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CMU: Plug-in Hybrids “More Sensible” Use of Coal Than Coal-to-Liquids

Comparing life cycle CO2 emissions from plug-in hybrids, coal-to-liquids gasoline, and conventional gasoline. Click to enlarge.

A study from the Carnegie Mellon Electricity Industry Center (CEIC) concludes that while enacting policies to subsidize the production of coal-to-liquids transportation fuel would enhance national security by lowering oil imports, encouraging plug-in hybrids powered by coal-generated electricity is a less costly policy that also reduces oil imports and does more to lower greenhouse gas (GHG) emissions.

CEIC produced the paper in the context of the current work by the US House Committee on Energy and Commerce on transportation energy legislation, the current draft of which includes significant support for CTL. (Earlier post.)  The CEIC paper compares GHG emissions of CTL gasoline to the emissions of plug-in hybrid vehicles powered with electricity generated from coal on a full life cycle basis.

Although CTL conventionally produces more diesel than gasoline, the process can be altered with catalysts to upgrade some of the diesel and waxes produced in the standard F-T process to gasoline, with an overall efficiency of around 52% (HHV).

The CEIC team used CTL inputs and outputs derived by Bechtel in 1993, and allocated the total emissions factor among the various CTL co-products using the method in the GREET model (by energy content of the co-products).

The allocated worst-case well-to-plant emission factor (no carbon capture and sequestration, current electricity generation mix) is 190 pounds CO2 equivalent per MMBtu of CTL gasoline, and 50 pounds CO2 equivalent per MMBtu of CTL diesel. With 80% CCS and zero-carbon electricity, the allocated factors drop to 50 pounds CO2 equivalent for gasoline and 15 pounds for diesel.

Adding in the other complete lifecycle factors (transportation for distribution, combustion in the engine) resulted in complete well-to-wheel CTL lifecycle emissions of 360 pounds CO2 equivalent per MMBtu of gasoline in the worst-case scenario and 220 pounds CO2 equivalent per MMBtu of gasoline in the best-case scenario.

CEIC then used a fuel consumption figure of 34 mpg and an annual driving distance of 12,000 miles to calculate the annual CTL gasoline emissions: 1.18 lbs/mile (536.7 g/mi) in the worst case; 0.72 lbs/mile (325 g/mi) in the best case.

For plug-ins, the CEIC researchers calculated the impact of both electricity and gasoline. For electricity generation, they used two scenarios: bituminous coal in a pulverized coal power plant and bituminous coal in an integrated gasification combined cycle power plant with carbon capture and sequestration (IGCC w/ CCS).

Well-to-Wheel Greenhouse Gas Emissions
Fuel CO2-equiv.
CTL gasoline 536.7
CTL w/ CCS gasoline 325.1
Gasoline base case 344.0
PHEV, coal generation 264.6
PHEV, coal IGCC w/CCS 105.8

For a vehicle, they assumed a plug-in hybrid built on a Toyota Prius platform in a parallel configuration with an all-electric range of 60 miles. To determine the fraction of vehicle travel powered by electricity or gasoline, they used the percentages resulting from the cumulative distribution function of daily vehicle miles traveled constructed in another paper from CMU (Samaras and Meisterling, “Decarbonized Electricity Needed for Plug-in Hybrids” 2007). The CEIC distribution estimates electricity would power about 85% of average annual vehicle travel for a plug-in hybrid with a 60-mile electric range, assuming vehicles are charged once per day.

The results: total well-to-wheel emissions of 264.6 g/mi for the conventional coal-generated scenario; 105.8 g/mi for the scenario with advanced IGCC with CCS). The conventional gasoline baseline in the study was 344 g/mi.

It can be seen that gasoline derived from CTL plants with no CCS could increase GHG emissions from vehicles by almost 60%. If CCS is available, then a reduction of less than 6% could be obtained. It is important to note, once again, that in this best-case CTL scenario, not only is there CCS at the CTL plant, but also a low-carbon electricity source is used for CTL production. This might not be a very realistic assumption, but is presented here to show that at best we could only obtain a very small reduction in GHG emissions following a path of increased CTL production.

