Miles Per Gallon Equivalent by Four Different Methods
...and why EVs alone are of doubtful environmental benefit.
As more of us, myself included, are transitioning to plug-in vehicles of some type or another, the controversial topic of mpge is being discussed with increasing frequency. It's a complicated but important subject, as people will use mpge as a factor when deciding which car to buy and which mods to make. We all have different goals and values. Some people want to reduce their carbon footprint, or reduce the rate at which we are depleting fossil energy resources, or rely less on petroleum, or just to save money. We won't all agree on a single KWh/gal factor because we have different values, but below I present four KWh/gal figures, and I recommend you use a figure somewhere in the middle. I will use 16KWh/gal.
The least contentious figure is cost equivalence. I pay $3.00 for a gallon of gas, and $0.12 for a KWh of electricity. 25KWh/gal. The simplest KWh/gal figure is direct BTU equivalence: buring a gallon of gas releases 33.4KWh of heat. However, that's not a useful figure: it does not represent resource depletion, CO2 emissions, or any other item people care about. If you wish to measure resource depletion or CO2 emissions, you must consider the entire life cycle of the fuel. The least efficient step in this life cycle is buring fossil fuels and converting heat to torque in a heat engine. For the EV, this happens in a power plant. For gassers, it happens under the hood. Direct BTU equivalence fails to capture this least efficient step for electrics but captures it for gas engines. Using numbers from the DoE (see p3 column 2 which cites but does not include "Docket No. EE–RM–99–PEF"), the US grid average power plant is around 33% efficient, and transmission is 92% efficient, thus giving 30.3% efficiency for electric. Refining and distributing petroleum is 83% efficient per the same source. Thus the DoE finds a 12.307 KWh/gal figure by the life-cycle energy equivalence method. This is probably the right figure for academic comparisons of the overall efficiency of one architecture versus another. Unfortunately, it values a coal and petroleum equally, even though one is more versatile, rare, and troublesome than the other. Take the above efficiency numbers and multiply by the values of 608g CO2/KWh and 8877g CO2/gal, and you have 16.18KWh/gal by CO2 equivalence. This varies with the carbon intensity of the grid. The number would be much higher in nuclear-powered France, and lower in coal-fired China. If you're purchasing renewable electricity, then the CO2/KWh figure is very low (but certainly not zero; it takes diesel fuel to put up a windmill or to turn Si into a PV panel and ship it from Taiwan). Likewise, the resource depletion per KWh is very low. Unfortunately, we do not have a renewable-rich grid, and mass adoption of EVs at present would be a massive fleet of predominantly coal-fired vehicles with a massive CO2 footprint. Consider a car that uses 250Wh/mi at the battery and 324Wh/mi at the wall. It gets:
You can imagine which of these metrics EV advocates are pushing for, but in fact, they would underestimate the GHG emissions of a fleet of EVs by a factor of two. If the X-Prize had used the more appropriate 16KWh/gal metric, only the X-Tracer electric Dalniks, the Li-ion EV, and the gas-fired Spira and Edison2 VLC's would still be standing. Aptera would have been eliminated with 67.8mpge before penalties. Once more plug-in cars hit the market, we'll be able to make more direct comparisons between EV and HEV variants of the same car. Until then, study after study suggests a BEV with 100mi range (BEV-100) will be carrying enough weight in batteries to increase its CO2 footprint to larger than that of a HEV. A short-range plug in hybrid is a good compromise, with a recent Carnegie-Mellon study suggesting a PHEV-7 was optimal for minimum CO2 emissions. There are other factors in the EV versus gasser debate that are beyond the scope of MPGe. These include the higher smog forming emissions of a gasser, the environmtental impact of oil spills, and mining for coal and rare metals to make batteries. There is also the matter of the cost of electric vehicles and windmills, and the rapid depreciation of current-generation high-density batteries. It's wrong of the X-Prize Foundation to fail to look at the big picture when calculating MPGe. It's also incorrect to call EV's "zero emissions" (yes, that claim has been made) or even that they're low-carbon. EV's will allow us to burn diverse fuels and weather a petroleum crisis with less disruption (which is bad news for environmentalists, as fuel crises drive conservation). We need renewable electric generation FIRST, and EV's afterward. I am voting with my dollars by selecting my utility's renewable electricity plan, and I'd encourage you to do the same. Your representatives in government also need to hear that it's an important issue to you, as I hope it is. When confronted with an MPGe figure, I hope you'll be a little skeptical and dig for a Wh/mi figure. Then consider which KWh/gal figure makes sense to you, and come up with your own mpge figure. I recommend 16KWh/gal as a weighted average. |
There was a note in the DOE paper, and I'm not sure of the entirety of its scope, but they skipped all non-fossil fuel sources in their analysis?
