Hino Motors signs as participant in Scuderi Split-Cycle Consortium
President Obama announces new $140M public-private manufacturing innovation institute focused on power electronics

Comprehensive modeling study finds electric drive vehicle deployment has little observed effect on US system-wide emissions

The results of a new, comprehensive modeling study characterizing light-duty electric drive vehicle (EDV) deployment in the US over 108 discrete scenarios do not demonstrate a clear and consistent trend toward lower system-wide emissions of CO2, SO2, and NOx as EDV deployment increases.

As explained in their paper published in the ACS journal Environmental Science & Technology, the researchers from North Carolina State Univesity and the University of Minnesota found that, while the scenario parameters can influence EDV deployment—even to a most extreme scenario of adoption—this EDV deployment does not in turn produce a discernible effect on total system-wide emissions. There are three reasons for this lack of observed effect, they concluded: (1) at present the overall share of emissions from the LDV sector is only 20% of US CO2 emissions; (2) EDV charging can still produce comparable emissions to conventional vehicles depending on the grid mix; and (3) the effect of other sectors on emissions is significant.

EDVs offer three key benefits over competing vehicle technologies: (1) reduced consumption of petroleum-based fuels, (2) lower refueling infrastructure costs compared to alternatives such as H2 and compressed natural gas, and (3) a shift in energy production from vehicles to the electricity grid, where emissions from large, centralized facilities are cheaper and easier to control. While previous work has applied different methodologies and models to quantify the environmental benefits of EDVs, several consistent insights have emerged.

First, HEVs produce less emissions than conventional vehicles. Second, PHEVs with smaller battery packs are more likely to deliver emissions benefits and reduced gasoline consumption at lower lifetime cost compared to those with large battery packs in the short term. Third, significant emissions benefits, particularly from vehicles with large battery packs, only begin to accrue with clean electricity. Fourth, CO2 prices as high as 100 $/t do not provide sufficient incentive for vehicle electrification.

While these studies (along with others) have made significant contributions to the literature, they only consider a single point in time or employ sector-specific models or calculations that ignore the interaction of EDVs with the rest of the energy system over time. Recent analyses based on energy system models mainly focus on CO2 emissions and have been run with a limited set of scenarios, which make it difficult to draw insight specific to EDVs.

This paper employs an energy system model to meet the following objectives: (1) identify the conditions under which EDVs achieve high market penetration in the U.S. light duty vehicle (LDV) sector through 2050 and (2) to quantify the system-wide changes in CO2, SO2, and NOx emissions at the national level.

—Babaee et al.

The researchers used a model consisting of two components: The Integrated MARKAL-EFOM System (TIMES), which serves as a generic energy optimization framework and operates on the National US TIMES Data set (NUSTD), a TIMES-compatible data set constructed specifically for this analysis. TIMES is a bottom-up, technology-rich energy system model, which represents an energy system as a network of technologies linked together via flows of energy commodities. TIMES performs linear optimization to identify the least-cost way to satisfy end-use demands, subject to user-imposed constraints such as emissions limits and maximum growth rates on technology capacity.

In their analysis, the authors examined the effect of 5 factors on EDV deployment: crude oil and natural gas prices; a federal CO2 policy; a federal renewable portfolio standard (RPS); and EDV battery cost.

Assumed values associated with each factor were blended to create the large set of 108 scenarios that capture a wide range of potential outcomes. Given the highly uncertain role of consumer choice in future vehicle adoption, they noted, their analysis focused on the economic and environmental performance of EDVs assuming minimal behavioral barriers to vehicle adoption. “Strong and persistent reluctance on the part of consumers to adopt EDVs will dampen or eliminate the EDV-related effects presented here,” they cautioned.

Across all the scenarios, the total EDV deployment ranges from 0−42% of the LDV market with an average value of 24%—a figure broadly consistent with other projections of EDV market development.

  • No EDV deployment occurs with high battery costs, low oil prices, and no CO2 policy. At least 1 of these 3 scenario assumptions must change in order for EDVs to achieve some level of market penetration in 2050.

  • As scenario parameters shift to values more favorable to EDVs—i.e., higher oil prices, a CO2 policy, lower battery cost—the median market shares increase. The maximum EDV market penetration is 16% with the low oil price assumption versus 42% with reference or high oil prices. Similarly, high and reference battery costs limit EDV penetration to a maximum of 34% and 37%, respectively, whereas low battery costs enable the maximum market penetration of 42%. The maximum EDV market share is 42% because EDV deployment is largely limited to the compact and full-size vehicle classes, due to the higher cost of electrification of larger vehicles.

