September 24, 2006
Plug-In Hybrid Car Pollution Benefits Seen As Small

Battery gasoline hybrid cars that can be plugged into the wall to recharge for shorter trips will not deliver large emissions reductions.

Washington, D.C.— Plug-in hybrid vehicles could contribute greatly to reducing automobile oil consumption and emissions, but reaching those goals requires major progress in key areas. According to a report released today by the American Council for an Energy-Efficient Economy, the environmental and economic appeal of plug-in hybrid vehicles will depend heavily upon cleaner power sources and further battery advances. The report, Plug-In Hybrids: An Environmental and Economic Outlook, examines the benefits of plug-ins relative to today’s hybrids. It finds that greenhouse gas emissions reductions associated with a plug-in powered by today’s electric grid would be about 15% on average across the nation, ranging from 32% using California electricity to zero using Upper Midwest electricity.

Note the lack of mention of particulates or mercury from coal burning electric plants.

Plug-ins’ oil savings could be quite large. Battery size and cost rise steeply with the amount of fuel savings, however, suggesting that plug-ins with modest electric-only range will appear first. According to report co-author James Kliesch, the “electric-then-gasoline” depiction of plug-in operation is not realistic and has contributed to overstatements of the fuel savings potential of plug-ins in the popular media. “Achieving adequate battery lifetimes and minimizing battery costs will require a vehicle control logic that turns on the internal combustion engine when extra power is needed, even within the ‘electric-only’ range of the vehicle,” said Kliesch. The ACEEE report estimates fuel savings relative to today’s hybrids of 30% for a plug-in with a 20-mile electric-only range and 50% for a 40-mile range.

We need better battery technology to make plug-ins cost effective.

Where the electricity comes from determines whether plug-ins deliver a net environmental benefit.

For a plug-in owner in California, where most electricity on the grid is generated by low-pollution facilities, driving a PHEV might cut emissions of carbon dioxide by one-third compared with driving a regular hybrid.

But if the same PHEV were charged in the Midwest, where coal-fired power plants supply the electricity, reduction of CO2 emissions would be nil. Nitrous-oxide emissions (which form smog) would fall slightly, but sulfur-dioxide emissions (which contribute to acid rain) would quadruple.

Still, environmental gains are possible.

Plug-ins would chop CO2 emissions by 15 percent on a national average, compared with conventional hybrid cars, the ACEEE report found. At the same time, the plug-in would emit 157 percent more sulfur-dioxide pollution. The need, plug-in proponents say, is for policies that would clean up the electricity grid so that PHEV technology supplies cleaner skies along with energy independence.

This report overstates the environmental benefits of plug-in hybrids. Anyone see the reason why? Hint: large scale use of plug-ins would require construction of new power plants. What about those plants would make things worse?

Answer: New electric power plants will be more heavily weighted toward coal burners than the existing fleet. Natural gas has become too expensive. Hydro power is all tapped out with limited potential for expansion and environmentalists want to see some existing dams dismantled. Nuclear power has fallen out of fashion. Coal looks set to become a larger percentage of total electric generating capacity. Not only would the coal put out more sulfur but also particulates, mercury and other bad stuff.

In California coal faces big regulatory obstacles and the politicians are forcing a big push into renewables. So a shift toward plug-ins here would probably improve air quality. But the cost in electricity will be higher. In the last year nationally electric power costs rose on average from 9.08 cents to 10.15 cents per kilowatt-hour (kwh) or 11.8%. But in California the cost rose from 11.82 cents to 13.84 cents for a 17% increase. New electric power capacity in California (e.g. wind mills) is much more expensive than existing capacity. So the demand for electric power to run cars will drive up average electric prices for all uses.

We could have regulations that require cleaner coal generators nationally. But that too would raise average electric prices. Plus, as demand grows the percentage of total electric power that comes from cheaper hydro-electric dams will decline and the average cost will rise for that reason as well.

If new electric power capacity came from nuclear plants then shifting to plug-in hybrids would deliver a clear and quite substantial environmental benefit. The same will hold some day when photovoltaics become much cheaper. But right now higher electric power demand translates into higher coal burning electric plant construction in most parts of the United States and in other parts it translates into higher electric power prices.

