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CMU study finds that coal retirement is needed for EVs to reduce air pollution

Electric vehicles charged in coal-heavy regions can create more human health and environmental damages from life cycle air emissions than gasoline vehicles, according to a new consequential life cycle analysis by researchers from Carnegie Mellon University. However, the anticipated—albeit now possibly delayed, per the recent Supreme Court decision—retirement of coal-fired power plants will make electric vehicles more competitive on an air emissions basis, the researchers found.

Among the findings of the study, published as an open-access paper in the journal Environmental Research Letters, was that battery electric vehicles with large battery capacity can produce two to three times as much air emissions damage as gasoline hybrid electric vehicles, depending on charge timing.

(Lifecycle emissions for greenhouse gases, PM, NOx and SO2 are higher under controlled charging scenarios than in uncontrolled charging due to the generation mix; the researchers found that charging late at night reduces power generation costs by a quarter to a third—largely by shifting to cheaper coal-fired power plants. But the extra emissions released as a result can cause 50% higher costs to human health and the environment.)

In the study’s future 2018 grid scenarios that account for predicted coal plant retirements, PEVs would produce air emissions damages comparable to or slightly lower than HEVs.

The researchers also found a significant difference between coal and natural gas generation. Even in one of the power systems in the country with the highest coal generation, PEVs could reduce transportation health and environmental damages in the near future, long before a zero-carbon electricity mix is achieved, due primarily to substitution of natural gas for coal on the margin.

Life cycle emissions by pollutant and life cycle stage for each vehicle type in the recent (a) and future (b) PJM grid. UC stands for uncontrolled charging and CC stands for controlled charging. Source: Weis et al. Click to enlarge.

Carnegie Mellon Associate Professor of Engineering and Public Policy Paulina Jaramillo; Professor of Engineering and Public Policy and Mechanical Engineering Jeremy Michalek; and former Engineering and Public Policy PhD student Allison Weis studied the electricity grid in the PJM region, which includes Washington DC, Philadelphia, Pittsburgh, and Chicago.

The team modeled the power plants in the PJM region and looked at how plant operation would change in response to electric vehicle charging load, said Jaramillo. They then modeled the emissions from those power plants, the effects of emissions on air pollution in downwind counties, and the resulting implications for human health and the environment.

The study modeled a conventional gasoline vehicle, conventional hybrid, two plug-in hybrids (one modeled on the 10-mile AER Prius PHV and one on the 35-mile AER Chevy Volt) and a battery-electric vehicles (modeled on the Tesla Model S).

The most recent year for which all of the necessary data are available to make this assessment is 2010, noted Michalek.

The largest source of damage stems from sulfur dioxide emissions from coal-fired power plants, which produce airborne particles that people breathe, according to the study.

The study, which was funded by the Doris Duke Charitable Foundation, the Richard King Mellon Foundation, the Electric Power Research Institute, the Heinz Endowment, the National Science Foundation, and Toyota Motor Corporation, also examined a hypothetical case with increased wind power.

However, the air emissions damages resulting from electric vehicle charging hinge primarily on the amount of coal in the system, not the amount of wind or solar power, said Jaramillo.

When EV charging load is added to a power system, wind and solar plant output can’t be turned up to respond because they are typically already fully utilized. Fossil fuel plants are the ones dispatched in response to new charging load. That’s why the shift away from coal is so important for EVs.Jeremy Michalek

While PEVs can double or triple air emission damages in the recent grid relative to HEVs, they could reduce damages in a future grid. However, we estimate that near future (~2018) potential air emissions benefits from PEV adoption in PJM are small relative to HEVs (or even negative when considering the net effect on the automaker’s fleet under federal fuel economy policy). Nevertheless, electrification may offer a promising long term option to significantly reduce air emissions from the transportation sector compared to some other alternative transportation fuels, including biofuels and natural gas, that have been shown to offer small-to-no reductions in GHG emissions and could have unintended consequences like higher global food prices. Indeed, the logistics of regulating emissions from individual vehicles over their functional lives are more difficult than regulation of power plant emissions.

Continued regulation of the electricity system can increase the benefits of vehicle electrification, and consequential air emissions implications of PEV charging are already lower in many regions than in PJM. While near-term benefits of PEV adoption in PJM are estimated to be small or negative, a transition of the transportation system could lead to long-term benefits outside the scope of this analysis, including greater benefits in other regions and future emissions savings enabled by a transition to electric vehicles as the electricity grid becomes cleaner and as public policy adjusts.