Plug-in hybrids look more promising as a pathway for reduction of GHG emissions. Even if coal electricity without CCS is used, plug-in hybrids could lead to a GHG emissions reduction of almost 25%. This demonstrates the worst case for plug-in hybrids, as GHGs would be further reduced with a low-carbon electricity portfolio. It is important to note however, that this analysis does not include the emissions from manufacturing the storage battery used in plug-in hybrids. If GHG emissions from lithium-ion batteries for plug-in hybrids are included, total annual GHGs from plug-ins would increase by about 800-1,500 pounds of CO2 equivalents, depending if a twelve or eight-year vehicle life is assumed (Samaras and Meisterling 2007). Battery technologies are difficult to predict, but even when emissions from current battery production are included, plug-in hybrids result in substantially lower emissions than CTL pathways.

The Carnegie Mellon Electricity Industry Center (CEIC) was established in August 2001 as one of 20 centers of excellence in different industries that the Alfred P. Sloan Foundation has established at 13 universities. CEIC’s core funding comes jointly from Sloan and from the Electric Power Research Institute (EPRI).



Stan Peterson

CTL is an answer to a question that few asked except in dire emergency. This study confirms its basic inefficiency for the overall enduse.

The only reason that we are seeking to convert to liquids hydrocarbons is that one particular industry as presently constructed REQUIRES liquid hydrocarbons, and has no effective substitute to date. If that key industry, Transportation, didn't need ONLY liquid hydrocarbons, there would be little need for phase, conversion of materials. This is the truth regardless of how much many here long for a CONSPIRACY basis to believe otherwise.

So it is quite expected that reducing the demand for liquid hydrocarbons, through diversification, will be the most efficient approach to solving this price and availability dilemma for those liquid hydrocarbons.

Resolve that demand fromn that one industry for liquid hydrocarbons, and replace it with satisfaction by diverse energy sources is the most efficient and probably least costly approach.

And that is what isgalloping toward us, in a massive wave, pushed by the blind hand of market efficiency manifesting itself as least cost, I.E LOW PRICES.

The electrification of ground transport is coming; and its operating cost is even now well below the present alternatives, (at $ .75 per gallon eqv). Its technical feasibility was long unknown, but is finally being established (LiIon & PHEVS). Only the capital cost is still in question, without the economies of scale and mass manufacture yet applied. So that issue too is being resolved.

These costs are not impossible at present, but not yet attractive. There is little reason from an engineering viewpoint, to believe it is intrinsically more expensive to construct a HEV/PHEV/BEV drive train than a conventional one, in the long term.

As for CTL its a good technology to have when we need some liquid hydrocarbons and it is cheaper to manufacutre liquid hydrocarbons than to mine them in the way distant future, perhaps several hundred years from now.

richard schumacher

There's at least one energy source that has negligible environmental costs: space-based Solar. The only drawback of it is, it's expensive to build. But it would meet all of humanity's energy needs forever with no pollution. We really ought to be taking the lead in this.

richard schumacher

But coal IS bad, period. Coal has greater relative environmental costs in every respect than every other energy source. The only current benefit in using coal is low direct cost to the producers and users. We could try to price all the indirect costs of coal into it and let market forces take their course, but the clock has about run out on the looming disasters of global warming. We're out of time; we need to start making coal illegal.


>The electrification of ground transport is coming...

Electrification of rail doesn't require any batteries at all. It requires some capital for overhead wires, and some local tax issues probably need to be resolved, but that's about it.

Stan Peterson


It is really too bad that your views are so extreme.

I can envision a dozen meretricious effects from beaming Solar energy from Space. How many birds would you like to fry? What extreme weather based phenomena are you willing to endure burning a hole in the atmosphere? What areas of receiving beamed energy are you willing to sacrifice from the inevitable "leakage" ? These will be just two or three of the inevitable meretricious side effects.

As to your comment about "COAL IS BAD". What drivel. Compared to what? Burning wood? No its not! Burning animal dung after we revert to Paleolithic lifestyle and kill off all but a few million of the world's population? No its definitely not.

I prefer Hydro. I will select and prefer Fusion. I will accept Fission in the meantime. IGCC with CSS is the next best alternative. All are technological answers that don't make requirements like killing off lots of the world's population.

This gloom over a little temporary increase in the level of a necessary trace gas is puzzling. That concern over trace gas increase that may or may not have a causal effect of the present tiny rise in global temperatures to a BETTER more BENIGN climate is throughly ridiculous.

Golden ages of the Man's' historical past came when the climate warmed. We emerged from the stone age to the bronze age and the rise of civilization in that first recorded warming. Man emerged from the Dark Ages to the rise of the Renaissance in another warm epoch.

