Charging losses at home
Discussion
Just got my first plug-in hybrid, Volvo XC40 T5.
Most days I do less than 20 miles, so running just on the battery works fine. I'm currently using the supplied 13A plug granny charger lead (10A limited).
The Volvo app is pretty good, showing electricity used and mileage for each leg of a journey. This correlates closely to the battery guage and range displayed in the car. Easy to see how elevation changes and climate control usage affect consumption, etc.
I've got a Tapo energy monitor on the plug, which shows how much electricity is used to recharge the battery. This matches very closely the numbers/duration shown on my smart meter IHD, so it seems to be correct.
Quite a difference between what the car says is used and what the meters say is used recharging. Yesterday I did 21 miles on the battery. Car said I used 6.7 kwh (3.1 miles per kwh) which seems reasonable.
However, it took 7.97kwh to recharge the battery - 2.6 miles per kwh. That's power loss of 19%. This difference seems to be pretty consistent each time I charge.
Googling the subject suggests that this is normal for AC charging at home?
Most days I do less than 20 miles, so running just on the battery works fine. I'm currently using the supplied 13A plug granny charger lead (10A limited).
The Volvo app is pretty good, showing electricity used and mileage for each leg of a journey. This correlates closely to the battery guage and range displayed in the car. Easy to see how elevation changes and climate control usage affect consumption, etc.
I've got a Tapo energy monitor on the plug, which shows how much electricity is used to recharge the battery. This matches very closely the numbers/duration shown on my smart meter IHD, so it seems to be correct.
Quite a difference between what the car says is used and what the meters say is used recharging. Yesterday I did 21 miles on the battery. Car said I used 6.7 kwh (3.1 miles per kwh) which seems reasonable.
However, it took 7.97kwh to recharge the battery - 2.6 miles per kwh. That's power loss of 19%. This difference seems to be pretty consistent each time I charge.
Googling the subject suggests that this is normal for AC charging at home?
A battery charger converts AC to DC.
There are several ways to do this, the simplest is with a rectifier made up of a number of diodes, depending on how many phases are being rectified and other factors, see here: https://en.m.wikipedia.org/wiki/Rectifier#:~:text=...
The rectifier creates harmonic distortion on the AC input waveform and a drop in power factor where the voltage and current waveforms go slightly out of phase.
If your AC measuring devices are unable to compensate for this they may over read the real power or they may be reading the kVA value (apparent power) rather than the kW value (real power).
The car will be measuring the output power from the rectifier in kW, so there are also the switching and conduction losses in the rectifier to take into account.
Some of the inefficiency you are seeing will be real power losses, some of it may be reactive power.
I have to be honest and say I don’t know that much about smart meters and how they bill these days. Does your smart meter allow you to display kVA?
There are several ways to do this, the simplest is with a rectifier made up of a number of diodes, depending on how many phases are being rectified and other factors, see here: https://en.m.wikipedia.org/wiki/Rectifier#:~:text=...
The rectifier creates harmonic distortion on the AC input waveform and a drop in power factor where the voltage and current waveforms go slightly out of phase.
If your AC measuring devices are unable to compensate for this they may over read the real power or they may be reading the kVA value (apparent power) rather than the kW value (real power).
The car will be measuring the output power from the rectifier in kW, so there are also the switching and conduction losses in the rectifier to take into account.
Some of the inefficiency you are seeing will be real power losses, some of it may be reactive power.
I have to be honest and say I don’t know that much about smart meters and how they bill these days. Does your smart meter allow you to display kVA?
The car's battery is 10.3kwh. From what I can make out, some capacity is kept for the car to use for "boosting" power at the wheels during hard acceleration etc., so not all available for electric-only driving.
Fully charged, electric range is shown on the dashboard as 27 miles. This seems to be quite accurate - went down to 5 miles remaining after driving 21 miles. The app showed 32% battery remaining, which ties in with the amount kept as "reserve".
I saw that Fleet News article. Looks like I'm slap bang in the middle of real life home usage. I can see how this difference between input/output and AC/DC charging numbers would have a major impact on business costs.
