Energy Efficiency

Energy Efficiency

I'm not even sure if this is the right place to ask this. But Elon Musk was asked in an interview if EV's are still cleaner even if the source of the energy is traditional carbon burning sources (oil, coal, etc.) and he said it still is due to the energy conversion efficiency of EVs compared with gasoline burning vehicles.

Just a geeky type thing but does anyone actually know the energy conversion rates for an EV like the Model S compared to a traditional gasoline vehicle? Thanks.

shs | 10 February, 2013

On the Go electric, Your Questions Answered section of this website it states that gas powered car only put 20 to 25% of their energy to the wheels, and that the MS is 3 times more effecient.

Hans (Amsterdam) | 11 February, 2013

Burning coal results in 900 gram CO2 emissions for every kWh of electricity produced. According EPA model S 60kWh consumes 35kWh per 100 miles. This means that driving 1 mile gives 315 gram CO2 emissions. Now compare this with (EPA) CO2 emissions of similar ICE cars. (note that I have left out transport losses of electricity in the grid).

i.e. EPA: Porsche Panamera S: 468 gram CO2 / mile

jemartin | 11 February, 2013

Here is a very interesting study by the Union of Concerned Scientists. On page 12 it shows your EV's carbon footprint as a function of where you charge it. I don't know much about the UCS, and how biased they are toward EVs, but I think it's well worth reading...

JOHN HOLLINGSWORTH | 11 February, 2013

There are transportation and refining losses in the production and delivery of petrol as well.

village33 | 11 February, 2013

It varies, but is basically always better to way better than a like ICE vehicle. Here in Connecticut it's 98% green/clean for example (table below) and around 13 cents/kWh.

Connecticut’s Electricity Generation:
Nuclear 47.4%
Coal 1.5%
Oil 0.5%
Gas 45.1%
Hydro 1.2%
Renewable and Other 4.3%

shs | 11 February, 2013

Except that Gas is not green, it is a fossil fuel.

pilotSteve | 11 February, 2013

Carbon emission is complex. IEA stats show that US use of coal has gone down from 49% in 1997 to 36.7% in 2012.

Total US emissions have fallen in 2012 due to replacing coal with Natural Gas; unfortunately coal is still predominate in India and China and they have more than made up the US reduction for a global increase.

Since US can only control what we do I choose to embrace the reductions made. Eventually when LNG pipelines and ocean transport becomes more cost effective it will be to the benefit of the whole world (US balance of trade and China/India reduction of coal and lower cost electricity).

Brian H | 11 February, 2013

If you're into cutting CO2, burning gas is 50% the coal CO2 output. Half its energy comes from the hydrogen in CH4.

50% may not meet your high standards, of course.

village33 | 11 February, 2013

For those in need of clarification, I was referring to nuclear as green and gas as clean. There are different views on this but it was a general comment (in particular as compared to coal/oil) based on common definitions, for example below (and yes, there are obviously others with different definitions):

EU defines gas as green:

British Columbia defines gas as clean:

Nuclear is generally considered to be green:

Hans (Amsterdam) | 11 February, 2013

Really green is Norway. 98,5% of their electricity comes from Hydro power. So Model S in Norway will have true zero emission.

Unfortunately during the day the Norwegians export a lot of their Hydro energy. During the night (when they charge their electric cars) the production of Hydro power is strongly limited (to save water for the day) so they have to import energy that comes from fossil fuels.

shs | 11 February, 2013


I think the natural gas is 50% better on CO2 relative to coal, but only about 20% better than oil and still makes CO2 as well as H2O when burned. The problem really is that natural gas or methane is a powerful greenhouse gas in its own right, and if even a few percent of the natural gas that is used leaks into the atmosphere, it is about 100 times more "warming" during the 10 years that it last in the atmosphere than a molecule of CO2 (it eventually becomes CO2). I really don't want to start of continue another global warming debate here, so over and out.

Brian H | 11 February, 2013

The methane numbers are BS. It's proportion in the atmosphere is almost below detection level. And the numbers are fudged by considering the combustion products H2O and CO2, whereas most of methane's reaction products in air are other molecules. None of which should be lumped in.

And CO2 is benign and beneficial. When the cooling starts, we'll wish it did warm the air a little. So sad that it doesn't.

olanmills | 11 February, 2013

Check this old page, which doesn't seem to be reachable anymore from any link I could find, :

Tesla claims that the battery-to-wheels efficiency of the Roadster is 88%. Of course, the efficiency of whatever electrical fuel source (hydro, coal, etc etc) to your outlet can vary, but that's a problem with the power station and its grid.

