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“and claims a charging rate of up to 11 kW and with an efficiency of about 90% for easy overnight charging.” That’s a some 9kW lost on a 80kW battery. I get th

by cromka 6d ago

“and claims a charging rate of up to 11 kW and with an efficiency of about 90% for easy overnight charging.” That’s a some 9kW lost on a 80kW battery. I get the convenience, but I think the best use for those would be when standardized and installed in public parking spots, for a brief charge bump, not to charge fully at home, e.g overnight, which is what Porsche aims for.

cisc 6d ago
> That’s a some 9kW lost on a 80kW battery It's about the same as wired AC charging. There are always charging losses: https://insideevs.com/features/711659/ev-charger-efficiency-losses/ https://insideevs.com/features/711659/ev-charger-efficiency-...
- onetwentythree 6d ago
  The 90% efficiency of the wireless transmission would be on top of the efficiency of typical charging (which is mostly losses after the power reaches the vehicle).
  - cisc 6d ago
    It's 90% from grid to battery.
    - 1970-01-01 6d ago
      It is not. It is "up to 90%" We all know what this means in reality.
      - unrented7977 6d ago
        Do we? Because if you're invoking scare quotes, I don't think you have a good grasp on what's actually happening here. 90% is pretty good efficiency at this level of power. One cannot give an exact figure because it depends heavily on environmental factors, primarily temperature. 90% is pretty much exactly what I'd expect to see in the real world under same conditions.
      - randerson 6d ago
        Porsche is famous for underpromising and overdelivering. For instance they claim a 0-60 time of 2.4s for this car. Car & Driver independently tested it and achieved 2.1s. They also claim 298 miles of EPA range (mixed highway & city driving). Car & Driver worked out 300 miles at a constant 75 mph (which is harder on an EV than city driving.) On the base model, which claims 303 miles range, MotorTrend achieved 350 miles of pure highway driving. Pick any Porsche and you'll see that they lie to make things sound worse than they really are.
joinHNtheysaid 6d ago
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beAbU 6d ago
> That’s a some 9kW lost on a 80kW battery. *kWh Using the right units is important.
- cheschire 6d ago
  "This may sound like one of those overly pedantic fixations... but it's not. Power and energy are very different concepts." -Technology Connections https://www.youtube.com/watch?v=OOK5xkFijPc https://www.youtube.com/watch?v=OOK5xkFijPc
helsinkiandrew 6d ago
> not to charge fully at home, e.g overnight, which is what Porsche aims for. Wouldn't an overnight (usually cheaper) 10+ hour charge be a great use for (slow) 11 kW charging?
solarkraft 6d ago
It will still be 90% efficient regardless of who uses it. In fact if it is used more, the total losses will be higher. (Some of this becomes clearer when you have a feeling for the units: kW is a measurement of power, not energy)
Rygian 6d ago
Charging rate of 11 kW, with efficiency of about 90%, means that the charger sucks around 12.2 kW of power from the grid, of which 1.2 kW is continually lost*, and only 11 kW is effectively being stored in the battery at any point in time. I don't understand the mention about battery capacity (80 kWh, which would translate to around 7½ hours of charging at 11 kW, if a battery could charge at a uniform rate) or where the "9 kW lost" figure comes from. *Which is probably useful to melt snow above the device, when installed outdoors on cold climates.

by cromka 6d ago

cisc 6d ago

> That’s a some 9kW lost on a 80kW battery It's about the same as wired AC charging. There are always charging losses: https://insideevs.com/features/711659/ev-charger-efficiency-losses/ https://insideevs.com/features/711659/ev-charger-efficiency-...

onetwentythree 6d ago
The 90% efficiency of the wireless transmission would be on top of the efficiency of typical charging (which is mostly losses after the power reaches the vehicle).
- cisc 6d ago
  It's 90% from grid to battery.
  - 1970-01-01 6d ago
    It is not. It is "up to 90%" We all know what this means in reality.
    - unrented7977 6d ago
      Do we? Because if you're invoking scare quotes, I don't think you have a good grasp on what's actually happening here. 90% is pretty good efficiency at this level of power. One cannot give an exact figure because it depends heavily on environmental factors, primarily temperature. 90% is pretty much exactly what I'd expect to see in the real world under same conditions.
    - randerson 6d ago
      Porsche is famous for underpromising and overdelivering. For instance they claim a 0-60 time of 2.4s for this car. Car & Driver independently tested it and achieved 2.1s. They also claim 298 miles of EPA range (mixed highway & city driving). Car & Driver worked out 300 miles at a constant 75 mph (which is harder on an EV than city driving.) On the base model, which claims 303 miles range, MotorTrend achieved 350 miles of pure highway driving. Pick any Porsche and you'll see that they lie to make things sound worse than they really are.

joinHNtheysaid 6d ago

[dead]

beAbU 6d ago

> That’s a some 9kW lost on a 80kW battery. *kWh Using the right units is important.

cheschire 6d ago
"This may sound like one of those overly pedantic fixations... but it's not. Power and energy are very different concepts." -Technology Connections https://www.youtube.com/watch?v=OOK5xkFijPc https://www.youtube.com/watch?v=OOK5xkFijPc

helsinkiandrew 6d ago

> not to charge fully at home, e.g overnight, which is what Porsche aims for. Wouldn't an overnight (usually cheaper) 10+ hour charge be a great use for (slow) 11 kW charging?

solarkraft 6d ago

It will still be 90% efficient regardless of who uses it. In fact if it is used more, the total losses will be higher. (Some of this becomes clearer when you have a feeling for the units: kW is a measurement of power, not energy)

Rygian 6d ago

Charging rate of 11 kW, with efficiency of about 90%, means that the charger sucks around 12.2 kW of power from the grid, of which 1.2 kW is continually lost*, and only 11 kW is effectively being stored in the battery at any point in time. I don't understand the mention about battery capacity (80 kWh, which would translate to around 7½ hours of charging at 11 kW, if a battery could charge at a uniform rate) or where the "9 kW lost" figure comes from. *Which is probably useful to melt snow above the device, when installed outdoors on cold climates.