adlr
Posts: 7
Joined: Sun Jul 14, 2013 7:59 pm
Delivery Date: 17 Jul 2013
Location: Belmont, CA

Public charging cheaper than home calculation?

Mon May 25, 2015 2:09 pm

Hi folks,

Recently some public chargers near me went from free from $1.50/hour. I'm trying to figure out if that's cheaper than home charging or not. Before you say it's more expensive than home, consider the things working against me at home:

I'm on PG&E E6 rate and typically hit tier 3, so the charge is $0.24163/kWh

I charge with an original L1 charger (which has 70% efficiency?).

When charging in public, I use the 6.6kWh charger L2 charger only (no L3 charger on my car).

I'm on a 2013 model year, fwiw.

Does anyone know how to do the calculation to figure out what's a good deal for public charging for me? I suppose this calculation would be further complicated by the fact that some public charging is on 208V rather than 240V.

Thanks so much!

billg
Posts: 195
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Delivery Date: 05 Aug 2014
Location: DFW, TX

Re: Public charging cheaper than home calculation?

Mon May 25, 2015 3:54 pm

Assuming you can add about 6 kWh in an hour of public charging, each kWh costs you about $0.25 ($1.50/6). So, it's a wash with your $0.24/kWh at home.

cwerdna
Posts: 9807
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Delivery Date: 28 Jul 2013
Location: SF Bay Area, CA

Re: Public charging cheaper than home calculation?

Mon May 25, 2015 5:08 pm

^^^
Yep. At my work, the EVSEs run at 208 volts (per the Chargepoint tech who came out). My car draws about 5.7 to 6.0 kW on those L2 EVSEs, so 5.7 to 6.0 kWh in 1 hour.

But, if you charge to 100%, once you pass a certain point (somewhere past 90% SoC per the dash display... maybe somewhere between 94 to 97%?), the taper begins, followed by bounces. See http://www.mynissanleaf.com/viewtopic.p ... 38#p338038" onclick="window.open(this.href);return false;. That takes up about the last hour of charging. So, the OP would want to unplug before that.

I can tell you that when the car's in its bounce or taper phase, the car often reads 98% SoC with maybe 0:50 or 0:40 remaining. If you unplug at that point, the SoC display often jumps to 100%.

If you charge to 80% or even 90%, it's full speed the entire time on L2.

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mjblazin
Posts: 240
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Leaf Number: 405999
Location: Dallas, TX

Re: Public charging cheaper than home calculation?

Mon May 25, 2015 6:13 pm

Most Leaf Spy measures I get with public are less than 6 kW/hr. I doubt public would ever be cheaper even with that extraordinarily high Home rate. In TX my rate is $0.114 and that is slightly above market since I go with wind company. We still have people here complaining about power companies post deregulation ripping them off. At $0.24, there would be serious complaints.

How could public ever be cheaper? Individually metered lines,one or two per site,no leverage with sponsoring business' usage + equipment depreciation + return on sales.
I doubt the publics need to give away the service so fully allocated pricing should fit.

Publics work fine for people like me that charge two or three times a week, usually 10-12 kWh at a time. I pay more at the Starbucks waiting for the charge to finish than for the actual charge.
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Graffi
Posts: 405
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Re: Public charging cheaper than home calculation?

Mon May 25, 2015 6:31 pm

By far, the largest cost of charging away from home is your time. For this reason I quit getting the "FREE" charging at the dealer L3 because my time was worth more than the cost saved. It is easier for me to pull into my garage and plug in any time I return home, and in less than an hours I am usually ready to go again. I only go to 100% once each week or so, usually just 80%.
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cwerdna
Posts: 9807
Joined: Fri Jun 03, 2011 4:31 pm
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Location: SF Bay Area, CA

Re: Public charging cheaper than home calculation?

Mon May 25, 2015 6:37 pm

mjblazin wrote:Most Leaf Spy measures I get with public are less than 6 kW/hr. I doubt public would ever be cheaper even with that extraordinarily high Home rate. In TX my rate is $0.114 and that is slightly above market since I go with wind company. We still have people here complaining about power companies post deregulation ripping them off. At $0.24, there would be serious complaints.

How could public ever be cheaper? Individually metered lines,one or two per site,no leverage with sponsoring business' usage + equipment depreciation + return on sales.
Public can be cheaper. Some places are $1/hr w/30 amp L2 EVSEs.

Our default non-TOU plan (E-1) on PG&E is at http://www.pge.com/tariffs/tm2/pdf/ELEC_SCHEDS_E-1.pdf" onclick="window.open(this.href);return false; (see page 1). If you're hitting tier 4 (201% - 300% of Baseline), it's 33.5 cents/kWh.

http://www.pge.com/en/myhome/saveenergy ... index.page" onclick="window.open(this.href);return false; says
The PU code specifically requires that baseline quanties fall between 50 and 60 percent of average use for basic-electric customers in both the summer and winter and for all-electric and gas customer in the summer. The PU code also requires that baseline quantities fall between 60 to 70 percent of average use for all-electric and gas customers in the winter. PG&E's baseline summer season is April 1 - October 31 for gas and May 1 - October 31 for electric. PG&E's winter baseline season is November 1 - March 31 for gas and November 1 - April 30 for electric.
What's my current baseline (100%)? 10.1 kWh/day because it's "summer" (I'm in area X, code B) or 303 kWh/month, assuming 30 billing days. So, if I were on E-1 every kWh from ~397 kWh to 606 kWh costs me 27.5 cents. Each kWh beyond 606 costs me 33.5 cents.

I'm E-6 though. See page 2 of http://www.pge.com/tariffs/tm2/pdf/ELEC_SCHEDS_E-6.pdf" onclick="window.open(this.href);return false; and page 4 for the definitions of time blocks and days.
Graffi wrote:By far, the largest cost of charging away from home is your time. For this reason I quit getting the "FREE" charging at the dealer L3 because my time was worth more than the cost saved. It is easier for me to pull into my garage and plug in any time I return home, and in less than an hours I am usually ready to go again. I only go to 100% once each week or so, usually just 80%.
I hear you. There's the whole time, value, money thing. As someone reminded me, you can always make more $ but time that's spent/gone, you can never get back.

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'13 Leaf SV w/premium package (owned)
'13 Leaf SV w/QC + LED & premium packages (lease over, car returned)

Please don't PM me with Leaf questions. Just post in the topic that seems most appropriate.

adlr
Posts: 7
Joined: Sun Jul 14, 2013 7:59 pm
Delivery Date: 17 Jul 2013
Location: Belmont, CA

Re: Public charging cheaper than home calculation?

Mon May 25, 2015 8:59 pm

Thanks, all! I was over-complicating my math earlier and after reading this, it's clear.

I also agree on the whole time vs. money thing. Sometimes, though, you find yourself at an L2 charger and even though you don't need to charge, it might be worth it if it's cheaper than charging at home. For these (admittedly rare) instances, it's good to know the price cutoff.

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