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How is backfeeding the grid to power it with EV batteries any different than backfeeding the grid with home solar generated power, this already happens with gri

How is backfeeding the grid to power it with EV batteries any different than backfeeding the grid with home solar generated power, this already happens with grid-tied solar installations (which is almost all of them)?

falcolas 4y ago
Lithium batteries can push a lot more current than solar panels. Orders of magnitude more current. For a point of reference, charging lithium batteries has to happen slower (lower wattage) than discharging, and a car battery pack with a fast charger can pull over 350kw. In comparison, a residential solar system for a house will provide somewhere around 5kw, peak.
- Johnny555 4y ago
  Yet somehow my car doesn't take down the grid every time I plug it in and the car tries to draw 150KW to charge the batteries at max rate. Why would grid storage configure the cars to supply power at the max battery rate? Even if my car and the grid-tie system malfunctioned and tried to send unlimited power to the grid, the 30A breaker its plugged into would trip before it hits 7500W. It's not like it needs to handle a lot of power because EV's don't have that much power to spare, if I have a 75KWh battery and am willing to give up 30% of my capacity to the grid, that's 25KWh, or around 2.5KW for 10 hours.
  - falcolas 4y ago
    The grid, even if its your connection between your mains and your car, needs to be set up to limit the output of the car's batteries. Or the car (powerwall, etc) does. > if I have a 75KWh battery and am willing to give up 30% of my capacity to the grid, that's 25KWh, or around 2.5KW for 10 hours. That depends on how much current you can push. The battery is quite capable of giving up that 25kWh in 10-20 minutes too.
    - Johnny555 4y ago
      The grid, even if its your connection between your mains and your car, needs to be set up to limit the output of the car's batteries. Or the car (powerwall, etc) does. Yes, and it does have those limits in place for charging, some in software (by the EV charge controller telling the car how much power it can use), some hardware (through at least 2 circuit breakers). Why wouldn't the same limits be enforced if using the car for grid storage? Why does the max power output of a car battery have any bearing on whether it can be used for grid storage?
      - falcolas 4y ago
        Because batteries can pump out magnitudes more power in a very short amount of time than solar. The two are not comparable. But ultimately, what speaks more than anything I could ever say is the requirement for backup power generation (including household battery arrays) requires mains power be cut off before engaging - to prevent damage to the grid.
        Johnny555 4y ago
        Because batteries can pump out magnitudes more power in a very short amount of time than solar. The two are not comparable. The batteries aren't connected to the grid directly, the grid can't absorb DC power, it has to go through an inverter. Even if your batteries can supply 500KW of instantaneous power, if they are connected to a 1KW inverter, the most the grid will ever see is 1KW - there's no failure mode that would let a 1KW inverter pump out 500KW of AC power, even for an instant.
kkfx 4y ago
A lot different: backfeeding the grid is not about stabilizing the grid but instead stabilizing the local MICROgrid of our homes, essentially a solar inverter take time to ramp up production when a load appear, take time to step down production when load drop. The grid compensate, with strict limitation, for instance in France you can't push more than 3kW if mono-phase, in Italy 6kW, even if you are allowed to have a monophase 10+kW for instance to being able to recharge your EV at 7kW, the needed common minimum to keep cells in balanced state (3kW slow charge is simply too low for most vehicles, they recharge but the battery might suffer). A simple practical example: my dishwasher start heating water is +2kW in an instance, my solar inverter take 2-3" to ramp up to +2kW. The home microgrid need or the national grid or a battery inverter to avoid collapsing due to a too big frequency drop. The dishwasher have finished heating water, again a sudden -2kW, again I need to divert extra energy to the grid or a battery to avoid a frequency peak big enough to make the inverter disconnect. AC grids are like a tense rope with various "needles" attached to it, some push the rope at a certain frequency, let's say 50 or 60Hz, some are dragged by that frequency. Those who push are generator, like a solar inverter, a NPP etc, those dragged are loads. Those who drag need to keep the frequency so when a new load arrive they need to push stronger at the same rate, when a load detach itself they need to push less at the same rate. It's NOT easy. We have made public grid of a certain size, not too little, not too big, to average the load, we have observed that at a certain size demand is "constant enough" to made easy keep the frequency. Below or above is hard, the resulting grid is unstable. Now, since served people became bigger and grid infra was not evolved with them we start to make "grids interconnections" to help compensate, that's worked a bit, but also sometimes that have made catastrophic cascading effects. We are at a point we can't compensate anymore. Witch means grid instability on grid complex enough that restoring might take time, non in seconds or minutes but in hours or days. Some hope that grid-tied EVs so batteries and powerful, fast inverters, can help absorbing excess energy when grid loads drop, pushing energy to the grid when grid load ramp up. I'm not in the field but given the very small example of my home system (solar + lithium storage) I really doubt such idea can work in practice. Also being an IT guy I fear about it's potential crapload of vulnerabilities. The sole solution I see is re-do the public grid, at State level, for current and foreseeable future needs, with enough NPP, gas PP and distribution networks to have again a stable national grid, no smartness needed. Since I doubt that's happen that's why I invest in a system with lithium storage witch here (France) is definitively NOT convenient economically speaking, preparing to more and more frequent blackouts, longer and longer...

falcolas 4y ago

Lithium batteries can push a lot more current than solar panels. Orders of magnitude more current. For a point of reference, charging lithium batteries has to happen slower (lower wattage) than discharging, and a car battery pack with a fast charger can pull over 350kw. In comparison, a residential solar system for a house will provide somewhere around 5kw, peak.

