Re: The Age of Electric Vehicles
Posted: Mon Jan 10, 2022 1:27 pm
A 50 litre tank of petrol contains enough energy to lift the Hoover dam up by about a foot (assuming 100% efficiency).
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Re: The Age of Electric Vehicles
Posted: Mon Jan 10, 2022 1:50 pm
OK, fine, half for the real world usable energy that gets translated into miles. It's energy measured in miles that everyone cares about. Not kWh.Grumble wrote: ↑Mon Jan 10, 2022 1:07 pmIf an EV battery contained half the amount of energy in a tank of petrol it would be able to go 800 miles.lpm wrote: ↑Mon Jan 10, 2022 12:05 pmI think people in general have very little idea how much energy it takes to shift 1.5 tons of car around. And very little idea on the amount of energy stored in a litre of petrol.
EVs battery packs are huge, for half the amount of energy in a tank of petrol.
This combines to make the general public pretty confused about what an EV needs and how to handle recharging.
Re: The Age of Electric Vehicles
Posted: Mon Jan 10, 2022 3:17 pm
Are you accounting for 70%+ of the petrol's energy being wasted as heat?Grumble wrote: ↑Mon Jan 10, 2022 1:07 pmIf an EV battery contained half the amount of energy in a tank of petrol it would be able to go 800 miles.lpm wrote: ↑Mon Jan 10, 2022 12:05 pmI think people in general have very little idea how much energy it takes to shift 1.5 tons of car around. And very little idea on the amount of energy stored in a litre of petrol.
EVs battery packs are huge, for half the amount of energy in a tank of petrol.
This combines to make the general public pretty confused about what an EV needs and how to handle recharging.
Re: The Age of Electric Vehicles
Posted: Mon Jan 10, 2022 3:31 pm
That was the idea. I believe EV’s tend to get the equivalent of, very roughly, 120-150 mpg.bjn wrote: ↑Mon Jan 10, 2022 3:17 pmAre you accounting for 70%+ of the petrol's energy being wasted as heat?Grumble wrote: ↑Mon Jan 10, 2022 1:07 pmIf an EV battery contained half the amount of energy in a tank of petrol it would be able to go 800 miles.lpm wrote: ↑Mon Jan 10, 2022 12:05 pmI think people in general have very little idea how much energy it takes to shift 1.5 tons of car around. And very little idea on the amount of energy stored in a litre of petrol.
EVs battery packs are huge, for half the amount of energy in a tank of petrol.
This combines to make the general public pretty confused about what an EV needs and how to handle recharging.
Re: The Age of Electric Vehicles
Posted: Mon Jan 10, 2022 4:24 pm
EV database, for my one, says 150 mpg equivalent for its real world range. The car's good to average for efficiency so 150 mpg is a reasonable guess for a typical EV.
Or for its official range 163 mpg "Rated Fuel Equivalent" or 185 mpg "Vehicle Fuel Equivalent". No idea what that means.
https://ev-database.org/imp/car/1532/Vo ... erformance
Or for its official range 163 mpg "Rated Fuel Equivalent" or 185 mpg "Vehicle Fuel Equivalent". No idea what that means.
https://ev-database.org/imp/car/1532/Vo ... erformance
Re: The Age of Electric Vehicles
Posted: Mon Jan 10, 2022 4:45 pm
I bought a used car with that add-on in Germany once (Nissan Maxima 3.0 V6, very nice for cruising and at a tiny price because nobody wants a 3-year-old V6). I had a garage but it was very useful if you parked the car outside for the length of a cold working day.
One memorable thing about it was the range of the remote control, which worked up to something like 500 metres. When I pressed the button before leaving the office I used to look around to see if anyone's hair was on end or their computer had rebooted.
Re: The Age of Electric Vehicles
Posted: Tue Jan 11, 2022 12:16 am
I’ve searched for those terms, including in my vague memories from having to read the actual WLTP a few years ago for a work thing, and the only place I can find them is on that website. Is it something they’ve made up? Bit naughty of them to list them under ‘WLTP’ if so.