  • The CO2 cap results in marginal CO2 prices of 37−125 $/tCO2, which with other conditions held equal, only increase EDV deployment by approximately 3%. This result is also consistent with other studies demonstrating that CO2 prices less than 100 $/tCO2 have little effect on EDV adoption.

Finding that oil price and battery cost had the largest effect on EDV deployment, they varied these scenario parameters while holding the others constant the better to isolate the effect of EDV deployment on emissions. The high EDV deployment scenario assumes high oil prices and low battery cost, while the low deployment scenario assumes low oil prices and high battery cost. All four scenarios assume reference case natural gas prices and no RPS. They found that, without the CO2 cap, there is no change in electric sector SO2 and NOx emissions because the air pollution constraints remain binding.

Further, the system-wide net decrease in SO2 and NOx (approximately 3% for each) is largely unrelated to EDV deployment: higher oil prices lead to fuel switching in the fuel supply, heavy duty vehicle (HDV), and end-use sectors. Also without the CO2 cap, high EDV deployment creates a 21% reduction in LDV CO2 emissions but a 13% increase in electric sector CO2 emissions.

Accounting for additional changes across other sectors, the system-wide effect of high EDV deployment is a slight 0.9% decrease in total CO2 in 2050.

…it is not enough to simply incentivize the purchase of EDVs and wait for emissions benefits to accrue. The emissions benefits—if any—will depend on a broad set of future conditions. Therefore, public policies that target EDV deployment should be formulated, reviewed, and revised with careful attention paid to evolving changes to the broader energy system over time. If the primary objective is to reduce emissions, policy makers should focus on implementing targeted emissions policy rather than the promotion of specific technologies or fuels. Among the scenario variables tested, the CO2 cap produced the largest and most consistent drop in CO2, SO2, and NOx emissions. Although the observed marginal CO2 prices do not drive significant EDV deployment, the results indicate that EDVs can help lower the marginal price of CO2, particularly if scenario variables favorable to EDVs (high oil prices, low battery cost) prevail.

In the absence of a CO2 policy, the promotion of clean electricity can provide direct emissions reductions and also lower the emissions footprint from vehicle charging. The new EPA proposed carbon pollution standard and the forth-coming proposed rule on existing coal-fired power (due out in 2014) could have a significant impact on national emissions and eliminate some of the potential emissions increases associated with vehicle charging. Finally, other alternative vehicles are worth a mention. First, compressed natural gas (CNG) vehicles are not cost-effective in any scenario, including those with low natural gas prices, because low CNG prices are not enough to overcome the higher investment costs. Second, the model deploys diesel and diesel hybrids in many scenarios, which may be a cost-effective way to reduce CO2 emissions given their higher efficiency compared to conventional gasoline vehicles.

—Babaee et al.

Resources

  • Samaneh Babaee, Ajay S. Nagpure, and Joseph F. DeCarolis (2014) “How Much Do Electric Drive Vehicles Matter to Future U.S. Emissions?” Environmental Science & Technology doi: 10.1021/es4045677

Comments

Davemart

This rather old analysis puts compression losses up to 800bar rather loosely at 'up to 14%' (pg46)
http://web.archive.org/web/20080307082839/http://www.iea.org/textbase/nppdf/free/2005/hydrogen2005.pdf

So taking that as a maximum figure, then the 51 mpge would becomes 44 mpge.

However, implicitly your own comparison was apples to oranges, as you took no account of refining losses to petrol to adjust the mpg ratings of the petrol version, so that 20/25 would become allowing 12% refining losses (conservative) becomes 17.5/22.

My figure of double the energy efficiency still holds good, using a maximal figure for compression losses.
In fact that is an area where good progress is being made on reducing losses with recovery of process heat, and some production methods actually producing hydrogen at 2000 psi so needing less compression.

Davemart

More concisely, hydrogen compression losses are in the same ball park as those from compressing natural gas and refining losses for petrol, and don't change the 2:1 efficiency advantage of fuel cells.

Petrol refinery losses here:
http://greet.es.anl.gov/files/hl9mw9i7

A.C. R.

Davemart, sorry but you did use apples to oranges. Mostly because you are comparing a battery hybrid with a non-hybrid.

