View Full Version : Are EV cars really green?
L. G. Butts, Ph.D.
01-15-2011, 01:09 PM
I have done no research into this, and have not even really given it that much thought, but off the top of my head it does not seem like EV vehicles would be all that green.
I would think that any positives, such as increased electrical generation efficiency at a fossil fuel fired power plant, or the fact that a certain percentage of the electricity is generated from wind or solar, would be offset by the inherent inefficiencies of electricity distribution and storage. Has anybody figured out what percentage of the electricity needs to be generated using renewable methods to balance out the power lost in the transmission and battery storage? What is the efficiency of an internal combustion engine compared operating on processed oil (i.e. gasoline, but i am sure we are losing efficiency making the conversion) to an oil fired power plant and transmission of 100 miles or so? How about diesels, I believe they are much higher efficiency (they get 50-70 miles to gallon in many cases), and less energy goes into processing the fuel, how does it compare?
What is the greenest vehicle for 2-4 people to ride around in?
01-15-2011, 01:18 PM
If no one beats me to it I'll be back later (out of time to play now) to post some links, but even assuming coal fired generation and some distribution losses, EVs are just so much less inefficient than ICEs that they are quite green.
The most green for two? A tandem bicycle. For four? Two tandems.
01-15-2011, 01:24 PM
Yes, there are inefficiencies inherent to electrical distribution and storage, but there are also inefficiencies in the distribution and storage of any kind of energy. Do you really think that high-voltage transmission lines that don't need to move anything but electrons (and mostly, not even them) are less efficient than trucking tanks around to gas stations? When you look at the whole system, electric vehicles work out to be a little more efficient than even hybrids, and electrics and hybrids both have some key advantages over non-hybrid gas-burners.
Plus, of course, even though most electricity right now (in the US, at least) is still produced by burning fossil fuels, not all of it is, and there's still plenty of room for improvement there.
Now, this doesn't necessarily mean that electric vehicles are the greenest vehicles out there, but that will depend on what you need the vehicle for. In a lot of situation, the greenest vehicle for 2-4 people to ride will be 2-4 bicycles. Even if you have an all-electric car and live in an area that's mostly powered by hydro, you'd still be better off biking to places within a few miles. Of course, it's probably not practical to bike on a 40 mile commute.
01-15-2011, 01:25 PM
The most green for two? A tandem bicycle. For four? Two tandems. Great minds think alike, apparently.
01-15-2011, 01:30 PM
There have been a LOT of threads on this subject. Here's one from last week: http://boards.straightdope.com/sdmb/showthread.php?t=592331
01-15-2011, 02:24 PM
Here's one study (http://www.greencarcongress.com/2010/08/notter-20100810.html) that attempts to answer your question.
Assumptions included a vehicle about VW Golf sized that "required a total of 17 kWh/100 km" and the average EU electricity generating mix.
A breakeven analysis showed that an ICEV would need to consume less than 3.9 L/100km (60 mpg US) to cause lower CED than a BEV or less than 2.6 L/100km (90 mpg US) to cause a lower EI99 H/A score. Consumptions in this range are achieved by some small and very efficient diesel ICEVs, the authors noted.
This recent report from MIT (http://web.mit.edu/mitei/docs/reports/electrification-transportation-system.pdf) (pdf) also addresses it. The answer really does depend on the generation mix.With the current fuel mix of the US power sector (about half coal, about 30% “carbon-free”), CO2 emissions for HEVs and EVs are similar. ...
... Conventional hybrids reduce CO2 emissions by 33% relative to ICEs.
• This compares to a 66% reduction in CO2 emissions for PHEVs fueled by carbon-free electricity, including nuclear, biomass, and other renewable generation.
• While PHEVs fueled with coal generation (without CCS) have lower CO2 emissions than those from an ICE, they all have higher CO2 emissions than conventional hybrids.
• PHEVs fueled with combined cycle gas generation can reduce emissions by as much as 50% and have lower emissions than ICEs and conventional hybrids. In addition, EVs have the potential to reduce point-source tailpipe emissions, particularly nitrogen oxide (NOx) and particulates.34 This occurs because EV charging at night favors dispatch from larger, more efficient generation units. This could translate into health benefits, reducing associated asthma and other respiratory diseases, especially in urban areas. These benefits, however, could be offset in areas with concentrated coal generation where the higher loads associated with EVs could also increase sulfur oxide (SOx) emissions.35 ...
... Another alternative to petroleum-fueled vehicles is Natural Gas Vehicles (NGVs). ... An NGV does not have comparable efficiency gains relative to electrification via natural gas generation. In general, 1,000 cubic feet (cf) of natural gas, converted to electricity, yields 457 miles in an EV. This same 1,000 cf in an NGV would only have a range of around 224 miles.42
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