Comparing electricity to a gallon of gasoline

The "burning" question for electric cars is how to compare them with gasoline. Last month I wrote about how wrong the EPA's 99mpg number for the Nissan Leaf was, and I gave the 37mpg number you get from the Dept. of Energy's methodology. More research shows the question is complex and messy.

So messy that the best solution is for electric cars to publish their efficiency in electric terms, which means a number like "watt-hours/mile." The EPA measured the Leaf as about 330 watt-hours/mile (or .33 kwh/mile if you prefer.) For those who really prefer an mpg type number, so that higher is better, you would do miles/kwh.

Then you would get local power companies to publish local "kwh to gallon of gasoline" figures for the particular mix of power plants in that area. This also is not very easy, but it removes the local variation. The DoE or EPA could also come up with a national average kwh/gallon number, and car vendors could use that if they wanted, but frankly that national number is poor enough that most would not want to use it in the above-average states like California. In addition, the number in other countries is much better than in the USA.

The local mix varies a lot. Nationally it's about 50% coal, 20% gas, 20% nuclear and 10% hydro with a smattering of other renewables. In some places, like Utah, New Mexico and many midwestern areas, it is 90% or more coal (which is bad.) In California, there is almost no coal -- it's mostly natural gas, with some nuclear, particularly in the south, and some hydro. In the Pacific Northwest, there is a dominance by hydro and electricity has far fewer emissions. (In TX, IL and NY, you can choose greener electricity providers which seems an obvious choice for the electric-car buyer.)

Understanding the local mix is a start, but there is more complexity. Let's look at some of the different methods, staring with an executive summary for the 330 wh/mile Nissan Leaf and the national average grid:

  • Theoretical perfect conversion (EPA method): 99 mpg-e(perfect)
  • Heat energy formula (DoE national average): 37 mpg-e(heat)
  • Cost of electricity vs. gasoline (untaxed): 75 mpg-e($)
  • Pollution, notably PM2.5 particulates: Hard to calculate, could be very poor. Hydrocarbons and CO: very good.
  • Greenhouse Gas emissions, g CO2 equivalent: 60 mpg-e(CO2)

Theoretical pure energy conversion

This is approximately what the EPA used. They looked at the inherent chemical energy in a gallon of gasoline -- this is roughly 120,000 BTUs. (It varies based on ethanol content and season.) Only the USA uses BTUs, but by surprising and useful coincidence, a BTU is very close to a kilojoule, and you can use that for back of the envelope calculations if you prefer joules, the metric unit of energy.

Electrical energy is a much lower entropy form of energy, and you can't convert the chemical energy of gasoline or other fossil fuels into electrical energy at 100% efficiency. Not even remotely close. Mainly we generate heat from the chemical energy of the fuels, and turn that heat to electricity. You can refresh your "Carnot Knowledge" for more on the limits of this, but the reality is that our power plants extract about 30 to 50% of the chemical energy, first into mechanical energy (spinning turbines) and then into electricity.

At perfect conversion, you get about 36 kwh in a gallon of gasoline. If you could do that, which you can't.

The EPA was not alone in this. The automotive X-Prize, which rewarded the best 100mpg car faced the same problem of how to compare gasoline and electric cars. It was controversial, and I believe they were in error when they selected the theoretical number, giving a huge advantage to the electric cars in the contest. It was so high that many presumed that it was pointless to do anything but an electric car, but surprisingly the winner, the Edison2, was a gasoline (or rather Ethanol 85%) car.

As you might guess from the name, the Edison2 team started thinking they would be electric. They learned they could do better with gasoline because they could make the car very lightweight. Their car got barely 100mpg, even though the near competitor electrics were rated at 170 mpge (miles per gallon equivalent.) In reality, 100mpg real is better than 170 mpg-e(perfect) and the Edison2 is a deserving winner.

Even the fans of perfect conversion accept there is about a 7% loss in transmission lines, and some further losses in chargers and the battery system, so they don't use the totally perfect number. The EPA used an 8% lower number than perfect, presumably for this reason.