Comment 7: The U.S. Average Electricity Generation factor (Tg = 0.328) is based only on fossil fuel generation, But that leaves out like almost 1/3 of the grid, at least as of 2009 (I'm rooting for the renewable section and gladly give my local windfarm a couple extra bucks) http://upload.wikimedia.org/wikipedi..._source_v2.png |
Even if an EV emits the same amount of pollution per mile as an ICE car, it's still beneficial, as they're often cheaper to run, and their pollution can be lowered without replacing the vehicle, as the power grid changes over time.
|
Quote:
Quote:
And of course, if you have an electric/plugin car, you've now got more incentive to install those solar panels on your roof :-) |
Matt,
You are conflating energy equivalence with carbon footprint. 1 gallon of typical gasoline = 33.4kWh of electricity. If you are applying all the embedded energy for electricity, then you also need to do the same for gasoline. Gasoline has emissions from the tailpipe *and* from the refinery, and the wellhead, and from the transportation. Electricity has it from the source and the generation stage. All use of carbon for both must be counted in order for the comparison to be fair. Because, if I have solar panels on my roof, or a wind turbine in my yard, then your numbers are no longer accurate. I'd like to see someone try to refine gasoline from oil at home! |
"...passing..." the carbon 'bucket-brigade' back to it's source = where does/did the original energy come from that now creates the electricity that we use?
|
Quote:
Regarding "The U.S. Average Electricity Generation factor (Tg = 0.328) is based only on fossil fuel generation". Efficiency of nuclear is around 30%. But how do you measure efficiency of hydro, solar, and wind? PV panels catch perhaps 8% of the sunlight hitting them, and windmills catch only a tiny fraction of the kinetic energy passing their swept area. But you can call them 100% efficient, because if the hydro dam weren't there, then zero percent of the energy would have been captured. So if you want to use 14.8KWh/gal by an energy-equivalence method, that sounds fine with me. Quote:
James, Unfortunately, the extra battery weight (and resultant extra structural and motor weight), and the added inefficiency of the battery and charger shifts the electric vehicle to parity with a conventional vehicle, and behind a hybrid. There's a very cool sensitivity analysis on page seven here: http://www.cmu.edu/me/ddl/publicatio...t-Charging.pdf , and a few other corroborating studies I can't put my fingers on right now. |
Nuclear is renewable?
|
Quote:
|
Quote:
|
Quote:
|
Quote:
Yes, gotta have faith :p http://www.freesmileys.org/smileys/s...angelic008.gif Quote:
|
Quote:
|
Ah, here's the study from Dr. Samaras that I was thinking about. http://solar.gwu.edu/index_files/Res..._for_PHEVs.pdf
Here's a Green Car Congress digest of the paper: http://bioage.typepad.com/photos/unc...07/samaras.png Green Car Congress: Study: Meaningful GHG Benefit from PHEVs Requires Low-Carbon Electricity @Neil: I have addressed each of your points in my OP. |
Quote:
In any case, what matters (as far as I'm concerned) is not the strict renewability, but the amount of fossil CO2 emitted. That's basically the same for hydro, nuclear, solar, etc: a bit in construction, but then zero in operation. |
The nuclear power plant requires a lot of energy during decommissioning, too, don't forget. And storage/security for the spent fuel, and low level radiation materials, too.