IHD only displays kwh, as does the Tapo monitor. The numbers shown on the IHD match up with what the supplier bills me for.
"Power factor" rings a bell. Isn't that how those dodgy "reduce your bills" gizmos worked on older whizzing wheel meters?
Bit annoying that it's costing me nearly 20% more than the official numbers (and double the losses that are often quoted) but still cheaper than running on petrol.
Need to get an EV tariff sorted, but EDF (current supplier) are refusing the switch.
Fully charged, electric range is shown on the dashboard as 27 miles. This seems to be quite accurate - went down to 5 miles remaining after driving 21 miles. The app showed 32% battery remaining, which ties in with the amount kept as "reserve".
I saw that Fleet News article. Looks like I'm slap bang in the middle of real life home usage. I can see how this difference between input/output and AC/DC charging numbers would have a major impact on business costs.
IHD only displays kwh, as does the Tapo monitor. The numbers shown on the IHD match up with what the supplier bills me for.
"Power factor" rings a bell. Isn't that how those dodgy "reduce your bills" gizmos worked on older whizzing wheel meters?
Bit annoying that it's costing me nearly 20% more than the official numbers (and double the losses that are often quoted) but still cheaper than running on petrol.
Need to get an EV tariff sorted, but EDF (current supplier) are refusing the switch.
clockworks said:
Bit annoying that it's costing me nearly 20% more than the official numbers (and double the losses that are often quoted) but still cheaper than running on petrol.
It's one of those things the Pro EV groups don't like to talk about.But as you say, it's still cheaper than running petrol.
TheRainMaker said:
It's one of those things the Pro EV groups don't like to talk about.
But as you say, it's still cheaper than running petrol.
I'm wondering why GT9 posted to try and explain above. But as you say, it's still cheaper than running petrol.
Surely everyone understands when transforming AC to DC or in fact the other way around that there will be losses. Good old Class A amps get nice a toasty for example.
So who are these Pro EV groups who are trying to keep this a secret?
Power conversion is not 100% efficient
There will be voltage drop in the cable
Charging and discharging the battery loses some energy, because charging requires a higher voltage than discharging gives.
This gets worse the faster you charge and discharge.
A hybrid has a small battery, so the current from the battery is large in relation to the capacity of the battery.
Going up hill you might be drawing 40kW from a 10kWh, that's a high '4C' rate which drops the battery volts noticeably.
Regen braking you could be charging at a similar rate, which raises the battery volts.
Energy Efficiency
While the coulombic efficiency of lithium-ion is normally better than 99 percent, the energy efficiency of the same battery has a lower number and relates to the charge and discharge C-rate. With a 20-hour charge rate of 0.05C, the energy efficiency is a high 99 percent. This drops to about 97 percent at 0.5C and decreases further at 1C. In the real world, the Tesla Roadster is said to have an energy efficiency of 86 percent. Ultra-fast charging on newer EVs will have a negative effect on energy efficiency, as well as the battery life.
From
https://batteryuniversity.com/article/bu-808c-coul...
There will be voltage drop in the cable
Charging and discharging the battery loses some energy, because charging requires a higher voltage than discharging gives.
This gets worse the faster you charge and discharge.
A hybrid has a small battery, so the current from the battery is large in relation to the capacity of the battery.
Going up hill you might be drawing 40kW from a 10kWh, that's a high '4C' rate which drops the battery volts noticeably.
Regen braking you could be charging at a similar rate, which raises the battery volts.
Energy Efficiency
While the coulombic efficiency of lithium-ion is normally better than 99 percent, the energy efficiency of the same battery has a lower number and relates to the charge and discharge C-rate. With a 20-hour charge rate of 0.05C, the energy efficiency is a high 99 percent. This drops to about 97 percent at 0.5C and decreases further at 1C. In the real world, the Tesla Roadster is said to have an energy efficiency of 86 percent. Ultra-fast charging on newer EVs will have a negative effect on energy efficiency, as well as the battery life.
