so let’s say we have a complete turnover from internal liquid fuel combustion to electric propulsion in cars. all the cars that now stop to refuel with liquid are stopping to plug in and recharge.
the electricity is coming from somewhere. wouldn’t power stations have to use more coal, gas or petroleum product to crank out more KW of power to feed the cars?
so what exactly is the trade off in pollution or CO2 emissions?
Do we gain by switching the production of energy from the roads to the various power stations?
I’ve heard this point cited as one of the reasons why Diesel cars are still more environmentally friendly than Hybrid or electric cars. Your source of power does greatly determine this. Electricity will always, as best I know, trump gasoline engines, simply because, all things being equal, combustion on a large scale will be more efficient than combustion in every single individual car’s engine. The time will come when petroleum has been exhausted, and the electric car will be fueled via nuclear power, making the level of emissions produced lower still.
internal combustion engines convert about 20% of the chemical energy in gasoline into mechanical energy to move the car. The rest is wasted as heat, friction, etc.
Coal plants have about a 40% conversion rate. So you can get more energy per ton of CO2 produced from a coal plant than an internal combustion engine in a car.
Not only that but about 1/3 of grid energy is nonpolluting as far as CO2 goes. About 1/3 is nuclear, hydroelectric or renewable. About 50% is coal (I think) and the rest is natural gas.
So overall it is far more efficient. Even if you are using strictly coal you are still producing only about half the CO2.
Plus sequestering CO2 from a coal fired plant is easier than capturing it from the tailpipes of a million autos. So there is that benefit too.
Consider that a hybrid motor is more CO2 friendly. It is so because the motor runs at a constant, known rate and the engine designers can optimize fuel intake to match that.
Less fuel = Less CO2 output
A centralized power plant has the same advantage in that it’s running at a constant rate. The size of the plant also means that the comparative tolerances are smaller, which drives up efficiency again. If you have a piston that’s 8 feet wide, a tolerance of 1/8" is something that’s nigh perfect when you scale down to a piston that’s 1" across, and of course they go much higher tolerances than that in practice.
Here’s a list of CO2 output per kWh of various centralized power sources:
Coal comes in the range of 960-1050 grams of CO2 release per kWh. In the US, only about 44.9% of fuel comes from coal plants. Averaging power sources, you are looking at about ((1000 * 44.9 + 443 * 23.4 + 66 * 20.3 + 10 * 6.9) / 99.5 = ) 570 grams of CO2 release per kWh.
According to the Wikipedia, the Tesla needs about 11.2 kWh for an average day’s 40 mile drive, or 0.28 kWh per mile. That’s about 160 grams of CO2 emissions back at the central power plants.
The EPA calculates an average MPG for passenger vehicles in the US as 23.9 MPG, or about 0.042 gallons per mile. 1 gallon produces 8,877 grams, so per mile your average car releases 371.4 grams of CO2.
A Tesla is made to be sporty, of course, and it’s the first of a generation without a working second gear. Economy electric cars made to higher standards with proper gearing can almost certainly run more efficiently. But even as is, the Tesla produces about 43% the emissions as your average passenger car.
It’s also worth noting that there’s secondary costs between centralized or distributed power. To get gas to your car, you need to employ a bunch of cars that deliver fuel to all of the various gas stations. With a centralized coal or nuclear power plant, it’s a single straight drive from the refinery to the plant. There is some loss in the power grid, distributing power to your garage or wherever you charge up, but I can’t imagine that it’s more efficient to tug around a few tons of steel to distribute power than by beaming it through copper.
Personal guess? Nuclear is the way of the future, electric cars can probably be at least 85-90% more efficient than the Tesla simply through having the production value that Honda or Toyota can bring, and electric battery density could very well double within the next decade or two which brings down the weight of the car by a fairly significant amount. I wouldn’t be surprised if we could get down to 10% the CO2 output of the modern day gas passenger within the next 20 years, but 30% is probably a safe bet at the max.
