Charging costs versus speed/rate of charge

tomdfw1

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How will home electricity companies bill us for charging our EVs? Is it purely by how many kWh are transferred? If I pay .15/kWh and I charge 50 kWh to my battery I should be charged $7.50. So, does it matter if I charge at 1kW or 10kW? I would be charged the same dollar amount? Does this also apply when charging my car for the first 85% of charge versus the last 15%, which charges much slower?
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Depends on the provider and card you use.


Ionity and Porsche card : 33 cents per KWH. No connection time charged . Porsche card with other chargers : 35 cents per kwh but also charged per minute. Leaving the car for hours at a slow charger is expensive.

Fasted / Tesla 80 cent per kWh and more for fastcharging.

Bottom line: all chargers and all cards have different rates, make sure you know what they are.

in Europe: best for fast charging on the road is Ionity with Porsche card. Best slow charging : at home, and if not possible, with a card that doesn’t let you additional pay per minute.

Porsche Taycan Charging costs versus speed/rate of charge 279284B6-BDE6-41DC-BDE4-622E0F585588
 
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W1NGE

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How will home electricity companies bill us for charging our EVs? Is it purely by how many kWh are transferred? If I pay .15/kWh and I charge 50 kWh to my battery I should be charged $7.50. So, does it matter if I charge at 1kW or 10kW? I would be charged the same dollar amount? Does this also apply when charging my car for the first 85% of charge versus the last 15%, which charges much slower?
At home it makes no difference as you pay per KWh.

If you have a reduced tariff for different times of the day then you will be charged differently.

Speed of charging doesn't factor here (UK, Europe).
 

W1NGE

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Depends on the provider and card you use.


Ionity and Porsche card : 33 cents per KWH. No connection time charged . Porsche card with other chargers : 35 cents per kwh but also charged per minute. Leaving the car for hours at a slow charger is expensive.

Fasted / Tesla 80 cent per kWh and more for fastcharging.

Bottom line: all chargers and all cards have different rates, make sure you know what they are.

in Europe: best for fast charging on the road is Ionity with Porsche card. Best slow charging : at home, and if not possible, with a card that doesn’t let you additional pay per minute.

279284B6-BDE6-41DC-BDE4-622E0F585588.png
OP is referring to charging at home.
 

McgR

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At home it makes no difference as you pay per KWh.

If you have a reduced tariff for different times of the day then you will be charged differently.

Speed of charging doesn't factor here (UK, Europe).
Sorry. Missed that.
In Belgium for now it doesn’t matter but soon we will be charged based on the generated peaks. So it would be better to charge slower (and more often).
 


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How will home electricity companies bill us for charging our EVs? Is it purely by how many kWh are transferred? If I pay .15/kWh and I charge 50 kWh to my battery I should be charged $7.50. So, does it matter if I charge at 1kW or 10kW? I would be charged the same dollar amount? Does this also apply when charging my car for the first 85% of charge versus the last 15%, which charges much slower?
If you are asking about charging at home, it depends on your tariff. I have no idea about tariffs for USA, but if it is straight forward per kWh, it does not matter at what rate you charge. 1kW at 10 hours is the same charge as 10 kW for 1 hour. The only difference might be about losses in the cars charging equipment. Calculate that loss at about 10% when charging at home.
If however you have a tariff that is depending on how much you draw down at mx rate and m]need to pay extra for that, it could trigger extra charges.
 

daveo4EV

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How will home electricity companies bill us for charging our EVs? Is it purely by how many kWh are transferred? If I pay .15/kWh and I charge 50 kWh to my battery I should be charged $7.50. So, does it matter if I charge at 1kW or 10kW? I would be charged the same dollar amount? Does this also apply when charging my car for the first 85% of charge versus the last 15%, which charges much slower?
purely based on kwh's consumed in 99% of north american residential rates…

kWh's are a "capacity measurement" - like gallons in a bath tub
kW is a "flow rate" - like the amount water coming out of the spout

the bath tub holds the same amount of water regardless of how quickly you fill it.

you're billed by the amount of electricity you use, not the rate at which you use it - just like your water bill.
 

