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EPRI-NRDC Studies Highlight GHG and Air Quality Benefits of Plug-in Hybrids

Two studies released by the Electric Power Research Institute (EPRI) and the Natural Resources Defense Council (NRDC) show that widespread use of plug-in hybrid electric vehicles (PHEVs) in the United States could significantly reduce greenhouse gas (GHG) emissions and has the potential to provide small but significant improvements in ambient air quality in most areas of the US.

Widespread adoption of PHEVs could reduce GHG emissions from vehicles by more than 450 million metric tons annually in 2050—equivalent to removing 82.5 million passenger cars from the road. Cumulative GHG emissions reductions from 2010 to 2050 could reach 10.3 billion metric tons under the most aggressive scenarios for the development of a lower-carbon electrical infrastructure and PHEV penetration.

The analysis is the first to combine models of the US electric system and transportation sector with atmospheric air quality models to account for the future evolution of both sectors in technological advances, electricity load growth and capacity expansion.

PHEV Impact on Nationwide Greenhouse Gas Emissions. The GHG research measures the impact of increasing numbers of PHEVs between 2010—the year the researchers assumed PHEVs would become available on the US market—and 2050. The “well-to-wheels” analysis accounted for emissions from the generation of electricity to charge PHEV batteries and from the production, distribution and consumption of gasoline and diesel motor fuels.

The researchers combined three scenarios for the development of the electric sector— high-, medium-, and low-levels of both CO2 and total GHG—and three scenarios for the rate of adoption of PHEVs—low, medium and high.

The different scenarios of CO2 and GHG intensity for the electric sector are:

  • High. There is limited availability of higher efficiency and non-emitting generation technologies and a low cost associated with allowances to emit CO2 and other GHGs in this scenario. Total annual electric sector GHG emissions increase by 25% from 2010 to 2050.

  • Medium. Advanced renewable and non-emitting generation technologies, such as biomass and IGCC with carbon capture and storage, are available in this scenario. There is a moderate cost associated with allowances to emit CO2 and other GHGs. Total annual electric sector emissions decline by 4% between 2010 and 2050.

  • Low. Carbon capture and storage retrofit technology for existing coal plants are available in this scenario. In addition, there is significantly slower load growth indicative of a nationwide adoption of energy efficiency, or other demand reduction, and a high cost to emit CO2 and other GHGs. Total electric sector emissions decline by 85% in this scenario from 2010 to 2050.

The three different PHEV adoption scenarios each presume PHEVs enter the market in 2010 and achieve maximum new vehicle market share in 2050. PHEVs reach a maximum of 20% new vehicle market share in the Low PHEV scenario, 62% in the Medium PHEV scenario, and 80% in the High PHEV scenario.

2050 New Vehicle Market Share by Scenario Vehicle Type
Conventional Hybrid Plug-In Hybrid
PHEV Fleet Penetration Scenario Low 56% 24% 20%
Medium 14% 24% 62%
High 5% 15% 80%

Total system emissions from a given level of PHEV use will be determined by a combination of the vehicle type (PHEV with a 0, 20 or 40 miles of electric range), annual vehicle miles traveled by vehicle type, and the types of generating resources that are built and dispatched to serve the electrical load from grid-connected PHEVs.

The researchers found that annual GHG emissions reductions were significant in every scenario combination of the study, reaching a maximum reduction of 612 million metric tons in 2050 (High PHEV fleet penetration, Low-electric sector CO2 intensity case).

2050 Annual GHG Reduction (million metric tons) Electric Sector CO2 Intensity
High Medium Low
PHEV Fleet Penetration Scenario Low 163 177 193
Medium 394 468 478
High 474 517 612

Air Quality Analysis. The air quality study evaluated two scenarios for the year 2030:

  1. A base case without any penetration of PHEVs in the US vehicle fleet; and
  2. A PHEV case with PHEVs having reached 50% of new vehicle sales and constituting 40% of on-road vehicles by 2030. In the PHEV case, the overall fraction of vehicle miles traveled by the US vehicle fleet using electricity stored in PHEV batteries is 20%.

The study used a high electric-sector emission case where nearly all additional electricity demand needed to power an aggressive market penetration of PHEVs was assumed to be met by an increase in the use of present-day coal-fired generation technology with only currently required environmental controls.

