I'm trying to calculate for a Model S P85 the MPG equivalent (MPGe), the cost per mile of driving and how much it costs to fill the battery 100%. The goal here is to compare it to the cost using gas.

My calculations are like this:

Current Max distance with full charge = 265 miles (there seems to be different values for this in the forum)

Maximum charge = 85 Watts

Cost of electricity in SF Bay area, California (using PG&E cost calculator http://www.pge.com/myhome/myaccount/charges/ and Tier 4@34 cents per kWh and 84 kWh) = $29

So

$29 / 265 = .109 = 11 cents per mile

and

265 / $29 = 9.13 = 9 miles per dollar

MPGe

I thought about using this link to figure out the Tesla Model S MPG3 but its too complicated

http://www.edmunds.com/fuel-economy/decoding-electric-car-mpg.html

Anyone have some simple way to do this calculation or a web site that will do it?

Thanks

Mitch

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It depends on your driving efficiency and of course cost of electricity. Calculate you ICE cost as above, using miles driven and mpg and cost per gallon. With an EV you need to know how many wH or kWh per mile (for me I average 340 wh/m, not the most efficient) and multiply that by the miles you drive. I believe recharging those miles back is about 85 % effiecient, so you need to multiply by 100/85.

rough calculation is based on the energy in a gallon of gasoline, ~33kwh.

so if you use the following fomula, you get ~104mpge, but on the sales sheet it says 89mpge combined city highway.

x 265

--- = ---

33.4kwh 85kwh

The rate used in your calculation is E9 summer partial peak tier4

Most charging will be overnight at off peak

Tier 1: about $0.04/KwH

Tier 2: About $0.06

Tier 3: about $0.16

Tier 4: about $0.20

I prefer a different method.

For examle, if I drive 40 miles in a day and use 12Kwh in my model S.

My energy cost is 10cents/Kwh. So 12Kwh costs $1.20.

Charging efficiency is approximately .85.

So total cost to drive 40 miles is 1.20/.85 or $1.41.

If the avg gallon of gas where I live is $3.75, then I used/spent the equivalent of 1.41/3.75 or 0.376 of a gallon of gas to drive 40 miles.

My personal miles per gallon equivalent is 40 miles/ 0.376 gallons or 106 miles/gallon.

I have 8315 miles on my P85, which has used 2702.6 kWh. That comes out to 104 MPGe. The formula I use is: (33.7 kWh/1 gal gas) * (miles driven/kWh used) = MPGe.

You can use Tesla's estimate on their website:

http://www.teslamotors.com/charging#/installation

Just keep in mind that it's on the low side. Your car needs more energy vs. what Tesla calculates as you lose some energy when you charge the car.

For example, I charged 165 miles and Tesla's website says it would use 55 kWh and it really used 66 kWh. So just remember that it's not as efficient as what the website shows. You will lose more than that.

Then just calculate what you pay per kWh with your electricity company.

For today's energy rates vs gasoline, I'm getting 151 mpg equivilent.

Bighorn, what is your rate of electricity that you are paying? That estimate seems high to me. So how did you calculate that? What's your energy per kWh rate? Where are you? Are you using solar, etc?

That estimate seems way high to me.

Also, what are you averaging in the car? What is your average burn rate in the car?

Mitch,

PG&E just announced new "EV" electric rates that are "time of use" with NO tiers. Under those rates, between 11pm and 7am, electricity costs $.09712 / $.09930 in summer / winter.

Also, charging isn't 100% efficient so it takes more electricity out of the wall than shows up in your battery (heat loss, etc) but Tesla has a hidden reserve so from empty to full is only about 82 kWh. Assuming an 85% charging efficiency, you will need 96.5 (82 / 0.85) kWh to "fill" your tank. My experience is that I get about 245 miles from a full tank (I know Tesla says 265 but I don't drive 65 mph, more like 72). 96.5 kWh will cost about $9.50. Assuming $4 for a gallon of gas (Bay Area), that is about 2.4 equivalent gallons or 102MPGe for my 245 miles of driving per "tank".

Call PG&E "Building and Renovation" at 1 (877)743-7782 and ask to be switched to the new EV rates. You will need your VIN to prove you have a qualifying EV.

@earlyretirement

Gas here costs ~3.69/gal and my cost per kWh is about 7.5 cents, so for the cost of a gallon of gas I get 49.2 kWH. With conventional driving ie not showing off to friends, I would actually get better than 151, but I think I used 325w/m to arrive at 151 miles. This does not factor for charging inefficiencies, though.

If I put in a more realistic 300w/m for sedate use and assume a 12% loss from outlet to output, I'd be at 144 mpge.

Am I missing something or did you not anticipate such cheap power?

Once my solar panels are paid off in 5 to 6 years doesn't my cost drop drastically? :-)

Best way to do this is plug in your info into an online calculator/analysis...

