4 ms·

So that would imply thirty or so KW of heat at 75% efficiency and a hundred delivered. I suppose road icing and snow accumulation would not be much of an issue

by VLM 11y ago

So that would imply thirty or so KW of heat at 75% efficiency and a hundred delivered. I suppose road icing and snow accumulation would not be much of an issue at those levels. On hot summer days, during traffic jams, a slowly rolling 30 KW heat source might cause road softness issues, something to think about.

mikeash 11y ago
If it's rolling slowly then it won't need anywhere near 30kW, though. Power consumption varies roughly by the third power of speed.
- JoshTriplett 11y ago
  Unless the vehicle is already fully charged, I'd expect it to draw as much power as it can for charging, regardless of its current power consumption.
  - Dylan16807 11y ago
    Sure, but the vehicle is not in charge of how much it can draw. And the metric that matters is kWh per mile.
    - JoshTriplett 11y ago
      > Sure, but the vehicle is not in charge of how much it can draw. The road determines a maximum, but the vehicle need not draw that much, for instance if already fully charged. > And the metric that matters is kWh per mile. That would also depend on vehicle speed; charge obtained per second seems more useful than per mile.
      - Dylan16807 11y ago
        What matters is that your vehicle is x% more charged at the end of the segment, or at least that you used no battery power over the segment. It really doesn't matter if your car isn't charging while you're stuck in gridlock.
  - mikeash 11y ago
    Even if it does that (and if this is a problem then you could simply design the system to only deliver enough power to sustain travel) then the car won't be charging for very long before it becomes full.
    - JoshTriplett 11y ago
      > Even if it does that (and if this is a problem then you could simply design the system to only deliver enough power to sustain travel) That seems far less useful; "your charge won't go down in this lane" means the lanes would need to go everywhere, while "your charge will slowly go up in this lane" would mean the lanes could sustain travel over a wide area even if they only appear on major highways. Also, different EVs require different amounts of power to sustain travel. > then the car won't be charging for very long before it becomes full. Depends heavily on the charging rate. Considering that many EVs can take hours to charge with a wired charger...
      - mikeash 11y ago
        Right now, EVs are fine for short-distance travel but most EVs have trouble with long-distance travel. An EV's battery will be fine with getting you to and from the highway, and you'll charge wherever you park as well. Your emphasis on "wired" is kind of out of place here. These wireless chargers will necessarily be able to provide substantially more power than a typical wired charger. A typical wired charger is 10kW or less, while highway inductive charging will need to provide 20-30kW just to sustain highway speeds. Let's say you draw 30kW no matter what until the battery is full. If you're in a traffic jam, you might be consuming 2kW or so on average, leaving 28kW available to charge the battery. If you're in a LEAF and your battery is completely empty, your battery will be full in less than an hour. And your battery is likely to be well above empty.

by VLM 11y ago

mikeash 11y ago

If it's rolling slowly then it won't need anywhere near 30kW, though. Power consumption varies roughly by the third power of speed.

JoshTriplett 11y ago
Unless the vehicle is already fully charged, I'd expect it to draw as much power as it can for charging, regardless of its current power consumption.
- Dylan16807 11y ago
  Sure, but the vehicle is not in charge of how much it can draw. And the metric that matters is kWh per mile.
  - JoshTriplett 11y ago
    > Sure, but the vehicle is not in charge of how much it can draw. The road determines a maximum, but the vehicle need not draw that much, for instance if already fully charged. > And the metric that matters is kWh per mile. That would also depend on vehicle speed; charge obtained per second seems more useful than per mile.
    - Dylan16807 11y ago
      What matters is that your vehicle is x% more charged at the end of the segment, or at least that you used no battery power over the segment. It really doesn't matter if your car isn't charging while you're stuck in gridlock.
- mikeash 11y ago
  Even if it does that (and if this is a problem then you could simply design the system to only deliver enough power to sustain travel) then the car won't be charging for very long before it becomes full.
  - JoshTriplett 11y ago
    > Even if it does that (and if this is a problem then you could simply design the system to only deliver enough power to sustain travel) That seems far less useful; "your charge won't go down in this lane" means the lanes would need to go everywhere, while "your charge will slowly go up in this lane" would mean the lanes could sustain travel over a wide area even if they only appear on major highways. Also, different EVs require different amounts of power to sustain travel. > then the car won't be charging for very long before it becomes full. Depends heavily on the charging rate. Considering that many EVs can take hours to charge with a wired charger...
    - mikeash 11y ago
      Right now, EVs are fine for short-distance travel but most EVs have trouble with long-distance travel. An EV's battery will be fine with getting you to and from the highway, and you'll charge wherever you park as well. Your emphasis on "wired" is kind of out of place here. These wireless chargers will necessarily be able to provide substantially more power than a typical wired charger. A typical wired charger is 10kW or less, while highway inductive charging will need to provide 20-30kW just to sustain highway speeds. Let's say you draw 30kW no matter what until the battery is full. If you're in a traffic jam, you might be consuming 2kW or so on average, leaving 28kW available to charge the battery. If you're in a LEAF and your battery is completely empty, your battery will be full in less than an hour. And your battery is likely to be well above empty.