Just using the base energy (heat)

Most of the electricity in the USA is generated by heat. The Department of Energy studies all the power plants in the USA, and their efficiency is calculated and averaged. They include the nuclear plants, which use heat, but generate it from nuclear reactions rather than fossil fuel. People react in many different ways to this methodology on nuclear -- but they are only about 20% of the grid so variations in the methodology there don't affect things a lot.

The DoE method says a kwh at the plug takes 10,300 BTUs, not the 3400 of perfect conversion. It's a very large difference, a factor of almost 3 to 1.

This method is also pure in that it deals with the real energy being released, either by burning gasoline, or coal, or natural gas, or "burning" nuclear fuel. It would be silly, but you could even imagine burning gasoline in power plants (and some power plants do burn oil distillates) to make the comparison more direct.

A fair criticism, however, is "who cares about the heat released?" The heat is waste, except in cases where the power plants are urban and pipe their heat out to provide hot water and interior heating for buildings. In the car it also heats the interior in winter and defrosts the windows.

The cost

One reason to compare gasoline and kwh is to find out the cost of driving. This is a pretty reasonable comparison. At the national average of 11 cents/kwh, the 320 watt-hours/mile of the Leaf is about 3.5 cents/mile. That's pretty good and about 85 miles for the cost of a $3 gallon of gasoline. Electricity is cheaper than gasoline, no doubt. To be fair, gasoline has about 15% tax put on it to support the roads, which electric cars should also pay, and that would bring it down to about 75 mpg(dollar-based). The price of electricity also varies locally. In California, the tier system makes heavy users pay 32 cents/kwh, which would make the electric cars more expensive than gasoline, but I believe that there is a special law which lets owners of electric cars avoid the tier system and pay a more basic rate.

This does not factor in the cost of the battery. The jury is still out on the cost of the battery as an "expendable" part of the car. Some worry the batteries need replacement at a certain rate which makes them cost as much as 10 cents/mile if viewed that way. Others report that vehicles like the Prius are lasting a long time on their batteries. Most agree that batteries do wear out and so eventually they do need a cost/mile associated with them. Of course, internal combustion engines also wear out, as do many other parts of cars.

The pollution

Another way you might want to compare your kwh and your gallons would be by the pollution emitted. Indeed this is probably the main thing in people's minds, since nobody is buying electric cars to save money right now, though they might in the future.

There are, alas, many ways to look at pollution. The biggest one today is greenhouse gas (GHG) emissions, which I will cover below. While we're all about GHG today, the reality is that gasoline and coal emit a lot of pollution of other forms. At present, nuclear power and hydro don't emit much pollution at all, but people are very divided on how green they are. Nuclear waste and the risk of leaks troubles many people, and the destruction of valleys and habitats and fisheries done by hydro is worse than the air pollution of other modes in the minds of different groups.

You have to judge for yourself how you want to compare nuclear and hydro to the other forms. They are about 30% of US power production, and much more of power in Europe and Canada for example.

Gasoline spits out tons of carbon monoxide, as well as nitrogen oxides and various hydrocarbon volatiles compared to coal. Gasoline emits a fair amount of particulates (soot) but diesel is far worse. Coal generated electricity has 2-3x time particulates of gasoline per mile driven and triple the acid-rain causing sulfur dioxide. There are arguments in both directions but I think coal is the big loser here, particularly in the particulates. It is not well known, but particulates are a huge cause of death. California calculated that 9,000 people die per year due to particulate pollution -- that's more than die from car crashes. And this is a state that does not burn much coal!

It is true that many of these deaths are older people whose systems can't handle the damage particulates do to their lungs but the numbers are staggering and trump just about anything here. This makes a strong argument that with coal powered electricity, the mpge(deaths by pollution) is lower for electric cars, though it's hard to figure an exact number. (As a plus for coal, the plants are sometimes located further from people than highways are.)

