« A 200 Mile Per Gallon car? The physics of MPG. | Main

April 3, 2010


Feed You can follow this conversation by subscribing to the comment feed for this post.


Thank you for walking us through the calculations in this article. The numbers might even become more convincingly in favor of the EVs when we arrive at being able to figure in clean renewable energy as an alternative to coal, for example. Thanks again for the numbers. As an engineer, I appreciate that.

Tom G.

This is really a good discussion of energy consuming devices like plug-in vehicles. I worked in the nuclear power industry for 20 years and there is one more factor to consider.

Nuclear plants are called base load plants. This means most utilities bring them online and they run at full power until they are shut down for refueling or maintenance. What this means is that many gas peaking units and coal burning power plants are throttled back or shut down in the evening hours when they are no longer needed while the nuclear units continue to run at full power. If you were to plug-in your hybrid or all electric vehicle most likely the amount of CO2 is going to be significantly less no matter where you live however not all areas of the U.S. are equal.

For example, in California almost all power in the evening hours is provided by local hydro, nuclear, renewables in the form of wind and some imported power from the Pacific Northwest usually in the form of hydro. Depending on the time of year [e.g. summer] some imported power does come from coal and nuclear plants in Arizona and New Mexico.

In the Eastern part of the U.S. where there are a large number of coal plants and some nuclear plants the ratio or portion of the power produced is quite different. Therefor plugging in your hybrid in the evening, while still better than in the daytime, but it might not be a whole bunch better because of the mix of power generation.

You have an excellent blog site and I check it frequently for new articles which are very well written.

[email protected]


As an Electronics Engineer I see that you are making the same mistake the Electric Car proponents always make -- transmission losses.
Please site some figures for BTU/KW fuel into the power plant, verses BTU/KW equivalent OUT, AT THE USESER WALL PLUG! Electrical transmission systems are VASTLY INEFFICENT.
A simple thought experiment: Just think of the losses in your usual consumer transformer (the villain in the vampire loads hoopla that is all the rage these days), now realize that the Steam plant generator must, at a minimum, step-up to Kilo/MegaV for transmission over distances, (we’ll neglect any I2R losses per mile of wire and intermediate State/County/City stations) then local sub-stations step-down to 14K-~5KV for street lines, and a pole pig from there to ~220Y2p to several houses!
How can you believe that ALL these transformers are so efficient, and operate/maintained at peak efficiency (remember, YOU pay for your electricity at usage, waste DISAPPEARS in costs to the Utility)! //CJL

The Energy Blog

Hi! Thanks for your comment. There are a couple parts to my reply. But first, my point was to simplify this calculation. Most often these types of comparisons are filled with so much unneeded mathematical trivia that the conclusion is at once meaningless, as well as hard for the average rocket scientist to understand.

But, to your points.

1 – The generation efficiency of the source plant, or the energy efficiency of the vehicle are of no consequence to this outcome. Whatever the efficiency, the plant produces a certain amount of CO2 per actual kWh produced, regardless of fuel efficiency. The same with the vehicle. It produces a certain amount of CO2 per mile, regardless of the source, and how well it uses that source. It is attempting to introduce all these extra variables into a calculation, and still ending up with the same conclusion, that unnecessarily complicates most of these analysis.

2 – You are absolutely correct there are electric transmission losses. I would not, however categorize them as vastly inefficient. Various sources, including the EIA, and the North American Electric Reliability Council, put overall average transmission and distribution losses at around 6.5%. OF course this is an average. There are numerous things that affect this, line loading, distribution voltage, allowable sag, etc. I thought about allowing for them, and probably should have mentioned them. Applying that 6.5% loss, however, will still not significantly (admittedly a relative term) affect the outcome of this calculation.


3 – Transformers. I believe the above figure accounts for distribution at and through the substation level, and it is widely referred to in the electric industry as overall losses. As an EE, you know that transformer losses are rather complicated, and there are a large amount of variables, temp rise, materials, wet vs dry, power factor, loading. The specific “vampire” losses you mention (for consumer equipment) are normally due to core losses (magnetizing the core) and a very small amount of I2R heating. The vampire draw (not really a loss) is somewhat fixed, and will become a lower percentage of the total as loading goes up. These transformers normally operate at a very low load factor compared to their capabilities, keeping overall efficiency much higher.

Distribution transformers however, operate at a much higher load factor. Losses normally go up as the loading goes up, and at this higher level of operation, it becomes more significant.

Various references to end use power transformer design and selection put standard transformer losses at (again, rough figures) 1% at no load to about 4% at full load. Here is a nice summary on those figures from EC&M magazine: http://ecmweb.com/news/electric_overcoming_transformer_losses/.

Even adding those losses to the above 6.5% to account for the pole pig, we get about a 10.5% total loss (or 89.5% transmission efficiency). The reality is likely quite a bit better than that. Applying those losses to the CO2 calculation still shows that electric vehicles emit substantially less CO2 than fossil-fueled ones.