On the other hand, We descended into uncivilized chaos in the cooling of the 300-500 AD when both Rome and China fell as many northern tribes had to move South or die. We call that time the Dark Ages.

At most, the temperature of Boston Mass would rise to that of Providence RI in a hundred years of full all out global warming. Philadelphia's temperature would climb to Wilmington Delaware's in a hundred years, Where is the problem? Where is th end of world consequences? The more realistic estimate is Boston warms to a place about one third of the way to Providence so Providence's temperature today is 300 hundred years in Boston's future.

That is ONLY TRUE if the Cassandras are all correct and WE DID IT (via CO2) which is becoming less and less obviously true, as more research emerges.

In the second IPCC, they didn't even recognize the Sun had any part of the climate. In IPCC III they suggested that the Sun could have some effect as much as two thirds maybe, but it needed research before including it.

Even the IPCC, the hallowed home of the enviro wacko bureaucrats who summarize not the Science the scientists offer, but their own opinions, now agrees the Sun is going through a periodic increase in output.

The bureaucrats say its still undetermined how the Sun warms the Earth, so we can't add its contribution until we do in the current IPCC IV.

If you can actually believe such a ridiculous position.

Roll that on your tongue once more. It's unknown if the Sun effects the warmth of the Earth!! Can You believe such pure Horse manure ?!?

The solar near constant is up about 0.2% and surprise so is the global mean temperature by a similar 0.2% or so.

Even if WE DID IT ALL, we have plenty of time to change our course, adopt other better approaches, say a thousand years or so before the warming aspects go from benign to even questionable.

As a Red Sox fan, I wouldn't want to live in a country so warm that it can produce a Team like the Yankees in the unbearably hot world of Mordor-like New York City. Boston might warm to that temperature in only 350 or 400 years or so, in the worst case,( mor elikely 900-1000 years). If global warming continues and WE DID IT ALL, and will keep on doing it for that long.



Or maybe people could be open minded and think about what he said.


When will solar activity effect get its due? For some reason it gets buried under tons of CO2 while there's significant science indicating its role in global temperature change. We should be able to address GHG and acknowledge solar activity without mutual annihilation - or have we yet to leave the dark ages?


Hat tip to Stan for somehow tying the superior if heartbreaking Red Sox to the globally overheated Yankees! Both great and temperate cities... (Boston's better).


If Stan Peterson is more than just a ranting denialist troll, let's see the peer-reviewed science which supports his assertions.  He can start by substantiating his claim about the relative climate of NYC and Boston.

As a counter-example to his assertions, the effect of a wind turbine is generally considered undetectable a mere 10 rotor diameters downwind.  Air flow is affected by a wind farm in much the same way it's affected by a forest.  Should we stop growing trees to avoid changing wind patterns?  That's the conclusion one is nearly forced to draw from his claims.


People! People! Focus! This is about using coal.

Pollution from fossil fuels is a problem. We don't want NOX or unburned hydrocarbons out of tailpipes. We don't want soot from anywhere. And that is true whether man's CO2 is causing GW or not.

It stays true if the sun is causing GW. Or the Earth's orbit. It is even true if there is no GW at all.

Similarly, pollution from fuels is separate from the issue of whether we are running out of oil. It is separate from whether Arab oil $$ fund terrorists. It is separate from US balance of payment problems or national debt.

We have a lot of coal. The report says CTL will emit much more CO2 than coal generated electricty(CGE?) On the other hand, it doesn't cover sulfur and mercury emissions from the different approaches. Or fly-ash. Or whether the magical, long suppressed, Fish carburator would solve all our problems.


It seems that various types of energy solutions will be implemented with the disapproval of a minority that put country survival aside. Maybe it does not matter, as 2012 the sun will do a flop and take care of all problems.


It seems that various types of energy solutions will be implemented with the disapproval of a minority that put country survival aside. Maybe it does not matter, as 2012 the sun will do a flop and take care of all problems.


Actually, we may not have a whole lot of coal left.  Our production of anthracite is down to less than 5% of peak, bituminous has peaked and is falling, and the only things still going up are subbituminous coal and lignite (EIA tables of US coal production).  Each step down the ladder means less energy per ton.  If we haven't already hit peak energy from coal, we will soon.

I'd love to know how much coal comes out from under a typical West Virginia mountain, vs. how much wind blows over the top.  If levelling a mountain only gives you 15 years of the energy obtainable from the wind blowing over its ridges—or even 50 years—the foolishness of flattening it for the sake of removing the coal cheaply becomes obvious.