Share |      Randall Parker, 2006 September 24 03:55 PM  Energy Electric Cars

Jake said at September 24, 2006 6:58 PM:

Excellent analysis.

Jerry said at September 24, 2006 8:41 PM:


I'm a much more optimistic about this long-term. I live in northern California where there already is some infrastructure (i.e. plug ins in parking garages and workplaces for the EV-1 during the 1990's all-electric vehicle fantasy that they had) and it was trivial to install and would be trivial to expand. Changing to hydrogen would be much more expensive to install the infrastructure than the electric was.

Most car trips are pretty short, and the hybrid power train is generally cost effective at about $3.50/gallon for most vehicle types. Current hybrids that use NiMH batteries can go a few minutes before the engine has to kick on. If the batteries are doubled in size (about $3k more) compared to current hybrids, half of the typical work commute could be all-electric (about 1.5 cents/mile). For a Prius-like car that lasts 150,000 miles and would otherwise get 50 miles/gallon, that would cut the gas needed over the lifetime from 3000 gallons to 1500. At $2.50 a gallon, that's enough to cover the additional cost of the bigger battery. If you make the battery very big, then the rolling resistance and size of the vehicle significantly increases so there's a happy medium.

If you run the numbers with typcial commuting patterns, and what is likely to be possible for vehicles 5 to 10 years from now, the plug-in hybrid makes solid economic sense if gas stays above $2.50 a gallon. Once you get over the not-yet-cost-effective "hump" to having a hybrid drive train, the economics of plug-ins makes sense.

Although coal dominates much of the upper-midwest's current power mix, there exists an enormous amount of currently untapped wind power in the relativly sparsely populated area (thus avoiding NIMBY problems) that could be used to charge the batteries when there's an excess of supply. Already wind power requires very little subsidy compared to coal (which is obviously under-taxed currently). Wind power is only going to get cheaper as IGBT's (Insulated Gate Bipolar Transistors) advance further (this is why wind power has suddently re-emerged from the 1970's as a cost effective generation scheme). The design of the blades gets the most popular attention but the real cool stuff is going on converting the power into a useable form.

Wind power cannot be relied upon for the whole energy mix because the wind doesn't blow all the time but it's cost and lack of reliability is an excellent match for plug-in hybrids, which could be programmed to charge only when there's excess non-coal supply.

Randall Parker said at September 24, 2006 9:12 PM:


I'm not worried about the infrastructure upgrade costs for electric delivery to vehicles. I agree that isn't a big problem.

In order to shift toward wind and other non-reliable power sources we really need dynamic pricing. If the electric meter could receive signals that tell it what the current cost is per kwh and if that signal then could be made available to appliances and to car rechargers then, yes, wind and solar would have bigger markets. But that regulatory change is needed and people who want to see more wind and solar ought to press for dynamic electric pricing.

Coal doesn't just dominate the mid west. Coal accounts for fully half of US electric power and that percentage is growing. For new build coal is a much higher percentage as nuclear isn't getting built and natural gas has become so expensive.

nathan es said at September 25, 2006 6:55 AM:

Hey a quick thought, The prius has been altered by many owners, to become "plug ins" for around the town driving with out being dependent on gas. Toyota has just jumped on the bandwagon offering the possibility of a factory option for late 2007, wouldnt this be a compromise that other manufactures could easily follow suit?

michael vassar said at September 25, 2006 7:28 AM:

How about wind? Wind's major problem is it's intermittancy, but with millions of plug-ins in garages the unreliable load from wind power could be smoothed. Smoothing it could be a revenue source for plug-in owners, reducing the cost of ownership. This system would also smooth solar loads, with similar effects.
Mostly-electric plug-ins with small (~10 horsepower) efficient diesel or rotary engines could themselves constitue, collectively, a significant part of the grid. In driving, the engine would compensate for friction and the electrical system would provide all acceleration and regeneratively recover all energy from decelleration.
Obviously this requires better batteries. What's taking so long?
By the way, it's really annoying to have two rounds of security codes

Eric McErlain said at September 25, 2006 8:44 AM:

But if you built more nuclear onto the grid, you would get two benefits: Abundant zero emission electricity at a reasonable price. Even better, additional nuclear would displace natural gas-fired electric capacity, freeing up its use for industrial applications, contribute to price stability in natural gas markets and free us from overdependence on a resource that will eventually have to be supplied from overseas powers like Russia and Iran.