When I get more research on the amount of PM2.5 emitted per mile by cars and per kwh by power plants, I will update it here. To do this I'll need more data on all the pollutants from the various sources, and also data on how dangerous they are. For example, some of the hydrocarbons are carcinogenic, and we need numbers on the scale of their effects.

Greenhouse Gases

Lots more research is being done on calculating "grams of CO2 (or equivalent) per mile" as a way to compare electricity and gasoline. If global warming is your big issue, this is the one hat you'll focus on. This also is highly locally variable, with very high numbers in the coal states and nice numbers in the hydro and nuclear powered areas.

Research I have seen suggests that coal-powered electricity has about 1000g of CO2 per kwh, while natural gas has about 500g. The others are much lower, though some argue that because of the large amount of energy needed to make today's solar panels, even they incorporate about 150g per kwh.

I've also seen credible arguments that due to the fact that about 1.5% of the natural gas pumped in the USA leaks into the air, and that methane is anywhere from 80 times (20 year average) to 20 times (100 year average) more potent a GHG than CO2 is, the figure for natural gas generation should be higher, more like 700g. As in all total cost "well to wheels" calculations you will find a lot of variation in the final numbers, but I think these are close enough for rough calculations.

The DoE cites 588 grams CO2 per kwh as the national average -- I think the NG leakage number pushes it higher. You will also see well-to-wheels numbers for gasoline around 11.5 kg of CO2 per gallon. From this, we can work out a national average number of 19.5 kwh in a gallon of gasoline, GHG based. That gives the Leaf 60 mpg-e(GHG) on the national average, and something like the same 37mpge we got from heat in a coal state but a much better number (closer to that perfect one) in a nuclear and hydro state. (Yes, it's possible to do better than perfect conversion when it comes to GHG emissions, in fact you can do an almost infinite number if you had completely GHG-free electricity.)

Fuel Content Factor

As a bizarre sign of the politics behind this, read the math in the DoE's electric and hybrid car report done 10 years ago. You'll see in their math that they want to use the heat formula (real energy used) but then they have to multiply it by something called the "Fuel Content Factor." It's amusing to read how they describe it, it's effectively a constant pulled out of thin air because politically they wanted to make alternative fuel vehicles look better. It's huge -- 6.6 -- so it means the DoE's 37mph on the LEAF would get multiplied out to 246 mpge! Problem is, had the EPA used that number, it was more than double the perfect energy conversion number and it would have looked really ridiculous. However, for a while before the cars came out, Nissan did tout numbers in this region, and so have other electric car makers. I do believe electric cars can be better, and particularly on the cleaner grids, but introducing a made up fudge factor for political reasons is a bad idea, because people will stop trusting you when they find out the reality.

So how are electric cars doing?

I'm studying this because as part of my robocar research, I have been predicting that we could gain a lot of environmental and efficiency benefits by switching people to electric vehicles.

What I've learned is that at least for now, the use of traditional sedan sized electric cars not a big win compared to hybrid gasoline cars like the Prius, at least on the average grid. It is a win in the low-coal places like California and the high-hydro and nuke places like Washington state. It's a definite loser in the high-coal places. I refer you to my earlier post and the linked flash application to see details of your own local power grid. I believe the local power companies should all publish these numbers on their web sites and on your power bill.

We can do better, though. We are working on making electrical generation cleaner. We can plug natural gas leaks (it just wasn't worth it from a financial standpoint but is worth it from a GHG standpoint.) We can put in more renewables. We can also use more biodiesel which is lower on particulates and sulfur.

Most of all, we can go for lighter more aerodynamic cars, particularly the single person commuter cars that robocars make palatable to the commuting public. What the X-prize showed was that going electric was not necessarily the answer, but that going lightweight was. And there are also lighter electric cars. The Aptera reports around 100 watt-hours/mile, and small electric velomobiles have gotten down to 30 watt-hours/mile. We are unlikely to get that low in practice, but I believe that 50-60 is a likely goal for single person urban commute vehicles.

