Where did the 19% or 23.5% go?

Where did the 19% or 23.5% go?

19% Kwh lost? or 23.5% more Kwh used than claimed by Model S? Seems too much lost.

So many of you on the forum are much more knowledgeable than I am, what am I missing?

Took delivery of Model S in early December. 2nd meter installed prior to delivery. Only one outlet at the other end of the 2nd meter - Nema 14-50. Just received my 2nd electric bill.

Total of 735 Kwh charged by PG&E from early December to Jan 31, 2013.
Model S instrument panel says I used 595 Kwh to Jan 31.
735 is 23.5% more than 595. Or, 19% of 735 is lost as Model S says only 595 Kwh used.

Where is the loss?
- Tesla ownership experience tells me charge efficiency is 92%. Perhaps 92% is ideal, so real life efficiency is less than 92%?
- Model S loses miles just sitting there (4.1 and 4.2 both). Does the control panel register the Kwh lost? I don't think so.
- When one is in the car with screen on, climate on, does control panel register the Kwh used? Not sure.
- Any other source of loss?

Regardless, In 8 weeks, Model S says I went 1694 miles on 595 Kwh, or 351 wh/mile.
PG&E says I used 735 Kwh, or 434 wh/mile. Big difference!! 23.5% more than 351 wh/mile.

My region has among the highest electricity charge in the country. For those in PG&E territory other than Palo Alto or with solar panels, virtually everyone quickly ends at 33.5 cents per Kwh. With the 2nd meter and on E9 time of use rate card, I averaged 11.2 cents per Kwh. The 2nd meter was costly to put in, but I should make it back in a few years.

brewdr | 6 February 2013

I am thinking of installing a second meter because SDG&E rates (tier 4) are 31 cents per Kw. Would you mind sharing the ballpark cost of the addition.

stuberman | 6 February 2013

Yes, the Model S does consume a rather large amount of electricity while parked. I asked Tesla about this and the folks said that it was a software issue that the company is working to fix. Apparently, one of the software updates included a fix, but led to the car not reliably waking from a sleep mode. Understandably, they returned to the earlier software.

I believe that this is something that they can solve. Some of you remember that earlier generation iPhones had a similar problem that was remedied through a SW update.


EVTripPlanner | 6 February 2013

My bill was also a bit higher than expected. 92% is peak efficiency - I would use something more like 88% to estimate (though that would only account for about 14% of your 23% difference). When you're sitting in one place, the trip meter total kWh measurement does NOT change - this makes me think that it is ONLY measuring usage while moving. The remaining range should account for *all* energy used, but I'm not sure where the total kWh in the battery is shown (or if it is shown), so that would be difficult to use to determine total energy used. I have some spreadsheets and reference charts posted at that might come in handy.

I'd also be interested in what it cost to put in the meter (I'm with SCE, but situation is similar)

Hills | 6 February 2013

My installation costs are shockingly high. My estimates are: it first cost me $2000 to put in the Nema 14-50, and then a month later the 2nd meter was put in for about $4000 more.

Why 2000 for the outlet? Electric panel is at the opposite end of the house, had to go down to crawl space, go 75 feet, drill through foundation, up wall of garage, cross two garage doors, etc.

Why $4000 for 2nd meter? $250 to PG&E, some nominal fee to city, multiple site visit by trusted contracter and electrictions, new panel, modify shed that houses the panel, etc. Many hours were spent just to determine feasibility. I know materials alone were more than $1000. Electricians' hours add up quickly, and the final stage was Electrician with two helpers spending entire day.

DonS | 6 February 2013

92% only applies from when you plug it in to when the charge is done, assuming ideal temperatures. All the rest of the time, the car is draining energy and lowering the overall efficiency, and its worse with extreme temperature.

jat | 7 February 2013

Yes, "up to 92%", which means it is going to be lower depending on the current SoC of the battery, temperature, etc. In addition, that describes only the losses in the charger itself - you have other losses:
- the battery loses about 2.5kWh/day just from running the electronics (we will get much of this back when they re-enable sleep mode)
- the mobile connector or other EVSE has some loss
- if it is cold, the battery needs to be heated
- running the heater when you aren't in it (ie, triggered from the mobile app) does not show up in the dashboard

I need to go through my data now that I have had the Model S a month, but when I analyzed it for the LEAF, I was averaging 87% efficiency for everything from the panel to the batteries.

In your case, after you subtract out the 2.5kWh/day, you seem to get about 90% efficiency (595/(735-77.5)), so I would say you have about what is expected and the big issue is the loss of sleep mode. If you had 4.1 for most of the month, then that would put your efficiency down to around 86%, which wouldn't be unexpected either (especially if you were mostly charging a battery that hadn't been depleted much).

Mark Z | 7 February 2013

There are a number of steps in having the charge station installed that are hidden from the customer but not the electrician. Southern California Edison has an excellent document on the subject geared toward electricians. It makes the process easy to understand for the customer as well. I found this single document helpful in deciding what meter changes to consider and the total work involved.