The California example is interesting, isn't it? All plug-in hybrids would do without additional nuclear energy on the grid would be to drive the price of electricity higher on a grid that's already heavily overdependent on natural gas-fired capacity.

It's time to start building more nuclear power plants. If you don't, you just trade oil dependence for natural gas dependence, limit the extent to which you can constrain emissions and drive electricity prices higher.

Paul Dietz said at September 25, 2006 8:57 AM:

If CO2 emissions are not regulated or taxed, there's little reason to expect those generating electricity to control them. So current CO2 emissions should not be taken as indicative of what could be achieved if the incentives change, or the cost of controlling those emissions. Remember, the predictions of the cost of SOx emission control in the US were too high by a factor of six vs. what actually happened after the emissions credit trading scheme was instituted.

I've been tooting this horn, but I'll do it again: EPRI and Alsthom are piloting a CO2 scrubbing system for existing coal plants that captures 90% of the CO2 at a projected cost of as low as $15/ton (while also effectively scrubbing NOx, SOx, and probably mercury) and half the parasitic energy cost of MEA-based solvent extraction. The scheme passes flue gas through chilled solution of ammonium carbonate in liquid ammonia, capturing CO2 as ammonium bicarbonate; the bicarbonate is then stripped to regenerate the solution.

KenG said at September 25, 2006 9:54 AM:

OK, I'll start by admitting I haven't read the report because it requires registration to download.

However, something is not making sense. Plug-ins won't reduct pollution in the upper midwest? Illinois gets about half of it's electricity from nuclear, the other half from coal. Michigan is 27% nuclear, Minnesota is 24% nuclear. On the CO2 side you have to remember that those coal plants, although they emit CO2, have efficiencies in the 40 to 50% range compared to more like 20 to 25% for internal combustion engines. And, while the California generation is mix is relatively clean (almost half nuclear, hydro, etc and about half gas), remember that during the temperature peaks they had this summer, they reached imports of about 10 GIGAWATTS. Some of that was generated by nuclear plants in Arizona but most by coal plants in other western states.

The bottom line is that other studies have shown that plug-ins are about the only hope to reduce transportation emissions of CO2. Hydrogen will only work if it's generated by nuclear or clean coal - which can also power plug-ins.

Jim said at September 25, 2006 10:26 AM:

Don't forget if we use more home grown electrical power then the demand for oil will decrease and the price will fall to make it more attractive. Yet the price for imported oil is more than the barrel price. Dependence on OPEC oil means huge expenditures by the government to keep those supplies secure. It seems we have inflated the value of those nations to us far beyond their historical norm. The clash of cultures was not a big deal until we became a net importer.

Tony Lekas said at September 25, 2006 11:36 AM:

Jim - I don't see how oil consumption would increase. Very little of our electricity is generated by oil. Any increased demand will likely be met by coal, or for peaking more natural gas.

KenG - While the midwest has some nuclear the question is, are those plants already going flat out most of the time supplying the baseload? That is normally the way nukes are used because they are the most efficient and easiest to operate that way. If that is so, any additional demand will be met by coal, or for peaking more natural gas. I don't think that the current nukes can do any more.

We should only consider hydrogen if we are unable to improve battery technology enough. The infrastructure to produce hydrogen cleanly, transport, store, and deliver it will be expensive.

We really need to get moving on new technology nuke plants. While renewables can help I don't see them producing enough reliably any time soon. Remember that the existing nuke plants that produce about 20% of our electricity will need to be decomissioned at some point. If we don't build new nukes by then we will be burning a lot more coal.

Tony Lekas said at September 25, 2006 11:40 AM:

Jim - Sorry - I misread your post. increase/decrease

KenG said at September 25, 2006 12:44 PM:

Tony - You're right, the nuclear plants are baseloaded. A new peak today would have to be met with gas fired peaking power. However, the report seemed to compare California with the upper midwest. California already runs their nuclear plants baseloaded and the renewables are 100% utilized. In addition, the California gas plants are much heavier utilized than in other parts of the country. Therefore, any additional load in California would be met with power imports - largely coal or gas fired.