Other factors

Electric cars mostly charge at night, which means they tend to use baseload power. What that is varies from place to place. Where there is nuclear, it will tend to that as nuclear plans don't shut down easily. Coal is another baseload provider, unfortunately. Hydro and natural gas can be turned on and off quickly and thus tend to be used for peak load. Wind runs at night more, PV solar entirely in the day.

Fuels for electricity are almost entirely domestic. Significant amounts of oil are imported, sometimes from unfriendly areas.

Emissions from cars are done in the urban areas. Power plant emissions sometimes are out of town. That matters for PM2.5 and Sulfur etc. but not for GHG.

Don't forget that the USA has the dirtiest power grid in the western world nowadays. Drive your electric car in Canada and you can put on a big green smile, pollution and GHG wise. Almost as good in mostly-nuclear France and other countries that have kicked the coal habit. On the other hand it is debatable if they should even licence an electric car in places that have 97% coal power like West Virginia.

What about solar cars?

Quite commonly people will say they just plan to run their electric car on solar and thus have no pollution at all. People go all irrational for this idea -- literally on my block there was a story that got national attention when a neighbour who was trying to have enough solar panels to power his car got a legal order forcing another neighbour to cut down his redwood trees which had over the years grown to shade some of his panels. Leaving out the issue of how much energy is needed to make the panels, there are some serious misconceptions here. I've explained this before but it's worth adding again here.

There are no solar electrons. To properly meet green goals, solar panels must be connected to the power grid. When you connect panels to the grid, you help make the grid a tiny bit greener, and that's good, but you don't make your driving green.

If you don't connect your panels to the grid, it's very wasteful. Panels not connected to the grid instead handle live loads or charge batteries. They might charge the batteries in the car, or they might charge a second bank of batteries which then charge the car. The wasteful latter solution is needed because the car simply isn't at home during the sunny part of the day for most people. It's home at night. Solar panels that just charge a car would throw away most of their power most of the time. But even without that factor, the reality is that batteries only take the full output of panels when the batteries are fairly discharged. When your batteries are only partly discharged, they throw away much of the power of the panels. When your batteries are full -- and most people insist on designing a system that makes sure the batteries fill up, both to give them power they need and to maintain battery life -- the solar power is entirely thrown away.

Throwing away so much of the power of your panels is non-green for several reasons. One is the power it took to make them and the emissions involved with that. The other is that, if you did grid-tie, you could be feeding that power into the grid, and thus reducing demand on grid power plants to burn fuel. A decision to not connect because you want no part of the grid is an environmentally destructive decision. This does not apply, of course, if you have decided to live out in the country beyond the grid. There it was your decision to live there that made the difference.

You may find this circular, but once you agree that you need to be on the grid with your solar power, you now have to accept that your driving is not emissions free, even though your net emissions are very good or even negative. Drive more and you will use more grid electricity from the very slightly greener grid you helped make. Each mile you drive will burn the fuel of the grid, and you can't get away from it. You're being green with your grid-tied panels but your driving is orthogonal to that. If you live in a coal state, you should actually put up solar panels and feed them to the grid, and drive a hybrid rather than an EV or PHEV! That's because the power from your panels will reduce demand for coal and you should put every watt-hour you have into that rather than avoiding gasoline.


Excellent article, but a watt should be capital W and a kilowatt kWh. :) notes that the US imported about $400 billion of oil in 2008; the numbers at suggest that if we could stop importing oil, that might correct at least half of our trade deficit (although if we import lots of lithium and other battery materials initially, the initial effect on the trade balance may not be so strong).

Wind and solar would be more effective with cheap batteries, and buying an electric car is probably the best way to help drive the price of batteries down. (Ultimately, vehicle to grid power also has some potential to reduce the environmental impact of new transmission lines, by allowing some of the peak load to be covered from local, distributed battery power.)

The state tax incentives for buying an electric car probably correspond reasonably well with states that have cleaner electric grids.

That so much oil comes from far away is troublesome. I just don't think that burning coal is a lot better. If we could stop the leakage on the natural gas that would be better, until the wind and solar we seek can come online.