Johnny555 4y ago
Yet somehow my car doesn't take down the grid every time I plug it in and the car tries to draw 150KW to charge the batteries at max rate. Why would grid storage configure the cars to supply power at the max battery rate? Even if my car and the grid-tie system malfunctioned and tried to send unlimited power to the grid, the 30A breaker its plugged into would trip before it hits 7500W. It's not like it needs to handle a lot of power because EV's don't have that much power to spare, if I have a 75KWh battery and am willing to give up 30% of my capacity to the grid, that's 25KWh, or around 2.5KW for 10 hours.
- falcolas 4y ago
  The grid, even if its your connection between your mains and your car, needs to be set up to limit the output of the car's batteries. Or the car (powerwall, etc) does. > if I have a 75KWh battery and am willing to give up 30% of my capacity to the grid, that's 25KWh, or around 2.5KW for 10 hours. That depends on how much current you can push. The battery is quite capable of giving up that 25kWh in 10-20 minutes too.
  - Johnny555 4y ago
    The grid, even if its your connection between your mains and your car, needs to be set up to limit the output of the car's batteries. Or the car (powerwall, etc) does. Yes, and it does have those limits in place for charging, some in software (by the EV charge controller telling the car how much power it can use), some hardware (through at least 2 circuit breakers). Why wouldn't the same limits be enforced if using the car for grid storage? Why does the max power output of a car battery have any bearing on whether it can be used for grid storage?
    - falcolas 4y ago
      Because batteries can pump out magnitudes more power in a very short amount of time than solar. The two are not comparable. But ultimately, what speaks more than anything I could ever say is the requirement for backup power generation (including household battery arrays) requires mains power be cut off before engaging - to prevent damage to the grid.
      - Johnny555 4y ago
        Because batteries can pump out magnitudes more power in a very short amount of time than solar. The two are not comparable. The batteries aren't connected to the grid directly, the grid can't absorb DC power, it has to go through an inverter. Even if your batteries can supply 500KW of instantaneous power, if they are connected to a 1KW inverter, the most the grid will ever see is 1KW - there's no failure mode that would let a 1KW inverter pump out 500KW of AC power, even for an instant.

kkfx 4y ago

A lot different: backfeeding the grid is not about stabilizing the grid but instead stabilizing the local MICROgrid of our homes, essentially a solar inverter take time to ramp up production when a load appear, take time to step down production when load drop. The grid compensate, with strict limitation, for instance in France you can't push more than 3kW if mono-phase, in Italy 6kW, even if you are allowed to have a monophase 10+kW for instance to being able to recharge your EV at 7kW, the needed common minimum to keep cells in balanced state (3kW slow charge is simply too low for most vehicles, they recharge but the battery might suffer). A simple practical example: my dishwasher start heating water is +2kW in an instance, my solar inverter take 2-3" to ramp up to +2kW. The home microgrid need or the national grid or a battery inverter to avoid collapsing due to a too big frequency drop. The dishwasher have finished heating water, again a sudden -2kW, again I need to divert extra energy to the grid or a battery to avoid a frequency peak big enough to make the inverter disconnect. AC grids are like a tense rope with various "needles" attached to it, some push the rope at a certain frequency, let's say 50 or 60Hz, some are dragged by that frequency. Those who push are generator, like a solar inverter, a NPP etc, those dragged are loads. Those who drag need to keep the frequency so when a new load arrive they need to push stronger at the same rate, when a load detach itself they need to push less at the same rate. It's NOT easy. We have made public grid of a certain size, not too little, not too big, to average the load, we have observed that at a certain size demand is "constant enough" to made easy keep the frequency. Below or above is hard, the resulting grid is unstable. Now, since served people became bigger and grid infra was not evolved with them we start to make "grids interconnections" to help compensate, that's worked a bit, but also sometimes that have made catastrophic cascading effects. We are at a point we can't compensate anymore. Witch means grid instability on grid complex enough that restoring might take time, non in seconds or minutes but in hours or days. Some hope that grid-tied EVs so batteries and powerful, fast inverters, can help absorbing excess energy when grid loads drop, pushing energy to the grid when grid load ramp up. I'm not in the field but given the very small example of my home system (solar + lithium storage) I really doubt such idea can work in practice. Also being an IT guy I fear about it's potential crapload of vulnerabilities. The sole solution I see is re-do the public grid, at State level, for current and foreseeable future needs, with enough NPP, gas PP and distribution networks to have again a stable national grid, no smartness needed. Since I doubt that's happen that's why I invest in a system with lithium storage witch here (France) is definitively NOT convenient economically speaking, preparing to more and more frequent blackouts, longer and longer...