I never said that there is no renewable liquid fuels, but I do think it would make a lot of sense to develop much more efficient ICE's. |
Quote:
Just to provoke thought, a large part of the carbon-cost of a nuclear plant is the concrete containment structure. Now if you've ever poked around Europe much, you'll run into a number of concrete structures that are still servicable - and being used - 1500-2000 years after they were built. See for instance the concrete dome of the Pantheon in Rome. So after investing all the time & materials needed to build a massive concrete structure, why "decommission" it a few decades later? |
Quote:
|
Quote:
|
|
Quote:
Have you seen a reactor in the Pantheon lately? |
Quote:
So here you've built - at great expense - a big concrete containment (note the root there: contain) in which you put a nuclear reactor. You run the reactor for 40 years or so, then tear everything down and ship it to a nuclear waste dump? Why not refurbish the current reactor, or put a next-gen one in the existing structure? *It's said that Britain's nuclear power plant workers couldn't vacation in Cornwall, because the natural radioactivity from the rock there would exceed their permitted dose. |
What would the US do if we were in the same situation as we were in WW2?
Now add to that scenario one additional issue hypothetically. We did not have enough oil to drive our wartime economy or our military. My purpose is presenting this scenario is to try to get people to think beyond their individual agendas. We are at war, but this time it is much more subtle, and its primarily economically driven. What we need to do, is to spend research funding to assist EVERY potential technological pathway to increased efficiency. I see the support for all electric as potentially beneficial, but I also see ignorance of other alternative pathways as very shortsighted. Hypermilers do more with less, and the tactics of driving for economy are available to every drive on the planet. The incentive is greater in other countries because the energy cost is significantly higher. My Patent demonstrates a method of improving fuel economy in ANY vehicle with wheels. It cares not how you create the power to drive the vehicle, only about your tank to wheel efficiency. The Patent was conceived on one basic assumption, that you can incorporate hypermiling techniques into the vehicle itself, and remove operator involvement from the equation. I don't know about the rest of you, as to how successful you have been in converting others to efficient driving techniques, but personally I find the ignorance astounding and the attitude that I am some kind of obsessed, semi nutcase, because I focus on efficiency. One of my acquaintances has driven 100 miles a day to work and back, averaging 20 MPG in a truck. Had he driven a very economical car for the last 28 years he has made that commute, he could have well over $250,000 in the bank today if the savings had been wisely invested, regardless of market fluctuations. It is a shame that something like the X-prize contest and the media even propagate the fantasy that you can get 300 MPG in an electric vehicle. I find the dis ingenuity to be about on par with the water for gas snake oil pitch. The problem is when you bombard people with so much misinformation, they would not know the truth when it was staring them in the face. I use the analogy of Cassandra, the priestess of Troy who warned the Trojans about Greeks bearing gifts. Although blessed by the Gods with the gift of prophecy, she was cursed by the same Gods with the disbelief of her countrymen. While that scenario may be fictional, the consequences are very similar to what we are facing today. Like the Canary in the submarine that showed the crew when the oxygen content was approaching the terminal point, we must succeed in our objective. Otherwise we may not see our children suffer the consequences of our inaction. It's not one or the other, electric or renew ables. It's not about fossil fuels or whatever alternative you feel is the future energy source we should employ. Like the early pioneers who first extracted energy from what was available, where factories grew in areas where water power was available, we must adopt the same, conscientious effort to make everything more efficient as well as cleaner. Politicising that priority will ensure our heirs will not even visit our graves. regards Mech |
Radioactivity exists in nature, but that doesn't mean that is okay. Asbestos is natural, too.
