Electricity vs Automotive CO2 Levels

[Pangloss]

I'm having an argument with a friend that I was hoping to get some scientifically-reasoned help on. Looking strictly at US domestic CO2 production for the sake of argument, I ask a hypothetical question: What would the cumulative effect on CO2 production be if all cars were immediately replaced with plug-in electrics?

 

This is a complex question and I'm hoping for an answer that takes into consideration increased electrical production and the percentage of that production that would have to come from current "dirty" coal-fired plants.

 

What I don't know is how much increased electrical production would be required. I've heard that the increase could come "within current capacity", so long as the cars were mostly charged overnight, which suggests that the net effect would be relatively minor. But I can't prove it.

 

Can anyone help me out with this?

[swansont]

I thought we've discussed this before. The closest I can find is http://www.scienceforums.net/forum/showthread.php?p=353665 in posts 14 and 15, which gives worldwide figures showing that production capacity worldwide is about 2x the average production, because of peak demand issues. (And the link there no longer works.)

 

add:

 

This table shows that coal produces about 50% of the US electricity. Coal and nuclear fulfill most of the base demand. AFAIK peaks are met by hydro storage, and additional hydro and natural gas (meaning they are normally running at less than 100%) and you'll notice that natural gas is ~3x total hydro (hydro storage is a negative number because it takes more energy to store it than you get back out, so that represents the losses. If we assume 90% efficiency, that represents 0.17 Billion kWhr/day, or 1.5% of total capacity, and, of course, can't be sustained and also represents a drain on the nighttime supply)

 

One question becomes can your run hydro at a higher capacity during off-peak hours and I think the answer to that is "no," if you are relying on the water being there during peak demand. So it depends on how much you throttle back your nuclear and coal at night, and I don't know the answer to that, but coal produces 2.5x more than nuclear on average. Any additional off-peak production you'd need, using current equipment, would almost certainly be comprised mostly by natural gas turbines.

[Pangloss]

Isn't it a bit of a stretch to assume that non-peak power production, which likely already includes coal in some percentage, can be ramped up without increasing the amount of coal consumed during those times?

 

I'm assuming current production methods (stuff already installed) -- I realize more capacity could be added using alternative sources, such as wind, solar, nuclear, hydro, etc. The reason I'm restricting the query to current capacity is to make the argument with only one variable in order to judge the value of the move in the current energy situation.

 

In short, if the night-time recharging of vehicles can't be absorbed by non-CO2-emitting generating capacity, and rather the ratio of emitting capacity is the same under the increased demand, then wouldn't we actually be making the situation WORSE by moving everyone to plug-ins?

 

This source from the EPA says that vehicular CO2 is around 20 pounds/gallon (near the bottom of the page). This source (warning: PDF) from the DOT says the average MPG is in the neighborhood of 24 (the EPA says it's lower here, but it's close enough once you divide by pounds per gallon.

 

So vehicles produce around 1 pound of CO2 per mile, if that's right. Now the DOE says (here) that we produce something like 1.35 pounds per kilowatt hour, which is a combination of emitting and non-emitting sources in current average ratios. So even if we assume 100% efficiency in the transmission and consumption of that electricity, isn't it already worse than what we're getting from vehicles?

 

I don't know how many miles a plug-in gets per kilwatt hour. But if it's one mile of travel per kilowatt hour of energy, then it looks kinda grim for electricity.

 

I guess I need to figure how how far an electrical vehicle can travel on a kilowatt hour.

[tvp45]

Isn't it a bit of a stretch to assume that non-peak power production, which likely already includes coal in some percentage, can be ramped up without increasing the amount of coal consumed during those times?

 

I'm assuming current production methods (stuff already installed) -- I realize more capacity could be added using alternative sources, such as wind, solar, nuclear, hydro, etc. The reason I'm restricting the query to current capacity is to make the argument with only one variable in order to judge the value of the move in the current energy situation.

 

In short, if the night-time recharging of vehicles can't be absorbed by non-CO2-emitting generating capacity, and rather the ratio of emitting capacity is the same under the increased demand, then wouldn't we actually be making the situation WORSE by moving everyone to plug-ins?

 

This source from the EPA says that vehicular CO2 is around 20 pounds/gallon (near the bottom of the page). This source (warning: PDF) from the DOT says the average MPG is in the neighborhood of 24 (the EPA says it's lower here, but it's close enough once you divide by pounds per gallon.

 

So vehicles produce around 1 pound of CO2 per mile, if that's right. Now the DOE says (here) that we produce something like 1.35 pounds per kilowatt hour, which is a combination of emitting and non-emitting sources in current average ratios. So even if we assume 100% efficiency in the transmission and consumption of that electricity, isn't it already worse than what we're getting from vehicles?