Re: The Age of Electric Vehicles
Posted: Tue Jan 11, 2022 10:06 am
I actually managed to get a chargemaster thing to charge my car a couple of weeks ago! Previously they've just been silent sentinels of pointlessness.
The science really has moved on. It's amazing to witness.
The science really has moved on. It's amazing to witness.
Re: The Age of Electric Vehicles
Posted: Tue Jan 11, 2022 10:24 am
A BP Chargemaster? I call b.llsh.t.
Re: The Age of Electric Vehicles
Posted: Tue Jan 11, 2022 11:39 am
Just been on VW website and they quote 264 miles, so 265 isn’t so far away?nekomatic wrote: ↑Tue Jan 11, 2022 12:16 amI’ve searched for those terms, including in my vague memories from having to read the actual WLTP a few years ago for a work thing, and the only place I can find them is on that website. Is it something they’ve made up? Bit naughty of them to list them under ‘WLTP’ if so.
Re: The Age of Electric Vehicles
Posted: Tue Jan 11, 2022 11:46 am
IIRC the WLTP defines range calculations and energy use per 100 km, but not an mpg equivalent. WLTP figures have to take account of any equipment that alters efficiency, so a small difference between one quoted figure and another could easily be down to slightly different variants of the same car with different wheels, climate control, sunroof or whatever.
Re: The Age of Electric Vehicles
Posted: Tue Jan 11, 2022 1:41 pm
The power consumption of climate controls etc. is also going to be climate dependent, so I'd expect different real world MPG equivalents for different countries. The UK should win out there as well as on range actually required, as you don't spend a whole lot of time driving at < -5 C or > 35 C.nekomatic wrote: ↑Tue Jan 11, 2022 11:46 amIIRC the WLTP defines range calculations and energy use per 100 km, but not an mpg equivalent. WLTP figures have to take account of any equipment that alters efficiency, so a small difference between one quoted figure and another could easily be down to slightly different variants of the same car with different wheels, climate control, sunroof or whatever.
Re: The Age of Electric Vehicles
Posted: Tue Jan 11, 2022 4:18 pm
Some more order of magnitude practical numbers.
A Nissan Leaf BEV has a maxium output of 110 kW, (first model I found). Clearly you don't drive at maximum power all the time. But it is a lot more than the 7kW you charge it at using a domestic charger. And if our rooftop solar array with a maximum output of 5kW in perfect conditions was being used directly to power the car without a battery, you wouldn't get it up much of a hill.
To compare that with ICEs, 1 kW is 0.75 HP. So a 100 HP car has a maximum output of 75 kW (that's motive - not fuel consumption reckoned in kWh of petrol).
It doesn't seem to be difficult to give EVs high outputs, which is why they can be zippy.
Comparing liquid fuel and stored electricity. 1 litre of petrol is about 9.7 kWh. 1 litre of diesel is about 10.7 kWh. Varies a bit depending on the precise chemical make-up and what temperature it is. And what you put in your tank these days often has a bit of ethanol in it. Let's call it 10 for easier sums.
My old wreck does about 16 km/l on longer journeys, that's 45mpg in old money, assuming a fair proportion is on country A-roads rather than foot to floor motorway all the way. If I fill up when the fuel warning light comes on, I can get about 42 litres in. So that's 672km range for this style of long distance driving.
16 km/l translates to about 1.6 km/kWh including the entire energy content of the petrol in that. But if we work out how much energy was needed just to drive the car, then maybe about 2/3 of the energy is wasted as heat (inc friction between moving parts) etc. (There are better ICEs than that, but 1/3 is probably fair enough in reality.) So that's very roughly about 5 km/kWh of actual motive energy needed to move the car. BEVs aren't lighter than equivalent cars. So maybe that's a fair reflection of the required motive energy to move a car reasonably sized family car.
So in a longer journey that I got this fuel consumption, we are talking moving at like 80km/h. So that is 16 kWh (motive energy) per hour. So normal longer distance driving on clear roads, the car is expending about 16 kW in mechanical power. Or about 50 kW (total petrol energy expended).