Again, thanks for your comment, and pointing out the legitimate omissions from my article. The electric distribution efficiency picture is one worth investigating further, as is the entire “vampire losses” issue. Those are both things I hope to address soon. Among other things, smart grid, by enabling better routing of power is set to reduce these losses somewhat. Your commentary has served to awaken the thought process for me as regards to this topic.

Mike -.

Tom G.

The following link might add some insight about transmission. About half way through the lecture high voltage transmission is discussed.


Tom G.

energy efficiency ratings

Very interesting. Good to see that solar panels are coming into their own now in so many more areas of life.

climate change facts online

Many chemical compounds found in the Earth’s atmosphere act as “greenhouse gases.” These gases allow sunlight to enter the atmosphere freely. When sunlight strikes the Earth’s surface, some of it is reflected back towards space as infrared radiation. Greenhouse gases absorb this infrared radiation and trap the heat in the atmosphere. Over time, the amount of energy sent from the sun to the Earth’s surface should be about the same as the amount of energy radiated back into space, leaving the temperature of the Earth’s surface roughly constant.

Bill Harrison

This is a good discussion and you did a nice job of crunching the numbers and keeping it simple. However, your bottom line conclusion seems to be that switching from ICE powered vehicles to electric powered ones is a panacea and I'm not sure you can make that case without examining all the qualitative issues as well as the quantitative ones. Your assertion is correct when you say, "...we do not need to factor in the relative mileage of different vehicles to determine the absolute CO2 emissions potential. Replacing a similar gasoline vehicle, with a similar electric vehicle will still result in similar energy needs." However, for the vast majority of drivers, it would be perfectly practical to replace their current gasoline vehicle with a very dissimilar gasoline vehicle.

Take your extreme example of the dump truck vs. the Honda Fit. While there are commercial operators who NEED a dump truck, there are also many personal use drivers who are driving something that is almost the equivalent of a dump truck (in terms of size, weight and emissions) on their daily commutes. Replacing these vehicles with much smaller, more efficient gasoline powered vehicles would immediately and drastically cut CO2 and other emissions. Size does matter - and the fact is, most Americans drive a much larger vehicle than they need 90 percent of the time. A policy that restricted the maximum weight of personal use vehicles on freeways (with special lanes for commercial vehicles like trucks and buses) would do far more to reduce emissions than a wholesale switch to electric vehicles of the same size as the ones we drive today. Furthermore, limiting the size of vehicles (to say, 2500 pounds) would also greatly improve survival rates and reduce injuries due to collisions. Of course, this will never happen because it would be extremely unpopular. Most Americans would much rather drive an electric Silverado Crew Cab and feel like they are saving the planet without sacrifice.

Another issue that no one else has mentioned is the impact of batteries (presumably Li-On battery packs) on the environment. Extracting and refining lithium is a messy business and so is disposing of all those huge battery packs after about 100,000 miles. This is already an issue with HEV vehicles. Also, if we switched our entire fleet of personal use vehicles from ICE vehicles to EV's overnight, the demand for electricity would skyrocket. What assurance is there that this wouldn't result in more coal plants, or at the very least in the current plant being operated at or close to 100% capacity?

It seems that the most important number - and the one I'd be most interested in seeing for multiple modes of transportation - is pounds of CO2 per passenger per mile - or kilos per passenger per kilometer. Using that metric, a Cadillac SRX carrying five passengers would probably have less impact than a compact EV carrying only the driver. The fact is, every time I see a Prius on the road it is carrying one person - usually commuting back and forth to work. That one person could significantly reduce their carbon footprint and have vastly more fun by driving a Harley Sportser instead. Of course, if the same person were able to use mass transit, or, even better, telecommute the reduction in CO2 emissions would be truly significant.

As your numbers show, switching from ICE vehicles to EV's might be a relatively easy way for Americans to enjoy the same lifestyle they do today and substantially reduce CO2 emissions. However, I think if you look beyond the numbers, there are some potential policy decisions in both public and private sectors that could make an even bigger difference by moving all of us to adopt more intelligent and sustainable lifestyles.

"Not everything that can be counted counts, and not everything that counts can be counted"

Manhattan Air Conditioning Service

The let out smoke by each vehicle adds to the pollution and the older the vehicle I think the emission gets worse.So it is much better to choose for healthier smoke and air.

Frederic Padilla

I think this is very good for the future. Using electric cars could overcome environmental problems. Yes, we should be looking for environmentally friendly fuels. I can not imagine what happened in this world if my son has grown up...


Companies can get a feel for sales based upon pre-orders. Not guaranteed, but sure beats NO ONE pre-ordering the Volt.

I even have friends pre-ordering them based upon the favorable lease rates, which are far below what a car payment would be if they bought.