From
https://batteryuniversity.com/article/bu-808c-coul...
Yes, I was expecting 10% losses. That seems to be the figure most often quoted.
I had no idea that the losses would be higher on a slower charger, which is the default for a hybrid I believe?
Would a proper 7kw home charge point be more efficient? Presumably less losses between the CU and wall box because of the thicker cable?
Not the end of the world.
The good news is that I spoke to Octopus, and the switch is now going through. She said that it failed because EDF had recently done some kind of billing change, which counted as a switch - not allowed to switch again inside a week.
I had no idea that the losses would be higher on a slower charger, which is the default for a hybrid I believe?
Would a proper 7kw home charge point be more efficient? Presumably less losses between the CU and wall box because of the thicker cable?
Not the end of the world.
The good news is that I spoke to Octopus, and the switch is now going through. She said that it failed because EDF had recently done some kind of billing change, which counted as a switch - not allowed to switch again inside a week.
clockworks said:
Yes, I was expecting 10% losses. That seems to be the figure most often quoted.
I had no idea that the losses would be higher on a slower charger, which is the default for a hybrid I believe?
Would a proper 7kw home charge point be more efficient? Presumably less losses between the CU and wall box because of the thicker cable?
Not the end of the world.
The good news is that I spoke to Octopus, and the switch is now going through. She said that it failed because EDF had recently done some kind of billing change, which counted as a switch - not allowed to switch again inside a week.
You may find this of interest in relation to losses.I had no idea that the losses would be higher on a slower charger, which is the default for a hybrid I believe?
Would a proper 7kw home charge point be more efficient? Presumably less losses between the CU and wall box because of the thicker cable?
Not the end of the world.
The good news is that I spoke to Octopus, and the switch is now going through. She said that it failed because EDF had recently done some kind of billing change, which counted as a switch - not allowed to switch again inside a week.
https://www.fleetnews.co.uk/news/latest-fleet-news...
I'm with Octopus with the Ohme charge unit. It seems to work well.
TheRainMaker said:
clockworks said:
Bit annoying that it's costing me nearly 20% more than the official numbers (and double the losses that are often quoted) but still cheaper than running on petrol.
It's one of those things the Pro EV groups don't like to talk about.But as you say, it's still cheaper than running petrol.
Otispunkmeyer said:
I watched Harry's garage the other day when he was talking about the RR P510e? the X5 PHEV and Taycan and he mentioned some surprise at this "charging loss" thing. I don't know why he was surprised. I was surprised that he was surprised! But then again if you aren't really of a science and engineering bent, you perhaps don't quite appreciate that laws of physics usually don't allow you to even transfer energy from a to b without a loss and certainly not conversion (AC to DC and vice-versa). Its obvious to me because I've spent 20+ years as an engineering student then engineer. But if you're a farmer or a accountant its perhaps then yeah, I guess you wouldn't really know about this stuff.
I've got a physics A level, but that was nearly 50 years ago.Out of interest, when you pay to use a public fast charger (DC charging?), do you pay for the DC power that comes out at the car end of the cable, or the AC that goes into the charger?
For a PHEV I would expect something like 15% charging losses so 19/20% losses, especially using a slow charger with a thin cable, would probably be abour right.
Just for info, the mi/kWh values quoted on official documentation are AC values as they use the energy pulled from the wall to drive the official cycle, not the DC from the battery. So if you compare you AC mi/kWh to the official figures you'll see how far off the drive cycle efficiency you actually are.
Just for info, the mi/kWh values quoted on official documentation are AC values as they use the energy pulled from the wall to drive the official cycle, not the DC from the battery. So if you compare you AC mi/kWh to the official figures you'll see how far off the drive cycle efficiency you actually are.
clockworks said:
Otispunkmeyer said:
I watched Harry's garage the other day when he was talking about the RR P510e? the X5 PHEV and Taycan and he mentioned some surprise at this "charging loss" thing. I don't know why he was surprised. I was surprised that he was surprised! But then again if you aren't really of a science and engineering bent, you perhaps don't quite appreciate that laws of physics usually don't allow you to even transfer energy from a to b without a loss and certainly not conversion (AC to DC and vice-versa). Its obvious to me because I've spent 20+ years as an engineering student then engineer. But if you're a farmer or a accountant its perhaps then yeah, I guess you wouldn't really know about this stuff.