But as otec sheldon pointed out, the Toyota model has a hybrid range of around 30 MPG. Actually its 28 MPG.

So that's great, we can compare the same model car in fuel cell hybrid with a gasoline hybrid.

Re hydrogen compression, your source,

http://www.hydrogen.energy.gov/pdfs/review12/pd048_lipp_2012_o.pdf

gives a figure of 8 kWh/kg for adiabatic compression. The theoretical cost is much lower but the theoretical efficiency is never reached for a lot of reasons (mostly cost related, for example infinite compressor intercooling isn't economically possible). If theoretical efficiency was achieved steam turbines would be 70% net efficiency rather than the 46% the best machines get even after 100 years of development. Similarly the theoretical fuel cell efficiency is 5/6 (83%), practical systems (high current density) with pump, electric motor and other parastics end up with around 45% efficiency.

Based on 8 kWh/kg, and a 45% efficient fuel cell to power the compressor, we get 17.7 kWh of hydrogen to compress 33.3 kWh (1 kg). So 17.7/(17.7+33.3) = 34%. In this case more than 1/3 of your hydrogen is lost to compression. It gets a bit better with a CCGT powering the compressor because you get a bit better CCGT efficiency and you avoid the recombination losses but its always way over the electrical kWh figure (since your natural gas running the CCGT to make the electricity for the hydrogen compressor can't be used to make hydrogen...)

The source mentions that electrochemical compression is most efficient, but we are not talking about that type of compression here.

A.C. R.

So let's use the CCGT of 60% efficiency and the three stage compressor case of 6.5 kWh/kg, needing (6.5/0.6) is 10.8 kWh of natural gas, we need another (33.3/0.7)47.6 kWh of natural gas to make the 1 kg of hydrogen.

So we need (47.6+10.8) = 58.4 kWh for 33.3 kWh. The natural gas to hydrogen in the tank efficiency is 57%.

So the 68 MPG is 39 MPG of natural gas in fuel cell battery hybrid.

That compares to around 28 MPG in natural gas battery hybrid.

So an accurate statement is that hydrogen in fuel cell- battery hybrid from reformed natural gas is around 1.4 times as energy efficient as the same natural gas in the same car but with ICE-battery hybrid.

Pretty decent, not quite twice as efficient though.

Davemart

ACR:
I don't follow your logic at all.

You are double counting:
'Based on 8 kWh/kg, and a 45% efficient fuel cell to power the compressor, we get 17.7 kWh of hydrogen to compress 33.3 kWh (1 kg). So 17.7/(17.7+33.3) = 34%.'
It is pretty clear that they are talking about total energy costs, with no more conversions needed.
That is pretty much what the report is about, the total energy needed.
They aren't going to have simply forgot to do that bit of it.
You then simply put in an unsourced claim that the fuel cell which would do the conversion would be 45% efficient.


In any case, you are not balancing the ledger as you continue to simply ignore refining losses for petrol.
This is an egregious error which you are making no attempt to correct.
You don't add up losses on one side and not on the other, which is what you are trying to do.

Davemart

As for:
'I should have compared to a hybrid, not a regular petrol model'
For starters there wasn't a hybrid when I first ran the figures.

Secondly all sorts of degrees of hybridisation are possible, and the idea is to get a clean comparison.

Thirdly I simply used the FCEV for which I had the best figures, not the most efficient one possible.

Since Hyundai does not compress air, it is likely that they get up to 5% extra efficiency.
IOW fuel cells are far from optimised, they are early stage technology.

Forthly if someone really wants to do a comparison against the hybrid, all they need to do is plug in 28/28 for the 20/25 of the petrol version.

Those who are using this as a stick to beat fuel cell vehicles with should be aware that Toyota, who know a thing or two about hybrids, are one of the strongest proponents of fuel cell vehicles.

Fifth my claim was that fuel cell vehicles are around twice as efficient as petrol or natural gas cars after all losses are accounted for.
That claim stands and has little to do with the efficiency against hybrids.

A.C. R.

As pointed out, the FCV model from Ford you mentioned has a regular hybrid version.

A clean comparison is NOT reached by comparing one hybrid with a nonhybrid.

Re efficiency, as far as I can make out, the input energy in the ref you gave was electrical. So it is subject to a conversion factor.

In my latest post I used a better figure for CCGT of 60% and no reforming losses. This gives a 40% advantage for the fuel cell hybrid, not 100%.

