Pure Economics: When to Pass Up Fee-Based Public Charging

[Steven B]

Does this sound reasonable for determining when to burn more gas in our Clarity PHEV based only on direct economics (no social/environmental costs included)?
To be cheaper than gas @ $3.00/gallon, Electric Charging Needs to Be:
≤ $1.75/hr or
≤ 3¢/min or
≤ 25¢/kWh

The assumption in the per unit time values is that the charge station will supply the full 6.6kW.

 

[KentuckyKen]

Exactly why I don’t use the few local pay to charge Level 2 EVSEs that cost $6!!! for 2 hours. Might make sense for a BEV but not for a PHEV as you have calculated.

 

[Roy2001]

In CA gas is $3.6-3.7, so 30c/kWh.

 

[lordsutch]

One thing you might factor in to your calculation is how much you value the time that putting gas into your car takes, since you can charge unattended but you can't do that with a gas pump. A full charge is the equivalent of about 1/6 of a tank, ergo every 6 full charges saves you a trip to the gas station. So each charge should also offset 1/6 of your "time/convenience" cost of filling up plus whatever marginal driving you need to do to get to the gas station that you otherwise wouldn't have to drive.

I doubt it makes a huge difference, but if your "time is money" or you value being home earlier by 10-15 minutes every day you need to get gas it could be worth paying a little more to effectively multitask.

 

[Rajiv Vaidyanathan]

Additionally, while respecting the fungibility of money, we cannot ignore the nobel prize winning work of Richard Thaler and his theories on mental accounting.

At the University of Minnesota Twin Cities, you pay for parking in their garages, but the charging is free. So, even though I sometimes can park cheaper and closer, i choose to park in a UM garage so I can "mentally account" the cost as regular "parking" charge and consider the charging "free."

 

[Steven B]

Exactly why I don’t use the few local pay to charge Level 2 EVSEs that cost $6!!! for 2 hours. Might make sense for a BEV but not for a PHEV as you have calculated.

Took a long road trip and used three different Chargepoint stations at various times / locations. Only one of those wasn't free: 5.9kWh for $0.89 = 15¢/kWh.

I don't know how Blink stays in business at their high rates.

 

[Rajiv Vaidyanathan]

Took a long road trip and used three different Chargepoint stations at various times / locations. Only one of those wasn't free: 5.9kWh for $0.89 = 15¢/kWh.

I don't know how Blink stays in business at their high rates.

How do you find the free stations? In my area all the stations charge by the hour (one charged me for three hours when I was plugged in during a show even though it used only 20 minutes of power to reach full charge).

Would love to have some easy way of identifying all the free stations when I travel.

 

[lordsutch]

Would love to have some easy way of identifying all the free stations when I travel.

You can use PlugShare.com or their app; it'll let you only search for free stations.

 

[M.M.]

The math there is solid, although if you wanted to get really obsessive the efficiency you get with gasoline varies with speed (increases at speeds above 50mph when the mechanical transmission kicks in), so the exact numbers would vary depending on what kind of driving you were going to be doing next. The OCD engineer in me has already been tempted to make a spreadsheet with efficiency curves to do the math precisely, but the lazy half has thus far resisted the urge.

Also, max throughput on a 30A, 240V charger is actually closer to 6.9kW (I happen to have just measured). I believe Level 2 can go down to at least 208V so if it's current limited (mine pegs at 29A normally) it might vary depending on the charger.

Exactly why I don’t use the few local pay to charge Level 2 EVSEs that cost $6!!! for 2 hours.

Is that in an area with really impacted parking? I could get a charger being that expensive if you're basically also being charged for the parking space (actually, $6/hr is pretty cheap depending on the city), but it seems like a spectacular ripoff otherwise.

Most Chargepoint stations in my area charge a connect fee of around 50 cents plus some amount per kWh (usually around 18 cents), so the exact breakeven point would depend on how far discharged the battery pack was.

 

[jdonalds]

If I charged at home on the grid it would cost $0.15/KWh (24/7). For a 14KW 100% recharge that would cost $2.10 (ignoring inefficiencies). I haven't found a free charge station yet. Every charge station I've looked into is way more expensive
than our local grid cost. On top of that there would be the charge time of up to two hours while I wait.

