The EV fact thread

[MikeInWimbledon]

Given the inefficiency inherent in charging with a 'granny cable' (which has a CO2 cost and will continue to until all electricity is from renewables) runs counter to decarbonisation, how long before it's outlawed?

Your point being that a granny cable powers a small EV at 2 pence per mile,

but because of the "inefficiency inherent in charging with a granny cable" it really should cost only 1 1/2 pence per mile?

Seems a strange argument compared to the "efficiency" of pulling oil out of the North Sea, Desert, or Russia.

 

[markjay]

Your point being that a granny cable powers a small EV at 2 pence per mile,

but because of the "inefficiency inherent in charging with a granny cable" it really should cost only 1 1/2 pence per mile?

Seems a strange argument compared to the "efficiency" of pulling oil out of the North Sea, Desert, or Russia.

I think he was referring to efficiency in terms of CO2 emissions (during the production process of electricity), rather than to the cost to the consumer.

Whichever way you slice it, charging wastes are wasted energy. More efficient charging is 'greener', regardless of the cost.

 

[MikeInWimbledon]

I think he was referring to efficiency in terms of CO2 emissions (during the production process of electricity), rather than to the cost to the consumer.
Whichever way you slice it, charging wastes are wasted energy. More efficient charging is 'greener', regardless of the cost.

Yes, good point. I'll make that point to Rachel.

20% VAT on ALL domestic electricity, and

50% higher council tax for homes with energy ratings below "C"

Good point, well made.

Can't believe that we don't tax people who live in homes without double glazing in ALL rooms, and triple glazing in the main living areas.

 

[markjay]

Yes, good point. I'll make that point to Rachel.

20% VAT on ALL domestic electricity, and

50% higher council tax for homes with energy ratings below "C"

Good point, well made.

Can't believe that we don't tax people who live in homes without double glazing in ALL rooms, and triple glazing in the main living areas.

So, clearly you're not one of those on here who keep reminding us that it's unfair for EV owners with home chargers to not pay the same VAT and Duty on their EV's electricity as ICE drivers pay on their fuel - good to know.

 

[MikeInWimbledon]

So, clearly you're not one of those on here who keep reminding us that it's unfair for EV owners with home chargers to not pay the same VAT and Duty on their EV's electricity as ICE drivers pay on their fuel - good to know.

Gotta raise those billions for civil servants' black holes somehow.

 

[190]

because of the "inefficiency inherent in charging with a granny cable"

I know it's the accepted wisdom but I'm curious to know why a granny charging cable is inefficient. I seem to recall figures like 20% losses being mentioned which doesn't make sense to me.

A quick search on the internet suggest many, including Googles AI output, don't understand what the word efficiency means because they equate it with slow charging. That's inconvenient not inefficient. Efficiency is the ratio of the useful work performed compared to to the total energy input. Losses equal heat generation so something is getting hot if losses are high. Does a granny cable get hot ?

As far as the actual cable is concerned then it's simply ohms law and if cable cross sectional area is big enough the loss will be very small. I've just done the sums and it comes to a loss of less than 0.25%. Ditto for the wiring between the house consumer unit and the socket outlet used to feed the granny cable. As an Electrical engineer I don't accept the idea that a suitable socket outlet in a garage is incapable of continuously supplying a granny cable load which I believe is typically only 2.3 KW. House wiring will do that with ease.

Where else do the losses occur then in Granny cable charging. It can only be be in the AC/DC or voltage conversion electronics and why are those conversion losses substantially bigger than for higher KW charging ? Is it because the EV manufacturer installs inefficient electronics in the car and if so why. I can see DC charging being more efficient at the car end but it had to be converted from AC to DC so losses still apply somewhere.

Without spending ages researching this, I'm beginning to think it might be at least partially a myth. Yes Granny charging is slow which is inconvenient and you might not be able to take advantage of low overnight tariffs but inherently inefficient ? I'm not buying that until I see a technical explanation of why the losses are higher than for other chargers.

