The sweet spot

[Everest]

I was musing over the thread about IM5/6 consumption of around 2.8 miles/kWh and wondering if anyone has done a study to find the sweet spot in terms of battery capacity vs. range - or at least a graph plotting the relationship graphically.

In other words, are we really gaining much by increase of capacity beyond say 80kWh or is it just a law of diminishing returns? Obviously a 100kWh vehicle will be heavier, so there will be a loss of efficiency. But then that vehicle will be more expensive and hence need to be bigger and more lavishly equipped to justify the price, which in turn will make it even less efficient.

 

[LenEV2016]

I was musing over the thread about IM5/6 consumption of around 2.8 miles/kWh and wondering if anyone has done a study to find the sweet spot in terms of battery capacity vs. range - or at least a graph plotting the relationship graphically.

In other words, are we really gaining much by increase of capacity beyond say 80kWh or is it just a law of diminishing returns? Obviously a 100kWh vehicle will be heavier, so there will be a loss of efficiency. But then that vehicle will be more expensive and hence need to be bigger and more lavishly equipped to justify the price, which in turn will make it even less efficient.

I don't think you can look further than Tesla for the sweet spot of range, efficiency and power.

Tesla model 3 LR rwd 79kwh usable and 360 miles range on average.

Lucid are up there also but not in the UK yet

 

[Gomev]

I have never had a Tesla and probably never will (purely for car reasons nothing else) but I do admire their efficiency.

 

[tsedge]

It's also possible that Tesla and Lucid are pushing efficiency beyond the economic optimum. Both companies are technology-obsessed to the point of innovation before their existing technologies have matured in adoption.

The market will determine this over time. To me, we have some established norms already:

- Sub-40kWh: used for city cars and/or cheap end of the market. Perfect for a second car that doesn't need to do long journeys. Typically up to 150 miles of range (dependably).

- 40-70kWh: the sweet spot for a family car, with long journey capability and enough range (200-300 miles) for the vast majority of the population.

- 70-100kWh: big car territory, including SUVs, executive saloons/hatchbacks. Big battery partly for range (300-400 miles) but mostly for weight and performance.

Tesla's batteries are smaller than average for the equivalent car, because of their great efficiency, but this doesn't mean that's where the market will settle.

On the contrary, Tesla are likely to have taken it farther than most manufacturers will, so I'd expect the normal to settle somewhere above the average Tesla pack size.

We should remember that the best technology/efficiency almost never wins in the long term. It's the "good enough" all round offering at a low price that tends to win out.

Edit: This is also why ICE cars don't on average do 80+mpg. That would be possible technically, but it isn't where the market settled.

 

[MG Clive]

That's a very comprehensive analysis @tsedge

 

[Everest]

Great points. I suspect that , over time, your 40-70kWh range (possible 50-70kWh) will become the most common when it can be coupled with even faster charging times. Having said that, a larger battery pack will always be able to be charged (in terms of range) faster than a smaller one as each cell needs less energy put into it for similar distance.

 

[LenEV2016]

70-75 kWh 300 + miles is optimum for me

 

[Gomev]

It's also possible that Tesla and Lucid are pushing efficiency beyond the economic optimum. Both companies are technology-obsessed to the point of innovation before their existing technologies have matured in adoption.

The market will determine this over time. To me, we have some established norms already:

- Sub-40kWh: used for city cars and/or cheap end of the market. Perfect for a second car that doesn't need to do long journeys. Typically up to 150 miles of range (dependably).

- 40-70kWh: the sweet spot for a family car, with long journey capability and enough range (200-300 miles) for the vast majority of the population.

- 70-100kWh: big car territory, including SUVs, executive saloons/hatchbacks. Big battery partly for range (300-400 miles) but mostly for weight and performance.

Tesla's batteries are smaller than average for the equivalent car, because of their great efficiency, but this doesn't mean that's where the market will settle.

On the contrary, Tesla are likely to have taken it farther than most manufacturers will, so I'd expect the normal to settle somewhere above the average Tesla pack size.

We should remember that the best technology/efficiency almost never wins in the long term. It's the "good enough" all round offering at a low price that tends to win out.

Edit: This is also why ICE cars don't on average do 80+mpg. That would be possible technically, but it isn't where the market settled.

I'm not sure at all what you mean by pushing efficiency beyond the economic optimum. Motor efficiency is motor efficiency regardless of battery or vehicle size. Given a choice of a more or a less efficient motor I know which I would choose.

 

[tsedge]

I'm not sure at all what you mean by pushing efficiency beyond the economic optimum. Motor efficiency is motor efficiency regardless of battery or vehicle size. Given a choice of a more or a less efficient motor I know which I would choose.

Market economics - i.e. what most people are willing to pay for. Most people don't make their decisions based on narrow concerns of efficiency, it is a combination of how the car looks, comfort, tech, practicality, price and efficiency.

We could have all been driving around in heavily streamlined highly aerodynamic lightweight ICE vehicles doing 80+ mpg 20 years ago. Basically like GM's EV1 (or VW's XL1) but with a small petrol engine.

But it turns out people like a wide variety of car looks (many not aerodynamic), safety systems that typically add a lot of weight, big wheels that look good although harm fuel economy and ride, much more performance than they can use etc... etc... and so that's what the market provides.