However, a major "plug in" auto demand would take 5 to 10 years to develop, as a minimum. By that time a significant number of nuclear plants could be under construction. However, I doubt that any of those would be in California. They would mostly be in the Southeast and upper Midwest. That's why I think this study may be missing the point. Pollution will be reduced in areas that nuclear and renewables can be built in 10 years, not where they exist today.

bbm said at September 25, 2006 2:46 PM:

It sounds like they're saying that he GHG emissions would be 15% over a regular hybrid (rather than only 15% over an ICE).

That is a key point, because the GHG emissions of a standard hybrid over a ICE car are already pretty substantial.

And 15% is nothing to shake a stick at.

Additionally, it is a lot easier to capture CO2 from a central coal station than from individual ICEs, and obtaining clean electricity from nuclear, wind, and solar advances is easier than obtaining low CO2 liquid fuels.

I think that the tone of the reporting on this report has been inadvertently negative.... in the MSM and across the blogosphere.

Rob said at September 25, 2006 3:04 PM:

You know, whenever I read about these plug-in hybrids reducing the gas used in short commutes, I wonder why the government can't seem to put any muscle behind telecommuting. I would think that at least 5% of city jobs could easily be performed at home, getting the car off the streets all together (which has many other benefits besides saving energy). I've had work-at-home jobs before and it works pretty well. All we need from the government are some tax incentives for companies to build out the VPN infrastructure they need and some public education about the benefits of telecommuting, management strategies for remote employees and so on. It's hardly rocket science and it's a whale of a lot cheaper than new energy infrastructure.

Randall Parker said at September 25, 2006 5:02 PM:

Paul Dietz,

What does $15 per ton of CO2 translate into as pennies per kwh?

As for taxing CO2: There's not enough political demand to make it happen. Heck, we can't even make the coal burners to stop emitting mercury and particulates.

Michael Vassar,

Again, wind will have a better chance when we get dynamic pricing.

Dynamic pricing will also reduce the demand for electric generated from natural gas while increasing demand for electricity generated from nuclear power.

Dynamic pricing will also lower the cost of electric power for cars. People will be able to charge up their cars whenever electricity is cheapest.


Yes, large centralized plants are technically easier to make cleaner. But politically the will has to exist to tax the polluters.

Yes, regular hybrids are substantially cleaner than conventional internal combuston engine (ICE) vehicles. They also cost more and most have long pay-back times. See my post Most Hybrid Cars Do Not Pay Back Higher Costs In 5 Years.

Randall Parker said at September 25, 2006 6:29 PM:


I can see a number of ways to reduce energy used in driving around:

1) More telecommuting.

2) Longer hours and 4 day work weeks.

3) Zoning ordinances to put housing and office buildings closer.

Randall Parker said at September 25, 2006 6:37 PM:


Regards your point about the advantage of non-plugin hybrids: That's saying that fuel efficiency is a net gain. Sure, burn less fuel, produce less emissions.

But plug-in hybrids shift the burning of fuel to elsewhere, to the electric generating plants. They do not increase fuel efficiency by much as compared to regular hybrids.

Seems to me there's an obvious lesson here: Pure electric cars will help only to the extent that electric generator plants have low emissions. Of course, that's not surprising. But it bears repeating nonetheless.

Engineer-Poet said at September 25, 2006 9:15 PM:

This claim smells funny to me, so it bears at least one BOTE analysis.

Let's consider a Prius vs. a Prius+.  Let's further assume that the Prius+ is using a carbon-foam lead-acid battery (cheap, cheap, cheap!) which gives the battery 30% energy losses (Li-ion is upwards of 95%).  It takes 280 Wh/mile at the plug, transmission efficiency is 93%, heat rate of the powerplants is 10,500 BTU/kWh.

The Prius gets ~46 MPG.  A gallon of gasoline is 6.167 pounds, of which about 5.3 pounds is carbon.  The Prius thus emits about .1149 pounds (52 grams) of carbon per mile.

