Will EV's get even more efficient?

[dvs_dave]

Evanivitch said:

bmwmike said:

Evanivitch said:

Regarding weight, EVs have bidirectional motors so the majority of energy consumed through acceleration of a large mass is returned to the system through regeneration braking.

My bold - majority? Are you sure about that?

Yes. Yes.

Don't confuse acceleration of mass with other losses.

At lower speeds, for sure. However at higher speeds where aero drag is in play, much less of a proportion can be recovered as a chunk of it is being absorbed by drag. Another reason why variable speed busy motorway driving batters the range of an EV and is why coasting is often more efficient than always-on lift-off regen.

Edited by dvs_dave on Friday 8th July 03:07

[blearyeyedboy]

I look at vehicles like the Carver EV, Citroen Ami and others, and wonder if we'll get a divergence of personal transport:

Larger/spacious/long range vehicles Vs smaller/cheaper low speed urban vehicles for 1-2 people, the latter being more akin to a mobile phone subscription or pay-as-you-go rental than what we have now.

That way, efficiency gains will come indirectly by vehicles being used for purposes for which they're generally more efficient.

[dvs_dave]

blearyeyedboy said:

I look at vehicles like the Carver EV, Citroen Ami and others, and wonder if we'll get a divergence of personal transport:

Larger/spacious/long range vehicles Vs smaller/cheaper low speed urban vehicles for 1-2 people, the latter being more akin to a mobile phone subscription or pay-as-you-go rental than what we have now.

That way, efficiency gains will come indirectly by vehicles being used for purposes for which they're generally more efficient.

It’s possible. But if the SMART car is anything to go by, and that was the whole idea behind it, it’ll likely be a failure.

[GT9]

dvs_dave said:

At lower speeds, for sure. However at higher speeds where aero drag is in play, much less of a proportion can be recovered as a chunk of it is being absorbed by drag. Another reason why variable speed busy motorway driving batters the range of an EV and is why coasting is often more efficient than always-on lift-off regen.

Edited by dvs_dave on Friday 8th July 03:07

If you are using kinetic energy to overcome drag then you are avoiding battery drain to overcome drag, so I'm not really sure what point you were trying to make.

Of course coasting is better than regenerative braking, but that's hardly practical if it means crashing into the car in front.

Higher speeds batters range because BOTH drag energy and kinetic energy increase with a square law.

Given that regen is not 100% efficient, you lose marginally more kinetic energy over the same distance for a higher average speed.

Let's be honest though, by far the biggest battering of range is due to the constant drag loss over whatever distance you cover at high speed.

[otolith]

It would be interesting to compare energy in with energy usefully consumed over a typical mixed usage cycle - so essentially how many kJ were drawn from the grid and how many were used to overcome aero and frictional resistances. In other words, how far the system is from 100% efficiency. I suspect that would indicate that the remaining gains from improving the efficiency of the batteries and motors in charging, discharging, driving, and regenerating are relatively small, and remaining improvements are mostly in reducing the "usefully consumed" figure, most of which will be aero. Reduced mass will reduce rolling resistance a bit.

I think the focus will probably shift to reducing the environmental impact of manufacture.

[Griff74]

Glosphil said:

Wouldn't motors in the wheels greatly increase the unsprung weight & have an impact on ride quality? How much does a (say) 120hp electric motor (for 2 wheel drive) weigh?

The Fully Charged YT channel test drove a new prototype EV recently that has specially designed motors that fit inside the wheels to reduce friction losses etc, I don’t think sports car like handling was high on the designers priorities tbf so unsprung weight probably not a concern for them, but I agree yes it wouldn’t be great from a handling pov……

[GT9]

Griff74 said:

Glosphil said:

Wouldn't motors in the wheels greatly increase the unsprung weight & have an impact on ride quality? How much does a (say) 120hp electric motor (for 2 wheel drive) weigh?

The Fully Charged YT channel test drove a new prototype EV recently that has specially designed motors that fit inside the wheels to reduce friction losses etc, I don’t think sports car like handling was high on the designers priorities tbf so unsprung weight probably not a concern for them, but I agree yes it wouldn’t be great from a handling pov……

It was over a decade ago that Michelin developed an all-singing wheel that included the motor, a disc brake AND electronically controlled suspension all within the body of the wheel, google Michelin Active Wheel.

Continental acquired something similar from Siemens around the same time.

Nothing much heard since though, so I guess there are issues with durability and/or unsprung weight. Either that or the car manufacturers don't want to be committed to so much tech from a single supplier.

There is also the issue around tyre changes and the potential for damage to precision equipment when the wheel is removed by all and sundry.

[Evanivitch]

dvs_dave said:

Evanivitch said:

bmwmike said:

Evanivitch said:

Regarding weight, EVs have bidirectional motors so the majority of energy consumed through acceleration of a large mass is returned to the system through regeneration braking.

