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UC Davis Study Finds That Near-Term Marginal Electricity Mix in California for Plug-in and Fuel Cell Vehicles Will Result in Fuel With Carbon Levels More Than 60% Higher Than Estimated in the LCFS

Well-to-wheels vehicle emissions (gCO2 by energy source, vehicle energy intensity (MJkm-1), and fuel carbon intensity (gCO2 equiv. MJ-1) by vehicle pathway and timing profile. Source: McCarthy et al.Click to enlarge.

A study by researchers at the UC Davis Institute of Transportation Studies suggests that the near-term marginal electricity mix for plug-in electric and fuel cell vehicles and fuels in California will come from natural gas-fired power plants, including a significant fraction (likely as much as 40%) from relatively inefficient steam- and combustion-turbine plants. The marginal electricity emissions rate will be higher than the average rate from all generation—likely to exceed 600 gCO2 equiv.kWh-1 during most hours of the day and months of the year—and will likely be more than 60% higher than the value estimated in the Low Carbon Fuel Standard.

The study also concluded that despite the relatively high fuel carbon intensity of marginal electricity in California, alternative vehicle and fuel platforms still reduce emissions compared to conventional gasoline vehicles and hybrids, through improved vehicle efficiency. The study will be published in the April 2010 issue of the Journal of Power Sources, and is currently available online.

This study used an hourly electricity dispatch model with plant-level detail—the Electricity Dispatch model for Greenhouse gas Emissions in California (EDGE-CA)— to simulate grid response to added vehicle and fuel-related electricity demand in the state in 2010. The authors developed hourly electricity demand profiles for seven vehicle and fuel pathway scenarios. Conventional ICEs (internal combustion engines) and HEVs (hybrid electric vehicles) are compared to PHEVs (plug-in hybrids), BEVs (battery-electric vehicles), and FCVs (fuel cell vehicles). Fuel cell vehicle pathways include hydrogen produced at refueling stations from either electrolysis or SMR. The model identifies the “marginal electricity mix”—the mix of power plants that is used to supply the incremental electricity demand from these vehicles and fuels—and calculates greenhouse gas emissions from those plants.

It also explores sensitivities of electricity supply and emissions to hydro-power availability, timing of electricity demand (including vehicle recharging), and demand location within the state.

Because electricity cannot be practically stored in significant quantities, the grid has evolved to meet continually changing electricity demands by using a suite of power plants that fulfill various roles in the grid network. Each type of power plant operates differently—using different size, technology, or energy resources to satisfy its function—and as a result, each has unique cost and emissions characteristics.

...Electricity generation must match demand continuously, and adding electricity demand from vehicle recharging or hydrogen production and refueling will require additional power to be generated. The key to identifying the marginal mix of electricity for vehicles and fuels is to understand which power plants will generate this additional electricity.

—McCarthy et al.

Overall, the study found that electricity demand from these vehicles would have a minor impact on overall demand. If 1% of VMT were to come from FCVs using grid electrolysis—“an unlikely near-term scenario”—total electricity demand increases by 0.7% and peak demand increases by 1%. Demand impacts from the other profiles are much smaller.

Among the findings on vehicle emissions were:

  • All of the pathways except for FCVs using hydrogen from electrolysis reduce GHG emissions compared to ICEs and HEVs.

  • Fuel cell vehicles using hydrogen from SMR (steam methane reforming) and BEVs recharging according to the load-level profile reduce emissions the most, by more than 25% compared to HEVs.

  • Battery-electric vehicles recharging according to the Offpeak profile reduce emissions by 21% compared to HEVs.

  • Driving a PHEV20 offers little emissions improvement compared to HEVs, only 3% in the Offpeak profile and 6% for the load-level profile.

  • The reduction in emissions from advanced electric-drive vehicles in the near-term is a result of improved vehicle efficiency, rather than reduced carbon intensity of fuel. None of the pathways here use “low carbon fuel,” compared to gasoline in the near term (although there is potential to do so in the future).

    In the base case of BEVs recharging according to the Offpeak profile, for example, the carbon intensity of electricity is 80% higher than that of gasoline, but BEVs use less than half as much energy, and are lower emitting than HEVs.

