EV Discussion thread

Martyn1981

Talking of regen, I see we are now recycling articles from a year ago. 

JKenH

Martyn1981 said:

Talking of regen, I see we are now recycling articles from a year ago. 

Fair cop! Don’t know why those articles came up when I went on the Electrek site.

Edit:  I’ve now worked out what happened. I had accidentally clicked on the Exclusives tab and the page was headed “Latest” - it was the third story down and that story contained a link to the second story. https://electrek.co/feature/exclusives/

JKenH

Martyn1981 said:

michaels said:

JKenH said:

JKenH said:

I am amused by some of the calculations adopted by some organisations to push the efficiencies of EVs. In this particular example 10% of the energy is lost in charging, another 18% in the drivetrain , 3% in power train and cooling and 0-4% in auxiliary electric use. Regeneration then recovers 22% leaving a net loss of 9-13%. 

Losses incurred in charging are lost forever as are drivetrain, powertrain and electrical losses. Regeneration cannot recover these losses. Those 31-35%losses are gone forever. Neither can regeneration recover losses due to rolling resistance or drag. Regeneration can only convert kinetic energy back into electricity, i.e. recharging the battery by deceleration or by converting the kinetic energy acquired descending a hill and to acquire that kinetic energy you have either had to use the battery to get the car up to speed or to the top of a hill. 

Electric Vehicles Are Way, Way More Energy-Efficient Than Internal Combustion Vehicles

https://www.motortrend.com/news/evs-more-efficient-than-internal-combustion-engines/

And even the EPA make the same mistake - an EV can be potentially 100% efficient despite losing 10% in charging the battery!

https://www.fueleconomy.gov/feg/atv-ev.shtml#:~:text=An%20EV%20electric%20drive%20system,All%2DElectric%20Vehicles%20for%20details.

I wonder if these are basic maths errors (it is journalism so not that unlikely) or a deliberate attempt to mislead?

Obviously the recovered percentages are as a proportion of the amount of energy providing propulsion.

The energy efficiency case for EVs over fossil fuel are undeniable so it would seem pretty silly to attempt obvious FUD which will just be jumped upon by opponents who will attempt to use it to discredit the whole concept.

Can I ask what your concern is? Maybe I'm being stupid, but all of the charts explain how much energy is put to the road. They aren't about efficiency, when driving, which is where over unity and exceeding 100% would be an issue.

So, with regen, in an extreme situation of acceleration, brake, acceleration, brake, you can of course put more energy to the road, even more than equal to the original 100% in the battery, since you are re-using the same energy.

For instance, let's imagine an extreme situation, with a BEV with a small battery. So the battery has 100% energy when you start driving. You then accelerate to 30mph, and drive a short distance. This has resulted in 14% of the battery energy being put to the road. 4% has gone as distance travelled, and the remaining 10% is kinetic energy in the vehicle travelling at 30mph. Now, the lights ahead go red, you just can't make it through, and regen to a stop, at say 40% efficiency (just an example figure), so of that 10% energy, 4% goes back into the batts.

The battery is now down to 90%. And of you pop again, quickly reach 30mph and drive a short distance, but have to stop at a roundabout. Same figures again, 14% (of the original 100%) is put to the road, taking you down to 76%, but regen takes you back to 80%. [At this point cumulatively you've put 28% to the road, but crucially, you've gotten 8% back.]

On we go, with pedestrian lights, someone turning right, but having to wait for a gap, a T junction, another roundabout, zebra crossing and so on.

After 7 of these examples, we've put 98% of the original energy to the road, but have 30% remaining in our battery.

I appreciate this is a very silly example, but the point is, whilst the efficiency of this trip is very low, and we won't get great mileage from our full battery, the point has always been to compare the energy put to the road - and a BEV (also a HEV and PHEV*) can actually re-use (regeneration) some of the energy more than once, whereas an ICE converts the kinetic energy into heat and brake wear, when it has to stop quickly.

Hope this makes sense, and please don't worry too much about the specific numbers. I appreciate the upper limits  may look like a trick, but it simply reflects the additional benefits of an EV over an ICE, when stop and go driving is involved.

*This will of course depend on the size of the motor and battery, since smaller units won't be able to manage peak loads as high as a BEV (typically), but gentle regen will help.

Comment deleted as in poor taste 

Ken

JKenH

This was the story I had heard and was seeking more information on when I went to the Electrek site. Tesla cut prices in the U.S. in December. No sign of any price cuts here.

Tesla cuts Model 3 and Model Y prices in China amid fierce competition

Tesla today lowered the prices of all two versions of the Model 3 by nearly 6 percent, and two of the three versions of the Model Y by nearly 3 percent.

https://cnevpost.com/2024/01/12/tesla-cuts-model-3-y-prices-in-china/

Grumpy_chap

This idea of expressing efficiency as greater than unity is deceptive and not conducive to furthering the cause in a rational way.