daveo4EV

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How will home electricity companies bill us for charging our EVs? Is it purely by how many kWh are transferred? If I pay .15/kWh and I charge 50 kWh to my battery I should be charged $7.50. So, does it matter if I charge at 1kW or 10kW? I would be charged the same dollar amount? Does this also apply when charging my car for the first 85% of charge versus the last 15%, which charges much slower?
charging is not 100% efficient - so if you need say 50 kWh in the battery - you'll end up pumping about 53-56 kWh to "land" 50 kWh of capacity in the battery

but you're 100% accurate in your calculations - you will be billed by the kWh used by your EVSE, not the rate of charge…your bill will be the same if you charge at 120V/12 amps (1.44 kW) or 240V/40 amps (9.6 kW)…(* - please see foot note)

so if you use 56 kWh (to deliver 50 kWh to the battery) you will be billed

56 kwh * $0.15 = $8.40

Taycan is about a 2.9 mile/kwh vehicle

so those 50 kwh you landed (costing you 56 kWh @ $8.40) can drive your Taycan about

50 * 2.9 = 145 miles - let's call it 150 miles

150 miles at a cost of $8.40 = $0.056 per-mile driven

28 mpg @ $4.50/gallon of gasoline = $0.16 per-mile driven

I hope this helps.

• - not entirely "true" - different charge rates have slightly different efficiency levels - I forget which is more or less efficient but charging "overhead" will vary based on charge rate - with for example charging at 1.44 kW (120V/12 amps) rate of charge might be slightly less efficient say a hypothetical 91% efficient, vs. charging at 11 kW (240V/48 amps) might have an efficiency rate of 92.5% due to differences in electrical loads, heat, time, and other factors…the major point is however you are typically billed for kWh actually used by the EVSE - but different rates of charging may have slight variations in charging efficiency causing your bill to vary in terms of absolute kWh's consumed to fill the battery.
 
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tomdfw1

tomdfw1

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charging is not 100% efficient - so if you need say 50 kWh in the battery - you'll end up pumping about 53-56 kWh to "land" 50 kWh of capacity in the battery

but you're 100% accurate in your calculations - you will be billed by the kWh used by your EVSE, not the rate of charge…your bill will be the same if you charge at 120V/12 amps (1.44 kW) or 240V/40 amps (9.6 kW)…(* - please see foot note)

so if you use 56 kWh (to deliver 50 kWh to the battery) you will be billed

56 kwh * $0.15 = $8.40

Taycan is about a 2.9 mile/kwh vehicle

so those 50 kwh you landed (costing you 56 kWh @ $8.40) can drive your Taycan about

50 * 2.9 = 145 miles - let's call it 150 miles

150 miles at a cost of $8.40 = $0.056 per-mile driven

28 mpg @ $4.50/gallon of gasoline = $0.16 per-mile driven

I hope this helps.

• - not entirely "true" - different charge rates have slightly different efficiency levels - I forget which is more or less efficient but charging "overhead" will vary based on charge rate - with for example charging at 1.44 kW (120V/12 amps) rate of charge might be slightly less efficient say a hypothetical 91% efficient, vs. charging at 11 kW (240V/48 amps) might have an efficiency rate of 92.5% due to differences in electrical loads, heat, time, and other factors…the major point is however you are typically billed for kWh actually used by the EVSE - but different rates of charging may have slight variations in charging efficiency causing your bill to vary in terms of absolute kWh's consumed to fill the battery.
Thanks both answers help...It would be nice to see the efficiencies of charging at the different rates as well as related to how full the battery is and to understand if efficiencies change (at any charging speed) when we try to fill that last 15% of the battery; which takes much longer to transfer per kWh and reason it raises my question.

It sounds like it is not very dramatic difference/efficiencies on any level. (10-15%?)
 
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daveo4EV

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Thanks both answers help...It would be nice to see the efficiencies of charging at the different rates as well as related to how full the battery is. It would be nice to understand if efficiencies change (at any charging speed) when we try to fill that last 15% of the battery; which takes much longer to transfer per kWh and reason it raises my question.