A.C. R.

"In any case, you are not balancing the ledger as you continue to simply ignore refining losses for petrol."

Wrong. It is an egregious error on your side for comparing petrol to natural gas.

I compare natural gas to natural gas.

A.C. R.

"You then simply put in an unsourced claim that the fuel cell which would do the conversion would be 45% efficient."

The most recent calculation assumed a 60% efficient NG CCGT. This got the 40% advantage for fuel cell hybrid over natural gas hybrid.

A.C. R.

"Fifth my claim was that fuel cell vehicles are around twice as efficient as petrol or natural gas cars after all losses are accounted for.
That claim stands and has little to do with the efficiency against hybrids."

No indeed, your claim fails. It is 40% by fair comparison, versus 100% of your claim.

A.C. R.

Here's a ref that gives 2.2 kWh/kg for 20 MPa.

http://www.nrel.gov/docs/fy99osti/25106.pdf

That's fairly consistent with my 6.5 kWh/kg @ 70 MPa.

A.C. R.

This source has the following on EHC:

"Pinakin Patel (FuelCell Energy): Mr. Patel described how electrochemical hydrogen compressor (EHC) technology is being developed to increase reliability and lower the cost of hydrogen compression. He noted that the feasibility of reaching DOE’s pressure target of 12,000 pounds per square inch (psi) has been demonstrated in a single-stage EHC cell, and that hydrogen capacity of up to about 1 pound per day has been reached in a short stack. He also noted that durability of the EHC cell architecture has been demonstrated at over 8,000 hours at 3,000 psi, and that efficiency has been demonstrated at 6-12 kilowatt hours per kilogram (kWh/kg) from <30 to 3,000 psi."

http://www1.eere.energy.gov/hydrogenandfuelcells/pdfs/2013_csd_workshop_report.pdf

A.C. R.

An NREL source:

http://www.nrel.gov/docs/fy10osti/46719.pdf

gives 4 kWh electricity for compression to 2500 PSI. So 8 kWh electrical to 10000 PSI again seems reasonable.

Davemart

So where the heck are your comparison figures for compressing natural gas?

And I did NOT mention a Ford.
My figures are for the Toyotas.

Davemart

I've got no idea at all what you are on about when you say that it is invalid to compare to a petrol model.
In that case why are you using a petrol hybrid?

Davemart

Your reference:
http://www1.eere.energy.gov/hydrogenandfuelcells/pdfs/2013_csd_workshop_report.pdf

did not contain the information you say.
It is also customary if quoting a multi-page source to put the page reference, although in this case you seem to have put in the wrong link anyway.

A.C. R.

Hi davemart. The petrol hybrid should get similar mileage on natural gas. It's just that if the hydrogen car uses natural gas, its more apples-to-apples to compare to a natural gas hybrid.

Re compression energy, I found an interesting thesis,

http://www.hydrogen.energy.gov/pdfs/9013_energy_requirements_for_hydrogen_gas_compression.pdf

"The measured specific energy was
approximately 8 kWh/kg compared to 1-1.5 kWh/kg for the thermodynamic models."

This shows the actual efficiency is a small fraction of the theoretical (this isn't really surprising for small fuelling station size compressors).

A.C. R.

For natural gas compression, I found the following:

http://www.igu.org/html/wgc2009/papers/docs/wgcFinal00193.pdf

From LNG to CNG is 74 kj/kg. More relevantly, starting with the gas is 1850 kj/kg. That's 0.5 kWh/kg.

Based on this,

http://www.gaselectricpartnership.com/08mckeewasteaudit.pdf

The efficiency should be about a quarter, so 2 kWh electrical would be a decent ballpark figure for CNG.

A.C. R.

"Your reference:
http://www1.eere.energy.gov/hydrogenandfuelcells/pdfs/2013_csd_workshop_report.pdf

did not contain the information you say.
It is also customary if quoting a multi-page source to put the page reference, although in this case you seem to have put in the wrong link anyway."


It's there. P. 3 - patel:

"Pinakin Patel (FuelCell Energy): Mr. Patel described how electrochemical hydrogen compressor (EHC) technology is being developed to increase reliability and lower the cost of hydrogen compression. He noted that the feasibility of reaching DOE’s pressure target of 12,000 pounds per square inch (psi) has been demonstrated in a single-stage EHC cell, and that hydrogen capacity of up to about 1 pound per day has been reached in a short stack. He also noted that durability of the EHC cell architecture has been demonstrated at over 8,000 hours at 3,000 psi, and that efficiency has been demonstrated at 6-12 kilowatt hours per kilogram (kWh/kg) from <30 to 3,000 psi."