I must admit I used to think the vehicle to grid power plan was neat, but I want to see more math on it. The cars need to be connected at the peak load time (3-4pm) which would not be true for many house connections but would be true if the cars parked at offices had connections. The other issue is getting a good handle on the cost of discharge on a battery. Providing peak power to the grid will shorten battery life, the question is how much and how much that costs. All this will depend on new battery chemistries and their life cycles, and how much you want to discharge.

Even so, there is a problem. Most people will resist draining off their car at 3pm to deal with the peak load, because in 2 hours they plan to drive home, and probably don't want to start with a partial charge. It's why they plugged in If their trip home is short they might go for it, as non-commute cars might.

I hope the incentives correspond to the right states with clean grids. I thought the big incentives were federal.

The USA doesn't have to have so dirty a grid. Our grid in Canada is several times cleaner, though in part that's because we're a big country with tons of hydro for a smaller population, and an advanced nuclear industry.

A Tesla Roadster battery pack is 53 kwh. has some details. I think the interesting question is what happens if the price of battery packs comes down to the point where the average automobile sold in the US has a 53 kwh battery pack, and we have approximately one automobile per person. (I think there is also the potential for some car buyers to end up with somewhat larger battery packs; that 53 kwh pack is about a thousand pounds with today's technology, and I don't think a thousand pounds is the upper limit of what light duty truck manufacturers might be willing to consider if the battery costs were a tenth of what they are now, plus there may be room to make the batteries a bit lighter for a given capacity as technology improves.) notes that average per capita power consumption is about 1.5 kw in the US, and 2 kw in Canada.

The typical American probably has a Nissan Leaf (~73 mile range) sized commute, but probably wants something closer to a Tesla Roadster ranged car (200+ miles) for the occasional road trip.

One potential vehicle to grid use case we might consider is the one in which a car owner tells the electric utility that the total vehicle to grid energy from that car in a year will not be more than three times the capacity of the pack, or 159 kwh in the case of a 53 kwh battery pack. In the US, this would mean that roughly 100 hours of the year's average electric use could be covered by vehicle to grid energy, which is a bit more than 1% of the total non-car-battery-charging electricity. And this could probably be the 1% that the electric utility finds most difficult to deal with, so that's really worth significantly more than 1%. If drawing an extra three complete discharge cycles in a year (which will more likely actually be 10+ partial discharge cycles) has any meaningful effect on the battery's lifespan, it's hard to imagine that the battery could be at all usable for transportation, therefore we should be able to infer that this usage pattern would not harm the battery. (And in the US, we don't have any significant amount of zero emissions dispatchable power, unlike Canada with lots of hydro.)

We could also consider what happens if it turns out that extensive vehicle to grid discharging has no significant effect on battery capacity vs calendar time since manufacture. In that case, if everyone has a Tesla Roadster sized battery pack, and most people usually only need their packs charged adequately for a Nissan Leaf sized commute, we can imagine that at any given time, half of all car owners might make half of the capacity of their batteries available to the electric utility, with the other half being folks who are about to go on a long trip, on vacation, currently commuting rather than plugged into a charging station, not interested in sharing their battery, etc. This would give us about 13kwh of storage capacity per capita, or enough battery capacity online at any given time to cover 8-9 hours of the grid's energy use. That's almost enough that if we had cheap enough solar, we could contemplate using solar panels during the day to charge batteries that would carry the grid through the night (although in practice, we probably want wind in the mix, too).

This does fail to account for the possibility of increasing the share of energy use that goes through the grid. I believe that currently about 1/4 of the US energy use goes through the grid; switching to battery cars will obviously increase this, but hopefully the vast majority of charging can be scheduled at the convenience of the generation and transmission line infrastructure. But we might also someday find that wind farms (which should have high output at times of high wind chill) might be a better way to heat homes than natural gas, etc.

This could work out, but in reality with an electric car the battery is a bunch of weight, even with NiMH, and you don't want to carry around a big one all the time but not get the range from it.