My bold - majority? Are you sure about that?

Yes. Yes.

Don't confuse acceleration of mass with other losses.

At lower speeds, for sure. However at higher speeds where aero drag is in play, much less of a proportion can be recovered as a chunk of it is being absorbed by drag. Another reason why variable speed busy motorway driving batters the range of an EV and is why coasting is often more efficient than always-on lift-off regen.

Edited by dvs_dave on Friday 8th July 03:07

Variable speeds means even though you can harvest the majority on regen, you're still losing the minority multiple times.

At higher fixed speeds then you're considering a different use case.

At higher speeds with deceleration the regen means your deceleration is faster than coasting and energy lost of parasitic loses (like drag) is smaller.

[GT9]

Evanivitch said:

At higher speeds with deceleration the regen means your deceleration is faster than coasting and energy lost of parasitic loses (like drag) is smaller.

But you've also covered less distance in that particular event so a for a fixed journey length it sort of balances out.

Kinetic energy increases with the square of the speed but drag power consumption increases with the CUBE of speed.

What this means is that in absence of any electrical or mechanical braking, drag will slow the car at a much higher rate of deceleration at higher speeds than at lower speeds, following an inverse square law.

Conversely, rolling resistance will slow the car at the same rate of deceleration regardless of speed.

It stands to reason then that you are more likely to require regenerative braking at lower speeds than at higher speeds, because drag works so much better as an airbrake the faster you go, and it is essentially 100% efficient in converting kinetic energy to drag energy that had to be overcome anyway.

The fundamental reason your range drops is because you chose to reach a higher speed in the first place, not so much because of how you choose to slow down.

[Panamax]

Do electric cars "waste" much energy? If not, there's very little scope to improve efficiency.

Economy, on the other hand, is something entirely different. Weight reduction and/or drag reduction will always deliver benefits.

[otolith]

Panamax said:

Weight reduction and/or drag reduction will always deliver benefits.

Weight reduction mostly delivers benefits when your strategy for slowing down is to take the car’s kinetic energy you have added to accelerate it (which is proportional to its mass) and turn it into heat. When you instead use it to recharge the battery, it’s less of an issue.

[GT9]

Panamax said:

Do electric cars "waste" much energy? If not, there's very little scope to improve efficiency.

Economy, on the other hand, is something entirely different. Weight reduction and/or drag reduction will always deliver benefits.

I suppose it depends on terminology really.

Is energy wasted by having a frontal area or drag coefficient higher than it needs to be?

Or tyres wider than they need to be?

One of the things that certainly makes a difference is if you can set a reasonably low (artificially limited) top speed, which is of course, what we are seeing from most manufacturers.

That allows the engineering programme to focus on efficiency improvements in several different areas relating to aero, drivetrain, tyres and cooling.

For a country like the UK, where our speed limits are under constant downward pressure and average journey distances are relatively short, what % of drivers would actually be compromised by a top speed of say 85 mph.

I get that it's a highly emotionally charged question, particularly for PHers, but I imagine sooner or later this sort of question is going to crop up in the relentless pursuit of efficiency.

[blearyeyedboy]

dvs_dave said:

blearyeyedboy said:

I look at vehicles like the Carver EV, Citroen Ami and others, and wonder if we'll get a divergence of personal transport:

Larger/spacious/long range vehicles Vs smaller/cheaper low speed urban vehicles for 1-2 people, the latter being more akin to a mobile phone subscription or pay-as-you-go rental than what we have now.

That way, efficiency gains will come indirectly by vehicles being used for purposes for which they're generally more efficient.

It’s possible. But if the SMART car is anything to go by, and that was the whole idea behind it, it’ll likely be a failure.

True. But more typical cars were cheaper to buy than EVs.

Much as the Fiat 500 mobilised a poor Italian nation after WW2, they may be a matter of necessity rather than desire.

[bmwmike]

GT9 said:

I suppose it depends on terminology really.

Is energy wasted by having a frontal area or drag coefficient higher than it needs to be?

Or tyres wider than they need to be?

One of the things that certainly makes a difference is if you can set a reasonably low (artificially limited) top speed, which is of course, what we are seeing from most manufacturers.

That allows the engineering programme to focus on efficiency improvements in several different areas relating to aero, drivetrain, tyres and cooling.

For a country like the UK, where our speed limits are under constant downward pressure and average journey distances are relatively short, what % of drivers would actually be compromised by a top speed of say 85 mph.

I get that it's a highly emotionally charged question, particularly for PHers, but I imagine sooner or later this sort of question is going to crop up in the relentless pursuit of efficiency.

Not just limiting top speed, but acceleration too - by reducing acceleration, which requires lots of amps, they can reduce the size of wiring/buses/controllers etc.

