reversed heat pump.

I presume that since an electric car's motor(s) don't need water cooling, that there's the necessity to either use resistive heating elements, or a heat pump, to heat the car, and this is the question we're discussing.

[dyqik]

Electric car batteries, inverters and motors do need cooling, although forced air is used as well as liquid cooling.

For example, our now dead 2010 Prius* had a liquid cooled inverter. I suspect there's more liquid cooling in hybrids, since you are installing a radiator for the ICE anyway, and you have to pack the electrical components alongside hot ICE components.

*I wrote it off last month. We're getting a RAV4 Prime plugin instead.

[nekomatic]

I presume that since an electric car's motor(s) don't need water cooling, that there's the necessity to either use resistive heating elements, or a heat pump, to heat the car, and this is the question we're discussing.

Yeah, that’s my understanding. Although I’m not completely clear on whether the heat pump is there to make the cabin heating more efficient, or to make the battery’s temperature control more efficient (or both).

I have never been in the financial position where either buying or PCPing a new car makes any sense, so up till now my attitude to any newfangled car technology has been ‘tell me in about four years time’. However my employer has just launched a leasing scheme for electric cars via salary sacrifice which looks like it might actually be worth it, so all of a sudden I find myself interested in this sort of stuff.

[Matatouille]

Yeah, that’s my understanding. Although I’m not completely clear on whether the heat pump is there to make the cabin heating more efficient, or to make the battery’s temperature control more efficient (or both).

Generally the latter. Often in markets where winters are harsher than the UK (Norway, Canada etc) you'll find that a given model of EV will have heat pump in the basic spec rather than a cost plus option as they usually are in the UK. Battery thermal management being more efficient at particularly cold temperatures can have a dramatic impact on range.

I took the view (buying a second hand EV) that heat pump was not to me worth paying more than £200 extra for over the likely life of the vehicle in my pattern of use, so did not bother limiting the options to include it and ultimately got one without.

The economics flip fairly dramatically if you think you might do a lot of driving through winters, using public chargers when cost can be 40-85p/kWh depending on charging network and time of day. I doubt many users fit this travelling sales rep use case though.

[TopBadger]

Question on practicalities for EV owners - do all public charging stations have their own cable to plug in? Or do you have to cart a cable around with you on longer journeys?

[Grumble]

Question on practicalities for EV owners - do all public charging stations have their own cable to plug in? Or do you have to cart a cable around with you on longer journeys?

You have to take a cable, not all chargers have a cable. All the high speed ones do, but not the cheaper lower speed ones.