It's a delicate trade off as far as I see. Batteries are not cost effective grid storage on their own (or utilities would install them) but might be when the battery has this other use in the car. But if you suck out the battery's big value, it may not be a good deal. To do this math we need to figure out the real cost of battery discharge.

Also consider that right now, we have the mining and manufacturing infrastructure to end up with something on the order of one pound of lithium ion batteries per person in developed countries (where the one pound is a very rough guess at the weight of laptop, cellphone, etc batteries). If everyone has a Tesla Roadster equivalent, that's about a three order of magnitude increase in production volume. Historically, when you increase manufacturing volumes by three orders of magnitude, that drives prices down, which might start to make this technology affordable directly to the utilities.

Still, if we can get people to install batteries in their garage as a side effect of them buying a new car, would it really make sense for a utility to instead spend time negotiating for rights to property on which to install the batteries in a highly localized fashion, followed by paying people to install them? (You could theorize that the dedicated batteries might be more reliable, but then look at how Google has built an entire data center in an area where no air conditioning works fine most of the year, and they simply planned to shut the entire data center down the few days of the year when it's too hot to run without air conditioning. If Google can build a data center that is unusable for several days of the year, an electric utility ought to be able to cope with intermittent availability of any particular battery.)

Utility owned batteries next to wind farms might make a lot of sense for getting better usage of the transmission lines connecting the wind farms to civilization. (And I keep wondering if lead acid batteries recycled from scrapped gasoline cars will ever be viable for this, or if lithium ion batteries will someday be produced in such vast quantities that the price per kilowatt hour will someday be lower for high volume lithium ion batteries than for low volume lead acid batteries.)

I'd like to see cars come with some default setting of perhaps no more than 10% discharge at a time, and some limited number of such discharge cycles throughout the year (maybe 20-30), and some integration with when the owner expects to need the full capacity to inhibit discharging, and then let the free market and owners' judgment figure out what the optimal settings are, also allowing a car owner to set a minimum price on battery discharge (perhaps coupled with some maximum predicted price to recharge the battery after the discharging), and select more discharging than default, or turn off discharging entirely. Maybe it will turn out that people need to leave the battery set to rare discharge to preserve battery life in an economical fashion, or maybe people will find that it makes sense to sell lots more power back to the electric company. And maybe automakers will find they have an incentive to tweak the battery formulations to enable car buyers to recover more money from the electric utility through discharging to the grid more often.

I'm not sure what NiMH has to do with any of this, as I thought it was heavier per kwh than lithium ion, and the Tesla and Nissan plug in designs all rely on lithium ion batteries AFAIK.

I don't see that as much of a win. Batteries are just a really expensive means of energy storage. Yes, they are local to the power load but the transmission losses are only in the range of 7%, and the battery is less efficient than that. And then there's the need for high power inverters, which may come down in price but also have inefficiencies and there are significant costs in both gear and in permits/inspection for doing a grid tie that feeds power back to the grid. I would hope we could cut that price but I don't see a win here. The only win is that with a car, you have the batteries already for another reason and they are already connected.

I think this is something you could do for like the true emergency peak, like during the California rolling blackouts, something that happens half a dozen times a year, not an everyday thing.

If we ever get sufficiently cheap solar, we may find that the 3 PM - 4 PM peak air conditioning loads will be very nicely covered by the peak solar panel output. Especially if we can distribute the solar panels to lots of people's homes so that we don't need to build a lot of transmission line infrastructure to make this work.

By dollar amount, it's true that the biggest tax incentive is the $7500 federal tax credit; the biggest state tax credit I've seen is $5000.

However, if you're looking at the cost of a Nissan Leaf plus a 30A, 240V home charger vs a car with a gasoline engine and nothing more than a lead acid starting battery, and the projected energy costs over time, I think it turns out that the extra $5000 state tax credit tips the scales towards the Leaf being cheaper for a Californian who can't bring themself to consider a used car, and who can put up with the range restrictions of the Leaf, whereas with no state tax incentive, I think the economy gasoline car can be expected to be cheaper by a bit.

