We have many threads, that have to do with well to wheel efficiency, but this seems to mix many concepts when different sources of energy are used. Even when oil is used we get confusing results for diesel versus gasoline. The epa has done well to get wall to wheels and pump to wheel efficiency. YMMV but we can look at their standards and get a good comparison. Efficincy to produce gasoline is 84%. We can multiply by mpg in a prius and get 84% x 50 mpg =42 mpge (energy oil). For diesel#2 0.88 gallons is the equivelent of a gallon of gas and efficiency to produce it is 92%. We can multiply by mpg in a jetta tdi and get 92% x .88 x 34 mpg = 28 mpge (energy oil) But for a phev or bev, we do not use oil to produce electricity. We need to create efficiency and energy equivalents. In many ways the doe would favor natural gas over oil. For cafe standards we use 82 kwh as 1 gallon equivalent, for epa purposes we use 33.7 kwh as 1 gallon gasoline equivalent. There is an idea of weighting the fuel but coal and natural gas do not get weighted differently for cafe purposes. Looking at some sources for electricity and only looking at fossil fuel numbers wind and solar don't use any fossil fuel A leaf gets infinite mpge (fossil fuel) on solar or wind. A new natural gas ccgt power plant, the kind we we have been building for the last decade now gets 60% efficiency. The grid is 93% efficient. For a leaf 60%*.93*99 mpge = 55 mpge (energy natural gas new ccgt) Eia said in 2009, many ccgt were being used as ocgt which lowers there efficiency. The average efficiency because of grid management was only 44%. For a leaf 44% x.93 x 99 mpge = 41 mpge (energy ccgt average grid) Then we get to old coal, which is about 32% efficient. For a leaf 32% x .93 x 99 mpge = 29 mpge. You can also do this exercise for pollutants, and others have those figures. Energy efficiency is a strange thing when looking at different power sources
Well you are really talking about two different metrics. First, you are talking MPGe which EPA has defined as (approx) = 100 for EVs @ 3 mile/kwhr. Second, you are talking MPGffe fossil fuel equivalent burning, unlike the EPA's number, tries to communicate how much coal+gas is used (CO2 is made) when electricity is used instead of gasoline. Your numbers (as low as 29 MPG CO2 or fossil fuel equivalents for Leaf on 100% coal) is in good agreement with the Union of Concerned Scientists report earlier this year. If we take an weighted average of the coal and gas we get something around 45-50 MPG fossil fuel equivs. is what a Leaf gets at the national average elec grid, which compares favorably to Prius at 50 MPG actual. Of course, that's not too shabby - both cars get good MPG, better than most. Then we get into the argument if you have greener grid in your state, or home PV, then the Leaf could be considered greener than a Prius in those cases, alternatively, if you live in a coal-power area, then the Prius could be considered greener than a Leaf in those cases. The EV fans tend to not concede the latter point, feeling the grid will become cleaner with time and coal is better than gaso anyways re: political correctness.
I used the epa's energy equivalence. If you start with 114,000 btus of oil in a well you will go 42 miles in a prius. If you start with 114,000 btus of natural gas in a well and move it through a new ccgt and the grid you will go 55 miles in a leaf. If you start with 114,000 btus of coal in the ground and burn it in a 40 year old coal plant you will go 29 miles in a leaf. Oh and YMMV. I am not confusing anything. The EPA is measuring wall to wheels and only uses energy. Efficiency is quite different than CO2. Nuclear is about the least efficient method to produce electricity and generates no co2. Do you want a weighted average for the next 10 years where the cars are charged, or a 2007 average for the country? Efficiency is difficult here, since it includes a number of assumptions. I don't find efficiency too valuable when comparing different fuel sources. I would rather be less efficient with natural gas, than really efficient, and high polluting with coal. Fortunately we don't need to make this last choice, since it is actually less expensive to build more efficient natural gas plants today then coal. I would say that we should at least try to project the grid out for 1o years, and geographic distribution of cars. This is difficult, and assumptions get made, but california the number one state is much cleaner than I would guess the bottom 15 states which will sell less cars combined. If its for you individually it is much easier. You probably can get the 10 year plan from your utility. I get to choose wind, so I don't even need to hit a key on a calculator if I am thinking about fossil fuel efficiency of my electricity. Others are stuck with coal heavy utilities and a lack of choice. Ah, but I would hardly define greener as more efficient. I might define it as using less oil and no coal You have the tools now to determine greener if you can do an adequate definition. I would say that cleaning your local grid if it is coal heavy will likely reduce co2 more than getting a phev or bev. Let's not confuse greener with produces less ghg on the national average grid with gasoline than brand T's bev.
Projections from the eia for 2020 are 39% coal and 28% natural gas for the national grid. I think they are pessimistic and coal will be a smaller percentage, this year we hit 34% coal for a few months, and we can make lower numbers happen. But given these projections lets see how the leaf does, with a 32% coal efficiency and a 50% natural gas efficiency assuming new ccgt continue to be built. Nuclear, hydro, and renewables are ignored as this is only fossil fuel efficiency. .39/.32 + .28/.5 = 1.78 fossil fuel equivalence to get 1 gge of electricicty 1/1.78 * .93 * 99 mpge = 52 mpge in a leaf in 2020 eia estimate of national grid, versus 42 well to wheel in a prius. In 2010 it was 45% coal and 24% natural gas That makes .45/.32 + .24/.44 = 1.95 gge 1/1.95 *.93*99mpge = 47 mpge in a leaf in 2010 Note these are fossil fuel efficiency figures. ghg are different. Coal produces much more ghg per gallon equivalent than gasoline, and natural gas produces slightly less.
somewhere in this analysis some consideration should be given for time of use/charging. i.e. what is the mix for night time electric generation. unfortunately this might not be positive if a lot of the coal burning plants, which just run 24/7, are providing the bulk of night time generation. While wind is blowing 24/7 it is often being curtailed at night, until more storage is implemented.