It sounds like it is not very dramatic difference/efficiencies on any level. (10-15%?)
I'm not an EE or Battery Engineer - but I play one on the internet - but I've worked with and done lunch with EE's and battery engineers…the level of efficiency remains most static across the charging session but does vary based on charge rate, but not in any way that is predictable or statistically significant - as the battery gets closer to full the charge rate is ramped down to avoid over-taxing the LiON battery cell chemistry (for battery warranty and longevity reasons) - as you ramp the charge rate down charge time increases - efficiency "drops" during this period because the "overhead losses" remain mostly fixed costs and therefore become an increasing percentage vs. the power being delivered…

example: if the "fixed" overhead loss is say 0.09 kW of overhead at 9.6 kW - that makes the "loss" percentage 0.09/9.6 = .009 or .9% overhead loss…

if you ramp down the charge rate the "fixed cost" losses remain at 0.09 kW but now you're only delivering 1.44 kW - 0.09/1.44 = becomes 0.0625 or 6.25% "loss"

now those are not real numbers above, but you get the idea

now the complexity is some of the overhead is "fixed cost" and some of the charging overhead is variable cost - and the variables are both time based (how long) and charge rate based (amps & voltage) - so while there is a fixed cost element to overhead, there is also a variable cost element that is directly related to charge rate - so while efficiency creeps down as you drop the charge rate it does not change that much…

you'd need a real EE/Battery engineer and the specifications of all the components involved (the eVSE and onboard vehicle charger) to calculate the efficiency variations based on variable charge rates for the same charging session…

in my 10 years EV driving experience charge rate overhead seems to be about 7-10% "cost" above what you actually manage to land in the battery in terms of kWh capacity - is a pretty good rule of thumb.

if you "need" 50 kwh in the battery - it's going cost you somewhere in the realm of 55 kWh or less to get that pure 50 kWh landed in the battery - any further accuracy is mostly noise.
 

daveo4EV

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I'm not an EE or Battery Engineer - but I play one on the internet - but I've worked with and done lunch with EE's and battery engineers…the level of efficiency remains most static across the charging session but does vary based on charge rate, but not in any way that is predictable or statistically significant - as the battery gets closer to full the charge rate is ramped down to avoid over-taxing the LiON battery cell chemistry (for battery warranty and longevity reasons) - as you ramp the charge rate down charge time increases - efficiency "drops" during this period because the "overhead losses" remain mostly fixed costs and therefore become an increasing percentage vs. the power being delivered…

example: if the "fixed" overhead loss is say 0.09 kW of overhead at 9.6 kW - that makes the "loss" percentage 0.09/9.6 = .009 or .9% overhead loss…

if you ramp down the charge rate the "fixed cost" losses remain at 0.09 kW but now you're only delivering 1.44 kW - 0.09/1.44 = becomes 0.0625 or 6.25% "loss"

now those are not real numbers above, but you get the idea

now the complexity is some of the overhead is "fixed cost" and some of the charging overhead is variable cost - and the variables are both time based (how long) and charge rate based (amps & voltage) - so while there is a fixed cost element to overhead, there is also a variable cost element that is directly related to charge rate - so while efficiency creeps down as you drop the charge rate it does not change that much…

you'd need a real EE/Battery engineer and the specifications of all the components involved (the eVSE and onboard vehicle charger) to calculate the efficiency variations based on variable charge rates for the same charging session…

in my 10 years EV driving experience charge rate overhead seems to be about 7-10% "cost" above what you actually manage to land in the battery in terms of kWh capacity - is a pretty good rule of thumb.

if you "need" 50 kwh in the battery - it's going cost you somewhere in the realm of 55 kWh or less to get that pure 50 kWh landed in the battery - any further accuracy is mostly noise.
however once you are close to full and the charge rate drops to low rates - there is also not that many more kwh's to be delivered to to the battery - so while the efficiency rate is dropping for those last few kWh's - the overall efficiency of the entire sessions dominates if you've delivered 74 kWh total - and the first 72 kW were at an efficiency of 93% and the last 2 kWh were at 89% efficiency - the overall efficiency of the entire session is going to be closer to 93% vs 89% - so the while the efficiency losses are increased as you get closer to full - they are less significant in the context of the efficiency of the entire session…
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