—Weis et al.




This may apply in USA, China, India and other places where CPPs are used to generate the majority of the e-energy used.

Would not apply in our area where the power grid is fed 100% with Hydro + Wind.


This is probably well intentioned (hard to tell since CMU is in the heart of coal country) but like other similar studies this will be used to bash EVs. The silly environmentalist are a gullible bunch and can not conceive of how this study may help them. They will simply take it as gospel (to them science is devoid of human foibles-they assume it is an absolute and contains no human opinion or spin)


You should add the pollution of producing this very polluted battery full of toxic material and the disposal of the battery that can caught fire anytime as it degrade by itself.

At first this was told by a lot of persons but the high Financial circles didn't want to changes their fraudulent planning and are imposing the ruin of battery electric cars but bevs are rejected by all consumers, LOL.


UCS says across the U.S. EVs are half the CO2 compared to gasoline. Coal will be used less for power plants. Combined cycle natural gas are most of the new builds now.

Account Deleted


Read the post. The problem is COAL, not batteries. In 2015 Natural Gas produced more electricity than Coal. Coal is on the way out. It is the dirtiest fuel known - Sulfur, Mercury, and other heavy metals from burning Coal pollute the air, ground, and water. I grew up in Coal country, Alabama. Our home was heated by this dreadful carcinogen, I still have nightmares about that terrible Coal bin in the basement.
Coal companies are going bankrupt, we need to help their employees. My first job was at Southern Company Services, a power company that at one time owned Coal mines. My first assignment was to optimize the allocation of Coal to Power Plants. Recently, Southern Company bought AGL a gas company, even they know the future is not Coal.


If you need on demand power, and you do, then by far the cleanest way to use natural gas, which is already of course much cleaner than coal, in a fuel cell.

Costs are high, but rapidly dropping.

And of course they can actually enable storing renewable energy as so eliminating fossil fuels from the loop altogether.

Even if there were not to be a single fuel cell car on the road, fuel cells still have a massive and beneficial role to play in transport.

Which is why the endless opposition to them from BEV only advocates is not only misconceived, but spectacularly daft.


Electrified trains/locomotives with 2 to 4 1000KW FCs instead of diesel generators and/or very costly overhead power cables could reduce GHG and pollution.

Clean H2 required could be supplied and stored different ways.

A few such locomotives could become powerful back ups for the grid. at low interconnections cost.

The soonest the world can do without CPPs and ICEVs the better. FCs may very be part of the solution.


which is hardly surprising as it is out of favour and part of the short term economic imperative.\
In the longer term it's todays young adults and children (who don't vote) will be paying off our fups.

Seems to be very favourable to NG
Makes a good case for more R.E. wind solar etc.

When EV charging load is added to a power system, wind and solar plant output can’t be turned up to respond because they are typically already fully utilized. Fossil fuel plants are the ones dispatched in response to new charging load. That’s why the shift away from coal is so important for EVs.Jeremy Michalek

Willy Nilly

"battery electric vehicles with large battery capacity can produce two to three times as much air emissions damage as gasoline hybrid electric vehicles, depending on charge timing."

They were comparing a 10 mile Prius and a 35 mile Volt as the HEV's vs. a 200 mile Model S as the large battery BEV.

The article could just as easily have said that since most people know if the are going to drive 200 miles the next day and that since most people go less than 35 per day, large BEV's present an excellent opportunity to offer large BEV owners the opportunity to contribute a buffer of say 35 miles or what every they drove that day or even several days of driving miles to the grid to allow a transition from coal to solar and wind. The timing of the charge being determined by the utility. I believe they are already doing that in California.


The act of charging EVs has nothing to do with how you create electricity and/or how you operate a power plant and certainly means nothing when you try to compare it with ICE smog...simply apples and oranges. An EV charge up is nothing more than another load on the grid. It could just as easily be 5 or 6 Mothers running a load of wash and heating water. Would you compare this to the pollution from a gas car? Certainly not as it means nothing also.

The smog and GHG problem is at the generating station, not at the load. And, the responsibility for cleaning up the air is the responsibility of the power plant operator, not the user of the power.