The best calculator to figure this out is here:

http://energy.gov/maps/egallon

Other cool calculator-type analysis is here:

http://teslarumors.com/Teslanomics.html

Simple enough math:

Electricity cost: $0.17 / kWh

charging efficiency: 0.9

Fuel cost: $6.7 / gallon (EU)

85 kWh = 265 miles

Full tank cost: 85 * 0.17 / 0.9 = $16

Equivalent amount of gallons: $16 / $6.7 = 2.4 gallons

Miles per gallon = 265 / 2.4 = 110MPG

There's no need to compute actual Wh / mile etc. Just take what you expect to get from the MS. If you think the rated miles are overestimated to your driving style account for it. If you drive at 45 km/h constantly, then use 420 miles instead of 265 etc :)

Now if you want to compute for your situation just swap the initial numbers.

@ Bighorn. Thanks for posting back. Ah, I see how your costs are so low . Wow, your rates are low ! Here the lowest with special EV TOU super off peak rates are lowest is 0.16 c per kWh. That explains it.

Here on Long Island it does not look so rosy at all, since no superchargers around, and assuming no other free charging opportunities:

Electricity cost: $0.22/kWh

Assumed total charging efficiency:85%

Premium fuel cost: $4.10/gal (US)

85 kWh is good for 265 mi.nominal (not the way I drive..)

True local charging cost:85*0.22/0.85= $22

Equivalent fuel amount: 22/4.10=5.37 gal (US)

Equivalent MPG: 265/5.37 = 49.4MPG

@ jdesmo. Yep. Your numbers look fairly accurate except I'd say that not many people in the real world will get 265 miles. To be conservative, I'd lower that #. Like you, I'm not getting 265 miles so that # is really not realistic.

Also, the point about the loss of efficiency is totally true. I've been tracking it each night as I have a dedicated meter for my EV. It looks to lose at least 15% to 18% based on what Tesla's website says it should take to charge it.

I think the 10% efficiency is too conservative as well. I'd use at least 15% to 18% for the charging efficiency. At least that's how I see it in the real world.

I've been driving quite conservatively, yet the range shown on the dash is consistently about 20% higher than the range I get in actual driving. I drive about 20,000 miles annually. Let me also add about 15% in charge efficiency loss plus another 8 miles per day of vampire loss... After taking my electricity rates and gasoline costs into account, my adjusted mileage is 133 MPG. And that's using $3.70/gallon for regular unleaded.

Not too shabby...

@earlyretirement/jdesmo/mario

I'd agree that most don't get 265 miles on a charge, but that's because the full 85 kWh don't get consumed. Some kWhs are held in reserve, so using 265 miles to simplify the equation doesn't really work. I think using Wh/m and guesstimating efficiency will be more accurate.

MPGe is just over 100 miles to the gallon (Electrical equivalent). Cost is dependent on your local rate.

If I view total ownership costs, compared to say jaguar XF-R (I averaged 16.5MPG over 3 years/45,000 mi), it would take the SP85 about 10 years to break even in Long Island/NYC metro area!! Certainly if you lease like I do, or otherwise replace the car every 3-4 years, the MSP does not make sense.

Not cool at all.

(not even considering the cost of money, as the P85 is ~$25K more to purchase).

I think it's very difficult to obtain any kind of useful ROI from a Model S. Maybe the lowest base model with zero options and a 100 mile one-way commute with free charging at work would price out ok but for the most part it's a losing proposition.

I bought it because it's fast. And big. And tons of storage. And I never have to fill it up with gas. And it is all technology.

The savings over gas on a monthly basis is neglible in my case, and downright a losing proposition against purchasing say, an Infiniti Q50 at half the price.

We have had solar for about 10 years and recently wound up with a free upgrade to higher efficiency panels. We are in the SF Bay area. Our bottom line is we only pay about $5 per month for electricity service and PGE keeps our excess generation to sell to someone else. We thought with our MS delivered 12/30/12 we would start paying something for the added load. So far after 8500 miles, it still looks like we continue to drive for "free". On longer trips we do use SC, but not for daily mileage.

We are pleasantly surprised!We average about 320wh/mile. We are also on the old time of use rates, 6pm to noon are off peak.

In many locals, solar can make sense. Not so on most of the north shore of Long Island......

I also forgot that with my 2011 XF-R, Jaguar covers all maintenance and wear items at N/C for 4 years (I only pay for tires!)That's additional savings, certainly great bonus if you lease.

I think BMW and others may also have a similar feature already baked into the MSRP.

@ Amped. "Vampire loss"??? Didn't your new car ship with version 5.0? Don't tell me you got stuck on 4.5?

Is it possible to see on the 17" screen how many kWh have been added to the battery pack in the past week/month/year?