I've got a physics A level, but that was nearly 50 years ago.Out of interest, when you pay to use a public fast charger (DC charging?), do you pay for the DC power that comes out at the car end of the cable, or the AC that goes into the charger?
So your battery might need 50 kWh to be full. There might be 10% losses, so 55 kWh have been delivered. You're paying for 55 kWh.
stavers said:
For a PHEV I would expect something like 15% charging losses so 19/20% losses, especially using a slow charger with a thin cable, would probably be abour right.
Just for info, the mi/kWh values quoted on official documentation are AC values as they use the energy pulled from the wall to drive the official cycle, not the DC from the battery. So if you compare you AC mi/kWh to the official figures you'll see how far off the drive cycle efficiency you actually are.
Yes this is how its done I believe ( I can check, the guys doing this work sit next door!). But as I understand it they'll deplete the car, charge it up (this is is monitored and we have 22 kW chargers in our test room) then it will run through the MCT (which is the range test). This will pretty much exhaust the battery again and then it will be charged fully again afterwards. Distance is recorded during the test. Just for info, the mi/kWh values quoted on official documentation are AC values as they use the energy pulled from the wall to drive the official cycle, not the DC from the battery. So if you compare you AC mi/kWh to the official figures you'll see how far off the drive cycle efficiency you actually are.
The test is essentially a WLTP cycle + WLTP Phase 1 and 2 repeated. Then a constant speed section. Then the WLTP combo again. Then constant speed to empty. The way its worked out is they monitor battery energy consumed for WLTP Phase 3 & 4 and then 1&2 (ignoring the first 2 phases initially, so they only get "warm" running consumption values). This is used to infer energy required to complete this section again at towards the end. They also know that they must start the final constant speed section when there is < 10% energy remaining. They monitor steady state consumption in the first constant speed section as well. And so with all those numbers, can work out when to break off the first constant speed segment with enough remaining to complete the WLTPs again and start the ending section with < 10% left.
Its a bit of a head scratcher for automating the test because you don't know how long it will be before you start it. That constant speed section is essentially dynamic in length or unknown until you start it and gather data. The total energy used actually is monitored from the wall for the final result so the losses are included in the final result.
I guess there is a regulated charging set up that they're allowed to use because I assume even changing quality of cables, length etc will have an effect as will whether you're charging at 7kW AC, 22kW AC or DC-fast charging.
clockworks said:
I've got a physics A level, but that was nearly 50 years ago.
Out of interest, when you pay to use a public fast charger (DC charging?), do you pay for the DC power that comes out at the car end of the cable, or the AC that goes into the charger?
The "metering" is on the DC side in most cases. It gets complicated doing the AC side when multiple vehicles can use one charger, whereas the DC side has to be monitored at each outlet in order to control the charge.Out of interest, when you pay to use a public fast charger (DC charging?), do you pay for the DC power that comes out at the car end of the cable, or the AC that goes into the charger?
Actual certified meters are relatively new for DC chargers though. Probably not many around in the public charging network. Most will be using the same voltage and current measurements they use to control the charge. Which are probably reasonably accurate but not certified to a certain actually like a "real" meter.
Another thing that can skew the figures is energy used for pre conditioning. This will obviously show on your meter but won't be included in any efficiency calculations on the car.
i.e. your 12kWh usage could be 10kWh recharging the battery and 2kWh heating the car up before its scheduled departure time. 2kWh is probably a bit high for a typical pre-condition but you get the idea,
i.e. your 12kWh usage could be 10kWh recharging the battery and 2kWh heating the car up before its scheduled departure time. 2kWh is probably a bit high for a typical pre-condition but you get the idea,
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