 

[ALFAitalia]

10 to 15 percent seems to be what I've seen. 25 is a hell of a lot and I'd like to see the maths backing that up.

 

[Bobby Dazzler]

I know it's the accepted wisdom but I'm curious to know why a granny charging cable is inefficient. I seem to recall figures like 20% losses being mentioned which doesn't make sense to me.

A quick search on the internet suggest many, including Googles AI output, don't understand what the word efficiency means because they equate it with slow charging. That's inconvenient not inefficient. Efficiency is the ratio of the useful work performed compared to to the total energy input. Losses equal heat generation so something is getting hot if losses are high. Does a granny cable get hot ?

As far as the actual cable is concerned then it's simply ohms law and if cable cross sectional area is big enough the loss will be very small. I've just done the sums and it comes to a loss of less than 0.25%. Ditto for the wiring between the house consumer unit and the socket outlet used to feed the granny cable. As an Electrical engineer I don't accept the idea that a suitable socket outlet in a garage is incapable of continuously supplying a granny cable load which I believe is typically only 2.3 KW. House wiring will do that with ease.

Where else do the losses occur then in Granny cable charging. It can only be be in the AC/DC or voltage conversion electronics and why are those conversion losses substantially bigger than for higher KW charging ? Is it because the EV manufacturer installs inefficient electronics in the car and if so why. I can see DC charging being more efficient at the car end but it had to be converted from AC to DC so losses still apply somewhere.

Without spending ages researching this, I'm beginning to think it might be at least partially a myth. Yes Granny charging is slow which is inconvenient and you might not be able to take advantage of low overnight tariffs but inherently inefficient ? I'm not buying that until I see a technical explanation of why the losses are higher than for other chargers.

I can’t understand where up to a quarter of the electricity goes either, that’s a lot of energy. The charger gets warm but not hot, certainly not hot enough to account for 25% of the energy transferred to the car.

Therre will always be some transmission loss, and in the conversion. The car will consumer some electricity as it will need need to be awake whilst charging too, however combined I’d be surprised if that could account for much.

I would like to test it but I don’t have a way of doing so accurately and without turning off all of the electrical consumers in the house which is somewhat inconvenient, so for now I’ll rely on @BTB 500 and ADAC’s data.

Edited to add; I assume some energy must be used to warm/cool the battery for optimal charging speed when rapid charging in challenging temperatures, but no idea how much of the time that would apply.

 

[Bobby Dazzler]

10 to 15 percent seems to be what I've seen. 25 is a hell of a lot and I'd like to see the maths backing that up.

Instinctively that seems more like it to me, but that’s based upon zero knowledge and data. One would assume that ADAC who Bill often refers to have both more knowledge and data!

 

[markjay]

I can’t understand where up to a quarter of the electricity goes either, that’s a lot of energy.

Heat. And, if there's a fan somewhere (in the charger? In the car? Etc), then also some (not much) converted to kinetic energy.

What also needs to be considered, is that fast DC chargers also warm-up the battery while charging, which is another element of loss.

 

[MikeInWimbledon]

I know it's the accepted wisdom but I'm curious to know why a granny charging cable is inefficient. I seem to recall figures like 20% losses being mentioned which doesn't make sense to me.

A quick search on the internet suggest many, including Googles AI output, don't understand what the word efficiency means because they equate it with slow charging. That's inconvenient not inefficient. Efficiency is the ratio of the useful work performed compared to to the total energy input. Losses equal heat generation so something is getting hot if losses are high. Does a granny cable get hot ?

As far as the actual cable is concerned then it's simply ohms law and if cable cross sectional area is big enough the loss will be very small. I've just done the sums and it comes to a loss of less than 0.25%. Ditto for the wiring between the house consumer unit and the socket outlet used to feed the granny cable. As an Electrical engineer I don't accept the idea that a suitable socket outlet in a garage is incapable of continuously supplying a granny cable load which I believe is typically only 2.3 KW. House wiring will do that with ease.

