10 ms·

DC charging stations sometimes have batteries on site so that they can charge up from the grid and then deliver bursts of power from the batteries during chargi

by NickM 3y ago

DC charging stations sometimes have batteries on site so that they can charge up from the grid and then deliver bursts of power from the batteries during charging. Apparently this is often worth it to avoid the high demand fees that utilities charge when you draw a lot of power at once. I assume this will become more ubiquitous as charging speeds continue to increase. (You're right that a megawatt is a high power draw in the context of normal household electricity usage, but keep in mind that if you can pump ten gallons of gas in a minute you're effectively drawing the equivalent of something like 20MW, so in the context of vehicle refueling it's not so crazy.)

saalweachter 3y ago
> but keep in mind that if you can pump ten gallons of gas in a minute you're effectively drawing the equivalent of something like 20MW, so in the context of vehicle refueling it's not so crazy If 15 Teslas pass through a stretch of road per minute with full 100kWh battery packs, you could also describe that as 90MW of current, but it's also not really.
- jorvi 3y ago
  I always forget just how energy dense petroleum and its derivatives are..
  - matthewfcarlson 3y ago
    When charging, the Tesla shows you a little miles per hour figure (how many miles of range you gain per hour of charging) and it can often reach 1000 or so on the super chargers I use frequently. It’s fun to calculate the miles per hour of gas (around 12,000).
  - athenot 3y ago
    This is true. Though the electric batteries do have the advantage of having already paid the "thermodynamics tax". Some of the energy in gas will go towards heat losses; energy that cannot be converted to movement.
    - davrosthedalek 3y ago
      And they are very efficient over a much larger rpm band. But the real win is the energy recovery from regenerative breaking.
    - mensetmanusman 3y ago
      But that thermodynamic tax is a negative in very cold climates where the electric vehicle will see a major change in total travel distance compared to ICE.
      - iknowstuff 3y ago
        Heat pumps make it more efficient to convert the fuel to electricity at a big, efficient power plant, and then to heat, than to burn the fuel itself for heat in an internal combustion engine (or at home for that matter) It’s overall a net positive.
        mensetmanusman 3y ago
        Yes, but note that this type of 'overall thinking' sometimes has interesting consequences. Eg overall globalization raises wages, but it decimated rural economies in the west and caused a lot of social harm leading to the rise of populism. The odometer shock that will start hitting low wage earners forced to migrate to EV may have less important but similarly surprising unintended consequences.
  - davrosthedalek 3y ago
    Yes. One of the usual YT channels had this interesting picture. Gas mileage is miles per gallon. Or in this case, do it the European way: l/100km. The unit of that is an area. Typically a rather small one, ca 0.1mm^2. That's the area of a trench you have to dig along your path if you want to supply your car from the trench instead of your gas tank.
    - NickM 3y ago
      That doesn’t make any sense to me. The amount of fuel a trench can hold is its volume, not its area.
      - somewhat_drunk 3y ago
        Probably means cross-sectional area.
Alupis 3y ago
The problem is obvious though, isn't it? Our current infrastructure simply cannot handle a ton of EV's all wanting to charge up all day long - as is done currently with gas stations all over the country. It'll take decades to bring our infrastructure up to where it needs to be to support this - yet people act like we're already there. Some states still struggle just to keep the lights on during major parts of the year...
- wilg 3y ago
  The load is spread out in a completely different way than gas, because 100% of gas cars get gas at a station, while 80% of people with EVs slow-charge at home (or work or whatever). Fast chargers are for road-trips only. Obviously, if we're going to move to cleaner energy we will need infrastructure investment. Worrying that it's not already there makes no sense. The demand for improved electrical infrastructure will be a forcing function. There's no need to wait for it. But again, most charging isn't fast charging and likely never will be. (Charging for apartments and stuff still has a bit of a way to go, so sometimes those people use fast chargers as part of their regular routine, but the solution to that is easy and underway: just put chargers in the apartment parking lot and/or on the streets.)
  - Alupis 3y ago
    > Obviously, if we're going to move to cleaner energy It is very unclear whether electric vehicles actually are more environmentally friendly. They sound great - but if you dig into where all the materials come from, it's shocking how externalized we've made that problem. It might be cleaner by time you get to drive it... but it's not cleaner to produce and operate, and in fact may be worse in some cases. Emissions aren't just from the tailpipe after all - yet that appears to be what most people focus on. > Worrying that it's not already there makes no sense It makes a lot of sense when the government (both state and federal) are pushing initiatives and incentives to force EV's into commonplace. Our infra just cannot handle it, even with trickle chargers like you've claimed. Which means it will be a net-worse experience for people, and they will resist future clean energy pushes as being disingenuous.