The customer pays the electrician for the installation of an optional extra meter panel plus junction boxes. However, SCE does not charge the customer for their part in consultation, planning, and the mounting of a second meter with the supply wiring changes to the meters.

Don't forget the rate plans. One web page makes it easy to compare all the SCE EV rates. Notice the 60 cent rate for a single meter time of use plan during peak 2nd tier usage.

stuberman | 7 February 2013

In tribute to Volker, here's an earlier discussion of the lost charge issue:


Hills | 7 February 2013

- Percentage math, two ways to look at the issue, both are correct. I used 23.5% more Kwh than indicated by Model S, or 19% of incoming Kwh lost to variety of factors. When one looks at the 350 wh/mile used for the 1800 miles, the reality is that model S used 432 wh per mile!
- For 7 out of the 8 week period, the car was on 4.1 with sleep mode, but I was never impressed with the sleep mode, as 4.2 did not improve the loss by much.
- Compared to most of the country, climate is mild in the SF Bay area.
- 75% of the charging is from 175 to 240 miles, this is rated miles, standard charge, not max charge.
- Modest heater use the entire 8 weeks, 1/2 the time climate not even on, but most of the time seat heater on setting 1, the lowest setting.
- I still maintain that 19% is the loss, for every Kwh I pay to electric company, 19% did not go to "driving". For those of you thinking about 2nd meter, I hope you can do it cheaper than I did. It is fairly easy to compute the savings per mile compared to gasoline.

For my driving style, the comparison is to my old ICE car.
- I used to get 23 miles/gallon on premium gas, full size hi end ICE. At $4/gallon, that is $1740 per 10,000 miles
- If I average 360 wh/mile on model S (we have been driving far too conservatively), then I will use 445 wh/mile from PG&E, and my estimate is I will average 13 cents per Kwh even with 2nd meter. Payment to PG&E will be $578 per 10,000 mile. I save $1160 per 10,000 miles compared to my old ICE.
- Compared to sticking with one meter, it would cost me 20.5 cents more per Kwh, For every 10,000 miles, would pay PG&E $912 more per 10,000 miles.
- None of the above accounts for green, no exhaust, no trips to gas station, driving pleasure, etc. Now that I have nailed down the costs, time to enjoy the driving!

Hope that helps. | 7 February 2013

Great info. I'm on PG&E's E9 with a single meter. I'm now looking at a second meter as the panel is less than 40 ft from the current wall connector. To bad PG&E can't deal with it as a single meter and just increase the baseline. I'm sure there is endless regulatory approvals required for any rate plan.

Hills | 7 February 2013

It took me many hours to figure out the PG&E requirements. Here are some of the steps. You need to call and then file application, PG&E needs to come out for site visit, need approval from your city, electricians to do the work (doubt that electric utility or city will accept unlicensed homeowner doing the work), need final inspections from city and PG&E to verify that the 2nd meter is for EV only. Even with 2nd meter, the peak rate rises quickly to 29 cents/Kwh in winter for off peak, and as high as 54 cents for peak in summer. The main point of 2nd meter is to get fresh new baseline.

Electron | 7 February 2013

Has anyone heard any details on PGE's "new" EV rate schedules coming in March?
They are replacing the E9 rate plans which will go away. Just curious as I'm considering
switching to E9A soon.

jat | 7 February 2013

@Hills, sure either way to look at it is fine, but you can't mix them -- 92% charger efficiency means that 92% of the power that reached the charger made it to the battery, so the number for comparison there is 19% loss, or 81% overall efficiency.

olanmills | 7 February 2013

Even with my electricity bill doubled, it still costs me less than 1/4 of what I used to spend on gas.

mal42north | 7 February 2013

The Web site says the new rate that replaces E9 will be an optional switch for those on E9 already. But by 2014 the switch will be mandatory. The new EV rate will be un-tiered time of use.
You can get a 19 page PDF which describes the new rate from the link below. Basically (approx) off peak ~ $0.1, partial 0.165 winter 0.2 summer, peak 0.27 winter 0.36 summer. Looks like the time of use will be same in summer and winter, and the same as the current E9-summer. For those of us on the coast, where the base usage tier is laughably low (unless you are single and live in a bedsit) this will probably be a significant improvement. If you live in the interior, not so advantageous.


Hills | 10 February 2013

Back in October, I managed to get someone at PG&E to run simulation of what my bill would have been in the past year on E9, E6, and E1. Start with the general PG&E number and ask. May have to try more than once as not everyone who answers the phone possess equal knowledge.

lov2krz | 10 February 2013

I posted th e PGE rate schedules for E6 and E9 on this post

I installed my NEMA 14-50 outlet for $250.00. Interoir Outlet was on same wall as the exterior service panel about 5 ft of power cable used.

I've decided to stay on E6 rates since I over produce on an annual true-up basis. Wondering if installing a second E9 meter is possible.