These findings counter the assumptions for marginal electricity included in the LCFS rulemaking. The statue assumes that marginal electricity comes from NGCC plants (79%) and renewable power (21%), with a GHG emissions rate of 104.7 gCO2 equiv. MJ-1, or 377 gCO2 equiv.kWh-1.

But in the near-term, the likely marginal mix and GHG emissions rate will be quite different. Renewable power does not operate on the margin and marginal generation from dispatchable power plants is unlikely to come entirely from NGCC plants operating with average heat rates. Rather, NGCT plants will supply an important fraction of marginal generation, and when NGCC plants do operate on the margin, they will likely have a higher heat rate and GHG emissions rate than average NGCC generation.

Assuming that the Offpeak profile represents likely near-term charging, the results here suggest that the marginal generation mix will be about 63% from NGCC plants and about 37% from NGCT plants, and marginal emissions rates will be more than 65% higher than in the LCFS. Vehicle emissions, then, are underestimated by a similar fraction for BEVs, and by 11–25% for the PHEV pathways. These findings, as discussed, are sensitive to a number of parameters.

...The results presented in this paper describe the emissions implications of using electricity as a fuel or as an input for hydrogen production from the current grid. Over time, the carbon intensity of the grid will decrease, as energy policies promote renewable generation or impose costs on GHG emissions, and as older power plants are retired and replaced with newer, more efficient ones. In the future, the carbon content of electricity supplying vehicles and fuels could be much lower than it is currently.

—McCarthy et al.


  • McCarthy, Ryan W. and Christopher Yang (2009) Determining marginal electricity for near-term plug-in and fuel cell vehicle demands in California: Impacts on vehicle greenhouse gas emissions. J. Power Sources doi: 10.1016/j.jpowsour.2009.10.024


Nick Lyons

I would like to see CH4-powered ICE cars included in this analysis.


The Honda GX natural gas Civic was the cleanest car made.

"..carbon intensity of marginal electricity in California.."

They might be referring to the natural gas turbine peak plants used in the summer for air conditioners. If we use more wind and solar, we can reduce this need. Concentrated solar thermal with evacuated tube collectors and absorption chillers can take many of the building ACs off the grid.


More evidence that the assumptions in the LCFS are biased and unrealistic.

"These findings counter the assumptions for marginal electricity included in the LCFS rulemaking. The statue assumes..."
"marginal emissions rates will be more than 65% higher than in the LCFS. Vehicle emissions, then, are underestimated by a similar fraction for BEVs"

Just as California lead the way in smog emissions legislation, the California LCFS will serve as a model for other states and countries. Hence it is important for the assumptions which have failed this peer review & others to be amended.

The UC Davis study can be downloaded for free from the university website:

See also the earlier post about the RFA legal challenge:

The RFA listed a catalgue of errors and bias in the LCFS assumptions, including:
"the agency’s GREET model assumptions overestimated fossil energy use on farms and at ethanol plants. RFA provided reports from Argonne National Laboratory (where the GREET model was created and is maintained) and Christianson & Associates showing that ethanol plants consume less fossil energy than assumed by ARB."


The idea of spinning reserves versus the recently mentioned smart grid come into play. If you know your load profile and can predict it with some certainty, less spinning reserves are required.


Why would they assume that the average car gets 30mpg today when the US fleet average is 25mpg? Why don't they include the emissions of refining each gallon of gas in their comparisons?

If you use Exxon's most efficient refinery as a model, then that adds another 47g/mile of CO2 to the gasoline and they also burn a lot of natural gas in that refining. Do they assume the electricity used by the refinery is all during off peak hours? LOL

Why don't we add these numbers in and assume that gasoline emits over 300g/mile and assume that all EV's are as efficient as the EV1 and emits about 100g/mile using standard grid electricity? Why not assume that we'll get SMR of natural gas up from 70% to 85% efficiency?

Funny how people keep making "worst case" assumptions about batteries or even fuel cells in these studies and ignoring the realities of our current gasonline infrastructure.