Where else do the losses occur then in Granny cable charging. It can only be be in the AC/DC or voltage conversion electronics and why are those conversion losses substantially bigger than for higher KW charging ? Is it because the EV manufacturer installs inefficient electronics in the car and if so why. I can see DC charging being more efficient at the car end but it had to be converted from AC to DC so losses still apply somewhere.

Without spending ages researching this, I'm beginning to think it might be at least partially a myth. Yes Granny charging is slow which is inconvenient and you might not be able to take advantage of low overnight tariffs but inherently inefficient ? I'm not buying that until I see a technical explanation of why the losses are higher than for other chargers.

Agreed. It’s one of those classic bits of nonsense, like EV’s catching fire as soon as their warranty ends

Too slow with Octopus Go? Maybe. Perhaps limited to a mere 60 miles a night, call it 420 miles a week, or 20,000 miles a year. To the folks in my neck of the woods, including our local Vicar (with her BMW I3), that’s more than enough.

For someone doing 25,000 miles a year, including 5,000 miles topped up away from home, a “proper” charger is worth that few hundred quid extra.

 

[BTB 500]

I know it's the accepted wisdom but I'm curious to know why a granny charging cable is inefficient. I seem to recall figures like 20% losses being mentioned which doesn't make sense to me.

This has been covered in detail several times but in summary there are two main sources of loss.

First, the car must internally convert mains AC into DC in order to charge the battery. The on-board equipment that does this is restricted in size/weight (because the car has to carry it around permanently), so it's not optimised for efficiency - there are significant losses involved, and usually a need for active cooling (fans). With fast charging the car is supplied with DC through the charge cable, so this isn't a factor (conversion losses still occur but these are inside the charging station and are bundled into the p/kWh tariff you pay).

Second, while charging various 12V systems in the car have to be running to control/monitor the process. So 10 times more power is consumed here in a 10 hour slow charge than in a 1 hour fast charge.

ADAC (an independent body in Germany, similar to our AA) measure home charging losses as part of the testing they do on EVs. Example for the BMW i3 here:



That's a charging loss of 28.4%.

BMW i3 im Test: Batterie, Reichweite, Verbrauch, Preis

Der BMW i3 wurde eingestellt. Für Gebrauchtwagenkäufer ist der i3 aber weiterhin interessant. ADAC Test.

www.adac.de

In general they quote a range of 10-30% for home charging losses, broken down as follows (in German but you get the gist):



As above the biggest losses are 5-10% in the on-board charger that converts AC to DC, and 5-15% consumed by the car's on-board 12V systems while charging.

Ladeverluste beim Elektroauto | ADAC

Wie hoch sind die Ladeverluste, wenn man ein Elektroauto lädt? Der ADAC hat es gemessen – und gibt Tipps zum effizienten Aufladen.

www.adac.de

Hope that helps.

 

[190]

Hope that helps.

It does help. The on board charger losses is where I expected to see some inefficiency and that's no different for 2.3KW or 11KW. The surprise and unknown to me was the extent of the losses in a cars 12 V system monitoring the charging. But there seems little excuse for Renault Zoe overall losses at 24.2% to be double that of a Fiat 500 at 12.7 % There's obviously some considerable room for improvement.

If we eliminate the Zoe as an old design and look only at the other 3 more modern EV's, the range of losses is 12.7% to 15.2 % which seems a more honest result for ADAC to headline rather than indicating up to 30% losses on the diagram. If people have also been seeing elsewhere that 25% is typical for granny cable charging losses then it probably stems from the Zoe and is the worst case not the typical case.

 

[markjay]

This has been covered in detail several times but in summary there are two main sources of loss.

First, the car must internally convert mains AC into DC in order to charge the battery. The on-board equipment that does this is restricted in size/weight (because the car has to carry it around permanently), so it's not optimised for efficiency - there are significant losses involved, and usually a need for active cooling (fans). With fast charging the car is supplied with DC through the charge cable, so this isn't a factor (conversion losses still occur but these are inside the charging station and are bundled into the p/kWh tariff you pay).