That seems broadly consistent with the idea that it takes all night to recharge a car at 7 kW to give a range of the order of 400 km. 12 hours at 7kW is 84 kWh. That's pretty much 5 km/kWh, as I gave above. Clearly specific cars vary, but these figures seem broadly consistent for some kind of typical family sized car.
A Nissan Leaf BEV has a maxium output of 110 kW, (first model I found). Clearly you don't drive at maximum power all the time. But it is a lot more than the 7kW you charge it at using a domestic charger. And if our rooftop solar array with a maximum output of 5kW in perfect conditions was being used directly to power the car without a battery, you wouldn't get it up much of a hill.
To compare that with ICEs, 1 kW is 0.75 HP. So a 100 HP car has a maximum output of 75 kW (that's motive - not fuel consumption reckoned in kWh of petrol).
It doesn't seem to be difficult to give EVs high outputs, which is why they can be zippy.
Comparing liquid fuel and stored electricity. 1 litre of petrol is about 9.7 kWh. 1 litre of diesel is about 10.7 kWh. Varies a bit depending on the precise chemical make-up and what temperature it is. And what you put in your tank these days often has a bit of ethanol in it. Let's call it 10 for easier sums.
My old wreck does about 16 km/l on longer journeys, that's 45mpg in old money, assuming a fair proportion is on country A-roads rather than foot to floor motorway all the way. If I fill up when the fuel warning light comes on, I can get about 42 litres in. So that's 672km range for this style of long distance driving.
16 km/l translates to about 1.6 km/kWh including the entire energy content of the petrol in that. But if we work out how much energy was needed just to drive the car, then maybe about 2/3 of the energy is wasted as heat (inc friction between moving parts) etc. (There are better ICEs than that, but 1/3 is probably fair enough in reality.) So that's very roughly about 5 km/kWh of actual motive energy needed to move the car. BEVs aren't lighter than equivalent cars. So maybe that's a fair reflection of the required motive energy to move a car reasonably sized family car.
So in a longer journey that I got this fuel consumption, we are talking moving at like 80km/h. So that is 16 kWh (motive energy) per hour. So normal longer distance driving on clear roads, the car is expending about 16 kW in mechanical power. Or about 50 kW (total petrol energy expended).
That seems broadly consistent with the idea that it takes all night to recharge a car at 7 kW to give a range of the order of 400 km. 12 hours at 7kW is 84 kWh. That's pretty much 5 km/kWh, as I gave above. Clearly specific cars vary, but these figures seem broadly consistent for some kind of typical family sized car.
Re: The Age of Electric Vehicles
Posted: Tue Jan 11, 2022 4:45 pm
Re: The Age of Electric Vehicles
Posted: Tue Jan 11, 2022 5:07 pm
Seems right.IvanV wrote: ↑Tue Jan 11, 2022 4:18 pmSome more order of magnitude practical numbers.
A Nissan Leaf BEV has a maxium output of 110 kW, (first model I found). Clearly you don't drive at maximum power all the time. But it is a lot more than the 7kW you charge it at using a domestic charger. And if our rooftop solar array with a maximum output of 5kW in perfect conditions was being used directly to power the car without a battery, you wouldn't get it up much of a hill.
To compare that with ICEs, 1 kW is 0.75 HP. So a 100 HP car has a maximum output of 75 kW (that's motive - not fuel consumption reckoned in kWh of petrol).
It doesn't seem to be difficult to give EVs high outputs, which is why they can be zippy.
Comparing liquid fuel and stored electricity. 1 litre of petrol is about 9.7 kWh. 1 litre of diesel is about 10.7 kWh. Varies a bit depending on the precise chemical make-up and what temperature it is. And what you put in your tank these days often has a bit of ethanol in it. Let's call it 10 for easier sums.
My old wreck does about 16 km/l on longer journeys, that's 45mpg in old money, assuming a fair proportion is on country A-roads rather than foot to floor motorway all the way. If I fill up when the fuel warning light comes on, I can get about 42 litres in. So that's 672km range for this style of long distance driving.
