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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



Stan / Harvey, efficiency and capacity factor are often mixed up when talking about wind power.

You are talking about capacity factors of 18-40% which is a function of wind resource rather than the technology. It would be possible to fit a large diameter wind turbine with a smaller generator and increase its capacity factor up to 60% or so but the energy production in kWh/yr would be reduced by around 20-30%


No hes talking about base load factor not load factor.

Lets say you have a 3 mw rated windmill and over the year it makes 1 mw per hour average. Its load factor is 33%...

BUT for 40 days of the year its output is only 300 kw. Its base load factor is 10%



We were referring to Name Plate (installed) capacity vs real average output. In other words a 1 mega-watt wind generator will produce an average of .18 to .41 mega-watt. The most common production average is about .33 mega-watt per one mega-watt installed.

By making your wind farms the primary supplier and hydro or NG the stand-by, you can use about all what the wind farms can produce. Of course, the WP limit should not be more than the low consumption (night) periods. By increasing night consumption with PHEVs and BEVs or other types of storage devices, you could increase the WP portion to the new night/low consumption periods. A wider area power grid can also be used to mitigate the use of WP production.


Too many assume that energy consumption will continue to increase year after year to keep up with our way of life.

This may not be true. We could reduce our energy consumption by 50+% by 2030/2040 with the following technologies.

a- very low cost, ultra high efficiency (300 lm/W) printed LED lighting.

b- very low cost high efficiency flexible printed displays, large and small for many (most)applications.

c- very low cost flexible printed solar cells.

d- ultra high efficiency (SEER 30+) low-high temperature double cycle heat pumps.

e- R-10+ power producing window panes

f- R-40+ wall, floor and ceiling insulation.

g- higher efficiency e-vehicles (up to 60+%) instead of current 18% ICE units.

h- high efficiency e-boat + other pleasure vehicles instead of current very low efficincy ICE units.

i- electric lawn mowers instead of current polluting 2-cycles units.

j. etc etc.


We dont have to assume it has gone up we plan for it going up and if it doesnt go up well that just fine we have extra capacity and thats just fine.


Great link on those oil sands. I still wish I could find a similar number for the electricity and natural gas for "normal" oil extraction and refining, but these numbers on the oil sands are scary!

They use over 1GJ of natural gas energy to extract and refine a barrel of bitumen from these oil sands. And that's just to get it to that tarry bitumen sludge, not to even "normal oil" that can then be refined! That 1GJ is the approx 278kWh! Wow.

You were being very generous when you only assumed 10kWh per gallon of gasoline from them because I'd bet you get a lot less than 28 refined gallons of gas from a barrel of bitumen. I know that the US refinery average is 19-20 gallons per barrel of "normal oil".

And I know they now have some major law suits. There will be hundreds of these lawsuits.


DaveD, yes I was assuming 42 gallons of product per gallon. Plus I was assuming only 2 kWh natural gas per gallon gasoline in the refinery and we are both having trouble finding that figure and I`m sure I`m being way over generous. Plus I wasn`t considering transportation emissions of oil and gasoline, which you don`t have for electricity, so when you do this my 4X energy efficiency of EV`s probably jumps to over 6.

There is this Gateway pipeline they want to push through to the BC coast from Alberta. The ridiculous thing is that our premier Campbell just won a medal at Copenhagen for introducing a carbon tax. Yet he is subsidizing natural gas and pushing for an oil pipeline. Talk about a hypocrite, apparently they don`t see a conflict of interest there, it`s all politics and PR. Here are some more links you may find useful regarding the oil sands:


The new wind farm in Aruba is up and running, and is showing a capacity factor of about 60%.  It is producing as much as 60% of the island's electricity during off-peak periods.

Just because people mix up efficiency and capacity factor isn't an excuse.  People use units like "megawatts per day", which is meaningless.  Such errors should be corrected, not tolerated.

Kit P

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

That is nice E-P. This is something that E-P does not understand. Electricity is produced by power plants not brochures. If you add new load it is going to come from the plant on the margin. The most efficient plants are all ready on line.

Look at Table 2 and Fig 2. LADWP is still 80% fossil, so much for being green.

Kit P

“The new wind farm in Aruba is up and running, and is showing a capacity factor of about 60%.”

What does Aruba have to do with EV's in California? California is at the bottom of the list of new wind capacity.

In 2008, 500 MWe of new renewable energy capacity was added to California but 430 MWe was built outside of the California.

Stan Peterson

Harvey D,

You live in such an unrealistic world of dreams and conspiracies.

"let phase our dirty coal...".

Harvey, There are no longer any coal power plants in California. They have all been closed down, already. But some electricity that they import does comes from coal power plants in other states or countries.

The crazy California watermelons are now trying to outlaw generation of electric power in these other States, by passing California state laws. Good Luck with that. But what it will probably mean is, that those other state or country based coal powered plants, can't export saurplus electricity to California, just hastening the day until California's BLACKOUT catastrophe.

I repeat Harvey, there are no longer any coal plants in California, anymore. More than half the nuclear power in California has been closed down. The tiny amount of geothernmal generation is shutting down too. Hydro power generation is dropping, as damns are closed down and destroyed. Other states are taking the hydro power that they are entittled to, but never needed before.

Most of California's power is NG powered, inefficient peaking plants or imported power. There is not nearly as much, more efficient NGCC plants either.

Get it through your thick head that NOTHING is being built in California. Not coal plants, not nuclear plants, not hydro plants, not geothermal plants; and not but a few isolated solar plants, and not even many wind turbines. These two renewables still don't even register for the minicule amount of power that they actually generate.

Nothing, Nada, Zero, Nothing.

The crazies want to return to the Stone Age, and they are getting their wish, although they and other Californians, are blissfully unaware of it, yet.

The crazies are in charge of the asylum, that is California.

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