The Prius+ uses 280 Wh/mile at the plug, or 301 Wh/mile at the generating plant.  At 10,500 BTU/kWh heat rate at the generating plant, this takes 3160 BTU of fuel per mile.  Assuming coal is 100% carbon (which it isn't, but that's pessimal) and carbon's heat of combustion is 93960 cal/mol (7830 cal/g or 14090 BTU/lb) it requires 0.2243 pounds of carbon per mile.

Damn!  Looks like they're at least close.

On the other hand, I was using pessimal assumptions.  Using Li-ion batteries, the Prius+ would use 200 Wh/mile; cut emissions to 0.16 lb/mile.  Substitute an IGCC plant at 8650 BTU/kWh, 0.132 lb/mile.  Replace 30% with wind, 0.092 lb/mile.  Put up enough solar to charge the car, as little as nothing.

A Tahoe getting 12 MPG would emit 0.44 lb/mile.

The last claim is the shakiest:  the PHEV would still require the combustion engine to meet peak power demands.  This is true of the hybrid conversions like the Prius+, but either lead-acid batteries or the latest crop of Li-ion cells (A123Systems) would easily supply all the power you could put to the road until they were flat.

Engineer-Poet said at September 25, 2006 9:19 PM:

I should mention one more thing here:  the PHEV substitutes domestic coal and wind for OPEC oil.  Even at 0.22 lb/mile, it would do about as well as the average US vehicle... and it would get better as the grid improved.

aa2 said at September 26, 2006 2:14 AM:

I think this study underestimates the impact of using plug-ins. However it does show that for very serious carbon reductions we are going to have to go nuclear. I don't believe the (rapid) global warming theory though, so for me its more about economics and pollution in cities. Burning the fuel in a plant away from a city lets us deal with the pollution more effectively.

Paul Dietz said at September 26, 2006 6:39 AM:

What does $15 per ton of CO2 translate into as pennies per kwh?

In a typical powdered coal plant, you get about 1000 kWh/ton of CO2, so that's about $.015/kWh.

However it does show that for very serious carbon reductions we are going to have to go nuclear.

Or sequester the CO2.

Nick said at September 26, 2006 9:55 AM:

This report completely ignores the synergy between wind and PHEV's: wind could provide essentially all new energy needed for PHEV's and EV's, with only a modest national will to making relatively minor regulatory changes. I agree that dynamic pricing is very important to make this synergy work. The 2005 federal energy bill mandated progress on this front, though utilities seem to be dragging their feet. One good sign: California's PGE is installing time of day meters throughout it's very large service area.

Randall, wind is a much bigger part of new generation construction than popular press indicates. See the NEI report, page 8:

You'll see that in 2007 wind is 44% of new generation, adjusted for capacity factor (please note that 2008 is beyond the planning window for wind, so it's not so useful). Note that coal doesn't become a big part of the mix until 2009, and that many of these plants are tentative and subject to change, should a national commitment to renewables become stronger.

KenG said at September 26, 2006 11:46 AM:

Nick -

I have trouble seeing the wind-EV synergy. Logically, the cars will have to be recharged during the night when they are home and out of service. This argues against the daily and seasonal unpredictability of wind and in favor of large base loaded nuclear or clean coal plants that have inherent dependable surplus capacity at night. Also, the documented you referenced doesn't seem to be adjusted for capacity factor at all. As I read it, the table is for peak capacity and, with wind predicted to be about 50% of the added capacity in 2007, I would estimate that wind will account for about 10 to 15% of the generation from the new 2007 plants. (That of course assumes the predicted plants will actually get built.)

Nick said at September 26, 2006 3:16 PM:


Wind has the same problem as nuclear and coal: high capital costs, which must be recovered by maximum production, much of which happens at night.

Yes, PHEV's and EV's work nicely with nuclear and coal, but they have a special synergy with wind because they can charge when extra power is available from wind. Whenever that extra power is available the cars can charge. It would be easier at night, but it could happen during the day: in Canada and Minnesota there are public power stations at parking meters and parking garages for engine heaters. Remember, the average car is only driven about one hour per day. Finally, no one is really worried about excess wind power during the day, which will be happily used: the problem with wind is when the power is at night, and might go to waste.

re: capacity factor: I did the adjustment using

You can see that natural gas has a very low capacity factor (I used a conservatively high factor of 37.6%), and coal is only 71%. So wind, at 32%, is only a little below the average for 2007 planned generation of 37%.