16 km/l translates to about 1.6 km/kWh including the entire energy content of the petrol in that. But if we work out how much energy was needed just to drive the car, then maybe about 2/3 of the energy is wasted as heat (inc friction between moving parts) etc. (There are better ICEs than that, but 1/3 is probably fair enough in reality.) So that's very roughly about 5 km/kWh of actual motive energy needed to move the car. BEVs aren't lighter than equivalent cars. So maybe that's a fair reflection of the required motive energy to move a car reasonably sized family car.
So in a longer journey that I got this fuel consumption, we are talking moving at like 80km/h. So that is 16 kWh (motive energy) per hour. So normal longer distance driving on clear roads, the car is expending about 16 kW in mechanical power. Or about 50 kW (total petrol energy expended).
That seems broadly consistent with the idea that it takes all night to recharge a car at 7 kW to give a range of the order of 400 km. 12 hours at 7kW is 84 kWh. That's pretty much 5 km/kWh, as I gave above. Clearly specific cars vary, but these figures seem broadly consistent for some kind of typical family sized car.
EV get 3.5 miles per kWh, broadly, because it's not chucking away all that engine energy as heat. And has regen to stop chucking it away on heating the brakes. An EV still has a fair bit of energy lost to heat because the motor's coils of copper wire will heat up and the battery will heat up. And a bit is lost to heat during recharging. And basically the same air resistance loss as an ICE.
Pump in 7kW for an hour overnight to get 25 miles worth. Which is the equivalent of pumping in about 2.5 litres of petrol on your old wreck's 45mpg. The typical four hours of charging while you sleep is like pumping in 10 litres worth of miles. Which is obviously more than enough for routine daily commutes. Few people pump in more electricity than that, mainly because the cheap charging window (in the UK) is four hours 00:30 to 04:30. Obviously anyone with a long range 400km car who gets home empty and needs to do another mega journey the next day will want that 12 hour recharge.
As a rule of thumb, the "rating" on a charger indicates how many miles you'll get from a 20 minute recharge - 20 minutes on a 7 kW gets you 7 miles, 20 minutes on a 100 kW gets you 100 miles.
It gets more fun if you want to charge longer than 20 minutes on a rapid due to charging curves. You get the full speed if you arrive off the motorway with batteries warm and ready to be filled. It slows down significantly once the battery is 80% full because the electrons start squabbling with each other when you squeeze them in. Hence two stops of 20 minutes gives much more recharge than one stop of 40 minutes.
But it only takes a couple of seconds to pump in a litre of petrol with its 10 kWh. Oil really is fabulous stuff, no wonder we love it.
Re: The Age of Electric Vehicles
Posted: Tue Jan 11, 2022 5:20 pm
Example of a charge curve. A 58 kWh ID.3 has a real world range of 215 miles (less in winter, more in summer, less on motorways, more in cities).
The green line show speeds on a 100 kW rapid. You don't actually get 100 for very long. Arrive with 50% SoC (state of charge) and you start on about 75 kW, and you're not that much quicker than if you plug into a 50 kW. And after 80% you're wasting time - you can drive quicker than the recharge delivers so are certain to save time by pushing onwards and making a second ten minute stop later on.
I think this is because the car deliberately slows down the rapid's DC charge after 80%, otherwise the battery gets too hot from those squabbling electrons. It doesn't apply to a 7 kW home AC recharge because that's so slow they've got plenty of time to shuffle around without getting argumentative.
The green line show speeds on a 100 kW rapid. You don't actually get 100 for very long. Arrive with 50% SoC (state of charge) and you start on about 75 kW, and you're not that much quicker than if you plug into a 50 kW. And after 80% you're wasting time - you can drive quicker than the recharge delivers so are certain to save time by pushing onwards and making a second ten minute stop later on.
I think this is because the car deliberately slows down the rapid's DC charge after 80%, otherwise the battery gets too hot from those squabbling electrons. It doesn't apply to a 7 kW home AC recharge because that's so slow they've got plenty of time to shuffle around without getting argumentative.