While it’s certainly true that depending on region you get more or less CO2 savings, even taking the worst case scenario of unscrubbed coal power, that’s still 294 grams of CO2 output per mile (versus 371.4 for a gas passenger car), presuming that the data on the Wikipedia page is accurate; about 79.2% of the CO2 emissions. At that level, diesel is competitive, and hybrids actually beat it: http://www.justlivegreener.com/greener-transportation/115-top-5-hybrid-cars-for-2010.html
Assuming the values on that page are accurate, a hybrid beats the average savings of the Tesla (though, probably not the savings if you’re driving in a green energy area of the US). Even considering the relative efficiency of a power plant compared to a small internal engine, coal is simply more CO2 producing than gasoline. Though, the Tesla still beats it regardless.
The interactive guide linked to by Mittu is fun, but not nearly as informative as the actual print article from which it was drawn in Scientific American. Basically, it all depends on where you live. If you live in the Northwest US, where 84.3% of the power is generated from natural gas and 15.7% nuclear (I know there is some hydro power from the Hoover dam, but it must be negligible), then a plug-in hybrid will save 20.0% of the carbon emissions and an all-electric vehicle will save 37.2%. By contrast, in the states of IL, MO, IA, WI, and MI, power is generated 24.6% natural gas, but 75.4% coal and, in that case, a plug-in hybrid will create 11.7% more carbon emissions and an all electric car will create 36.0% more. These are the two extremes. Unfortunately, this map is only for the US. In Quebec, 99% of the power is hydro-electric and I am sure the percentages will be much better for electric vehicles.
If you look just at the engines, an internal combustion engine is at the very top end about 25% efficient at turning the potential energy of gasoline into momentum. An electric motor tops out at darn close to (but obviously not quite) 100% efficient in converting electrical energy to momentum under lab conditions.
Once the things are built, your emission figures depend entirely on things like how the power is produced and transmitted.
Add to the points above that in theory electricity can be generated without the emission of any gaseous, solid, or particulate pollution == nothing other than “heat pollution”, by extensive and creative use of nuclear, tidal, geothermal, wind, and other non-combustion electrical generation. While in practice we’re unlikely ever to get there, setting it as a mark to be striven for, with scrubbed coal plants as a relatively-environmentally-friendly balance, might be an effective energy strategy.
There’s one other issue. Currently (sorry) electrical power systems must be built to handle peak load, unless you are Enron and turn plants off during peak to jack up the spot price. So the plants that supply eonugh power to cook dinner or run noon-time air conditioning and light or A/C the malls are idle at night. Creating a market for all that surplus generation capacity at night means added efficiency for the system.
If we factor in the ability to use hydrogen-powered fuel cell cars, then the people with H2 Fuel cells can park and plug in the car at night and sell power back to the grid to charge the electric cars…
Those figures can’t be right… Even if we ignore the Hoover Dam, there’s still plenty of hydroelectric generation in Washington and Oregon themselves (see the Grand Coulee Dam, for instance, which produces over three times more power than the Hoover Dam does). And I don’t think there’s anywhere in the country with more natural gas generation than coal.
Back to the OP, you can also charge cars with, say, wind power. The biggest drawback of windpower currently is that it’s not always on, but if you’re willing to wait a bit to charge your car (if, for instance, you’re charging it at night), then that’s not an issue. And there are other advantages to electric cars besides the environmental ones: It also means greater energy independence. We have to import oil from parts of the world we’d really rather have no business with, but there’s plenty of coal right here in the US.
What about flywheels to store the energy? Are they better than batteries? Although they may not be good to “wind up” your car, think of what would happen in an accident…at least gas is pretty safe. Why cant flywheels be used to store energy?
I believe the Scientific American article was focusing on how the additional electricity needed for electric cars would be generated. Non-fossil fuel plants (nuclear, hydroelectric, wind, solar, etc) tend to have constant output, or at least not easily controllable output. So most of them are already operating at full capacity today. Any additional power needs, such as electric cars, would come from power plants that can easily vary their output, such as natural gas and coal.
I think there is some merit to this argument. Until we have enough renewable energy (or nuclear) power plants to meet non-automotive demand for electricity, each electric car represents additional electricity that needs to be generated from fossil fuel.
First of all, a hydroelectric plant can vary its output a lot more easily than a coal plant can. In fact, in some places they keep the coal plants running at full all the time and pump water back up into the reservoir when there’s a surplus of power. Second, usage varies through the day, and the peak time for recharging cars would be when the other usage is lowest (overnight), so switching to electric cars would actually bring the output closer to constant.