by NickM 3y ago

saalweachter 3y ago

> but keep in mind that if you can pump ten gallons of gas in a minute you're effectively drawing the equivalent of something like 20MW, so in the context of vehicle refueling it's not so crazy If 15 Teslas pass through a stretch of road per minute with full 100kWh battery packs, you could also describe that as 90MW of current, but it's also not really.

jorvi 3y ago
I always forget just how energy dense petroleum and its derivatives are..
- matthewfcarlson 3y ago
  When charging, the Tesla shows you a little miles per hour figure (how many miles of range you gain per hour of charging) and it can often reach 1000 or so on the super chargers I use frequently. It’s fun to calculate the miles per hour of gas (around 12,000).
- athenot 3y ago
  This is true. Though the electric batteries do have the advantage of having already paid the "thermodynamics tax". Some of the energy in gas will go towards heat losses; energy that cannot be converted to movement.
  - davrosthedalek 3y ago
    And they are very efficient over a much larger rpm band. But the real win is the energy recovery from regenerative breaking.
  - mensetmanusman 3y ago
    But that thermodynamic tax is a negative in very cold climates where the electric vehicle will see a major change in total travel distance compared to ICE.
    - iknowstuff 3y ago
      Heat pumps make it more efficient to convert the fuel to electricity at a big, efficient power plant, and then to heat, than to burn the fuel itself for heat in an internal combustion engine (or at home for that matter) It’s overall a net positive.
      - mensetmanusman 3y ago
        Yes, but note that this type of 'overall thinking' sometimes has interesting consequences. Eg overall globalization raises wages, but it decimated rural economies in the west and caused a lot of social harm leading to the rise of populism. The odometer shock that will start hitting low wage earners forced to migrate to EV may have less important but similarly surprising unintended consequences.
- davrosthedalek 3y ago
  Yes. One of the usual YT channels had this interesting picture. Gas mileage is miles per gallon. Or in this case, do it the European way: l/100km. The unit of that is an area. Typically a rather small one, ca 0.1mm^2. That's the area of a trench you have to dig along your path if you want to supply your car from the trench instead of your gas tank.
  - NickM 3y ago
    That doesn’t make any sense to me. The amount of fuel a trench can hold is its volume, not its area.
    - somewhat_drunk 3y ago
      Probably means cross-sectional area.

Alupis 3y ago

The problem is obvious though, isn't it? Our current infrastructure simply cannot handle a ton of EV's all wanting to charge up all day long - as is done currently with gas stations all over the country. It'll take decades to bring our infrastructure up to where it needs to be to support this - yet people act like we're already there. Some states still struggle just to keep the lights on during major parts of the year...

wilg 3y ago
The load is spread out in a completely different way than gas, because 100% of gas cars get gas at a station, while 80% of people with EVs slow-charge at home (or work or whatever). Fast chargers are for road-trips only. Obviously, if we're going to move to cleaner energy we will need infrastructure investment. Worrying that it's not already there makes no sense. The demand for improved electrical infrastructure will be a forcing function. There's no need to wait for it. But again, most charging isn't fast charging and likely never will be. (Charging for apartments and stuff still has a bit of a way to go, so sometimes those people use fast chargers as part of their regular routine, but the solution to that is easy and underway: just put chargers in the apartment parking lot and/or on the streets.)
- Alupis 3y ago
  > Obviously, if we're going to move to cleaner energy It is very unclear whether electric vehicles actually are more environmentally friendly. They sound great - but if you dig into where all the materials come from, it's shocking how externalized we've made that problem. It might be cleaner by time you get to drive it... but it's not cleaner to produce and operate, and in fact may be worse in some cases. Emissions aren't just from the tailpipe after all - yet that appears to be what most people focus on. > Worrying that it's not already there makes no sense It makes a lot of sense when the government (both state and federal) are pushing initiatives and incentives to force EV's into commonplace. Our infra just cannot handle it, even with trickle chargers like you've claimed. Which means it will be a net-worse experience for people, and they will resist future clean energy pushes as being disingenuous.