This argument is nonsense and has always been nonsense. I'm surprised CMU isn't embarrassed to be associate with this kind of anti-EV propaganda. Blaming an user for smog produced by a dirty power plant by comparing the dirty power plant with smog cars, indeed. Did you people not see this when you got sucked in?


The questions regarding grid capacity must be asked and answered for whole fleet conversion to EVs to happen sooner rather than later. The central question I bring up here is which EV tech creates the most incentives to drive less? Reducing emissions, reducing traffic and its hazards and waste through energy conservation? Which EV tech offers the most incentives to walk, bicycle and use mass transit? Which EV tech promotes rooftop and small scale photovoltiac energy production? Which EV tech promotes local economies that can eventually disempower corporate control over our lives? The answer seems to be Plug-in Hybrid PHEVs, rather than BEVs and FCEVs.


A lot of electric vehicles with partially filled batteries provides an opportunity to design a market that would encourage or require charging of vehicles from surplus renewable energy when it is available.

Electricity will not a major cost of an EV. At 10 cents per kwh the cost for a Bolt like car will be 2 cents per km compared to 8 to 10 cents for a comparable ICEV. The EV owner could probably afford to pay 20 cents occasionally and there would probably be stored renewable electricity available at that price. You might need to require the electric vehicle to identify itself as an EV when it is plugged in. The availability of renewable energy should be predictable on both long term and short term basis so EV owners could plan their charging. EV's could be programmed to limit their charging during low supply high demand periods.

Sixty KWH EV's will probably have 3-4 days of typical commuting reserves so the owners would have flexibility, though the demand for charging on weekends might exceed the supply of renewables.

Such a system would not be simple but given all the technology out there it could probably be designed.


Many Hydro power plants are built/equipped with over capacity to meet peak demands and are throttled back to save water during off peak periods.

Much the same can be done with wind power plants. Output can be reduced to match lower demand or stored during off peak periods. Storing excess e-energy is better unless one has to reduce production for maintenance etc.



"In 2015, the U.S. saw 16 gigawatts of new renewable energy capacity installed...while 11 gigawatts of coal-fired electricity came offline as old plants were retired amid rising costs and stricter environmental regulation. The clean energy transition is very much underway."

Henry Gibson

A recent combined cycle gas-turbine-steam-turbine power plant is likely the highest efficiency power plant that burns natural gas, even more than many fuel cell combinations. It could be even lower carbon release if it were built in New York City and pumped the heat into the city steam pipe heat system which did not fail even when all the lights went out during the storms of recent years. That steam could have even been used to operate steam eductor pumps that require no electricity to prevent some flooding in cellars and tunnels. The waste of natural gas at some oil wells make it one of the most damaging of fuels in regards to green house gas releases. Nothing that the US can do will substantially reduce green house gas release in the world.

But eliminating coal fired power plants is far more expensive than just requiring every new and some old buildings to install natural gas micro-turbine co-generation systems for all of their power because such systems pay for themselves in a few years.

Coal can be burned without any sulphur or other particle released into the air.

It is the people who buy electricity who cause the pollution. If they did not buy there would be no pollution. If the people would study and understand nuclear energy they would demand nuclear power which releases no CO2 and prevents much more CO2 from being released because iron and steel and copper and aluminum etc. even hydrogen could be produced with almost no carbon release. Ships could use sodium powered fuel cells with nuclear, hydro, wind or solar produced liquid sodium.

The Russians have proposed a nuclear reactor powered railway locomotive recently; as small reactors of the proposed type have little residual (not like Fukushima) heat problem after the reactor shut down, such a unit would be less dangerous than a tank car full of propane or chlorine.

Actually it is less a problem than some people believe to partially fuel a locomotive with 95 percent natural gas and five percent diesel. In an emergency, a locomotive with low fuel could spray propane gas from a tank car with a hosepipe into the air intake to reduce diesel use substantially. A similar trick could be used to keep some modern automobiles idling to provide a shelter with no gasoline fuel available in a storm; natural gas could be used.

A US railroad is investigating the use of Liquid natural gas in locomotives when it should just be using it. ..HG..