Re: The Age of Electric Vehicles
Posted: Wed Jan 12, 2022 12:24 am
I often wonder what's the most efficient speed to drive at. If I bumble along at a solid 90km/h it maybe adds a few minutes to my commute compared with 120km/h, but it keeps the revs so much lower I assume I'm saving fuel.
Presumably you can also extend an EV's range by driving efficiently? I've even seen suggestions of lowering the speed limit to reduce CO2 emissions.
Presumably you can also extend an EV's range by driving efficiently? I've even seen suggestions of lowering the speed limit to reduce CO2 emissions.
Re: The Age of Electric Vehicles
Posted: Wed Jan 12, 2022 12:35 am
If a motorway has a 50mph limit because of roadworks, our average mph goes up to c50/52 mpg rather than the c46mpg we average when travelling at our usual 66/70mph.Bird on a Fire wrote: ↑Wed Jan 12, 2022 12:24 amI often wonder what's the most efficient speed to drive at. If I bumble along at a solid 90km/h it maybe adds a few minutes to my commute compared with 120km/h, but it keeps the revs so much lower I assume I'm saving fuel.
Presumably you can also extend an EV's range by driving efficiently? I've even seen suggestions of lowering the speed limit to reduce CO2 emissions.
ETA: air resistance goes as 4th power of speed (i think), so high speeds can make a big difference
Re: The Age of Electric Vehicles
Posted: Wed Jan 12, 2022 12:58 am
I find that driving around Perth on roads with 60-80 km/h speed limits I can usually get ~6 litres/100 km (sorry, that's the way my car reports it!).Bird on a Fire wrote: ↑Wed Jan 12, 2022 12:24 amI often wonder what's the most efficient speed to drive at. If I bumble along at a solid 90km/h it maybe adds a few minutes to my commute compared with 120km/h, but it keeps the revs so much lower I assume I'm saving fuel.
Presumably you can also extend an EV's range by driving efficiently? I've even seen suggestions of lowering the speed limit to reduce CO2 emissions.
But when doing long drives on roads with higher speed limits (between 100 km/h and 130 km/h) I could get down to 4.5 litres/100 km quite easily. I'm not sure lpm's idea:
is accurate, as on motorways you do drive faster and so have more drag, but you also tend to drive more consistently and so have fewer accelerations and decelerations. (Oz highways may be different to UK motorways, though!)
Re: The Age of Electric Vehicles
Posted: Wed Jan 12, 2022 1:17 am
With EVs I guess regenerative braking improves the efficiency of urban driving considerably.
Unfortunately my car doesn't report anything at all. Even the petrol gauge is broken.
Unfortunately my car doesn't report anything at all. Even the petrol gauge is broken.
Re: The Age of Electric Vehicles
Posted: Wed Jan 12, 2022 1:23 am
In our Prius, the most efficient is around 40mph on country/exurban roads - rolling terrain, not much in the way of stop signs or traffic lights. That gets around 55 mpg (US).
80 mph on the highway is not as efficient. But still 45 mpg (US), pretty much the same as stop-start traffic driving.
The regeneration helps a lot for 10-50 mph driving. Below 10mph there's more actual braking and you tend to need to accelerate away harder to avoid being cut up or honked at.
80 mph on the highway is not as efficient. But still 45 mpg (US), pretty much the same as stop-start traffic driving.
The regeneration helps a lot for 10-50 mph driving. Below 10mph there's more actual braking and you tend to need to accelerate away harder to avoid being cut up or honked at.
Re: The Age of Electric Vehicles
Posted: Wed Jan 12, 2022 6:57 am
It’s the square I think, you might be confusing it with damage to the road and axle weight.Gfamily wrote: ↑Wed Jan 12, 2022 12:35 amIf a motorway has a 50mph limit because of roadworks, our average mph goes up to c50/52 mpg rather than the c46mpg we average when travelling at our usual 66/70mph.Bird on a Fire wrote: ↑Wed Jan 12, 2022 12:24 amI often wonder what's the most efficient speed to drive at. If I bumble along at a solid 90km/h it maybe adds a few minutes to my commute compared with 120km/h, but it keeps the revs so much lower I assume I'm saving fuel.