 

I don't know how many miles a plug-in gets per kilwatt hour. But if it's one mile of travel per kilowatt hour of energy, then it looks kinda grim for electricity.

 

I guess I need to figure how how far an electrical vehicle can travel on a kilowatt hour.

 

I've spent a fair number of nights sitting in coal fired power plants, measuring flue gases as the operators ramped up for peak power. I cannot say whether the fuel consumption is perfectly linear, but I can say that the ramp-up is done by increasing the coal flow to the burners and that the pollution percentages stay approximately stable before and after. Now, coal-fired plants have a several hour hysteresis and some of that heat may indeed be lost in the process, so there may be an efficiency gain by keeping peak power around the clock. There is almost nothing to be gained from gas or oil fired furnaces. Nuclear plants should give a huge increase.

[swansont]

Electric vehicles seem to get at least 4 miles per kWh; how much more depends on the type of car and the speed. So that's 6 kWh to get the equivalent of an average car, or 8.1 lbs of CO2. And at current prices, that's somewhere around 60 cents' worth of electricity. You have to get ~60 mpg for break-even on the CO2.

 

http://www.ev1.org/msg/11.htm

 

I think the problem is behavioral, as the batteries currently available limit you to 100-150 miles driving range, and a "fillup" will take longer than a few minutes, so a long trip will take longer. Convince people that it's worth the extra time and hassle. $4 a gallon should help with that.

[iNow]

We might consider making parallel improvements in both load density and size of batteries, so more higher efficiency batteries could be used to power the car (thus extending range).

[Pangloss]

Swansont, check the math against the sources I posted before, which are government statistics rather than some guy's pro-EV web site. They seem to suggest something more like 1.35 miles per pound of CO2 versus cars at 1.0. And actually when you say 8.1 pounds of CO2 for 6kwH you're saying over 1.0 pounds per mile -- a disadvantage for cars.

 

In other words, a net increase in CO2 if we switched everyone over today. Of a whopping 20-35%.

 

Ouch.

[swansont]

No, check your numbers again.

 

I saw the same numbers on several sites, 4-7 miles per kWh. So 24 miles is 6 kWh, and at 1.35 lbs per kWh, that's 8.1 lbs vs a gallon of gas at 20 lbs. 8.1 lbs for 24 miles is a third of a pound per mile, or three miles per pound of CO2.

 

http://baltimorechronicle.com/2005/083005Korthof.shtml

http://answers.yahoo.com/question/index?qid=20070418082407AAIBIx2

 

Electric motors are more efficient, about 80-90% vs ~30% for internal combustion engines. And you have regenerative braking for electric vehicles. So this result shouldn't be too surprising.

[Pangloss]

Man I'm trying but I'm getting lost in all these variables and conversions. But ok, your calculation suggests we could immediately cut domestic CO2 production by 67% by immediately switching everyone to EVs (which was the original claim I made to my friend). But is there really enough certainty in the data here for me to make a claim like that? It seems like there's enough here to suggest an improvement but not necessarily a major one.

 

What do you think?

[swansont]

I think you have to recognize that the 1.35 lbs of CO2 per kWh counts nuclear and other green sources, so added production would probably raise that number initially. But I think a ~50% drop in CO2 emissions from autos counts as a major improvement.

[Rev Blair]

There's also the green energy you buy from Canada. Manitoba, Quebec, and BC provide a lot of your energy from hydro dams. They reduce output during off-peak hours, but can increase it with no additional emission should there be a place to send it.

 

A simple decision to use the lowest emissions services first, then bring the dirtier sources on-line as needed would reduce emissions further.

 

Then there's the matter of all cars not needing full recharging every night. You may only have to plug in for an hour, depending how far you travelled the previous day.

 

Another variable is weather. Currently we heat our vehicles with waste heat from the engine...it costs us nothing. Electric heat is generally produced by running current through a resistant wire, which sucks a lot of energy.

 

Batteries also don't work very well in cold weather, so there will be some loss there.

 

I think electric vehicles are part of a larger solution, and I think that they are leaner than gasoline vehicles, but I've yet to see anything that takes all of the variables into account, especially when it comes to regional variations.

[Pangloss]

I think you have to recognize that the 1.35 lbs of CO2 per kWh counts nuclear and other green sources, so added production would probably raise that number initially. But I think a ~50% drop in CO2 emissions from autos counts as a major improvement.

 

That was my take on it too, but the numbers don't really seem reliable enough for definitive statements one way or another. It's such an apples-and-oranges kind of scenario and the variables are so large that even a slight skew here or there can produce a completely opposing conclusion.

 

I guess a more detailed approach is probably needed, but I assume there are people out there who study this sort of thing carefully and have more experience with the numbers. It would be useful if there were some sort of universal measurement standard or conversion technique.