Tennessee is 61% coal and has a $2500 credit, and Georgia is 64% coal and has a $5000 credit, so the state credits may not be as negatively correlated with coal as I had initially hoped.

I'd be happy to see coal phased out, too.

I'm wondering what is going to happen with the long term cost of wind power off the Atlantic coast. The Cape Wind and Deepwater Wind projects that have been proposed in New England are somewhere vaguely in the ballpark of double the cost per kilowatt hour of average grid generation. But those are the costs for the first such wind farms off the Atlantic coast of the US, where there is uncertainty about the federal leasing/permitting process, and there are various other potential startup costs. What happens to the price when we build the 50th or 100th project of this scale? Will wind power end up cheaper than coal?

You are all over the place. Many of your numbers are correct and well applied however you have some gaping gaping mistakes. The latest EPA data I suggest we burn 320,000,000 gallons of gasoline in the United States a year that is a big difference from your 140 6 billion.The only way to make up this conversion is to build electric plants out of gas to supply this electricity. Using your incorrect number of 146,000,000,000 gallons of gasoline it would require 2000 electric plants of 1000 MW each. That gas can come either from Russia the number one reserved of gas in the world or a radius of 300 miles around Pittsburgh Pennsylvania the second largest source of gas in the world. These plants let’s assume are built on the oceans ias only 1/3 of the energy is converted to electricity. It takes about 100,000,000 miles of 36 inch gas pipeline to supply these plants with the gas to fuel the electric cars that now use this nonexistent product. We kicked at 1:336 inch pipe line across the Appalachian trail they just gave up for several reasons. Electric cars or an absolute joke and if we ever develop excess electric capacity if you’re 20% 8 AM it will be a true miracle


It seems to me that we should compare the number of kWh that an electric generator could generate from a gallon of gasoline. I know that wouldn't make sense to get a number from a small portable home generator, but I know there are much bigger diesel generators that we could at least approximate with.

Then we could compare the cost of that energy with the cost of the electricity from a locality.

Randy -- oramilookingatthisallwrong?

What I concluded in looking at this is you want to ask "why is somebody comparing the two?" And there are many answers to that question. I think the approach you describe best fits the DoE appoach, which is they look at the total energy released from the various fuels (coal, gas, nuke) to make the electricity in today's real plants, and compare that to the total energy released in a gallon of gasoline. There are no big gasoline power plants, though there are some oil ones.

But the other motivations are also valid, except I think the perfect conversion one and the fuel factor. People really do want to know how much the energy will cost to go a mile. They do want to know which one will pollute more, and in particular right now they are keen on which one will cause more GHG.

I think that the right answer would be a mix of those 3 factors, as most buyers seem to care about all of them. That requires more study of the non-GHG pollutants which was more popular in the past and I should be able to find more solidly with a bit of research.

Many people wonder about the very best power plant, which in fossil fuels would be a modern natural gas plant getting a bit over 50% of the energy out as electricity, if we could also get rid of the leaking. But there aren't that many of them so that's a goal, not a practical consideration for a car today.

This was largely his "Pickens Plan" and he's spent a lot of his money promoting it. Not to be green, but to be domestic.

Natural gas is cheaper than gasoline, perhaps half the cost, and that's why a lot of fleets run on it. However, it's a lot harder to store and fuel with and it requires a bigger tank. Now if you compare it to electric cars with big batteries it may not be quite as bad.

The big question in many cases is "If I drive an electric car, will they burn more coal because of it?" In some states the answer is clearly yes, in others clearly no. In the mixed-case states, it is probably yes because coal is used for base load when you charge at night, and it's cheap. When there is nuclear, that gets used more for base load.

I keep wondering when the government (various!) will start noticing that their gas tax revenues are dropping and will simply start adding them to kilowatt charges for electricity being used for transportation.

There are various jurisdictions where you get fined if you make your own fuel (e.g. alcohol or diesel)and use it without paying the appropriate taxes.