The study consisted of four steps:

  • Transportation Sector Modeling. For both the base case and the PHEV case, the transportation sector and its emissions were modeled out to 2030. Emissions offset due to vehicle miles traveled using electricity (and reductions in upstream emissions) are calculated by the transportation models. In addition, the incremental electricity demand due to PHEVs was calculated for the PHEV case. The incremental load takes into account losses during transmission and battery charging. This incremental load is also attributed to different hours of the day assuming an overall charging profile for the fleet.

  • Electric Sector Modeling. For both the base case and PHEV case, the US electric sector was modeled from 2006 to 2030. New generation capacity and electricity dispatch is simulated by the models to account for increased load due to population and economic growth. Emissions associated with electricity generation is also calculated and constrained by environmental regulations as explained earlier. In the PHEV case, the incremental electrical load due to PHEVs is added for all intermediate years in which PHEVs are present as well as 2030.

  • Emissions Processing. For each scenario, emissions from the transportation sector and electric sector were merged with emissions from all other sectors into an emissions inventory. Natural emissions from vegetation and soil are also added into the emissions inventory. The emissions inventory is then transformed into a format suitable for use in a three-dimensional model of air quality for the entire continental United States.

  • Air Quality Modeling. The US Environmental Protection Agency’s Community Multiscale Air Quality (CMAQ) model was used to simulate US air quality in 2030 in each scenario. The key air quality indicators investigated in the air quality modeling were: ozone mixing ratios; daily and annual particulate matter concentrations (for both PM10 and PM2.5); deposition of sulfate, nitrate, total nitrogen (sum of oxidized and reduced nitrogen) and mercury; and visibility at Class I areas (e.g. national parks). In addition, population-weighted exposure indicators were also calculated for ozone and particulate matter.

The study found that:

  • In most regions of the United States, PHEVs result in small but significant improvements in ambient air quality and reduction in deposition of various pollutants such as acids, nutrients and mercury.

  • On a population weighted basis, the improvements in ambient air quality are small but numerically significant for most of the country.

  • The emissions of gaseous criteria pollutants (NOx and SO2) are constrained nationally by regulatory caps. As a result, changes in total emissions of these pollutants due to PHEVs reflect slight differences in allowance banking during the study’s time horizon.

  • Considering the electric and transportation sector together, total emissions of VOC, NOx and SO2 from the electric sector and transportation sector decrease due to PHEVs. Ozone levels decreased for most regions, but increased in some local areas. When assuming a minimum detection limit of 0.25 parts per billion, modeling estimates that 61% of the population would see decreased ozone levels and 1% of the population would see increased ozone levels.

  • Mercury emissions increase by 2.4% with increased generation needs to meet PHEV charging loads. The study assumes that mercury is constrained by a cap-and-trade program, with the option for using banked allowances, proposed by EPA during the execution of the study. The electric sector modeling indicates that utilities take advantage of the banking provision to realize early reductions in mercury that result in greater mercury emissions at the end of the study timeframe (2030).

  • Primary emissions of particulate matter (PM) increase by 10% with the use of PHEVs due primarily to the large growth in coal generation assumed in the study. In most regions, particulate matter concentrations decrease due to significant reductions in VOC and NOx emissions from the transportation sector leading to less secondary PM.




That nice.

Now when will the NRDC stop ignoring the air quality downsides of Ethanol?

Stan Peterson

I love analyses that don't analyze anything; and make other than projections that are straight forward and not really applicable.

Of course PHEVs would have improved air quality. But that assumes that direct anti-pollution action will not have solved that question anyway. The US auto fleet produces 1/1000 th of the pollution of the auto fleet in 1975.

And that includes the fact that the US auto fleet today is another third larger in the number of vehicles. Despite continued pressure for even more, the US auto fleet has risen in efficiency by about 5.1% per year compounded. Most of this went into larger, safer vehicles, equipped with more safety subsystems, and better performance. But changes in that direction, has gone about as far as is necessary, or likely.

Even if the auto fleet stayed based on fossil fuels, the un-written and un-appreciated fact is that air quality is essentially coming into compliance virtually everywhere in the USA, without a single PHEV in the fleet, as yet.

