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Hi, I have a survey for a proposed rapid charging system for home use. The research is part of a university project and is just an idea but would hugely appreciate any responses. It's only 6 questions and takes one minute! The questions are for EV owners and ask about charging habits etc.

Rapid EV charging at home - here's the link at Survey Monkey!

The premise would be to use second-life electric vehicle batteries in a home charging system. The grid would 'slow' charge the battery when not in use and then discharge into an EV quickly. The charger would also have the capability to charge slowly if the owner wanted. There are several companies using this idea for rapid charging, however, it seems only in the public charging network.

Thank you :)
 

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Answered, but think you're going to get the same answers from everyone here.

There's no need for rapid charging capability at home - I come home, I chill out for the evening and eat a meal, go to bed, get up in the morning and go to work again. There's 12 hours or more that the car is sitting still, so even a big battery could be fully, or almost fully, replenished in that time by the 7kW charger that I already have.

The cost and complexity of what you're proposing comes with no real-world benefits for domestic use. Far better to put the second-life batteries into regular grid/domestic storage for load-shifting and elimination of grid pick-up.
 

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Good idea, but in practice the cost would be prohibitive. Because there's so few use-cases it's not worth the cost.

The idea of EV is to park up and let it charge while you do other stuff. A 7 hour charge on a standard home 7kW charger gives 49kWh, enough to cover 200 miles in an efficient EV (Model 3, Hyundai/Kia).

The ONLY use-case that might be useful is when you arrive home empty, and need to go somewhere quickly. But that can be easily solved by a 15min en-route stop, just as petrol/diesel cars do.

A far better pitch, as I-s said, is for the home-battery to act as home battery and grid stabilising device. Your car is also Vehicle-2-Grid capable, so when at home, car battery add to your home storage. Then the rapid charging makes sense.
This rapid charging capability is using existing hardware intended for home battery and V2G, not buying all new hardware JUST to be able to rapid charge at home.
 

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I have done your survey. However I think there are problems with your premise.

1) The requirement for Rapid Charging at home is minimal.
2) It is outstandingly poor value for money in respect of both capital cost and operating cost due to the increased inefficiency of moving energy across a chain of two batteries.
3) It is used in public charging because of grid supply problems. This issue does not really occur for domestic supply unless somebody wants to charge two EVs at the same time. As battery capacity is increasing and average mileage in the UK is 28 miles a day it means charging a vehicle once or twice a week and thus it is easy to deconflict charging two vehicles on a single domestic charger.
 

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There will be occasions when we would like faster home charging for our Model 3, for example we get back at low SOC and need to go out again, but it will be rare and I doubt we would pay much vs. "affordable" 7kW charging.

There may be more of a market in mainland Europe where houses often have a limited supply so charging can be slow or difficult.

We have just 20A in Spain and upgrading supply is expensive! As we do holiday rents we considered fitting a charger, but have little supply left when cooker, AC and water heater are all on! At some point we might add one capable of load sensing - I hadn't realised the latest Podpoint Solo could do it, so may look at a used one.

If a home DC charger was developed, my suggestion would be to allow single or three phase AC input and perhaps 22kW DC output (or less?). I believe the V2G trials for Leaf are just 6kW CHAdeMO

As @donald has suggested, in long term it may be that cars don't really need onboard AC chargers. Removing is one way to reduce cost and complexity.
 

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There could be merit in battery backed storage at a community level as a shared resource instead of in a single household.

Thus ensuring one could still charge a vehicle at any time without being dropped off the network because of a peak load issue.

One could also use it with metering to store excess local solar PV and use the stored energy at the best time for:

a) reducing local DNO supply stress
b) lower cost per kWh
c) more nearly equal efficiency since battery storage efficiency (one way) is about the same as loss due to transmission one way over the National Grid
d) ensuring the battery is discharged and able to accept a fresh charge the following day when local Solar PV generation is good.

Without the EV dimension this is being tested small scale on the island of Iona by the following company.

Home » Swanbarton
 

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Discussion Starter #11
Thanks for all the feedback it's hugely appreciated, It's clear that the use case for such an idea is problematic in a household setting. To give a bit more info on the project, we are looking at this solution for the public charging network as well. For the assignment we had to show we had done some primary research so wanted to see what EV owners had to say for home use. Here's the article we got the idea from if anyone is interested: https://www.sciencedirect.com/science/article/pii/S0301479718313124

:)
 

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Also, consider that the next gen EVs will have 40+ kWh to fill; that's a huge battery by home-battery standards! Not a lot of point in having a modest 10 kWh home battery, then try to rapid-charge yr EV at say 50 kW - you'll only put about 40 miles range in! If the journey you're in a rush to do is local, then surely you should have enough capacity with your 160 mile range, to be able to manage a local trip. If your journey's a long one, say over that 40 miles, then you'll probably find a significantly faster 150 kW Rapid somewhere else, maybe it's only 10 miles away, so you've wasted time putting 40 miles in to begin with, when you're better off time-wise putting 10 in at home, and the 30+ at the super-fast Rapid.
 