The only edge case I can see where a journey could achieve an efficiency greater than unity would be a purely down-hill journey.  Even then, it would not be a true efficiency greater than unity as the potential energy at the start of the journey has been lost by the end of the journey - gravity won't push the car back to the start.

Martyn1981

Grumpy_chap said:

This idea of expressing efficiency as greater than unity is deceptive and not conducive to furthering the cause in a rational way.

The only edge case I can see where a journey could achieve an efficiency greater than unity would be a purely down-hill journey.  Even then, it would not be a true efficiency greater than unity as the potential energy at the start of the journey has been lost by the end of the journey - gravity won't push the car back to the start.

Correct, and it can make your head spin a bit, trying to think about the two different issues here - efficiency or energy to the road/wheels.

The good news, is that in a simple example, we see the BEV being about 3x as efficient in terms of extracting and applying the energy from its fuel tank to the road.

But then as we consider driving conditions that have more acceleration and braking elements, we will see the efficiency of both the BEV and ICE fall, since kinetic energy will be wasted for the ICE, and only around 40% returned for the BEV. [Probably also need to mention here that as the ICE accelerates back up to speed, it needs to use lower gears, at lower efficiency, v's the single gear (typically) for the BEV, and the high torque delivery nature of an electric motor, even at low speeds.]

In that less efficient driving situation, the 'comparative' efficiency of the BEV will be improved from the regen braking, over the ICE. And that's also where the headspinning part comes in, since the BEV is actually seeing reduced levels of efficiency, but at the same time raised levels of energy to the road, as some of the same energy gets used over and over.

I do appreciate that reapplying the same energy, over and over, via regen, can look like a trick, so perhaps the best way to think about it, is simply that the BEV is more efficient than an ICE, especially when regen v's braking is involved.

Plus, you gotta love one pedal driving. 


Edit - Thought of an example that might better clarify the difference between efficiency and energy to the road, a bit like the busy road driving I mentioned before, but taken to the extreme (always worth testing to the extreme, as Z taught me).

So, we take the BEV to a dragstrip. Very hard acceleration, then heavy regen at the end, and return for multiple passes.

This will mean extremely inefficient driving, no chance of getting 75%, nowhere close, just a fraction.
But on each run, the BEV will put a huge amount of energy to the wheels, before reclaiming some of it.
If we add up the total amount of energy that reaches the wheels and the road, from run after run, it may add up to more than the energy capacity of the batts. But of course this isn't over-unity, as some of that energy, was 'picked back up' off the road, and put back into the battery.

That drag racing day, will result in extremely low efficiency, but high energy to the road, which is where a mental contradiction can reasonably be expected to make us go 'what!'

For an ICE doing this, we will see huge amounts of energy being applied to the road, but without regen it can't be reclaimed and re-used. Also, the comparative efficiency of the BEV v's the ICE may rise higher again, thanks to the regen, but overall will still be woefull.

I apologise, if I'm making your head spin more than the drag cars wheels. But this is sort of fun.

Reed_Richards

thevilla said:

In the last few months this thread has become a fossil fuel promotion. I'm out!  Bye.

Somebody here with a Tesla should really start a Tesla-only thread.  There is a lot of content here that is specific to Tesla and a model-specific thread should mitigate against discussions on other types of vehicles.      

Martyn1981

Sorry, couldn't resist this for utter excess, and presumably horrific efficiency. My brain's not even sure if energy to the road counts, if you don't actually go anywhere. 

And does the term 'tank turn' apply almost perfectly to Mercedes EV equivalent of the G-Wagon!

[Just to say, the vid may show a length of 0:00, I had to press play a couple of times for it to kick in. M.]

Watch The Electric Mercedes G-Class Do Synchronized Spins On The Vegas Strip

A tank turn – or, a rapid spin in place driven by electric motors – is one of the most incredible things an EV can do. Mercedes-Benz added to the spectacle by getting four EQG prototypes to do synchronized 360-degree turns, or G turns as the German brand calls them, on the Las Vegas Strip during CES.

The EQG can accomplish tank turns thanks to using an electric motor to drive each wheel. By applying forward or reverse power to each corner, depending on what side of the vehicle you're looking at. This allows the SUV to rotate on its axis.

michaels

Weirdly although this was allegedly filmed round about the 10th Jan on visibly wet tarmac, the Las Vegas weather records suggest it has not rained at all this month....

Netexporter

I assumed they deliberately wetted the road, otherwise you wouldn't have seen anything through the tyre smoke.