[GT9]

bmwmike said:

Not just limiting top speed, but acceleration too - by reducing acceleration, which requires lots of amps, they can reduce the size of wiring/buses/controllers etc.

It is true that acceleration is by far the biggest power demand for a speed-limited EV.

But by its very nature, this is a transient load.

If you design the motor and cables for a given constant power rating, then they will have a higher short-term rating, just by virtue of thermal mass.

Power electronic devices tend to have lower thermal mass, but to improve constant load efficiency it's often desirable to run them well within their thermal limits.

And then there's regen, if you have limited the accelerative power of the system, then you've also probably done that to the decelerative capability.

So you may be more reliant on mechanical brakes for emergency braking, admittedly that's not likely to be a common occurrence.

Anyway, what I'm getting is that in order to maximize constant load efficiency you will get a certain amount of transient load capability that might give you decent acceleration without the need to increase the size of all the bits.

[bmwmike]

GT9 said:

bmwmike said:

Not just limiting top speed, but acceleration too - by reducing acceleration, which requires lots of amps, they can reduce the size of wiring/buses/controllers etc.

It is true that acceleration is by far the biggest power demand for a speed-limited EV.

But by its very nature, this is a transient load.

If you design the motor and cables for a given constant power rating, then they will have a higher short-term rating, just by virtue of thermal mass.

Power electronic devices tend to have lower thermal mass, but to improve constant load efficiency it's often desirable to run them well within their thermal limits.

And then there's regen, if you have limited the accelerative power of the system, then you've also probably done that to the decelerative capability.

So you may be more reliant on mechanical brakes for emergency braking, admittedly that's not likely to be a common occurrence.

Anyway, what I'm getting is that in order to maximize constant load efficiency you will get a certain amount of transient load capability that might give you decent acceleration without the need to increase the size of all the bits.

Right, but by definition if we want to consume less energy overall, building slower EV's both in terms of top speed and max acceleration will contribute to lower overall consumption, simplify builds, reduce mass, etc.

[GT9]

bmwmike said:

Right, but by definition if we want to consume less energy overall, building slower EV's both in terms of top speed and max acceleration will contribute to lower overall consumption, simplify builds, reduce mass, etc.

Agreed.

What we've seen to date are EVs generally with a high battery capacity and high kerb weight. To get better market acceptance for their perceived shortcomings related to range, weight , involvement, etc., the cars come with sledgehammer performance to make up for this. High performance is an almost freebie by virtue of the battery size for these high capacity cars.

At some point in the not too distant future it will no longer be necessary to overcome the resistance towards EVs seen in the early days, which is borne mostly out of ignorance and bad information in my opinion. Then the performance will matter less as cost of ownership will be more important to mainstream buyers.

[OutInTheShed]

A few people mentioning kinetic energy.
By my o level physics, it looks like 0.35kWh energy in a 2 tonne mass doing 80mph.

So if you can keep your cruising speed for a few junctions of the M5, kinetic energy is not your biggest problem.

Around here, it's not flat.
Max 150m elevation on a typical A road route.
For 2 tonnes, I make that 0.8kWh

Some of my pushbike routes have 800m of climbing in a 20 mile ride.

Frequent up and down knocks the economy, particularly if you have traffic. If you can coast down hills and retain some speed at the bottom, it's not so bad.
In a queue of tourists who brake to 20 at the bottom it's significant.

The thing that's less easy to put a simple number to is the effect of corners and curves. How much extra drag due to the tyres etc turning the car? extra aero drag due to not going straight?

Driving style makes a big difference. I think my car revises its remaining range to refuel when the driver's seat is moved...

In my IC car of course town driving and idling are the killers of MPG.

[NerveAgent]

blearyeyedboy said:

I look at vehicles like the Carver EV, Citroen Ami and others, and wonder if we'll get a divergence of personal transport:

Larger/spacious/long range vehicles Vs smaller/cheaper low speed urban vehicles for 1-2 people, the latter being more akin to a mobile phone subscription or pay-as-you-go rental than what we have now.

That way, efficiency gains will come indirectly by vehicles being used for purposes for which they're generally more efficient.

Along the same lines I think we will potentially an increase in electric bikes, scooters, mopeds etc for some of those local journeys/commutes.

[DMZ]

I think I’m good with less efficiency, more battery, and more power. I’ve driven stuff like the ID3 and it’s [painfully] lethargic by EV standards. I guess I’m “stuck” in an ICE mindset but if an EV isn’t punchy then why bother? ICE is very good at lethargic too and you can drive them with zero hassle.

Speaking of that, Renault made a big song and dance about the new Megane E-tech’s efficiency with a lighter thinner battery and reduced cabling or whatever it was. And it turns out to be less efficient than the ID3 in the real world. I guess in reality it’s about aero mostly. I think the ID3 is nearly 200kg heavier.