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As said the obvious domestic use is to either arbitrage overnight cheap electricity, or store daytime solar, or both.
Rapid home is a complete non starter from an economic, practicality and usefulness POV.
 

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If houses become capped to 3kW supply each to ease the load on the local network then having 20kWh of old LEAF might be very helpful to deliver 7-11kW of charging.

Might be a solution for areas that would struggle to facilitate every home charging an EV.

Not sure if it's still the case, but I recall Italy largely having houses with a ~3kW supply - if you wanted more you paid a bigger standing charge (eg if you wanted a 15kW max supply you'd pay 5x the standing charge) but the kWh charge remained the same.

That's how they managed their grid issues.
 

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If houses become capped to 3kW supply each to ease the load on the local network then having 20kWh of old LEAF might be very helpful to deliver 7-11kW of charging.

Might be a solution for areas that would struggle to facilitate every home charging an EV.

Not sure if it's still the case, but I recall Italy largely having houses with a ~3kW supply - if you wanted more you paid a bigger standing charge (eg if you wanted a 15kW max supply you'd pay 5x the standing charge) but the kWh charge remained the same.

That's how they managed their grid issues.
Aside that's not going to happen (especially as we are going to be banning gas central heating eventually so the network will have to cope with everyone heating their house , bottom line is a 20kWh old battery can only supply 10-15 kWh of charge into what will be a 60kWh or bigger car battery so what would be the point?
No point going to all that expense supplying 11kWh if its just for an hour. As said upthread people will just go and rapid charge commercially to fill up in that circumstance since they will need to anyway, with the exception of a tiny handful of unlikely edge cases that don't make the expenditure worthwhile. Am I going to spend £5k so once every three years I can save 15 minutes? A limo service would be cheaper.
V2G or V2H would be a better solution for any local supply issues, with much bigger batteries in much better condition.
 

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I have always considered it possible to install a 'buffer' battery at home that is always taking a very small charge ( or a timed one to cost shift the operation) and then able to download the stored charge to the car at a very high rate. Obviously, the cost of such a store of DC energy prohibits the idea for most people but that doesn't take away the usefulness of the concept.

If such a store is also linked to solar or a smart energy supply that can also power the house so much the better but that again raises the cost implication as the store would need to be much larger. But the overall idea of time shifting input for home use and/or the ability to rapidly fill a car is sound. Just a minority uptake project due to the unrealistic cost implications for people with modest means.
 

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This might make sense as an addition to general home battery storage rather than a thing in its own right but I don't just think the economics or physics make sense at the moment.

Let's say you want to give the home owner the ability to DC charge their car at 50kW. What size battery would you need to support that kind of discharge rate over and over without damaging the battery?

A Tesla Powerwall 2 has 13.5kWh capacity is rated for 5kW power output so you would need 10 of those to support 50kW charging. That's 135 kWh! I'm sure it's possible to do 50kW safely with less batteries but even if you halved that to ~70kWh that's still a LOT of batteries and would be very expensive.
 

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Driving my Ampera at 100 mph continuously (assuming I still got the 40 mile range!) would drain my 10 kWh in 40/100 hour, so that's a 100/40 = 2.5C discharge rate, or 25 kW. As I wouldn't get that far, the battery would actually discharge at a higher rate, so maybe 30 kW or more. But lets be a bit conservative. So a 2.5C would seem possible.

So you'ld be looking for maybe a 20 kWh battery, to power a 50 kW Rapid, and draining it 100% in that 24 minutes it lasted. That's a bit harsh on the battery, so make it say 25 kWh & use 80% of the capacity. Still rather pricey for the saving of relatively little time. I'd rather have that extra 25 kWh in my own car to begin with, thank you!
 

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I have always considered it possible to install a 'buffer' battery at home that is always taking a very small charge ( or a timed one to cost shift the operation) and then able to download the stored charge to the car at a very high rate. Obviously, the cost of such a store of DC energy prohibits the idea for most people but that doesn't take away the usefulness of the concept.
The cost of the battery would be a rounding error compared to the fast charger you'd be paying £100k+ for just so you could once in a blue moon charge at best 25% your car in 10 minutes. Then you'd have to wait whilst the other 75% trickled in a domestic speeds .

If you had that much spare money you'd just buy a car with the biggest battery you can get or even a spare car you kept topped up would probably be cheaper and certainly more useful.

There are no upsides to this idea for very high rate charging which was the initial proposition. Time shifting electricity cost isa different case entirely.
 
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