Most of the current comparisons seem to be cost of electricity without taxes to cost of gas with taxes.

I suspect that electric cars will not get their electricity taxed for some time. Right now the reverse is true, they are subsidized. When they get to be perhaps 30% of cars it might change.

Given that fuel taxes in the US are expressed in cents per gallon, and legislators haven't been able to adjust them to keep up with inflation in many years, my expectation is that the switch to battery cars is going to a be process that phases out energy taxes on driving, for better or worse.

In that fuel taxes are probably basically regressive, this may not be entirely terrible.

I don't know about other states, but here in Texas you can choose your own electricity production company and billing plan, and most of the big providers have plans for pure renewable power. Now according to the laws of quantum mechanics all electrons are totally identical and it's impossible to tell whether any particular electron feeding into your car was pushed by a turbine generator spun by coal-fired steam or one spun by solar-heated steam or was pushed by a generator driven directly by wind. So the power company simply makes sure that for every kWh of power you use, they buy the same number of kWh from wind farms and other renewable sources. If you drive an EV or PHEV, you can feel comfortable knowing that your driving represents that many tons of CO2 that hasn't been put into the air. A gasoline-charged hybrid is more efficient, to be sure, but a 28 mpg Toyota Highlander Hybrid is still going to dump 20% more of everything into the air than a 34 mpg Honda Civic even though the Civic runs on gas 100% of the time with no electric assist ever.

I note that in the article (though I only added it a few days before your comment.) In the 3 states that still let you choose your power source, you can (and should) buy a greener one.

Brad, your commentaries (that I have read so far) are quite interesting and informative. If you are interested in information that you may not be aware of, and may have even in part dismissed when you ran across it (as many do) due to the context it may have been embedded in or whatnot, take a look at this: . This is an effort to at least point out where to find ideas and information for potential productive approaches to long-standing problems in energy and many areas of technology and science. Sometimes one can make assumptions without getting the entire picture of something. Identifying and questioning those assumptions is the first step. Creative thinkers and investigators such as yourself can help save this planet!

For those who are looking to be 100% off grid but are still connected.. you can cycle your powerwall(s) daily. This will store the solar energy before the meter and you can draw from the powerwall battery in the evening. Even the largest Tesla EV battery (100 kWh) can be fully charged from the sun without interacting with the utility grid.

That's OK, because as long as you are tied to the grid then any extra power (ie. when the batteries are not low) goes to the grid to offset dirty power.

Depending where you are it may not make economic sense. Solar electricity is valuable, especially from 2pm to 7pm, because that is the time of peak demand on the grid. If you get a variable price, that is the time to sell it, not store it. Powerwalls work when you store power when it's cheap, and pull it out when it's expensive. Or when the power is out.

I travel 650 miles to my cabin and it takes about 10 hrs. If I buy buy a model 3 Tesla I need 3.2 charges. this adds at least 3 hrs .That is my hang up the electric cars are fine for for city driving.

While many don't have a problem with the stops, where do you get 3 hours? Try putting your trip into I probably will underestimate the charging a bit, but its estimate is in the range of 1 hour 15 minutes not 3 hours, for a trip of 650 miles.

Now I personally would not want to do a 650 mile trip without at least one and probably two meal breaks, and a few other stretch and pee breaks, and probably a shopping break when approaching the cabin to get the groceries etc. for my visit. This will easily take more than an hour. If so, the charging takes close to zero extra time.

However, it does involve some compromise, in that today you must eat and shop near some superchargers. This is always possible but can limit your food choices and what store you get your groceries at. As time moves forward, the choices will expand as chargers go into more places, so it won't seem like a big compromise at all.

Brad, Wonderful article. I want to say how impressed I was to read your motivation to research this subject and the preconceptions you had at that time. Yet, you remained objective in evaluating and reporting and considered the facts.
I also want to congratulate you on maintaining your page over this long period from the initial article written in 2011! Keep it up.
I will be reading more of your blogs going forward and predict I will continue to be impressed. Thank you.

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