Do these guys have an agenda because of who funded their study or did they just make some strange assumptions???


So California had better start aggressively regulating electric power generation with the same zeal they have gone after automakers to shift fuel consumed from petroleum to electricity, if they would like to reap any real benefits from all the work they instigated.

I think that what CARB must really want is more hydro and more nuclear generated electricity. With EVs and E-REVs; both are cheap, and work wonders for air quality and CO2.


I have a hard time believing that CA would get on board with either more Hydro (the poor fishies!) or nuclear (waste disposal).

California has some interesting options - the most realistic option to me is to go after the solar thermal + storage power generation. Those NGCT (combustion turbine) plants are low efficiency - I think 15-20% efficiency, and contribute the most to those very high g CO2 per kWh numbers. Replacing half of those plants (5GW) with 55% efficient NGCC and then the other half solar over the next 10 years seems reasonable, if not a little aggressive.


There are a couple of things I don't get - A 3g Prius generates 89gms/km. They are quoting 150 - are the other HEVs that bad?

How much capacity have they got to add wind ?
They get a lot of Hydro from Hoover etc so could they use that to buffer the wind.
Or are the greens in California against wind?
You can go to about 10% with wind - after that it gets a bit hairy, but there is no reason not to go to 10%

Stan Peterson

California's zany green watermelons have been actually reducing the total quantity of electrical generation that California possesses. Their constant opposition to any and all new generation, even including Wind and Solar polluting facilities, is the method they use to return all to their ideologically favored Paleolithic age.

As a consequence the oldest and dirtiest still functioning electrical generation remaining, is all that is left.

The UC Davis study is merely reflecting this reality in sort of a fashion. But I doubt that it is quite correct. California generates less than 75% of its electricity needs, and that figure constantly drops. You can't analyze California's antiquated dirty generation but must look to the much more modern and cleaner electrical generation from the sources of its electrical power: surplus power from Oregon, Washington, Nevada, Utah, Colorado, Arizona, New Mexico and third world Mexico, which is rapidly disappearing.

Californian greens are living in a dream land where California can import all its needs and others will suffer the consequences of providing all the goods that Californians desire, but are way too delicate to have to dirty their hands producing.

Californians need produce nothing. Not agriculture, oil, autos, rail stock, heavy manufacturing, silicon chips nor any other product, including even movies. The World will be glad to just give them all they desire, because they are just such fine people.

It can't go on much longer. California's government is beyond bankruptcy. Its bonds are virtual junk, and almost unsaleable. Official unemployment is at 13%, but real unemployment is approaching the 20+% of the Great Depression. Democrat government policy is producing unemployment and the same unemployment levels that socialist policies have long created for forty years or more in Europe.

Industry is fleeing as quickly as possible and/or forced into closing.

One day a single state Public Utility Commission will order its Utilities to cease selling to California, as its own reserves are too slim. Like a cascade all others will be forced to follow, or sever links, to survive, since none can meet the demand. California will be in the dark, but unlike the era of Grey Davis, who started buying power from elsewhere as Enron showed could be done, will remain in a period of rolling blackouts and brownouts that way for years, until other generation is built.


There are many winning combinations for California, i.e.

Wind + NG power for back up

Wind + Hydro for back up.

Solar + Wind and NG + Hydro for back up.

Dirty coal fired power plants could be progressively phased out and replaced with the above combo.


There was a plan to put solar Stirling dishes in the desert east of San Diego, it was nothing more than a plan to put a transmission line through a state park.

When companies and interest groups try to pull fast ones like that, it is no wonder that people are cynical and skeptical. Some people on Picken's Plan figured that there was a hidden agenda, maybe there was and maybe there wasn't, but you were not going to convince those people that there wasn't.

Stan Peterson

Study of the accompanying chart tends to show that fuel usage of PHEV 40 are set at at a mere 75-90 mpge.

I defy anyone to justify the calculated measures for FCEV as anywhere near accurate. Nor is the estimate, of the the minimal energy costs for obtaining Hydrogen to consume in FCEV vehicles, anywhere near reasonable. This study seems to go out of its way to justify FCEVs as a preferred method of propulsion.