As mentioned above there is also the advantage of not pulling into a gas station. I figure it takes about 2 seconds to push the button in the Clarity to pop open the door. Then another couple of seconds to plug the charge cord in. Perhaps a couple of more seconds to unplug when leaving home. It already has become routine to plug and unplug at home. My eight-year-old son often does it.

Each of us has a different driving pattern, distance, and conditions so my situation is somewhat unique. Like many others though we simply don't use gas for very long periods of time. We drive, charge, drive, charge all in a day. It's not uncommon to drive 70-90 miles in a day, all electric. We are both retired so our trips all end at the house where the car can easily be charged for the next trip on the same day. Last Friday we took four trips easily totaling 90 miles.

I can't imagine having to go back to an ICE only car. I used to really enjoy driving the 2005 4Runner limited with leather seats, comfortable seats, lots of room, etc. Now when I get in the 4Runner it seems a bit ridiculous. There is the initial engine start up noises. The engine never shuts off even at traffic signals. What a waste! Most of the energy expended goes to simply keep the V8 engine running, not power to the wheels. The 4runner of course sits in the garage most of the time. At 13-16 mpg it makes no sense to drive it unless we have to.

The Clarity is a fantastic car. I believe it sets a new standard.

 

[Wall-e]

Im in Southern California currently pay 0.13 cents/kWh for time of use at night and next month it will go to 0.12 cents/kWh. This is my super off peak rates between 10pm to 8am. I currently get a discount since im an employee of the utility so my net pay is 20% less.

At work they charge us 0.11 cents/ kWh but thats more than I pay for at home so I wait until home.

We also have 4 volta chargers (free charging) within 4 miles of our house so we usually go there to charge if we want to hang out at the mall or grab a bite to eat.

Overall charging makes the most sense at home or at the free volta chargers.

 

[spaj223]

In CA, it let us to switch to EV-A Plan.
If charge of the peak time, it is $.12 KW. It 's much cheaper than my E1 plan which is $.22.

 

[KentuckyKen]

The math there is solid, although if you wanted to get really obsessive the efficiency you get with gasoline varies with speed (increases at speeds above 50mph when the mechanical transmission kicks in), so the exact numbers would vary depending on what kind of driving you were going to be doing next. The OCD engineer in me has already been tempted to make a spreadsheet with efficiency curves to do the math precisely, but the lazy half has thus far resisted the urge.

Also, max throughput on a 30A, 240V charger is actually closer to 6.9kW (I happen to have just measured). I believe Level 2 can go down to at least 208V so if it's current limited (mine pegs at 29A normally) it might vary depending on the charger.

Is that in an area with really impacted parking? I could get a charger being that expensive if you're basically also being charged for the parking space (actually, $6/hr is pretty cheap depending on the city), but it seems like a spectacular ripoff otherwise.

Most Chargepoint stations in my area charge a connect fee of around 50 cents plus some amount per kWh (usually around 18 cents), so the exact breakeven point would depend on how far discharged the battery pack was.

Nope, that’s in Lexington KY and parking is not a problem. One charger owned by the city and one by the utility co., KU. It’s a backward state. No off peak lower rates, no EV tax rebates, no subsidies, and KU is even lobbying to stop allowing solar homes to sell their excess at the going rate. And the Legislature is fixing to tax all EVs $100/yr because they don’t pay enough gas taxes. Is this state even in the 21st century?

 

[ManKo]

Also, max throughput on a 30A, 240V charger is actually closer to 6.9kW (I happen to have just measured).

I have a JuiceBox 40 and the stats when I’m charging my Clarity show a charge rate that typically hovers around 7.28kw (29.9-30amps, 242-244 volts).

 

[Steven B]

How to find stations: I have the ChargeHub app and the Chargepoint app (both free in the app store). I start by looking at the ChargeHub app. You can apply filters to only show "Level 2", "24/7 Only', 'Free', and 'EVPlug' (not sure why they use this term rather than J1772) for our connection type. The ChargeHub app doesn't do a good job of showing 'In Use' status, so you might want the app from the specific network. That's why I have the Chargepoint app. Plus, to unlock the connection to start charging at a Chargepoint station, you've got to either use the app or when you register with them have them mail you a small RFID card to keep in the car. I used the app and had no problems. When you use a Chargepoint station that does charge a fee, you will be assessed $10 regardless of the cost. This amount is basically 'loaded' into your account as credit toward all future Chargepoint usage where a fee is assessed. So after my $0.89 charge, I've got $9.11 left in my Chargepoint account for future use at their stations. I think they will charge in these $10 increments each time your balance reaches zero.