If reusing a nuclear power plant was possible/economical, then I think they would be doing it? The risk of reusing things is that you cannot be as sure about how they will work -- and the risk is too great to be be making assumptions. |
I believe that a KW-h based system on total energy used from wall or fuel pump is much more practical as it allows liquid fuels to be on a more comparable basis with EVs and allows for more accurate FE comparisons. From calculating Kw-h per mile you can calculate cost per mile easier as well. It allows more practical comparisons between the liquid fuels like Diesel, Gasoline, and Ethanol. Diesel doesn't get placed on a shelf while Ethanol looks like a pig. They can be compared and the KW-h per mile will show more accurate results.
Using CO2 to calculate energy consumption is not going to get anywhere, it's just not rational. Calculating KW-h efficiency is just as important as finding the cost per gallon. If you are paying less per Kw-h but using more Kw-h per mile it isn't paying off. This works for Premium fuel comparisons too, some people have gotten results from using higher octane gasoline. Comparing them by KW-h is just simpler. |
Quote:
Your 250Wh/mile "battery-to-wheel" and 324Wh/Mile plug-to-wheel is off a bit: state of the art BEV (like say the TW4XP) are 85% efficient plug-to-wheel, so the 324 number becomes 288Wh/mile. By the way, almost nobody uses a "battery-to-wheel" number, because it is virtually impossible to measure. The plug-to-wheel is what is typically used, because that is what is most easily measured. The Illuminati '7' can use just 155Wh/mile plug-to-wheel: Illuminati Motor Works: Blog So, by putting solar PV panels on your roof, you have "magically" made the carbon equivalency about 89kWh/gallon (92% efficiency because the generation losses are zero, and only the grid loss is applied), and with your example EV (324Wh/mile), that would be 274MPGe carbon equivalency. If it was similar to the TW4XP plug-to-wheel efficiency, it would be 309MPGe carbon equivalency. And the 4 seat Illuminati '7' would get 574MPGe. So coal can be improved up to ~45% efficiency, and natural gas plants are already ~60% efficiency; and renewables that use zero fuel to generate power, only the carbon used to construct the system is used -- which gets amortized out over the lifespan of the system. It also takes carbon to build coal, natural gas, nuclear -- all types of power plants, so in fairness, renewable energy has about 99% generation efficiency. |
Here's a synopsis of more than 40 studies on source-to-wheels carbon use:
http://www.pluginamerica.org/images/...onsSummary.pdf Page 5 in particular shows ICE's producing ~500g/mile, and EV's ~220g/mile on today's US grid. Another source for carbon emissions: http://www.plugincars.com/doublechec...rs-104202.html Quote:
Edit: Another interesting link about using solar panels to offset the electricity used for an EV: http://www.teslamotors.com/blog/elec...ic-solar-cells Also, note that the Tesla Roadster uses about 200Wh/mile; which is lower than the numbers used in the original post of this thread. |
My tdi runs on renewable energy too, it is besides the point here. The question is how do you do a fair comparison of vehicle efficiency when multiple power sources are being compared. Electricity has already gone through the major conversion from it's source, be it sun or coal or whatever, so a straight btu-energy equivalence may over simplify it. In fact I'm not convinced that there IS a good way to compare the two, might as well keep them separate, not letter grades or mpge dumbing down.
|
renewable nuclear...