Under the SAE J1711 standard that EPA /CAFE are proposing to use to measure PHEV40s, show mileages of around 230 mpge for C-segment sized vehicles. That would translate to figures of around 20g/km of CO2 equivalent. Hence:

Garbage In, Garbage Out.


Has any noticed who is publishing this study?
University of California proposed the LCFS!
The Project Managers: Alexander E. Farrell, UC Berkeley; Daniel Sperling, UC Davis.

One of the contributors to the technical analysis was C.Yang.
Now we have a study by McCarthy and Yang of UC Davis which reviews the estimate of GHG emissions for marginal electricity used by ARB. This peer review finds the GHG emissions should be 60% higher.
So even the scientists who proposed the LCFS disagree with a key assumption made by ARB!

Nick Lyons

To the California bashers: almost none of California's electricity comes from coal-fired plants these days, and several large-scale renewable power projects(wind and solar mostly) are in the works.

Nick Lyons

To the California bashers: almost none of California's electricity comes from coal-fired plants these days, and several large-scale renewable power projects(wind and solar mostly) are in the works.

Stan Peterson

Harvey D.

All your 'renewables' couldn't even makeup for the short fall of energy generation already created by the noveau Stone Agers, and promoted by these zany Californian would-be Eloi in the past 20 years, in the next 30 years. California is missing by 25% of meeting its own electrical generation demand. Nationally your renewables can generate a scant 1% of electrical needs despite all the massive subsidies. In Californai its might be double that, if indeed 'renewables' even actaully worked. But that still leaves another 23% to go, merely to get back to where the system should be today.

When the adjoining States have no more surplus to sell, which must happen soon, the Golden Bear State inhabitants will be plumb out of luck.

Then real electrical generation will have to be built on a crash basis. The zanies will have to authorize several LNG terminals to import vast quantities of NG to feed realtively inefficient single stage turbo-generation. If indeed any one will accept financing or can find the monies or financing to do so.

And your solar and wind installations can continue to rot away and rust in the sun, unused, as they mostly are today.


Today's simple-cycle gas turbines can hit 46% efficiency (per GE), so at least it's not all that bad.

The assumptions of the critics may not be all that solid either.  Sure, RE isn't schedulable and isn't going to be the marginal supply... but if dynamic charging for BEVs and EREVs becomes the rule, more RE can be added to the grid and the marginal supply gets used less.  More nuclear would be great, but the public votes for what it wants and deserves to get it good and hard.


Most of the plants in cal are old tho and so not that good.


E-P, RE isn't just wind and solar, it's also biogas which can be schedulable; There's also dual basin tidal power: "With two basins, one is filled at high tide and the other is emptied at low tide. Turbines are placed between the basins. Two-basin schemes offer advantages over normal schemes in that generation time can be adjusted with high flexibility and it is also possible to generate almost continuously. In normal estuarine situations, however, two-basin schemes are very expensive to construct due to the cost of the extra length of barrage. There are some favourable geographies, however, which are well suited to this type of scheme."



Are you aware of the lattest California plan to multiply clean energy power plants with an added 69,000 MW.

When completed, it could replace most of the energy currently supplied by other States.

Clean energy production does not have to be limited. It could supply a very high percentage of all the energy consummed in Clifornia.

A progressive (tobacco style) ban on dirty energy sources may eventually be required.

Stan Peterson


Proposals, are just that proposals. The Nimbys and California nouveau Stone-agers defeated a proposition to bring already built, so-called 'renewable' power to the demand, when they refused the power lines necessary to transport such electricity.

The reality is the California's electrical generation is decreasing outright, as the oldest plants decay into oblivion and nothing is built to replace it except phony 'renewables' that never produce but about 8% of suggested nameplate ratings and that is very intermittent and almost useless and unusable.

Ai vin,

Where is the EIS study to actually authorize the 'killing of, and disruption of, all that marine life' in your tidal pools. You couldn't get an approved EIS out in less than half a century. Do you really think that the green zanies would allow such a course of action even as they starve humans and destroy farms for the possible protection of a 1" smelt that is not even endangered, as it lives in many other watersheds?