Stephen Pearlman

Read the paper and check the math. This study starts with the assumption that a plug-in gasoline/electric hybrid will get 44 miles per gallon when burning gasoline. This is based on what a standard hybrid available at your dealer today will do. However, the gasoline that comes from the CTL plant will be used in a car that gets 34 miles per gallon. Why? What possible reason could there be for assuming that the CTL gasoline is used in a car that is less efficinet than the gasoline engine in the hybrid? Redo the calculations just using the same 44 mpg in both cars, and the conclusions of the study are not so clear. CTL gasoline without carbon sequestration still produces more CO2 than the coal to electricity case. But CTL gasoline with carbon sequestration actually produces less CO2.

Why not put the CTL gasoline in an out-of-tune 1996 Chevy Suburban that gets 9 mpg? Then, the results would show even more benefit from the plug-in hybrid.

On the other hand, why assume that the output of the CTL plant is converted to gasoline? Most likely it would not be, because the normal output of the process is predominantly an ultra-low polluting form of diesel. Why not assume that the diesel goes into a diesel engine which is 30% more efficient than a gasoline engine? Why not assume it is a diesel hybrid?

I have spent my career in the electricity industry. If I have a bias, it not in the direction of CTL. However, I am very concerned about both climate change and national security. Carnegie Mellon needs more more rigerous and more intellectually honest if they expect to be listened to in this policy debate.


Stephan: At least you looked at the report. But I think you are mistaken.

The reason they give less MPG to the gasoline vehicle is that CTL doesn't produce any electricity for the hybrid.

So the hybrid receives some mileage from gasoline and some from electricity and it totals to more than a straight gasoline vehicle.

They state what model they used for allocating electric miles and gasoline miles.

Why do they assume gasoline and not diesel output? Think about it. If the CTL makes diesel and they compare a diesel to diesel hybrid the electric miles still aid the hybrid.

I am never too adamant about this stuff. Maybe I misread or misunderstood the point. Technical matter or even a synopis sometimes has that effect.


Here's a couple more studies.

84% of all US vehicles (220 million) could be supported by offpeak electric capacity without building even 1 new power plant.

Driving a PHEV Prius off of the dirtiest coal electricity availible in the US, as compared to a conventional Prius would produce near identical CO2 emmisions.

We already have the batteries.
AltairNano makes batteries which can get 96 mile range in 1 minute of charging.

A123 Systems plans to market 50 mile lithium polymer batteries for Prius PHEV conversions for 2008.

Here's an interview with everything you ever wanted to know about AltairNano's battery specs.

richard schumacher

Mentioning hybrids in a discussion of CTL is like putting lipstick on a pig. There is no demonstrated economical CO2 sequestration technology on a scale within orders of magnitude of what would be required to make a significant difference to global warming. Please, prove me wrong: show us where anyone has demonstrated storing even as little as one billion tons of CO2 somewhere with a reasonable expectation of permanance.

In contrast, there are no technical limits to building as many fission, Solar, and wind power plants as we like, anytime we like. Hydro, unfortunately, is pretty nearly tapped out globally. It would be difficult to even double the existing installed capacity. As for future options, someone who thinks that space-based Solar power stations will "burn holes in the atmosphere" needs to do some basic reading on the subject.

The deniers need to explain how drowning our coastal cities and turning central North America (the world's grain belt for wheat and corn) into a dustbowl will lead to another Golden Age for humanity.


Though admittedly a side trip, there are apparently lots of studies on the sun's significant effect on global temp.

Curious and typical of media cracking, this NASA scientist's data changes in a somewhat whimsical and unconvincing way. When tinkering with data becomes so ubiquitous - the exercise of education falls on deaf ears.

hampden wireless

So if coal is ok despite puttings tons of mercury, co2, particulates and radiation in the air...

Why not just go nuclear instead? Almost zero air polution and no global warming. With a well thought nuclear fuel cycle and breeder reactors or fuel reprocessing its a very secure source of power.


Once you've dealt with the 10-year lead time for putting a nuclear plant on line, I agree that it's far better than coal.


Lets look at the efficiency here:
Coal to Electricity: 30-40% (new combined cycle plants can do ~50%), Power grid: ~95%, EV: 80-90%, Total: 24-32%

Coal Gasification: 60%-70%, Car gasoline ICE: 25%, Total: 15-18%

So you could power nearly 1.5-2 times as many cars on Coal-to-Electricity then on Coal Gasification.

