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the dark side of cobalt
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mikeselectricstuff:

--- Quote from: nctnico on July 11, 2023, 08:39:42 am ---Secondly using a car's battery as storage means using a battery in a way that it hasn't been designed for and you'll be wearing the most expensive part of the car without getting the monetary value for that wear. The idea is similary stupid as using solar roadways to heat roads in the winter. The power companies love it though because it means a free lunch. No, it is making money with a lunch on top for them.

--- End quote ---
That has been debunked by trials in the UK - the charge rates and levels were shown to have no negative impact on battery lifetime, and in some cases actually improved things by keeping the battery in its most healthy SoC range for more of the time.
However home V2G is probably too expensive and inconvenient in practice to be worthwhile. Using it for home solar storage & backup is more likely to be useful, as well as fleet type situations where usage patterns are more predictable and hardware is more concentrated.
Siwastaja:

--- Quote from: mikeselectricstuff on July 12, 2023, 12:21:33 pm ---That has been debunked by trials in the UK - the charge rates and levels were shown to have no negative impact on battery lifetime

--- End quote ---

Yes. People who assume that cycling a li-ion cell is like incrementing a cycle counter or something always make this mistake. Most wear happens when charging at relatively high current near full battery. V2G cell wear can be easily optimized next to nothing by some simple limits in place, that's not the problem. The question is more about the cost of the bidirectional inverter. The low-hanging fruit is to just cut charging current to zero when necessary, and that already has a lot of potential for grid stabilization / cost management.
PlainName:
Could you imagine using a UPS where your colleagues randomly take the battery away to power the coffee maker or something? A bit ridiculous, but grid storage using cars that will be going AWOL, and typically all at the same time, strikes me as somewhat similar. I guess they figure that if the car is gone then there won't be anyone using electricity at the home, but that's not a valid assumption so I'm sure they don't!
tom66:

--- Quote from: mikeselectricstuff on July 12, 2023, 12:21:33 pm ---
--- Quote from: nctnico on July 11, 2023, 08:39:42 am ---Secondly using a car's battery as storage means using a battery in a way that it hasn't been designed for and you'll be wearing the most expensive part of the car without getting the monetary value for that wear. The idea is similary stupid as using solar roadways to heat roads in the winter. The power companies love it though because it means a free lunch. No, it is making money with a lunch on top for them.

--- End quote ---
That has been debunked by trials in the UK - the charge rates and levels were shown to have no negative impact on battery lifetime, and in some cases actually improved things by keeping the battery in its most healthy SoC range for more of the time.
However home V2G is probably too expensive and inconvenient in practice to be worthwhile. Using it for home solar storage & backup is more likely to be useful, as well as fleet type situations where usage patterns are more predictable and hardware is more concentrated.

--- End quote ---

It doesn't even have to be using the battery to charge and discharge either.

A lot of resource is expended on grid stability, this is expensive.  Often times there can be an excess of wind but because it is going to vary a lot the turbines are shut down and gas is used instead.

Well why not push that into cars... If you just say "I need 60% for my commute tomorrow" the car can charge up to 80% if there's an excess of wind or whatever, and it can happen anytime the car is plugged in.

1 million cars at 7kW is 7GW of dispatchable load... about half of the UK's installed wind power.  So while making hydrogen is a good idea for storage, even better is to use EVs.
tom66:

--- Quote from: Siwastaja on July 12, 2023, 12:25:54 pm ---Yes. People who assume that cycling a li-ion cell is like incrementing a cycle counter or something always make this mistake. Most wear happens when charging at relatively high current near full battery. V2G cell wear can be easily optimized next to nothing by some simple limits in place, that's not the problem. The question is more about the cost of the bidirectional inverter. The low-hanging fruit is to just cut charging current to zero when necessary, and that already has a lot of potential for grid stabilization / cost management.

--- End quote ---

The neat thing about bidirectional inverters is the capability usually comes for free once you replace the input diode bridge with a synchronous rectifier.  The power stage is usually a full bridge topology, with a synchronous output rectifier, and the PFC will often have a synchronous switch too.  All of these devices are used to improve efficiency and reduce cooling requirements.  At 7kW it makes a real difference.

This is what the MG4 charger does: it's a fully synchronous design, so it can charge the car at 7kW and discharge at 7kW too. 
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