Second, while charging various 12V systems in the car have to be running to control/monitor the process. So 10 times more power is consumed here in a 10 hour slow charge than in a 1 hour fast charge.

ADAC (an independent body in Germany, similar to our AA) measure home charging losses as part of the testing they do on EVs. Example for the BMW i3 here:

View attachment 162781

That's a charging loss of 28.4%.

BMW i3 im Test: Batterie, Reichweite, Verbrauch, Preis

Der BMW i3 wurde eingestellt. Für Gebrauchtwagenkäufer ist der i3 aber weiterhin interessant. ADAC Test.

www.adac.de

In general they quote a range of 10-30% for home charging losses, broken down as follows (in German but you get the gist):

View attachment 162784

As above the biggest losses are 5-10% in the on-board charger that converts AC to DC, and 5-15% consumed by the car's on-board 12V systems while charging.

Ladeverluste beim Elektroauto | ADAC

Wie hoch sind die Ladeverluste, wenn man ein Elektroauto lädt? Der ADAC hat es gemessen – und gibt Tipps zum effizienten Aufladen.

www.adac.de

Hope that helps.

I think that while your long answer detailed the various electric consumers, the short answer is that the vast majority of waste electricity is simply converted to heat and then dissipated one way or another, the rest (very little) is converted to the kinetic energy required to spin-up cooling fans or operate flaps where applicable.

 

[BTB 500]

It does help. The on board charger losses is where I expected to see some inefficiency and that's no different for 2.3KW or 11KW. The surprise and unknown to me was the extent of the losses in a cars 12 V system monitoring the charging. But there seems little excuse for Renault Zoe overall losses at 24.2% to be double that of a Fiat 500 at 12.7 % There's obviously some considerable room for improvement.

If we eliminate the Zoe as an old design and look only at the other 3 more modern EV's, the range of losses is 12.7% to 15.2 % which seems a more honest result for ADAC to headline rather than indicating up to 30% losses on the diagram. If people have also been seeing elsewhere that 25% is typical for granny cable charging losses then it probably stems from the Zoe and is the worst case not the typical case.

The worst case would presumably be the 30% that ADAC mention (I have no idea which car this was though).

'Granny cable' charging is capped at around 3 kW (13A) so higher capacity EV batteries would obviously take longer to charge, however there do seem to be significant variations in the power consumption of the on board systems. It may well be that there's more focus on improving this now, but of course plenty of people will be buying older models as used cars. I've no idea what an 'average' loss figure for current models would be but as mentioned ADAC's website gives test results as a PDF for most of the cars they've tested. Volvo XC40 as an example:



Usable capacity 79 kWh, full charge took 94.7 kWh, so charging loss of 19.8%

Their comparison reports only list the 'best performing' cars from their tests - August 2024 here:

https://www.adac.de/rund-ums-fahrzeug/autokatalog/autotest/beste-elektroautos/

It's a shame they don't have a 'worst performing' list of cars to avoid!

 

[BTB 500]

I think that while your long answer detailed the various electric consumers, the short answer is that the vast majority of waste electricity is simply converted to heat and then dissipated one way or another, the rest (very little) is converted to the kinetic energy required to spin-up cooling fans or operate flaps where applicable.

Yes of course, but I think @190 was more interested in where this happens.

 

[SmartAmg]

To be honest, I'm not really bothered, what percentage you lose, with a Granny charger.
What will be, will be.
It works, so that'll do for me.

 

[Bellow]

To be honest, I'm not really bothered, what percentage you lose, with a Granny charger.
What will be, will be.
It works, so that'll do for me.

And that, is why government will no doubt intervene soon.

 

[SmartAmg]

And that, is why government will no doubt intervene soon.

Why?

 

[markjay]

Why?

Tax, tax, tax.... it's what (some) governments do.