Monday, May 25, 2015

Public chargers in SoCal

This could be simply summed up as eVgo "on the go" (OTG) membership. Their billing sucks, but they are the widest available DCFC for SparkEV. It's almost a monopoly. But they are cheap.

There are three ways to get billed for charging: one time fee, $ per kWh, $ per time. At home, one gets billed for kWh.

Home base rate : $0.17/kWh (SDGE Tier1, up to 531 kWh)
Home typical rate : $0.37/kWh (SDGE Tier3, 690 kWh to 1062 kWh)


eVgo has 3 plans. If you use DCFC more than 2 times a month, their OTG plan is cheapest. They are billing at $ per time; for L2, it's $1/hr, for DCFC, it's $0.10/min ($6/hr). I've discussed SparkEV's DCFC charging speed in previous post, which is roughly 1 second per 0.01kWh (36 kW) until about 82% SoC then dropping off gradually to 4 seconds per 0.01kWh (9 kW) at 99%. Times are actually bit faster than the estimates I give as covered in my previous blog, but we'll use conservative estimates. L2 charging is 3kW.

DCFC: $6/hr * 1hr / (36kW * 1hr) = $0.167 / kWh
DCFC at 99% SoC: $6/hr * 1hr / (9kW * 1hr) = $0.667 / kWh
L2: $1/hr * 1hr / (3kW * 1hr) = $0.33 / kWh

eVgo's L2 charging cost is 15% higher than base rate home charging. There's no reason to use L2 unless DCFC is currently being used and you are in a hurry. If you are in tier3, eVgo's L2 would still be cheaper. But this is my blog; I only care about my usage, which is Tier1.

eVgo's DCFC is cheaper than home charging at base rate. Topping off can get expensive, so one should monitor this. Timer included with most cell phones would be handy to warn you. Considering it takes 20 minutes to charge from 4% to 82% and 30 to 40 minutes to charge to 100%, extra 10 or 20 minutes is only $1 or $2. Still, that extra waste comes from your pocket as MPGe worse than Chevy Suburban, so one would be wise to avoid it.

Home charging or L2 charging uses on-board charger. As discussed in previous post, home charging was found to be about 80% efficient which means 20% of $ is lost. L2 would be better, but I haven't measure it (yet). We assume the same efficiency, but it won't make much difference at such high cost to begin with. DCFC is more efficient at over 90%, and only 10% of $ is lost. Normalizing for efficiency,

DCFC : $0.167/kWh / 90% = $0.185/kWh
Home : $0.17/kWh / 80% = $0.21/kWh
L2 : $0.33/kWh / 80% = $0.41/kWh

True cost for DCFC is about 12% cheaper than charging at home when efficiency is taken into account.

But keen observers will note that eVgo OTG plan has $15/mo fee, and that should be factored in. That cost is spread among each charging session; the more you use their chargers, the cheaper it gets. Considering that their $/kWh is cheaper than charging at home, one would do well to use them often. An example for me would be 8 DCFC in a month with 12.5 kWh per session on average to 85% SoC.

8 * 12.5 kWh = 100 kWh
100kWh * $0.167/kWh + $15 = $31.70
$31.70 / 100kWh = $0.32 / kWh

MPGe from table = 50 MPGe at $4/gal gas
MPGe at 5 mi/kWh = 50 MPGe*5/4 = 62.5 MPGe

Well, well, well! Their true cost comes through! It is about 50% higher than home charging! But you don't really have a choice of not using DCFC. You can opt for cheaper "plan" with $0 monthly with $5 per session fee and twice as expensive per minute if you use less than 3 DCFC per month. For me, having the peace of mind of not restricted to 2 sessions is well worth the cost.

If I only charge at DCFC while keeping under lease mileage of 800 miles / month, and assuming 5 miles/kWh and each DCFC on average to be 12.5 kWh

800 miles / 5 mi/kWh = 160 kWh
160 kWh / 12.5 kWh = 12.8 sessions, round up to 13
160 kWh * $0.167/kWh + $15 = $41.72
$41.72 / 160kWh = $0.26/kWh

MPGe from table = 62 MPGe at $4/gal gas, 4 mi/kWh
MPGe at 5 mi/kWh = 62 MPGe*5/4 = 77.5 MPGe

Even with membership fee, DCFC ends up being cheaper than typical home's tier 3 rate (but more than base rate). DCFC is just too convenient not to have. But it shows SparkEV at low efficiency of 4 mi/kWh would still be better than Prius. It's not as impressive as 90+ MPGe, but still very good.

What is the worst case scenario for OTG plan? You could pay $15/mo and not use the service or use it just once, but that's silly; you'd be better off not having the OTG plan. Argument will be made for using DCFC only 2 times. Let's assume 15kWh charge is taken per DCFC session. Why not 12.5kWh? Because if you're only using it 2 times a month, you're probably in dire situation to get the most bang for the buck. Again, this assumes more conservative estimates.