 

[Gomev]

Market economics - i.e. what most people are willing to pay for. Most people don't make their decisions based on narrow concerns of efficiency, it is a combination of how the car looks, comfort, tech, practicality, price and efficiency.

We could have all been driving around in heavily streamlined highly aerodynamic lightweight ICE vehicles doing 80+ mpg 20 years ago. Basically like GM's EV1 (or VW's XL1) but with a small petrol engine.

But it turns out people like a wide variety of car looks (many not aerodynamic), safety systems that typically add a lot of weight, big wheels that look good although harm fuel economy and ride, much more performance than they can use etc... etc... and so that's what the market provides.

Very true, however you can put the same efficient Tesla motor in all of those or you could put a less efficient one in. My choice would be for the Tesla variant.
Tesla car batteries vary between roughly 50-100kWh and body shapes for S,3 X and Y, but still an efficient motor. Why would you choose a less efficient one given a choice ?

 

[tsedge]

Very true, however you can put the same efficient Tesla motor in all of those or you could put a less efficient one in. My choice would be for the Tesla variant.
Tesla car batteries vary between roughly 50-100kWh and body shapes for S,3 X and Y, but still an efficient motor. Why would you choose a less efficient one given a choice ?

Well, everyone will have a different answer I suppose, but I don't base my car buying decisions on efficiency. I didn't buy an MG4 because it was the most efficient. In fact it was distinctly average even at the time. But it was efficient enough and ticked many other boxes that were more important.

If you are talking about manufacturers, then cost is the usual reason they don't go the most efficient route. Small cheap older-tech motors do the job. Tesla motors are not readily available for other makers to use anyway, they are not on the open market.

I'm not arguing manufacturers cannot make more efficient cars - they can. I'm arguing market economics will dictate that they (mostly) won't, at least no more than they need to in order to compete with most other makers.

 

[Gomev]

Well, everyone will have a different answer I suppose, but I don't base my car buying decisions on efficiency. I didn't buy an MG4 because it was the most efficient. In fact it was distinctly average even at the time. But it was efficient enough and ticked many other boxes that were more important.

If you are talking about manufacturers, then cost is the usual reason they don't go the most efficient route. Small cheap older-tech motors do the job. Tesla motors are not readily available for other makers to use anyway, they are not on the open market.

I'm not arguing manufacturers cannot make more efficient cars - they can. I'm arguing market economics will dictate that they (mostly) won't, at least no more than they need to in order to compete with most other makers.

And I totally agree with that sentiment, however I can't agree that making something like a motor more efficient is pushing efficiency beyond the economic optimum. As the motor does not affect anything other than the cost of it in a vehicle are Tesla motors so much more expensive than others to the extent that it is the overriding cost of the car. Hard to know since we can't buy the motor new on it's own.

 

[LenEV2016]

It's a good debate and a point I've raised in the IM threads about how we are just chucking huge batteries in huge heavy cars and claiming fantastic ranges, the reality is we all know we are not getting those ranges, for a variety of reasons,
At the moment this is the cheapest option for some manufacturers.

As I've said previous the balance has to tip the other way at some point as the way the UK government is going I think the day is fast approaching where cars over a certain weight are going to be massively taxed in some form or another.
We have already seen it in Cardiff with parking, anything over 2.1 tonne (I think) is paying more. There is already talk of other cities adopting that.
If Tesla can make bigger family sized cars under 2 tonnes then there is nothing stopping others.

 

[Bam Bam]

I was musing over the thread about IM5/6 consumption of around 2.8 miles/kWh and wondering if anyone has done a study to find the sweet spot in terms of battery capacity vs. range - or at least a graph plotting the relationship graphically.

In other words, are we really gaining much by increase of capacity beyond say 80kWh or is it just a law of diminishing returns? Obviously a 100kWh vehicle will be heavier, so there will be a loss of efficiency. But then that vehicle will be more expensive and hence need to be bigger and more lavishly equipped to justify the price, which in turn will make it even less efficient.

The more chargers there and the faster the charge speed the less you need additional battery. Range anxiety will drop as people get more used to EVs.

Bigger batteries do seem to correlate with faster charging speeds, though, so I can imagine ending up with "regular" cars being 40-60kWh and "long distance" cars being 60-85kWh.

In the US and Russia they might need larger batteries because there are larger differences between places and more extreme temperatures.

Things like Hummers and G-Wagens will need larger batteries because they weigh so much in the first place. Those aren't normal cars, though. They are inefficiency machines designed to demonstrate wealth through wastefulness.

 

[tsedge]

As I've said previous the balance has to tip the other way at some point as the way the UK government is going I think the day is fast approaching where cars over a certain weight are going to be massively taxed in some form or another.
We have already seen it in Cardiff with parking, anything over 2.1 tonne (I think) is paying more. There is already talk of other cities adopting that.

That's exactly it - there needs to be a forcing function to make manufacturers become more efficient. Right now, there doesn't seem to be and with the low cost to "fuel" EVs the normal economic pressure isn't there.

Perhaps it does need to come from government:

• Taxing weight (as you suggest)
• Efficiency or range affects tax bands
• Recycling obligations that incentivise smaller batteries

 

[Anon70]

I guess the other thing will have an impact are improvements in energy density. If you can halve the battery weight and store the same amount of energy you will improve efficiency.