My brother would save about $150 a month in fuel costs because of his long commute (even if he had to dip into using gas everyday). His old clunker is costing him an annualized average of $150 a month in repairs, too.. Not having airbags is also a problem of safety for my brother, and the Volt has a great airbag arrangement for safety.

Truck Rental

I would be the last to claim that the electric car is as green as it gets! No- this baby is still only at the beginning of its way, but if anyone would ask me which one to bet- I would choose the electric car without a doubt. There is a lot of work to be done, but it is a very promising beginning.

Javier N.

Thanks for the article. It is well written and informative. And about your "electric" dump truck... Kenworth truck company of Renton, WA is currently producing a hybrid medium duty truck that is most likely to be used in urban areas of our country. It isn't a straight electric solution but we are on our way to a cleaner future. Here is a link to the company's article concerning this vehicle. Thanks again!


Dr. Stephen Harper

If I simplify some of your numbers...
1 gallon of gas yields 20 pounds of CO2
The same gallon yields 20 MPG (or more in a car the same size as an electric)
So 20 pounds of CO2 are generated to go 20 miles.
That is 1 lb of CO2 per mile.

Then you say electrics get 0.24 Miles per KWH and our power plants generate 1.5 lbs per kwh.
So 1.5 pounds of CO2 are generated per 0.24 miles.
That is 0.36 Lb of CO2 per mile.

Another way to spin the CO2 story is if we could get 20/0.26 or 55 mpg out of a gasoline car - the CO2 emissions are the same. Or we could put CO2 absorberson cars, or on power plants, and turn the numbers on their heads.
That should be easy... but the oil companies dont want that as their patriotism stetches to about half a dollar.

Next, consider this spin on energy use.
Your article uses 36 KWH per gallon of gas. this is 36KWH/20 miles = 1.8 KWH/mile. At 28% efficiency.
An electric car uses 0.24 kWH/mile per your article.
Electric power plants on average (today) run at about the same efficiency. Some do a much better job than others at capturing waste heat. The future holds a lot of promise for making new power plants much more efficient - but the same can't be said of a gasoline car.

So the baseline today is that gasoline cars use 7.5 times more KWH per mile. So if a gasoline car could get 150 MPG it could compete with electric cars wo get electricity from a power plant at 28% efficiency.
If the electric power plant efficiency is 33% or more, as it will in the future, the gas car would need to get more than 200 MPG.

While 55 MPG is doable, 150 or 200 isn't. Buy electric.


Can't anyone do math correctly anymore?

"Then you say electrics get 0.24 Miles per KWH and our power plants generate 1.5 lbs per kwh.
So 1.5 pounds of CO2 are generated per 0.24 miles.
That is 0.36 Lb of CO2 per mile."

The original article stated .24 KWh per mile, not .24 miles per KWh. Also, 1.5 lbs CO2 per .24 miles results in 6.25 lbs per mile.

San Diego Mobile Notary

I prefer electric cars because the main advantages of electric cars are convenience, environmental benefits and fun.

tyre equipment

The fact that electric cars are environment-friendly is perhaps the most important point that you need to take into consideration when you pit them against their gasoline counterparts. Gasoline cars burn fossil fuels to generate power, and thus contribute to environmental pollution. However, comparatively-speaking, gasoline-powered cars are by far the cheapest option on the market.

Leisa Dreps

Honestly, I don't know much of the science in this. I'm fairly happy that people are looking for alternatives to too lessen the Carbon emissions, like using electricity as an option for gasoline. I do find it weird that the plants used to produce electricity are being run using gasoline. But nevertheless, maybe in the near future this could be innovated.

plumbing supplies

Diesel is often thought of as smelly and noisy. Many think that the only place for diesel is in a tractor or a semi, there are many other vehicles that are diesel powered however. Each person must determine what their individual needs are. A person has to do their research before making a purchase of any kind, but especially a large purchase such as a vehicle.

Green Energy

With fuel prices soaring and no end in sight, it only makes sense to look for alternatives.I go for electric cars, they are clean fueled vehicles which are good for the environment.

driving school solihull

Fuel cost comparison: the Tesla Roadster sport car's plug-to-wheel energy use is 280 W·h/mi. In Northern California, the local electric utility company PG&E says that "The E-9 rate is mandatory for those customers that are currently on a residential electric rate and who plan on refueling an EV on their premises.


Electric cars have a lot of benefits to the environment which is a very nice thing. However, there is a problem with its energy range in which you constantly needs to charge after 6-8 hours. I think that they need to find a better solution to this.

Garage Equipment

EV cars will definitely help in reducing gas emissions in the environment. If we invest in too something, we better invest it in to not just beneficial for ourselves but also for the environment.

Essay writing help

this is a good discussion on energy saving i prefer solar energy to use

Essay Writing Services

vehicle using gas in place of diesel is more appreciating because it decreases the sound and smoke pollution

The comments to this entry are closed.