Yes, many plants won't get built, but that applies equally to all forms of generation.

Randall Parker said at September 26, 2006 5:02 PM:

Paul Dietz,

The 1.5 pennies per kwh is similar to a US Department of Energy estimate I came across a couple of years ago which was 2 cents per kwh to sequester coal CO2. So that's ballpark.

Paul Dietz said at September 26, 2006 6:47 PM:

Randall: yes, but the interesting thing about this is that it can be retrofitted onto existing plants that were not otherwise intended for CO2 sequestration. Was that DOE figure assuming a new plant with technology (such as IGCC) that enables CO2 to be more easily separated? There are lots of existing powdered coal plants and more being built.

Paul Dietz said at September 26, 2006 6:54 PM:

You can see that natural gas has a very low capacity factor (I used a conservatively high factor of 37.6%), and coal is only 71%. So wind, at 32%, is only a little below the average for 2007 planned generation of 37%.

Oh please! You are being deliberately misleading here.

Gas and coal does not have a 100% capacity factor, but you get to decide when they're on. Those peaking turbines are churning out power when the power is most valuable, and can be sold for a premium.

Wind, on the other hand, blows when it wants to. This is often not when electricity is most in demand. This makes wind generated electrical energy inherently less valuable, per kWh.

Unless PHEVs provide dispatchable demand to compensate for the poor quality of wind generation, they will not help wind much at all.

Engineer-Poet said at September 27, 2006 5:06 PM:

PHEV's provide not just dispatchable demand, but with vehicle-to-grid they can provide dispatchable supply.

To see the usefulness of this, consider a grid operator with some combustion turbines, a big wind farm and a pile of vehicles plugged in.  A front is due to blow through the area in a few hours and max out the grid's transmission capacity from the wind, but the current demand requires more than the base-load can supply.  V2G would let the operator shut down the combustion turbines, meet demand from the vehicles, and recharge the vehicles when the front arrives.  This cuts fuel requirements and makes better use of the wind resource.

GCC has this today.

Paul Dietz said at October 2, 2006 11:35 PM:

with vehicle-to-grid they can provide dispatchable supply.

Only if the batteries have much better cost/cycle than those available today. A car owner will not want to let the utility drain the batteries if this significantly increases his battery replacement cost.

Nick said at October 4, 2006 9:06 AM:

"Wind, on the other hand, blows when it wants to. This is often not when electricity is most in demand. This makes wind generated electrical energy inherently less valuable, per kWh."

Sure. That applies to both wind and nuclear, and to some extent to coal. OTOH, solar, like nat gas peaking plants, is more valuable than it's capacity factor would suggest. We really need a way to discount both wind and nuclear, and uprate the value of nat gas & solar, but at the moment my metric of average production is about as close as we get to a standard nomenclature.

"Unless PHEVs provide dispatchable demand to compensate for the poor quality of wind generation, they will not help wind much at all."

I don't understand your objection. My point was precisely that PHEV's will indeed provide dispatchable demand (either through price signals, or direct 2-way communication). You're correct that V2G won't be economic for daily peak power until battery cycle life times improve, but don't forget 1) cycle life times appear to be improving dramatically, with A123systems and other new Li-Ion chemistries, and 2) that V2G could be used for less frequent and more valuable backup even now. The cost per kwhr of Tesla's configuration is about $.80 (or less - that's the guaranteed value which they hope to comfortably beat), which is a cost which is periodically exceeded on the electricity spot markets.

alternative fuels said at November 16, 2006 4:48 PM:

hybrid?? cars, corn, pig, chicken what else..

oppss... out of topic. hybrid cars were meant to be as transition vehicles from gasoline to electric vehicles.

since consumers dont easily adopt to abrupt change in thier transportation mode, automakers are clever enough to combine gasoline/deisel engine with electric motor to form hybrid engines.

hybrid cars mainly uses electric motors to power the car while the engine are simply used to charge the batteries and to give extra power if needed. but in the end the ultimate goel is to go for 100% electric power. Lets wait for the fuel cells..

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