Presumably you can also extend an EV's range by driving efficiently? I've even seen suggestions of lowering the speed limit to reduce CO2 emissions.
ETA: air resistance goes as 4th power of speed (i think), so high speeds can make a big difference
As EVs generally have one gear unless there’s a sweet spot with the motor the most efficient speed will be as slow as possible, I think.
Re: The Age of Electric Vehicles
Posted: Wed Jan 12, 2022 8:59 am
EVs have a different profile to ICE. They do best in slow city travel because they just regen any slowing. They enjoy a nice traffic jam on the motorway but can't defeat drag at 70 mph.Martin_B wrote: ↑Wed Jan 12, 2022 12:58 amI find that driving around Perth on roads with 60-80 km/h speed limits I can usually get ~6 litres/100 km (sorry, that's the way my car reports it!).
But when doing long drives on roads with higher speed limits (between 100 km/h and 130 km/h) I could get down to 4.5 litres/100 km quite easily. I'm not sure lpm's idea:is accurate, as on motorways you do drive faster and so have more drag, but you also tend to drive more consistently and so have fewer accelerations and decelerations. (Oz highways may be different to UK motorways, though!)
There's loads of nerds who do self-racing. Drive for 300 miles at 60 mph, do the same the next day at 70 mph, and see who wins. Does the shorter recharge at 60 mph defeat speed? It's all nonsense for the real world of course. When they have to stop and pee they exclude that time, plus British motorway traffic makes this a sport for foreigners.
Re: The Age of Electric Vehicles
Posted: Wed Jan 12, 2022 9:07 am
I think air resistance goes as the square of speed, so the energy used per unit time goes as the cube of speed, but of course you get there faster, so energy used per unit distance goes as the square of speed again.
But engines which are driven by lots of tiny explosions have a certain overhead - idling while stationary gives you infinity litres per 100 km - and also going at the same speed in a higher gear is more efficient.
My ~20 year old sports car achieved about 6.6 l/100km (35.6 mpg(US), 42.8 mpg(UK), 0.066 mm2) on my trip to Slovakia and back (to Italy) including however much evaporated in the two weeks it was parked in Slovakia hardly going anywhere. Normally I get somewhere between 8 and 10 l/100km. Note that I don't have a fuel consumption gauge or anything, this is based on how many km I did and how many litres I filled up with, so also includes the angel's share.
But engines which are driven by lots of tiny explosions have a certain overhead - idling while stationary gives you infinity litres per 100 km - and also going at the same speed in a higher gear is more efficient.
My ~20 year old sports car achieved about 6.6 l/100km (35.6 mpg(US), 42.8 mpg(UK), 0.066 mm2) on my trip to Slovakia and back (to Italy) including however much evaporated in the two weeks it was parked in Slovakia hardly going anywhere. Normally I get somewhere between 8 and 10 l/100km. Note that I don't have a fuel consumption gauge or anything, this is based on how many km I did and how many litres I filled up with, so also includes the angel's share.
Re: The Age of Electric Vehicles
Posted: Wed Jan 12, 2022 9:09 am
Average car usage in the UK seems to be roughly 10 miles/day. That will be some distribution with road warriors driving a million miles/day at one end and OAP's driving a mile once a month to the bingo hall down the road.
At 3.5 miles/kWh that translates to an average energy consumption of 3kWh/day, which is less than half an hour in a 7kW charger. Say you charge once a week, that's less than four hours on a week on a charger.
Driving across Europe on your summer hols is the corner case, Lidl/school runs are the vast majority of trips.
At 3.5 miles/kWh that translates to an average energy consumption of 3kWh/day, which is less than half an hour in a 7kW charger. Say you charge once a week, that's less than four hours on a week on a charger.
Driving across Europe on your summer hols is the corner case, Lidl/school runs are the vast majority of trips.