Account Deleted

Yes Coal can be burned without the Sulfur and Fly Ash going up the stack.
Then what do you do with the Fly Ash, Sulfur, Arsenic, Mercury, Lead, Chromium, etc. You put it in a Fly Ash Impoundment Pond. Duke Energy is spending $Billions cleaning up the spill into the Dan River.
Annually, North Carolina’s power plants generate 5.5 million tons of coal ash making the state 9th in the nation for coal ash generation. There are 13 documented damage cases where North Carolina power plants have contaminated water resources.
Duke Energy retired the three coal-fired plants creating all of this Fly Ash and added 7 Combined Cycle Natural Gas Power Plants with 2,760 MW – more than tripling the original capacity while significantly reducing emissions. NOTE: these are not MICRO turbines and they are more cost efficient than the Coal Plants.

Henry Gibson

The installed turbines were yes not micro-turbines but they also did not save all of the heat for use for heating buildings and houses or for air-conditioning. They still were some of the most efficient combined cycle machines which are more economic and efficient than some fuel cells.

You forgot that some coal has much uranium in it and it is used by the Chinese for nuclear fuel. Also sulphur is a much needed fertilizer for farmland. It is properly proposed by some that coal should be burned at the mine and the ash that is not useful can go back into the mine. It was not even proposed that the future coal burning was the same as it is now with ash collections from the flues.

If coal burning were stopped now, millions if not billions of people around the world would lose their jobs, starve and die and so would their children. Except for France The train systems of Europe and India and China is almost entirely fueled by coal. While the burning of coal has its health effects, the population in general increases because of the vast benefits of fossil fuels. As a net result of fossil fuel use, more and more humans live on the earth even if many die.

Many die in automobile crashes and of lung diseases from the emissions of automobiles. The US has not forbid the use of automobiles or fossil fuels in them.

Duke was a major promoter of nuclear power but was stopped by the false fears promoted by people who are driven by opinions instead of knowledge and do not even know that they themselves and all living things are radioactive wastes that expose others to gamma rays as they do themselves to even more gamma rays when they eat certified organic foods or just any vegetable foods.

Nuclear reactors produce energy with no direct release of CO2 and any CO2 used in construction of them and preparation of their fuels is quickly compensated for by the use of the energy as a substitute for fossil fuels or fossil fuel produced energy in many processes including transportation.

A pound of uranium can produce heat equivalent to three million pounds of coal and produces less than a pound of radio-active isotopes and even these are not true wastes. There is enough uranium in the ocean for billions of years of energy at the current use rate for all energy supplied now by all means, and there is the uranium on land too and three times as much or more thorium. Much uranium is discarded in the process of producing nuclear fuels and is stored. If used in known efficient reactor types, it could produce all the energy needed in the US for the rest of the century without mining another pound. To this could be added the "waste" fuel rods stored from use in US reactors, which themselves could provide enough electricity for all of the US for fifty years if merely repackaged and used in newly built heavy water reactors. Some of the discarded uranium from making these fuel rods might have to be mixed in to slow the reaction if used in existing designs. This process is being tested in the Chinese heavy water reactors.

The prior was written knowing that a Nuclear locomotive was proposed in the US at the University of Utah in the 1950s with much publicity.

The United States has enough isotope 238 to produce about 7000 watts of steam continuously. This could be converted into about a horsepower in a steam locomotive. There were two fireless steam locomotives operating in Switzerland a few years ago. The isotope 238 is likely in oxide form and short steel pipes could each be filled with about 200 grams for 100 watts of continuous heat per pipe. Almost no nuclear radiation escapes the pipes; perhaps even less internal nuclear radiation than escapes each human every day. The pipes could be inserted into the water tank of one of these locomotives, and every day or so depending on the insulation, The locomotive could move a few feet or even a mile.

Used in a specially made, known technology, free piston Stirling engine, the isotope could produce as much as 2500 watts of electricity. A TESLA owner would have to drive slowly at times but would not run out of fuel in his life. This power is enough for 40 miles per hour or more on a level road. ..HG..


HG could add, if solar power can propel a plane 24/7 for many days, a solar car could eventually be driven around 24/7 for 1,000,000+ Km or for as long as tires last.

The sun is the most abundant, free and reliable source of clean energy. We have to learn how to capture and store it more efficiently. All transportation modes, homes, offices and commercial buildings, factories etc could be 100% electrified. We have more than enough unused desert space for solar facilities to feed the world many times. Roof tops, windows, open parking places, highways etc could also be used for local production.

Wood, coal, tar, oil, NG burning and current NPPs is not required and should be curtailed.

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