I wonder if the efficiency of the Model S is better or worse than the Roadster. It's bigger and heavier, but also it's newer and designed from the ground up as EV, so presumabley it's designed better and has better technology. Either way, I'm sure it's way better than ICE.

Timo | 11 February, 2013

+ if you start comparing "long tailpipe", then you need to add CO2 from refining and transport too.

dtesla | 12 February, 2013

Don't forget there is an overhead to charge you car. That is power consumed while the car is "off", charging inefficiency, battery warmers, etc.. You must include this in your calculations (go electric page does not).

I have been keeping power records on my home for years (I love data). So when I got my Model S on Jan 9th I added it's stats to my collection of data.

For January the car displays reported using 267 KWh to move the car 680 mile for 393 Wh/m. For the record January was cold so the battery heater ran a bunch (I drive many short trips). And some days I had both seat heaters and cabin heater on. All things considered I consider this a good average. Don't forget even ICE cars get lower MPG in the winter.

However, My home's power meter indicated 533 KWh going into the MS for the same 680 miles for a gross 784 Wh/m. That is almost a 100% overhead. I assume most of the overhead was to keep the batteries warm at night. Plus computer running 24/7, charging inefficiency, etc.

The first 10 Days of February were overall warmer then January and the overhead for the Model S is down to 50%.

January 9-31 MS gross MPGe ~45. CO2 533 lbs. Equivalent ICE (@ 20 MPG) 680 Lbs. Prius 302 Lbs.

Febuary 1-10 MS gross MPGe ~60. CO2 146 Lbs. Equivalent ICE (@ 20 MPG) 300 Lbs. Prius 133 Lbs.

To Timo point my figures are long tailpipe for MS and short tailpipe for ICE. So apples to apples ICE numbers are actually higher. Does anybody know the national average for gasoline's overhead to my tank?

dtesla | 12 February, 2013

MS and ICE numbers assuming long tailpipe

January 9-31 MS gross MPGe ~45. CO2 533 lbs. Equivalent ICE (@ 20 MPG) 768 Lbs. Prius 341 Lbs.

Febuary 1-10 MS gross MPGe ~60. CO2 146 Lbs. Equivalent ICE (@ 20 MPG) 339 Lbs. Prius 150 Lbs.

noel.smyth | 12 February, 2013

100% solar runs my car. :-)

Cattledog | 12 February, 2013

Noel - Y yo tambien.

dtesla | 12 February, 2013

100% solar for me also. So we can imagine I really typed 0 for the MS's CO2.

When my solar PV was installed, in July 2010, I installed enough cover my home's usage. Also by July 2010 I had already made the decision to get the MS + a second future EV or ERV for my wife, so I added some panels to cover that. I am disappointing in the overhead for the MS, since the MS is using most of the future second EV/ERV car's power budget.... I hope the overhead continues to drop as the year get warmer and be at or close to Tesla's ideal overhead for the majority of the year.

CO2 production cost for solar PV is 2.25 Lbs per watt. It take about 1.0 to 1.25 years (depending on how much sun you get) to cover the CO2 cost of solar PV production.

dtesla | 12 February, 2013

Opps... July 2010 = July 2011

STEVEZ | 12 February, 2013

Someone posted the following link earlier in the thread.

There's an eye-opening table on page 33, which shows that our local RMPA electric grid (all of Colorado, plus eastern WY and bits of several other adjacent states) is the 'dirtiest' in the nation. It shows that an ICE car would only have to get 34mpg to equal the 'long tailpipe' emissions footprint of a Leaf. For the 'cleanest' grid, in NY state, an ICE car would have to achieve well over 100 mpg to equal the emissions footprint of a Leaf. I don't know what the Leaf's MPGe rating is, but the model S can't be so different.

Questions of dollar savings aside, the inescapable conclusion is that those of us in Colorado for whom environmental concerns were a part of our decision to buy a Tesla have a strong incentive to charge our vehicles with solar PV, or some other form of clean electricity.

dtesla | 12 February, 2013 talks about incentives and solar PV in general for Colorado residents (other states can click your state on the right of the page). Also walks you through the system payback for PV system and your federal and state incentives. Good general solar PV information. will tell you how many KWh/year to expect from x KW of PV. NOTE "DC to AC Derate Factor" of .82 is more realistic... .77 is very Conservative.

pchan8800 | 20 February, 2013

Thanks for the replies everyone. Haven't had a chance to check until now.

For the Prius I remember reading an article that the Prius is actually just as bad for the environment because of how they assemble all the parts in different parts of the world and the shipping required to move these parts around.