If air quality targets were the same as originally targeted in the the 1970's, ALL the USA would be in compliance, today. But job justification creep has tightened the EPA targets for defining "good air". Of course, PHEVs would have helped, but there would not be actual improvement because the air will have been cleaned anyway, even up to the toughened targets in but a few more years and long before 2030.

The other stupidity is assuming that the present electrical generation mix or emission levels will remain as they are today. In other words, they are making a straight line projection.

Three points about that non analysis.

There are 29 Nukes in the pipeline in the USA, where as a few years ago there there were none.

Nuclear is making a gigantic comeback.

Over the next 25 years there will be many more, and the percentage of clean electrical power will rise from 20% to as much as 40-50%. Starting about then the earliest Nukes will start to permanently retire, so the percentage may then stabilize or even decline. But Fusion will be looming then as a viable and inexhaustible solution that will start to take over.

Hydro will remain essentially the same,as it is built-out. Wind, solar, wave and geo-thermal will increase from today's insignificant nothing to twice or three or four times the insignificant nothing, with government subsidy, knocking off another percent or two of fossil generation.

The coal power plant of 2030 will be significantly cleaner than today's coal plant. IGCC, with optional sequestration, will be much more common. Even with out sequestration, the emission levels, are at least an order of magnitude cleaner than today's plants. Even the present "dirtier" plants are much, much cleaner than the "clean" auto fleet. As noted, the cleaner coal plants will constitute a smaller percentage of electrical generation than it does today as well.

By the 2030 time frame the Global warming nonsense will have died; pollution will have been conquered; dependency on a petroleum basis for the ground transport application will have diversified; productive lifespans will have increased as auto immune debilitating diseases, (atherosclerosis, diabetes, MS, Alzheimer's) will have been conquered one after another. Cancer will likely be much better in control too.

What will the Cassandras worry about then?



It would be helpful to read the article in context before bashing it. The air quality side of the article was clearly secondary to the GHG side of the article, and its analysis was obviously meant as a "worst case" sort of scenario.

The subtext of the article was that PHEVs can be expected to reduce GHGs under most any circumstance, but will that be at the expense of pushing the pollution upstream, to the power plant level? If power plants become very green, this is obviously not a problem, but in a "worst case" scenario, where all new power plants are the dirtiest we can think of (conventional coal), would widespread introduction of PHEVs come back to haunt us, through the creation of worsening air quality?

The answer this study suggests is no. Even with fairly high PHEV penetration and usage (20% of all vehicle miles powered by grid electricity), the consumption of all that extra coal-fired electricity will still not worsen our air quality. This is because even though modern cars are rather non-polluting, they still emit enough to be noticeable, so reducing the amount of gasoline consumed still has enough benefits to outweigh the cost of some increase in coal consumption.

As an aside, I find your remark about "job justification creep" and our increasingly strict air quality regulations to be rather misdirected. Forty years of advances in atmospheric science sound like a plausible enough source for the revised pollution criteria. To make a comparison, the results of forty years of biomedical research seem to contain reasons enough to justify the fact that our medical treatments are not the same as they were back in the late 1960s and early 1970s.


I agree with what NBK-Boston said here. The study of this subject is a good thing and the results are very interesting.

One of the great things about PHEV and BEV solutions is that they give us the option for powering our vehicles with wind and solar power.

I am doing both right now with an electric motorcycle I built myself. My next conversion will be a car that I can use next winter.

I also got a call today from the local Vectrix dealer that they now have an electric scooter in stock for test drives. We need more options like this to choose from.


KJD: let us know what you think of the Vectrix. Not just the ride but your impressions of its quality. That would be great!


Yeah KJD - that sounds awesome. The more people we can get motivate to working on similar projects and pushing alt autos the better - I'll all for supporting those types of efforts (not much of an engineer myself - but I walk to work now so I don't need one). Also, something cool I saw today is a new push by the Center for American Progress for alt fuels is their new Clean My Ride project where they're getting a ton of celebrities to make web videos that support the cause - the first one is up and has Ben Affleck in it (actually really funny) and its at CAP is doing a great job with this by trying to generate some popular buzz for this.

Felix Kramer

This summary is great -- especially because it includes a table that is not in the study's own Executive Summary: the matrix that shows the worst-case (low PHEV penetration and high-CO2 grid still delivers 162 million metric tons of CO2/year, while the best-case (high PHEV penetration and a much cleaner grid) will result in 612 million metric tons/year.