Stan Peterson

Thanks for the efficiency calculations. They point to the obvious better approach of Coal to electricity for PHEVs, over CTL.

Thanks for the points you made about the relative efficiency gains to be made from Combined Cycle.

For the non engineers here, IGCC coal plants first wash the coal and then heat it to turn it into gas without burning it, the gas is scrubbed and them burned in gas turbines (think jet engines) attached to generators making electricity. The jet exhaust is then used to boil water and make steam, fed through steam turbines connected to generators, making more electricity from the same rediual lower temperature heat. Hence the "combined cycle".

The beauty is that the coal gas prior to burning is easy to clean of sulfer, mercury, heavy metals, and other pollutants. Similarly, the burned gas turbine exhaust is pretty clean CO2 gas and can be sequestered after extracting heat,(to boil the water), making it easier to capture and Sequester if you need to do so.

Overall efficiency is 50% or so; much, much, better than anyother electrical generation including natural gas one-pass gas turbine generatation. Its really a similar first cycle, with a standard steam palnt on the back end.


Thanks to the rationalizing of standardized Fission designs and combined building and operating approvals, fission plants are aimed at 48 -60 month building cycles, not 10 year cycles as of old. These are the benefits, as well as knowing that it should be a higher construction quality plant having built multiples of the same design. That sloppy construction was one of my concerns ando why I was a charter member of the UCS.

There is a drawback though. The way progress used to be made, was that improvements were incorporated in every plant built, each subsequent one slightly better than its predecssor. Now that will be be impossible with frozen designs. Eexcept on "model turnovers" every generation or so.

Thanks for the refereneces to the Sun's not quite steady output. I didn't think any one would question the great and omnipotent Wizards of The Integovernmental Panel on Climate Change in their periodic summaries of the Climate Science. If even these global warmists admit the Sun might have some possibilty of warming or cooling the earth, who would complain?

To re-iterate: in IPCC TARI they ignore the sun; A few years later in IPCC TAR II they did the same although pressure was now building for a variable solar contribution that was ignored.

In the subsequent update in IPCC TAR III, they said well it could account for a lot, maybe most, but didn't know how much, so they wouldn't count it at all.

In the latest IPCC TAR IV, just released, they said the Sun definetly contributes to the curwent gloal warming, but warms by two methods, direct radiation responsible for about 15% of the observed warming (previosuly assigned to CO2); and an indeterminate amount of indirect warming, not thoroughly understood, so they ignored that much bigger piece. And attributed it to CO2.

A lot of research is piling up now coming from the Solar space probes flown since the turn of the century; and mapping of the Earth's cloud cover by satellites since too, revealing coordinated response to solar activity. Meanwhile CO2 continues to have problems. Research tends to confim it as a consequence not a cause of warming as more and more historical core samples are researched. It appears the Oceans expell or more accurately slow down absorbing CO2 as the climate warms, leaving an elevated CO2 level in the atmosphere.

When I refer to The Electrification of Ground Transport, I am talking primarily about the conversion from hydrocarbon to electric LDV fleet not the Rails. Ssome more rail electrification will come but not much. Transmission losses limit how much is efficient The RR have built out about all the useful electrical mileage by now. But rail series diesel hybrids are coming.


Hand you the Prize for keeping your eye on the ball. It IS ALL ABOUT POLLUTION. That is the target. Removing Real baddies H2S, CO, NOx, SOx Paeticularites from the air. Although that job is 99.9% done, it's not finished yet.


How about getting solar panels with PV systems outside of each home garage in America where we can plug in on natural juice. Well, especially in the southern states. Or how about a better idea. Diversify all our energy needs between geothermal, wind, solar and refuel and cellulosic ethanol/butanol and lets stop allowing the coal and big oils to hold us all hostage while they make their pockets fatter. Clean coal technology sounds like BS to me. All these companies want to do is keep feeding is their own crack whether it be at the pumps or what powers our homes. By diversification, the citizens of America bring it back to the PEOPLE. That is true democracy and capitalism. Imagine all homes with solar power. Solar power makes sense even in Germany where they have much more cloud cover on average than we do even in the Northeast, USA. So Coal can kiss my you know what. We need tostart thinking of fuel and water as something owned by everyone not by a few big companies who control us like robots on crack fuel!

Sick of the Bull

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