Fast charge profile at 10°C and time-based pricing

[KiwiME]

Here in New Zealand the government is going to add road taxes to our EVs in two years, adding costs of about $0.072 per km. Because I charge exclusively at public chargers I've been studying the cost effect of fast chargers that bill on a units + time basis. I was going to base my calcs on the widely-distributed charge profile from www.fastnl.nl that most of you have seen (bottom image) but thought I should verify at least part of it, noting it's winter here.

In 10°C ambient I did a short test from exactly 60% to 70% (using the charge limiter). I noted the charge rate at every 1% SoC and integrated that (in Excel) to calculate the kWh the car indicated has been delivered to the battery.

The billed amount was higher than calculated, presumably due to the car being 'on' so I could read the display, what I called 'overhead' in the spreadsheet.

You can see that instead of the 47 kW rate we would get in summer temps past 70%, it's down to around 22-23%. This ABB 50kW charger bills at $0.40/unit but if it was billing at the more common $0.25/unit+$0.25/minute the effective cost per unit is doubled to $0.80/unit.

It's also interesting that the calculated energy delivered to the battery at 7.43 kWh was a fair bit higher than the 6.4 kWh that 1/10 of the battery capacity would represent. There must be charging losses due to heating but 6.4/7.43 = 86% is far more than I would expect.
Is charging really that inefficient at a mere 10°C?

 

[electriceddy]

Here in New Zealand the government is going to add road taxes to our EVs in two years, adding costs of about $0.072 per km. Because I charge exclusively at public chargers I've been studying the cost effect of fast chargers that bill on a units + time basis. I was going to base my calcs on the widely-distributed charge profile from www.fastnl.nl that most of you have seen (bottom image) but thought I should verify at least part of it, noting it's winter here.

In 10°C ambient I did a short test from exactly 60% to 70% (using the charge limiter). I noted the charge rate at every 1% SoC and integrated that (in Excel) to calculate the kWh the car indicated has been delivered to the battery.

The billed amount was higher than calculated, presumably due to the car being 'on' so I could read the display, what I called 'overhead' in the spreadsheet.

You can see that instead of the 47 kW rate we would get in summer temps past 70%, it's down to around 22-23%. This ABB 50kW charger bills at $0.40/unit but if it was billing at the more common $0.25/unit+$0.25/minute the effective cost per unit is doubled to $0.80/unit.

It's also interesting that the calculated energy delivered to the battery at 7.43 kWh was a fair bit higher than the 6.4 kWh that 1/10 of the battery capacity would represent. There must be charging losses due to heating but 6.4/7.43 = 86% is far more than I would expect.
Is charging really that inefficient at a mere 10°C?

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I have seen on occasion a 22kW rate on the same type ABB machine ( Terra 53CJ) with 60% SOC at mid teens ambient, never could figure out why, maybe started charging at too high a SOC? (Just wanted to top up to 75% or so). Could be software related to ABB. Any other brands of DCFC machines you can test on?

 

[Vanryan]

Here in New Zealand the government is going to add road taxes to our EVs in two years, adding costs of about $0.072 per km. Because I charge exclusively at public chargers I've been studying the cost effect of fast chargers that bill on a units + time basis. I was going to base my calcs on the widely-distributed charge profile from www.fastnl.nl that most of you have seen (bottom image) but thought I should verify at least part of it, noting it's winter here.

In 10°C ambient I did a short test from exactly 60% to 70% (using the charge limiter). I noted the charge rate at every 1% SoC and integrated that (in Excel) to calculate the kWh the car indicated has been delivered to the battery.

The billed amount was higher than calculated, presumably due to the car being 'on' so I could read the display, what I called 'overhead' in the spreadsheet.

You can see that instead of the 47 kW rate we would get in summer temps past 70%, it's down to around 22-23%. This ABB 50kW charger bills at $0.40/unit but if it was billing at the more common $0.25/unit+$0.25/minute the effective cost per unit is doubled to $0.80/unit.

It's also interesting that the calculated energy delivered to the battery at 7.43 kWh was a fair bit higher than the 6.4 kWh that 1/10 of the battery capacity would represent. There must be charging losses due to heating but 6.4/7.43 = 86% is far more than I would expect.
Is charging really that inefficient at a mere 10°C?

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Road taxes would be awful for me... my commute is over 100 KM daily.

 

[electriceddy]

Road taxes would be awful for me... my commute is over 100 KM daily.

Lets not give them any ideas

 

[KiwiME]

Any other brands of DCFC machines you can test on?

In a month or two there will be a 50kW Veefil unit here at the 0.25+0.25 rate. But next week I will do a 300 km round trip and visit the four Terra 53 units starting here and along the way, all are $0.40 per unit. I'm planning on doing the same session 60-70% exactly (7 times) to verify that the costs and kWh are consistent. I won't do the profile because I want the car 'off' for best accuracy.
Hard to find but research says that the kWh is almost certainly based on the DC side.