Plug-in Hybrid Cars: Chart of CO2 Emissions Ranked by Power Source
by Michael Graham Richard, Gatineau, Canada on 04.15.08
The chart on the left shows CO2 emissions by gas-electric plug-in hybrids depending on the electricity source. As you can see, plug-ins beat the conventional gasoline-powered vehicle at the top in all situations, but the comparison with a regular hybrid vehicle is more complex. Depending on the power source, it can go from slightly worse than the hybrid to about twice as good (and three times as good as the conventional car).
Not surprisingly, coal without carbon capture is the worst power source, and even "advanced coal burning" isn't much better. And as the source of 43% of U.S. electricity, it must be taken seriously.
Two Reasons for Hope: Night Charging & Other Power Sources
A study on plug-in hybrids by the Oak Ridge National Laboratory shows that if charged at night, off peak, the vehicles might not put much additional strain on the grid. That's because coal plants cannot be shut down and restarted rapidly, so they generally don't stop producing at night. So while it is true that a plug-in hybrid charged by coal-generated electricity would generate more CO2, the alternative might be to burn burn that coal anyway and get zero miles out of it. Plug-ins could actually make the grid more efficient by putting more of the electricity generated to productive use.
The second reason is that if coal represents 43% of production in the U.S., that means that there's 57% of things that aren't as bad as coal. A lot of it is natural gas, nuclear, and hydro. Wind power, solar and geothermal still represent a small fraction of the total, but they are the fastest-growing energy sector.
This means that plug-ins not charged with coal power would still be doing quite a bit better than regular hybrids, especially if you drive less than the electric range between charges, and as time goes on more of the grid should get power from clean sources. There is also a benefit to air quality when you move the emissions from millions of tailpipes that are close to people's lungs to a few centralized power plants. Ideally all energy would come from renewables, but even in the meantime, we might get clean air benefits.
Outside the U.S.
It also means that the environmental performance of plug-in hybrids will vary from country to country, and even from region to region. You can find out about where your power comes from by contacting your local utility, and in many places even if your local grid is dirty, you can switch to green power.
Plug-in Hybrids Will Keep Getting Better
Another question we might ask ourselves is: What model of plug-in did they base the chart on? Chances are, as time goes on and as oil prices rise, batteries and ultracapacitors will improve, more advanced light materials will be used (such as carbon fiber), there might be breakthroughs in nanotechnologies, aerodynamics will improve, etc. So future plug-in hybrids might be quite a bit more efficient than the one this chart is based on.
And for those worried about all these battery packs from plug-in hybrids, know that they can be made from recyclable and non-toxic materials.
CO2 storage raises some questions. We're mining carbon in the form of fossil fuels and then combining with atmospheric oxygen trough combustion. Unless we are mining oxygen also, aren't we going to be reducing the atmospheric oxygen levels?
It would be interesting to see a biodiesel powered sedan put into the comparison.
I think a conservative estimate would be that a diesel version of a sedan gets 20% better mpg than the equivalent gasoline version. For example the 2008 E320 Bluetec Mercedes vs. the E350 Gasoline Mercedes.
If we reduce the 452 grams CO2/mile in the chart by 20% we arrive at 362.
The DOE study says using biodiesel reduces net CO2 emissions by 78%. This reduces the 362 value down to 80.
80 grams CO2/mile is almost 50% better than any other option on the chart.
Now if we had a plug-in *diesel*/electric hybrid we'd be even lower than 80.
Jay, the chart above is well to wheel. I'm not sure if the biodiesel study you cite is, or if it is just tailpipe. That might make a pretty big difference.. Especially if we take into account the recent studies on the land use impacts of soybean production.
Algae biodiesel might do well, though.
Yeah, I think the land use issues associated with biodiesel might begin to negate the positives. Algae may be advantageous, but I don't know enough about it to comment.
An excellent and informative chart indeed.
I'd like to get a good resolution copy of the chart but can't find any link to a source for it.
Anybody know where I can get it?
Can't help noticing that coal gasification with CO2 storage looks real good in the chart, and makes coal look like a real good way to go. But as far as I know there are no such practical cost-effective utility-scale installations anywhere and there's reasons to think there may not be any in the next decade or two or longer. Might as well throw fusion power into the chart while you're at it, another nifty save-our-butts technology that's unlikely to deliver the goods anytime soon or ever.
I hate to say it, but look how good nuclear looks relative the best case coal example (which is using unproven CO2 sequestering)
We can't use 100% wind/solar without massive storage capability, so nuclear is starting to look like a real option.
There are lots of great comments about this "study" over at Green Car Congress. In short though, it's pretty worthless.
It's not peer reviewed and based on a faulty model that is also not peer reviewed.
Basically, it's someone's (ill-informed) opinion.
I'm happy to see that not only are we looking at electric cars as our future, we are also looking at the power grid and where our power comes from as a BIG part of making our future green.
As is typical, only a fraction of the picture is presented. The chart ignores the CO2 'tail' that comes from building the hybrid and the heavy-metal batteries required to store the electricity. Factor in the limited lifetime of the batteries and the CO2 required to dispose of or recycle them and the differences between the hybrid and the conventionally powered car disappear. There is no free lunch as they say.
Hybrids only push the CO2 'footprint' further away from the vehicle. At best the footprint is the same size as a conventional vehicle, its probably bigger in the end....
Nice chart. The moral of this story is that technology can only give you options. It doesn't solve your problems for you. Eventually, we have to decide to promote and subsidize one form over another--think about how the US government subsidsized the auto industry with the interstate highways, when they could have chosen trains instead.
And, trystero is right. However, eliminating 10,000 individual CO2 sources and replacing it with 1 big source opens up a lot more options for controlling the emissions. Most of our technology is just not cost effective when mounted on automobiles (like hydrogen fuel cells, etc.). We have a lot more feasible options for controlling powerplant emissions.
What is interesting about this graph that hasn't yet been commented on is the 150g of CO2/mile driven that are the baseline for all plug-in hybrid electric vehicles in the study. If we consider however, moving to a 100% electric vehicle then in theory emissions can be zero if sourced from renewable electricity. Given that most trips are within the range of electric vehicles, why keep the internal combustion engine at all (after all, its heavy). If you want to travel further, then put a small generator on a trailer whenever you're going on holiday.
The basic premise behind advocating charging hybrids at night is faulty. It is true that coal-filed plants aren't quickly able to start up, so they keep operating 24/7, but when load drops off they certainly stop burning as much coal. And if load drops off enough, utilities will shut down a boiler, or even a whole plant. They don't keep generating the same amount of power and throw the excess away. That's nonsense both economically and physically. When load goes down, utilities cut back on power generation in the order of the cost of generating it. This should be obvious. First to get shut off are diesels (if they even have them), then gas-turbine peakers. And on down the line working towards the cheapest fuel, nuclear. By the way, they won't reach nuclear -- load never gets down that far; so nuclear plants stay at 100%. To reiterate, utilities back off coal & other non-renewables in order to keep nuclear plants at 100% power. Rest assured that, even during off-peak (i.e., night), the load you put on the grid to charge your car will come from the next most expensive source, probably coal. It won't ever be coming from solar, wind, or nuclear. These will already be at 100%. Nobody's cutting in another wind generator because somebody plugged their charger in.