A.C. R.

Ok, so 2 kWh electrical would consume about 3.4 kWh of natural gas (CCGT plus transmission loss).

With natural gas at 14.9 kWh/kg, this consumes 3.4/(3.4+14.9) = 19% of the natural gas!

That's a lot.

Lets run the numbers again.

...the CCGT of 60% efficiency and the three stage compressor case of 6.5 kWh/kg, needing (6.5/0.6) is 10.8 kWh of natural gas, we need another (33.3/0.7)47.6 kWh of natural gas to make the 1 kg of hydrogen.

So we need (47.6+10.8) = 58.4 kWh for 33.3 kWh. The natural gas to hydrogen in the tank efficiency is 57%.

So the 68 MPG is 39 MPG of natural gas in fuel cell battery hybrid.

That compares to around 28 MPG in natural gas battery hybrid. But we lose 19% in the compressor so we end up with 22 MPG!

Credit where credit's due Davemart. Thats looking more favorable towards hydrogen now, 39/22 = 1.77x advantage for hydrogen.

Hats off to you Davemart.

A.C. R.

I was comparing some gas vs petrol cars, and found this website, where there's a honda civic natural gas.

http://www.fueleconomy.gov/feg/PowerSearch.do?action=make&path=4&year=2012&make=Honda&srchtyp=yearMake&rowLimit=10&pageno=1

That's interesting, the natural gas civic gets 41 MPG reported, whereas the same year (2012) gasoline civic gets 35 MPG. But the combined EPA ratings are comparable (31-32 MPG). Might be just the driver.

HarveyD

One should not assume that FCs and H2 facilities are be static and will not evolve significantly every 10 years or so.

What is not efficient enough and too costly today may not be so in 10+ years from now.

We also have to be worried about false news given out by interested industries:

1. A recent extensive study published in Nature concluded that 97% of trees capture more and more carbon as they grow older and not the opposite.

2. Another worldwide study concluded that the countries mostly responsible for accumulated GHG in the last 100 years are: 1) USA, 2) UK, #3 Canada, 4) Japan, 5) Russia, 6) Australia etc and that China and India are nos 19 and 20 respectively.

A.C. R.

Don't really agree completely there, Harvey. Compressors are very conventional technology. They aren't going to get much more efficient.

Rather the hope for gaseous fuels, which to my amazement have very large compressive losses, is high pressure electrolysis. This starts out at or near 10000 PSI (some 690 atmospheres), by compressing the water. That'd only take a few percent of the energy content of hydrogen. Whether that is cost effective in terms of the electrolyser (that now has to operate at insane pressure) remains to be seen, but at least its easy to see how that will be very low in compressive losses.

A risk with hydrogen as it stands today is that it could lock in natural gas. Natural gas reforming is so much more economical and practical than electrolysis, this could be a big problem. Natural gas is already highly locked in due to Brayton cycle developments making this fuel more attractive, and due to its role as a chem feedstock.

A.C. R.

"1. A recent extensive study published in Nature concluded that 97% of trees capture more and more carbon as they grow older and not the opposite."

Interesting. I guess that actually makes sense when you think about it: tree rings get bigger and bigger as the tree grows so it makes sense that more and more carbon is in these yearly rings as the tree gets older.

CheeseEater88

EP I would welcome a molten salt/metal battery to do that. I for one think that Li batteries are coming up short, but molten batteries look promising.

Just imagine all the possible regen braking, you could probably use hub motors on a big rig too... and since the battery will be so large, it could adequately absorb almost all of the braking energy.

I am curious to any other information you have on that particular chemistry of battery. I will say this most companies wouldn't like to have a truck that takes a day to charge, so it could get interesting. If the battery could charge under 6 hours or atleast 8 hours you'd have a game changer for sure. 4 hours with good battery retension and you'd have a mass exodus from diesel.

IF and its a big one, IF a distibuters worked with the stores they were supplying like walmart, (which is its own distributer to the stores) where that a truck could sit and charge while being unloaded and be done in 2 hours because of some fast charge network, it would be incredible.

The comments to this entry are closed.