As I was travelling along, it occurred to me that in the not too distant future, they should start showing charging station options on the big blue billboards along the interstates. Maybe some of the $2 billion settlement from Dieselgate will pay for that upgrade.

 

[Steven B]

The math there is solid, although if you wanted to get really obsessive the efficiency you get with gasoline varies with speed (increases at speeds above 50mph when the mechanical transmission kicks in), so the exact numbers would vary depending on what kind of driving you were going to be doing next. The OCD engineer in me has already been tempted to make a spreadsheet with efficiency curves to do the math precisely, but the lazy half has thus far resisted the urge.

Also, max throughput on a 30A, 240V charger is actually closer to 6.9kW (I happen to have just measured). I believe Level 2 can go down to at least 208V so if it's current limited (mine pegs at 29A normally) it might vary depending on the charger.

Is that in an area with really impacted parking? I could get a charger being that expensive if you're basically also being charged for the parking space (actually, $6/hr is pretty cheap depending on the city), but it seems like a spectacular ripoff otherwise.

Most Chargepoint stations in my area charge a connect fee of around 50 cents plus some amount per kWh (usually around 18 cents), so the exact breakeven point would depend on how far discharged the battery pack was.

The max throughput value is not for the full duration of the charge. (Likewise, being an engineer), I'd be interested to see what the power profile looks like over the course of a full charge. For purposes of determining cost, the 'average' power draw is what would matter, right? Is the average 6.6kW over the 14kWh?

 

[Rajiv Vaidyanathan]

PlugShare vs. ChargeHub

Which is the better app to identify available free charging stations? Any opinions? Any other apps that people have particularly liked?

 

[KentuckyKen]

One vote for Plug Share.
Easy to use and customizable.
Shows all the stations as far as I can tell.

 

[M.M.]

The max throughput value is not for the full duration of the charge. (Likewise, being an engineer), I'd be interested to see what the power profile looks like over the course of a full charge. For purposes of determining cost, the 'average' power draw is what would matter, right? Is the average 6.6kW over the 14kWh?

It's pretty close to the whole charge, but the average might work out to 6.6kW. I happen to have recently put a power meter on a 5%-100% charge cycle (percentages according to the app; it had already turned on HV mode at around 9% SOC and I ran the AC for a while in park to bleed it down a little more). It only ramps down for the last 8-9 minutes:

This is AC current at 240V. Note that the noise at the very start is due to an electrical problem, and is not part of the normal charge routine. It's also deceptive; due to a broken waveform (discussion and graphs elsewhere here) the real power in that segment is not actually any higher than at steady state, just the current.

This is measured at the charger, so I don't actually know what fraction of this is going to cooling systems; that may account for the variability. I don't have a good kWh number for that span, only an estimate from the current, but for a 48%-100% charge I got 8.232kWh over a charge time of 1 hour, 17 minutes, 37 seconds, which is only an average of 6.36kW even though all but the last 8 minutes of that was at a steady-state 6.8-7.0kW (mostly in the high 6.9s).

 

[Steven B]

If I charged at home on the grid it would cost $0.15/KWh (24/7). For a 14KW 100% recharge that would cost $2.10 (ignoring inefficiencies). I haven't found a free charge station yet. Every charge station I've looked into is way more expensive
than our local grid cost. On top of that there would be the charge time of up to two hours while I wait.

As mentioned above there is also the advantage of not pulling into a gas station. I figure it takes about 2 seconds to push the button in the Clarity to pop open the door. Then another couple of seconds to plug the charge cord in. Perhaps a couple of more seconds to unplug when leaving home. It already has become routine to plug and unplug at home. My eight-year-old son often does it.

Until you take longer trips and start looking for charging stations, you don't have to think about what to do during the time the car is charging. Sure, pumping gas takes more time that plugging and unplugging your car, but if you don't have purposeful activities to fill the charge time with, filling with gas is much more time efficient. I feel for the BEV folks out there who plan out their trips to make the optimum use of their time while the car is charging. Many of the charging stations along my recent road trip were at car dealerships with zero nearby time sinks, such as restaurants. And since the Blink network is what Cracker Barrel has and their rates are absurd, I didn't use those.