Most published analyses of the energy costs of the nuclear fuel cycle end up using a lot of hand waving. The biggest problem is the storage of the high level wastes. Best imaginable scenario for waste storage is a relatively short 300 years by avoiding storing the uranium and plutonium waste streams. Then we burn the uranium waste and plutonium waste in Mixed Oxide reactors built for the purpose. The biggest problems are, fuel reprocessing itself is quite energy intensive, quite dirty, quite expensive, and unavoidably produces bomb grade plutonium, which is a terrorist's dream. How many countries can 100% reliably keep that out of terrorist's hands? For hundreds of years? Really!?! And even the 300 years worth of storage, what is the energy cost for that, considering that industry proponents paint this as the best case scenario. If you don't go down the fuel-reprocessing path, then the uranium and plutonium high level waste must be securely stored for, ummmmm, 300,000 years. That has an exquisitely expensive price tag in terms of energy and money, and the whole thing becomes a net energy loser. Further, just burning the uranium once, we will run out in a relatively short time. Unworkable really. And how many breeder reactors and reprocessing plants are planned or being built right now? Just because it is theoretically possible doesn't do us much actual good in the real world. And how many would we need to drive the new electric transportation sector? I am not opposed to nuclear energy, just show me the positive EROEI for the whole fuel cycle, including long term storage. That also has to include the energy costs associated with a few clean ups, like Cherynoble, Three Mile Island, and a couple future events. Finest regards, troy |
Personally, I don't like any of the methods of calculating mpge.
Life Cycle Energy Equivalence - Unfairly compared Well to Wheels for EV to Tank to Wheels for ICE. CO2 Equivalence - Makes an assumption on where I get my electricity and it's CO2 content. Cost Equivalence - Makes an assumption on how much I pay for electricity. Direct BTU Equivalence - Gives unrealistic expectations on the range and cost of operation for EVs. What I need to know is capacity of battery pack in kWh, and "fuel economy" in wh/mi, and I can figure the rest out. |
Quote:
Conversation typically goes like this: Him: Hybrids don't make any sense because you never make up the cost premium in saved gas, everyone knows that. Me: Don't you drive a $50k SUV that gets 15mpg. Him: Yes. Me: So then you don't actually believe in this economic model of car buying where the car has to somehow pay for itself. Otherwise you'd own a Geo Metro. (long pause while that sinks in) Him: You're a hippie. These conversations typically end with me being called a greenie, treehugger, or hippie. |
Quote:
Let me stand up for the first two methods. Life cycle energy equivalence: I have presented well-to-wheels data for gasoline (not tank-to-wheels), and well-to-plug data for electric, so you must measure power consumed by the charger, not by the inverter as reported on the dashboard. CO2 equivalence: Considering that electricity is fungible, and we're all on the same grid, grid average figures are appropriate for estimating the impact of mass adoption of EV's. |
I don't have any disagreement with your W2W analysis of EV vs ICE. The comment on mpge being Life cycle energy is unfair to EVs was because mpg is always tank to wheels. So if mpge is Life cycle energy then it isn't really "equivalent" to mpg as the name suggests.
|
Quote:
|
Someone explain to me why mpge is even necessary?
What is so terrible about listing mpg and kw/mile separately? Mpge is a solution in search of a problem, while making new problems in the process. |
Quote:
|
Quote:
|
Matt, did you read this?
http://www.pluginamerica.org/images/...onsSummary.pdf From page 3: Quote:
|
Quote:
'Combined mileage' numbers, such as the 129 MPG number used by an auto magazine for a Volt test, and a 80 MPG number used in a plug-in Prius test, are very misleading and should not be used - Does a driver only drive 5 miles a day? Does a driver commute 200 miles a day? What happens to the combined mileage number when a plug-in hybrid can't be plugged in for some part of a particular trip? The MPGe rating comes into place with plug-in hybrids. Comparing a Volt with a Plug-in Prius (both are basically plug-in hybrids; neither is an EV) an MPGe number would have more significance - perhaps a depleted-pack MPG over electric-only wh/mi. As an example, a Volt may get an MPGe number along the lines of 40/266 (MPG depleted over wh/mi) and a plug-in Prius may get 50/220. These numbers are speculative, but close based on some auto magazine tests. For an efficient plug-in hybrid, one would look for a high first number and a low second number. |
Quote:
|
All times are GMT -4. The time now is 05:51 AM. |
Powered by vBulletin® Version 3.8.11
Copyright ©2000 - 2024, vBulletin Solutions Inc.
Content Relevant URLs by vBSEO 3.5.2
All content copyright EcoModder.com