As a ground vehicle gets bigger, its energy consumption to travel a given journey at high speeds (the speed range where you typically operate when needing range) tends to rise as the square of the increase in linear dimension, in proportion to the increase in frontal area. The volume of the vehicle meanwhile increases as the cube of the increase in linear dimension. This means a larger EV has more room for batteries in relation to its energy consumption, and from first principles the larger vehicle can achieve longer range.
We’ve been through this before. A large proportion of the mass of of an electric car, but a small proportion of its volume, is accounted for by its batteries. You could double the battery volume of a Tesla (with the batteries in the floor) and keep the cabin room the same, simply by making it 9cm taller. This would increase the frontal area by about 6-7%. (car height = 144cm; some of that will be ground clearance).
It’s not analogous to a steamship where you need a vehicle of a certain size in order to cross an ocean.
Indeed. It’s not really a volume issue for large vehicles, it’s a weight issue.
But if it were as simple as you make out, the EVs on the market today would not have such limited ranges that represent an enormous capability compromise compared to ICE vehicles. Instead we see numbers that are just about tolerable for average use, and those are the claimed ‘up to’ figures that no-one will ever achieve in the real world.
aart wrote:
Source?Maybe I’m an optimist by nature and only seem to stumble on articles like:
https://newatlas.com/science/lithium-metal-ev-battery-benchmark-density-stability/
The internet is full of puff pieces like that, promising a game-changing technology that’s just been discovered in just about every sphere of human endeavour. Do you believe those articles?
Graham wrote:
It isn’t acceptable for trucks to slow to e.g. 40mph because of disruption to other traffic,
But off the motorway they’re legally restricted to 40 mph in the UK.
The internet is full of puff pieces like that, promising a game-changing technology that’s just been discovered in just about every sphere of human endeavour. Do you believe those articles?
I’m still interested in your source that says that battery technology is leveling off. I’m asking an open question.
Who would have believed 20 years ago what actually happened to semiconductor capacity?
Who would have believed 20 years ago what actually happened to semiconductor capacity?
Wasn’t there some guy called Moore?
As for battery technology – there are all sorts of interesting things out there – lithium-air, sulphur-something, for all I know technetium-promethium. But the best anyone is willing to talk about is maybe a factor of 2. At some point you’re restricted by the fact that all those electrons have to go SOMEWHERE, and atoms are around 150 pm across, so there’s only room for so many of them.
And all of these new batteries are wonderful and world changing – except they explode on contact with air, or they can only be recharged three times, or… or… or…
@kwlf, small EVs of current design have very limited range because they have inadequate room for the required battery volume and people volume combined – because of simple scaling laws. It doesn’t matter where you add the volume from the point of view of energy storage, but you have to put it somewhere and the car gets bigger to achieve more range. Making it taller is not the best way to make the car bigger, as it needs to be. Tall, small SUVs get relatively poor fuel mileage for exactly the reason that they are pushing substantially bigger wall of air. Nor do you necessarily want to uniformly increase size of the car, even if the scaling laws provide a theoretical advantage in range, particularly in comparison to making it taller, because batteries cannot be uniformly distributed across a uniformly increased available volume. It might be best to make it longer with the same frontal area, as I suggested by mentioning streamlined trailers, in which case range at higher cruising speeds will increase despite higher weight and higher rolling resistance.
Range will similarly increase for in-town use, where frontal area and aero drag is not so much a factor in determining range and in both highway and city use there will be increased energy use at all times, associated with increased rolling resistance to carry around the heavier battery system at all times. You can’t drive reduce the weight of an electric vehicle by carrying a smaller fraction of the available energy storage.
I’m smiling because I travelled roughly 45 miles by car while completing this post, the second leg of a 90 mile round trip completely unanticipated when I got up this morning 
Silvaire wrote:
The best way to make the car bigger is not to make it taller. It might be best to make it longer with the same frontal area, as I suggested by mentioning streamlined trailers, in which case range at higher cruising speeds will increase despite higher weight and higher rolling resistance.
Personally I doubt it. The aerodynamics of vehicles with trailers tends not to be great, and the handling is no better. Alternatively if you make a vehicle longer, you increase skin friction, and also lose out on handling. Adding more batteries lower down would improve handling. Rather than adding a simple layer you could put them under seats and perhaps even keep the external dimensions of the vehicle the same. Obviously it would get considerably heavier as everything else got beefed up to cope with the weight. It would still weigh less than an SUV so I doubt that in itself would be a problem. It would be expensive.
I have toyed with the idea of electrifying my velomobile (one person vehicle weighing about 35kg) and doing Land’s end to John O’Groats on one charge (about 850 miles). I think it’s just possible – the limiting factor is a legal restriction on how much a pedal powered vehicle can weigh. Legally you have to pedal, and it would inevitably be a few times slower than a car. However, if you removed the legal restriction and added batteries with the difference in weight between myself and the heaviest rider the vehicle is rated for, you could go a lot further, a lot faster.
kwlf wrote:
I have toyed with the idea of electrifying my velomobile (one person vehicle weighing about 35kg) and doing Land’s end to John O’Groats on one charge (about 850 miles). I think it’s just possible
Calculate how far you could go if you were traveling at a useful speed, like 70 mph, instead of 15 mph 
Maybe 50 miles or 100 miles, allowing for the unchanged effect of rolling friction? Going slowly and nearly eliminating the squared versus speed effect of aero drag on range surely does increase the range of ground vehicles.
It doesn’t eliminate it; if anything it’s more apparent on a pedal powered vehicle, but I appreciate the point.
Google Maps suggests that 50mph is a more feasible speed for the journey, by car.