Tell me more about why you think nukes are less efficicent...I have never heard that. ...right I do not think we should ignor nuke, hydro etc costs. I am not enamored with analyses to date which basically assume CO2 is the key parameter. We need to focus more on cost to generate this electricity, which is basically the cost of the plants, so now solar, wind, nukes, everything has a cost. If someone insists we could add in carbon tax as one way to look at it.
Same here, but I guess it's because they still run steam powered turbines like traditional coal plants. Natural gas and, I'm guessing, clean coal fire the turbine directly, like the engine on a jet.
austingreen - I encourage you to download the latest version of Argonne National Laboratory's GREET model (GREET1_2012). It's available for download on the GREET web site - Argonne GREET Model. It's a free download, but you need to register. It appears that EPA uses the GREET model at least as a basis for its WTP calculations. There's extensive documentation for the model development at http://greet.es.anl.gov/list.php. Some pre-selected fuel pathways/vehicle technologies graphics are available at Argonne GREET Sample Results. The model also allows some of the default parameters to be changed, e.g., electricity generation can be changed to all coal, or all natural gas, etc. It also has many "alternative" fuel pathways. Of course, this is still a model, with all of the assumptions and estimates associated with models, but it's probably the premier tool for estimating WTW emissions. By the way, if anyone downloads the GREET2_2012 model (vehicle cycle emissions) and gets it to work, please let me know because I haven't gotten it to work for me.
Thus my love/hate relationship with php. Betwixt permissions, paths, and version conflicts I usually end up screaming for an executable I can run on OS X
EPA website is stuck in the 2007 grid data from the 2010 model. I thought we would update it to at least 2010 grid. We don't live in the static world. The greet model is a good starting point, but IMHO it needs to be modified greatly for current grid and plug-ins. I thought real cars in my examples would be better than theoretical cars in the government models. I was putting up efficiency numbers not CO2 numbers. Greet 2012 will get you ghg numbers for electricity and gasoline for 2009 data.
The nuclear reactors we use consume less than 1% of the fuel - uraniaum - to energy. The rest is stored as waste and not reprocessed. Since Uranium fuel is so cheap, people are not concerned about wasting it, but we should be concerned about the nuclear waste. Breeder reactors can be much more efficient with the fuel, and produce less waste. Unfortunately you can use some of that waste to make bombs, which is one reason we have not built breeder reactors. Since uranium is not a fossil fuel, I don't count it in fossil fuel efficiency. If fuel ever became expensive and we wanted nuclear power plants, breeder reactors could be built much more efficiently and use thorium and/or uranium as fuel. Both of these fuel sources are much much less expensive per unit energy than coal. Nuclear efficiency doesn't make much sense to talk about. Cost of nuclear power, safety, and pollution - nuclear waste - all mean it will likely become a smaller portion of the US grid. New Nuclear does not compete well at today's prices with wind or gas ccgt. Already built plants are inexpensive to run with fuel costs. In the future we may decide nuclear waste is better than ghg, but that does not appear to be the consensus today in the US.
I thought I would update this with CO2 projections. Remeber, IMHO coal will fall faster than projections, which will reduce pollution faster, but YMMV. EIA - AEO2012 Early Release Energy-Related Carbon Dioxide Emissions In 2010 it appears there were 568 grams of CO2/kwh. for a leaf 568 g/kwh /.93 * 33.7 kwh/gge / 99 mpg = 207 g/mile prius is 222 g/mile Let's also look at a volt, say 63% @98mpge electricity and 37% @ 37 mpg gasoline. That works out to volt = 210 * .63 + 300 * .37 = 243 g/mile For reference the epa site gives 230 g/mile for the leaf. I assume the difference is mainly that I am using 2010 instead of 2007 data. YMMV, especially with the volt depending on your driving pattern. But the range 207-243 is very low for any of these cars. In 2020 using the eia projections carbon insteansity of the grid should drop 11% from 2010. We actually have fallen quite a bit already in 2012. Leaf 2020 projections from eia, 184 g/mile You'll notice this is not much better than the prius. If your sole purpose is lowered ghg, plug-ins will help, but unless you choose wind or solar or live in a low carbon state the change is not high. Reducing oil consumption and reducing unhealthy pollution are better reasons to go plug-in.
Absolutely, there are many assumptions when it comes to marginal impact of phev and bevs, and I was using the throwing a dart approach, and picking average efficiency but not including special peaking power sources. As more plug-ins get added we should get a much better idea. The best case scenario for texas is that plug-in buyers choose wind, and help to pay for cleaning the grid. More plug-ins charging at night with more wind, might have coal plants close down during most of the year and only run in summer, shifting to a much cleaner grid. If technology progresses, the utilities might pay you to draw power from the cars during the peak (3pm-7pm) and give you free power at night. The worst case is that everyone charges during the day, allowing coal plants to run above capacity and without scrubbers during peaks at lower efficiency just to stop black outs. The night wind is curtailed since there is no demand. The likely scenario is that these cars run mainly on combined cycle gas turbines. There is about as much renewable added to offset the additional coal. We still are running the plug-ins on fossil fuel, but we import less oil and have less smog in the big cities. Choose your scenario. I know that our utility Austin Energy is in a program monitoring charging patterns which should give us better predictive patterns.
