Woodchopper wrote: ↑Tue Apr 09, 2024 2:25 pm
Likely a dumb question, but would use of a car battery for day to day storage reduce the long term life of the battery? I'm assuming that it would have a lot more charge/discharge cycles than typical use for private transport.
Not at all, it's a very intelligent question. And by chance, it is one of the questions I have been looking at recently as part of a wider V2G/X project. It is a survey project, not primary research. V2G is the acronym for "vehicle to grid" for the idea of using car batteries as temporary storage which can send power back to the grid when that is useful. V2X is the acronym for "vehicle to everything" which includes the notion of communications, which includes both V2G and smart charging - where the car charging is potentially delayed to avoid taking power when that would be inconvenient for the grid - but recognising you still want it charged for 7am or whatever.
First, we should understand that in a typical situation you need extra equipment to be able to use the car battery in this way. There is such a thing as an AC car, (and I'm not talking about
AC Cars) where this equipment is onboard the car, so that the car can input and output AC. Because AC output is what you want to be able to use the electricity in the house or back to the grid. You can't just run the DC current from the battery back through a normal car charger and expect AC to come out the other end. Because such transactions are not reversible. You have to actively put an inverter within the car charger to be able to receive DC back from the battery and feed it into the house or grid. So, in the typical situation, for a normal DC car, you need a special V2G car charger which provides for V2G. And then you will probably need a lot of comms and algorithms, as probably the actual transactions that take place need to be based on the grid situation, and other factors like when you need the car, to determine what happens when.
It turns out that the answer to your question is, it depends. V2G/X can actually be used to extend the life of your battery. Because naive charging behaviour isn't actually best for the battery either. So if you set out entirely to maximise what you might earn from a V2G programme, that might well shorten the life of your battery. But if you set it up for optimal battery management, then you can earn some money and extend the life of your battery. And probably there is some kind of intermediate compromise that does reasonably well for your battery and increases what you can earn from V2G.
There have been a number of trials of V2G. What you conclude from it depends upon what price parameters have been set, and what kind of grid benefits the V2G provider can seek to earn. In one major trial, what the customer saved through V2G was only about a 20% improvement on what they would save through just smart charging - when grid conditions are used to determine which part of the night is the best time to deliver the amount of charge you need. When I read that, my reaction was, why should I do V2G for the small additional gain, when that cycles my battery more and potentially reduces its life. I was thus very interested to learn that there was an even better management program that actually improved battery life.
So V2G is looking rather more promising than I thought - I had tended to think it rather compromised precisely because of the thought raised by your question.
The missing piece in V2G, what could make V2G really useful, is responding to local distribution conditions, rather than to broader grid conditions. Mostly these programmes only consider the broader grid conditions, though not exclusively. Sometimes it has been possible - at least in some other countries, to take local distribution conditions into account. Though the value of doing so depends on you local distribution network, if it is very oversized then there is no benefit. But using V2G to avoid local distribution overloads - which also greatly increases grid loss because of the I
2R loss factor - can potentially be a major source of value, as it avoids or delays proportionately very expensive local grid upgrade requirements. We don't have any kind of a system to reward small-scale providers for that value atmo in Britain, or direct their discharges for that reason.
Maybe when the project is over and if the client publishes the report, I should be able to give a link to it.