Here's CalCars' overall take on the report:

The EPRI-NRDC studies finally give an environmental stamp of approval to PHEVs. Scientist have confirmed that unlike gasoline cars, plug-ins will get cleaner as they get older -- because our power grid is getting cleaner.

For people looking for the most effective way to end our addiction to oil, PHEVs have made sense because carmakers can build them now, with today's technology and using today's infrastructure. But they've needed definitive proof that PHEVs won't increase pollution. The main study shows that under all nine scenarios for both rates of market penetration of PHEVs and the evolving power grid's characteristics (capacity/carbon intensity), PHEVs will vastly reduce greenhouse gases for the next 40 years. In the second study, for the next 20 years, even if, worst-case, we still use lots of coal, nationwide air quality for other emissions will also improve.

Three more points: Both reports match up well with previous studies. They reinforces the Pacific National Lab's January 2007 findings that we won't have to build new power plants for cars that charge at night. And we're gratified that General Motors recognizes sees this study as validation of its decision to evolve to the electrification of transportation.

BTW, the studies are huge -- If you want to spend a worthwhile hour on this, at the URL cited, read the press release, then get the Executive Summary for part 1 (9 pages, 8 charts & tables) and the Frequently Asked Questions that covers both reports (7 pages, 24 questions).

-- Felix Kramer, Founder, The California Cars Initiative

Kit P

Cause and effect. For those who made the effort to actually read the report, that burning sensation in the eyes was virtual smoke being blown in your face.

So how much could I save on energy bills with a PHEV with a 20 mile range? About $1/day while increasing ghg from 'old coal' 11%.

The data does support ways to reduce ghg, reduce energy bills of Americans, and increase energy independence. Replace CCNG generation with new nuclear power plant until LNG terminals are out of business.

Mike Z.

NRDC is the ultimate late comer to technology. They were still pushing natural gas power as late as 2005 with price forecasts that were off be almost 100%!

I met a senior member of them in early 2006 and he never even heard of cellulotic ethanol, then three months latter he was talking it up like crazy on a radio interview!


Just in case anyone believes Stan's outrageous claims for the "efficiency" improvements in the US auto fleet I have excerpted a scientific study below. Indeed, pollution from automobile exhaust is being reduced but not nearly 1000 times and it is still the major source of air pollution in the US.

The reason for the rash of permits for nuclear power plants is due to the huge subsidies in the energy bill, 2 cents/KWH for the first reactors constructed. Do away with this production subsidy, the subsidies for decommissioning, yucca flat, Price-Anderson liability limits etc. and nuclear could not compete.

The History of Improving Automobile Emissions...

Department of Chemistry, Pepperdine University, 2003


The steady reliance on the automobile for transportation over the past several decades has resulted in a dramatic decline in our nation’s air quality. Over 50% of all United States air pollution is generated by motor vehicles, and transportation accounts for over 75% of U.S. CO emissions, nearly 50% of U.S. oxide of nitrogen (NOx) emissions, and 40% of the volatile organic compounds (VOC) emissions [1]. Ground-level ozone, the most problematic constituent of smog, forms when volatile organics combine with NOx in the presence of sunlight; urban areas having sunny, warm climates are particularly prone to ozone problems [2]. A strong correlation between breathing smoggy air and an increased incidence of respiratory and cardiopulmonary disease is emerging. In general, slower lung growth in children appears to be associated with exposure to constituents of smog [3]. These findings continue to prompt new legislation associated with motor vehicle emission controls.

In the 1960s, a typical new car produced 228 pounds of smog-forming hydrocarbons in a year; today the typical new car produces less than five pounds annually [4]. Over the past four decades, emissions of carbon monoxide and oxides of nitrogen have also been substantially reduced. For example, a pre-1966 automobile emitted 84 g of CO/mile and 4.1 g NOx/mile; the current federal standard is 3.4 g CO/mile and 0.4 g NOx/mile (Tier 1) [5]. Aggressive air pollution control programs in the U.S. stimulated changes in engine design and emission control devices in the 1970s, and later use of reformulated gasoline and low-emission automobiles in some states also mitigated vehicle emissions. Since the phasing out of leaded gasoline in the 1970s, several oxygenated compounds, including ethanol and methyl tert-butyl ether, have been used to enhance octane ratings and to reduce carbon monoxide emissions.


