Comment by CoffeeDregs | Hacker News Reader

Comment by CoffeeDregs | Hacker News Reader

Unless I'm misunderstanding how it works, some questions about this idea:

  * Presumably, you have to fully empty and then fill your tank?
    Over twice as long to refill as for gasoline/diesel.  (Still:
    not terrible.)

  * How do you get refunded for your partially used "fuel"?
    I generally refuel around a quarter of a tank.  In this case,
    that means I'm sending back 25% unused fuel.
    (Pump it out, analyze the mixture, provide credit?  Seems seriously game-able.)

  * Is the power output constant regardless of charge?  Can I get 20kW
    of output at 25% charge?

Extracting the fluid is already going to be an interesting task (it seems like it'd probably be uneconomical to suck it out with a vacuum). I can see the cars having separate input and output holes. With a clever design in the car you could probably start refilling while you finish emptying.

A recharge should be pretty cheap. The national average cost for electricity is ~13¢/kWh, so refilling a 100 kWh battery would only be $13 of energy. Other costs - storage, maintenance, labor, land, etc - add to that, but you still aren't out that much. It's possible that you just pay full price regardless, since they are giving you totally fresh solution.

One of the most important things about flow batteries is that they're basically invariant with charge and scale, so almost certainly (until you really hit the dregs - you probably lose voltage at 4%).

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