Calculate electricity cost? - Kia Niro Forum
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post #1 of 22 (permalink) Old 04-11-2019, 11:23 AM Thread Starter
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Calculate electricity cost?

I'd readily admit I'm not the sharpest knife in the drawer when it comes to numbers, it I think some of you are.
I'm trying to figure out operating costs for the EV power of the Niro PHEV. Here in Seattle the electric rate is 11 cents / Kilowatt hour. How would I determine the cost of juice to drive 26 in BEV mode? Thanks
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post #2 of 22 (permalink) Old 04-11-2019, 02:32 PM
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Quote:
Originally Posted by Dovidan View Post
I'd readily admit I'm not the sharpest knife in the drawer when it comes to numbers, it I think some of you are.
I'm trying to figure out operating costs for the EV power of the Niro PHEV. Here in Seattle the electric rate is 11 cents / Kilowatt hour. How would I determine the cost of juice to drive 26 in BEV mode? Thanks
the epa sticker claims 32Kwhrs per 100miles.

26miles x 32kwhr / 100miles x 0.11 cents/kwhr = $0.92
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post #3 of 22 (permalink) Old 04-11-2019, 03:24 PM
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I use not to trust that much the stickers

I would say :
- 80% of battery used for EV (26 miles)
- battery is 8.9 kWh
- charger efficiency is ~80% (20% lost in conversion)

So the end result is:
((8.9 * 0.8) / 0.8) = 8.9 kWh required
8.9 * .11 = $0.97 (which is very close to what charlesH found)

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post #4 of 22 (permalink) Old 04-11-2019, 03:26 PM
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Originally Posted by charlesH View Post
26miles x 32kwhr / 100miles x 0.11 cents/kwhr = $0.92
Just as a remark, your calcul does not take in account the efficiency of the charger which is close to 80%.

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post #5 of 22 (permalink) Old 04-11-2019, 03:35 PM
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Originally Posted by padonion View Post
Just as a remark, your calcul does not take in account the efficiency of the charger which is close to 80%.

Christophe.
I assume the epa spec takes charging losses into account.

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post #6 of 22 (permalink) Old 04-11-2019, 05:49 PM
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Originally Posted by charlesH View Post
I assume the epa spec takes charging losses into account.
I don't think that EPA takes charger efficiency in account as it is function of charger used (some may be very efficient, some other like home-charger less efficient).
This is why I used a common rule of 80% knowing that in some case scenario it can be worse, in which case you will pay more kWh for the same amount in your car.

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post #7 of 22 (permalink) Old 04-11-2019, 06:39 PM
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I don't think that EPA takes charger efficiency in account as it is function of charger used (some may be very efficient, some other like home-charger less efficient).
This is why I used a common rule of 80% knowing that in some case scenario it can be worse, in which case you will pay more kWh for the same amount in your car.

Christophe.
The niro "charger" ( converts 120/240 AC to battery level 400v? DC) is in the car. The cord that plugs into the wall plug is just a WIRE (plus signals). It's not converting anything. 100% efficient.

Don't you think it is reasonable to assume gallons/mile and Kwhrs/mile are handled the same way. Measure gas at the pump or Kwhrs at the plug and then measure resulting miles.

I've measured at the plug Kwhrs for a full recharge after ~26 miles ev driving. It's ~ 8.3 Kwhrs. Consistent with 8.9Kwhrs total and the epa spec 100miles/32Kwhrs x 8.3Kwhrs = 26 miles.

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Last edited by charlesH; 04-11-2019 at 06:49 PM.
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post #8 of 22 (permalink) Old 04-11-2019, 08:31 PM
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Originally Posted by charlesH View Post
I've measured at the plug Kwhrs for a full recharge after ~26 miles ev driving. It's ~ 8.3 Kwhrs. Consistent with 8.9Kwhrs total and the epa spec 100miles/32Kwhrs x 8.3Kwhrs = 26 miles.
your calculation is consistent if you consider that the Niro uses 100% of the battery, but each time I plugged it with '0' miles EV remaining, I'm still at ~20% battery, this is why I consider that full charge is only 80% of 8.9kWh and not the full battery.

And I'm pretty sure that between your home power meter and your battery in the car, there are some lost energy in conversion (conversion is never 100% efficient). And all discussion I read and video on energy consumption on EV car, the average number used for that conversion loss is ~20%.

This video explains the loss of EV at 9:33 using the efficiency of Tesla charger at 90% which is high.


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post #9 of 22 (permalink) Old 04-11-2019, 10:48 PM
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Originally Posted by padonion View Post
your calculation is consistent if you consider that the Niro uses 100% of the battery, but each time I plugged it with '0' miles EV remaining, I'm still at ~20% battery, this is why I consider that full charge is only 80% of 8.9kWh and not the full battery.

And I'm pretty sure that between your home power meter and your battery in the car, there are some lost energy in conversion (conversion is never 100% efficient). And all discussion I read and video on energy consumption on EV car, the average number used for that conversion loss is ~20%.

This video explains the loss of EV at 9:33 using the efficiency of Tesla charger at 90% which is high.
https://www.youtube.com/watch?v=f7MzFfuNOtY


Christophe.
Sure, the in car charger is not 100% efficient. But the charger inefficiency is included in the epa 32kwhr /100miles spec, just like the ICE inefficiency is in the epa mpg spec. You don't need to adjust the EPA spec for either powertrain losses .

Do you adjust the epa MPG spec for the ICE 40% efficiency ?

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Last edited by charlesH; 04-11-2019 at 10:51 PM.
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post #10 of 22 (permalink) Old 04-12-2019, 12:46 AM
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If you're driving a PHEV, then with a full charge, you have an approximate 26 mile range. When you've depleted that range to 0 miles, you're likely to observe a 20% state of charge reported on the instrument console. The car drops out of full-time EV mode around 20% state of charge (SOC). The car depends on the traction battery to start the ICE, so driving the battery to 0% SOC would be a disaster, because you wouldn't be able to start the ICE (and it would also be bad for battery "health" to let it deplete to that extent). Essentially, the PHEV begins to behave like an HEV when the PHEV battery hits 20% SOC. Or you can invite the car to begin behaving like an HEV sooner than that by toggling the EV button while there's still more than 20% SOC in the battery.



When you are looking at the EPA numbers, I believe you are looking at the KWh that the charger consumed to increase the charge from 0 miles EV range to 26 miles EV range, and SOC wasn't a consideration. I don't recall for certain, but I think the EPA numbers measured the KWh consumed by the charging device, not the KWh absorbed by the battery.

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