There are 29 Nukes in the pipeline in the USA



I probably do not understand the study. The way I read the article, they coupled a degrading picture of generation air pollution to minimize the effect of Hybrid plug-in vehicles. The new fossil fuel generating units such as the GE combined cycle approach 60% thermal efficiency, whereas the older boiler technology ran around 38%.

Now I certainly concur with the observation that PHEV shift the source of the pollution to the electric generators, and therefore is the generation is coming from buring fossil fuel, no real improvement is achieved. But, if at the same time (2010-2050) we shift away from fossil fuel to nuclear and renewables, then significant reduction seems in the cards. Especially for me, I live in Southern California near a freeway packed with cars crawing along spewing unbreathable exhaust.


Man, the trolls are out today. Stan Peterson trolls:

By the 2030 time frame the Global warming nonsense will have died
If you mean the denial that it's already happening and rapidly getting worse, you're probably off by about 20 years. But I think you mean the opposite.

And the Kit P trolls:

So how much could I save on energy bills with a PHEV with a 20 mile range? About $1/day
If you replace the average 25 mpg vehicle and gasoline is $3/gallon at the pump (it's really costing you a lot more, but the various agricultural and military expenses come from income taxes) your fuel savings would be saving $2.40/charge or up to $4.80/day for a commuter who recharges at work. Figure half that on weekends, so 260*4.80 + 104*2.40 = $1497.60/year. Savings would go up as fuel prices increased, of course.

It would be more interesting with you around if you'd at least try to make your falsehoods more subtle than gross arithmetic errors.


For those of you who seem to have a problem with this study, and PHEVs in general, there is another option. Do nothing and wait until the oil runs out. Problem solved. But I suspect there are posters here who want it both ways. Do nothing and magically wish for a substitute for oil.

Having said that, it is guaranteed that as long as we use oil, carbon emissions will not improve unless we simply cut back, increase efficiency, and/or switch to smaller vehicles, which isn't necessarily a bad approach and one that many of us are personally following.

But even with all the above, there will need to be alternative ways of running our vehicles in the future. Electricity has the advantage that it can be made with a wide variety of fuels, including those which emit little or no greenhouse gases. We need to move to those alternative sources regardless of how we choose to run our vehicles. Converting our vehicles to electricity will compliment what should be done anyway.

One issue not mentioned is that for the next decade, the baseload can take care of most of these new vehicles. At night, especially if one is using coal, the demand for electricity is typically below what is produced anyway because the generators need to run at a certain capacity, a wasteful exercise. In essence, then the first crop of PHEVs can run on fuel that would be wasted anyway. The net contribution to emissions in the early stages, therefore, will be zero.

In a saner world, we would drastically cut back our use and need for the automobile, which I consider one of the most destructive, dangerous, and harmful technologies ever developed and put into widespread use. In the mean time, however, we will need to find ways to mitigate the otherwise destructive effects of this monster.

Kit P

E-P, how about if you replace the average 25 mpg vehicle with a Corolla and you commute 20 miles a day?

Speaking of smoke, did you get a whiff of what E-P was blowing. He might think it is cheating, but I took the numbers out of the report. I multiplied by the price I pay for gasoline and subtracted price I pay for electricity. I did not consider the added costs of a PHEV which would most likely negate any savings at all.

Increasing ghg from 'old coal' by 11% came straight from the report.

The list of nuclear power plants in the 'pipeline' is not about 33. The PTC for the first 6 and is the same that wind power gets. Each nuke plants pays its own cost for spent fuel disposal and decommissioning.

Here is a link to a list:

What may not be apparent form this list, is that most of these nuke plants will be merchant plants run by companies that also own CCGT. The reason this is relevant is that the mix of electric generation will likely be such that ghg emissions have significantly reduced to the point where the cost of a PHEV can not be justified unless the price of gasoline doubles In which case, biofuels will be very economical.

Maybe E-P does not consider himself a troll when he ignores the price of electricity, the fuel economy of a sticker price comparable POV to a PHEV, and the most likely energy sources.

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