You sound like the zany writers of an article in that formerly be good periodical, Un-Scientific American where in they proposed with a straight-face, to pave all of Arizona and Nevada with Solar cells. They never even suggested doing an EIS study. Sacrificing these two states and all the biota in them would provide enough energy to power the City of NY, if they could only figure out a way to get it there. They completely disregarded the right-of-way problems.

Such is the 'quality' of writing, since the ideological clowns at Columbia took it over, and who have been revealed to be active members of the Climategate correspondence scandals.


I mostly agree with Stan's assessment of the wisdom of California regulators. Very political, very low on scientific or understanding of the nature of business. Put and kept in place by weak politicians.

My suggestion for more California Nuclear and More California hydro was actually sarcasm.

The hypocracy is that California uses 30% more electricity than it generates.


"More nuclear would be great, but the public votes for what it wants and deserves to get it good and hard."

The public has been manipulated and misled by all manner of interests for the last 40 years. Gov. Arnold is trying to produce a 33% renewable base by 2020. That's 10 short years away with few hardened systems to build on. It seems far more appropriate for Cali to fastrack some nuclear, fund the alternatives (including alternative H2 electrolysis) and a major move to NG turbines.

Alongside this is the very real alternative of CCHP for residences - mass produced and subsidized by fossil producing energy companies controlling NG. The problem can only be tackled by a broad portfolio of solutions.

Or major disruptive energy decisions will be made for us. The hard way. It really depends on whether adults in charge can bring themselves to say: "We were wrong."


I have a few issues with this:

Firstly, I find it hard to believe that considering that it will be at least a couple decades before all passenger vehicles become electric, that charging an initially small number of electric vehicles overnight on the grid (when demand is low and you aren't running marginal generation), is going to push electricity demand to levels where inefficient marginal NCCT plants are needed. It will be decades before there are enough electric cars to do that, and by that time the electric generation situation will have improved.

Secondly, does this study incorporate the reduced electricity demand when oil refineries no longer need to make gasoline? At 3 kWh per gallon to produce, that same electricity would power an EV to go half as far as a regular ICE car, even before it's started its engine!!!

And another thing relating to GHG emissions is the amount of natural gas needed to make the gasoline. Dave D might have interest in this because we were before discussing this issue on ABG. It was found that refining oil into gasoline requires about 3 kWh electricity per gallon. I did some more research and found that turning Alberta oil sands into oil requires about 0.8 kWh / gallon. So overall you are looking at 3-4 kWh / gallon electricity to make the gasoline.

But then there's natural gas, where it gets more interesting. I don't know how much natural gas is needed to refine oil into gasoline, but in order to turn tar sands into oil, it appears that about 10 kWh is needed per gallon. And let's say for sake of argument that oil refining uses another 2 kWh of natural gas. It gets a little complicated because of cogeneration plants also supplying heat to the refineries though. But let's assume then that 12 kWh / gallon of natural gas is needed to turn Alberta tar sand into gasoline. Let's say that is burned in a NGCC plant at 60% efficiency with 10% line loss, and generously assume a 50% loss in efficiency in producing electricity. That is 6 kWh.

Let's add that to the previous 4 kWh, for a total of 10 kWh of electricity per gallon. At 225 Wh per mile plug-to-wheel mileage of the Nissan Leaf, that would drive an EV 44 miles! And that's just to make the gallon of gasoline in the first place!

Now, let's add in the mileage you'd get from burning the gasoline. A typical ICE gets 25 mpg. There you go, that's it, no more, end of story. A PHEV gets 50 mpg, so you'd go 50 miles. Then add on the previous 44 miles for a total of about 100 miles. So essentially, the EV goes 4 times as far as the ICE car per unit energy.

It's ridiculous.

Dave D you might find this interesting.



Recent wind farms production efficiency is 18% for poor sites and 41+% for better mountain top sites.

Larger future well designed turbines intalled in high quality winds areas or off shore can reach 50%.

A wide area transmission line network could mitigate the variable wind factor. Hydro and NG power plants could be used as back ups.

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