2 * 15 kWh = 30 kWh
30kWh * $0.167/kWh + $15 = $20.01
$20.01 / 30kWh = $0.667 / kWh

MPGe from table = 24 MPG at $4/gal gas (half of $0.33/kWh number)
MPGe at 5 mi/kWh = 24 MPGe*5/4 = 30 MPGe

It's not absolutely the worst (that would be 0 MPGe), but 24 MPGe is pretty bad. Of course, you're only spending $20 (assuming solar covers the rest) vs $42 when always using public DCFC. But it's all about your convenience. One should do what is convenient and require less dedicated time. If our time is worth $10/hr, bit over 2 hours would cover the difference. Most of our personal time is worth far more than that, even if one gets paid less than $10/hr at work.

But no one drives so little (about 120 miles with 2 DCFC per month). If you assume rest of 800 miles per month comes free from excess home solar or leeching off your friend's electricity, then,

$20.01 / 800 miles = $0.025/mi
$0.025/mi * 4 mi/kWh = $0.1/kWh

MPGe from table = 146 MPGe at $4/gal ga
MPGe at 5 mi/kWh =  146 MPGe*5/4 = 182.5 MPGe

Whether 182.5MPGe is worth the cost and hassle of installing extra solar capacity (or leeching from your friend) is completely dependent on your situation. For me, where I pay base rate at home and don't charge at home much, solar makes no sense. But if you're a high polluter (aka, electricity waster) who cannot DCFC often, home solar could make sense.

One would ask, why is eVgo charging by time instead of energy use? The answer is that not all cars behave this way. As discussed in Nissan Leaf DCFC bashing, their charging speed drops very quickly. If the charging time is cost metric, Leaf would end up paying more. Because they are most popular EV with DCFC as of May 2015, eVgo can make money from them while we benefit. I doubt eVgo would raise the rate to the ire of most popular EV on the road.

There's also the regulatory issues. Some states do not allow metering to be done on kWh basis, but only on time basis. For eVgo to have nation wide roll out and keep their billing the same, they'd have to go with least common denominator, which is billing by time. Seeing how their billing is so messed up even as is, giving deals to SparkEV to simplify things for themselves would be cheaper for them.

I'm not complaining about the cost, but eVgo has pretty bad billing. Their web site is next to worthless, and I have to keep track of all my charging sessions as there's no receipt or any record I can view. But they're just about the only game in town for SparkEV DCFC with clear pricing and convenient locations.


Blink is another popular charging network, but they only have L2 chargers. I haven't seen any DCFC in SoCal for SparkEV, only few Chademo for Japanese EV. Their L2 rate is $0.49/kWh. If they had DCFC for SparkEV, it would be $0.59/kWh. I'm glad I can't use their DCFC. Even their L2 rate is substantially higher. Considering charging efficiency,

$0.49/kWh / 80% = $0.61/kWh

Their L2 rate is approaching eVgo's DCFC rate when the battery is almost full. I did not know this, and I used their charger once when I went to dog beach. But in the future, it's best to avoid them. They may be necessary in a pinch, but that has to be some dire pinch.

To give you an idea of how expensive Blink can get, you'll be getting roughly 25 MPGe when gas prices are $4/gal, 19 MPGe when gas prices are $3/gal (from half of $0.31/kWh in MPGe table post). You'll be better off driving a recent model V8 pick up truck.

Chargepoint, Greenlots

Biggest problem with Chargepoint and Greenlots and others is that their pricing is vague. I haven't used them, but Greenlots are present in many Kia dealerships. When I called to ask how much it'll cost, they told me it's free. But I read at other places that it's free for first few charges, and the cost goes up to $5 or even $15 per session, because they can set whatever price they want. Unless clear pricing is known, I'd avoid using them if there's eVgo near. If there's no eVgo and only Blink is available, I may take a chance to inquire how much it'll cost.


Semacharge seem to have partnered with Walgreens. They are exclusively L2, and no DCFC. I have their card, and they charged me $10 in my credit card for cushion, but I haven't used them. L2 is just not practical and much more expensive in most cases. I'm afraid my $10 has gone to dollar heaven.

And the rest

There are several DCFC at shopping centers in Orange County that take credit card. This is convenient way to charge your car; I don't have to enroll in special membership with card that can get lost or misplaced. But all of them I've seen charge $5/session. This could get expensive for getting small bit of charge to top off to get to destination. I have not used any of them.

When you have eVgo membership, it's better to use them only. For the time being, eVgo OTG plan is the most clear-cut and cheapest for SparkEV.

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