# How much would we cut GHGs if we all switched to electric cars?

Assume, hypothetically, that everyone replaced their gas-powered cars with either electric cars, or plug-in hybrids, such that 90% of ordinary passenger driving was electric-powered. Assume further, pessimistically, that all the electricity for these cars came from a 50/50 mix of coal and natural gas power plants. Would we reduce our net GHG emissions, and if so roughly by how much? (bonus points for sources)

Update:

either as a total figure, or as a percentage of driving-related GHGs...

Update 2:

d/dx: can I have a ballpark guess of the GHG reductions? Trying to at least get an order of magnitude here...

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• 8 years ago

Even within the information you give there is potentially a great variation: Where are we replacing the vehicles. If you are thinking of almost anywhere than the US then the gasoline mileage for the cars would be higher. It is with gasoline mileage that we start. For every gallon used in an internal combustion engine about 19.5 pounds of carbon dioxide are produced (about 154 lbs per 1 million btu .) As a vehicle travels further on a gallon the greenhouse gas emissions per mile will be reduced.

Not only does the typical mileage vary per country but so also does the energy mix used to produce electricity. If you are considering France than 80% of the electrical power is generated with nuclear energy. The Northwest and Canada uses a lot of hydro. Australia like the midwest US is over 80% coal. There is probably no place that is 50% coal and 50% natural gas. The US mix is about 40% coal 24% natural gas 20% nuclear with the balance mostly renew ables. Coal is on the decline and is being replaced by natural gas and renew-ables.

But for the sake of calculation we assume 50% coal 50% natural gas for electricity for 90% of vehicles. What are we assuming as the starting point? Market penetration for the EV in the US is now less than 1/2 of 1%. Do we assume 0% If we are going to present any numbers we need a working population. The US has about 200 million vehicles. More? Less? What will we assume as the annual mileage for each vehicle. The US average is about 12500 but some use 15000 miles per year. European average mileage is less. In some places like Manhattan 80% of the people don't even own cars.

Because you are considering the replacement of 90% of present vehicles there are factors that are not normally considered. It takes a great deal of electricity to refine gasoline. There are estimates as high as 6.5kWh/gallon. http://greentransportation.info/how-much-electrici... At this rate the EV can travel further on the energy used to refine a gallon of gasoline than an average petrol car (24mpg) can go using the refined product. The EV would be costing no "new" pollution and we would be avoiding all the pollution of the petrol vehicle and the refinery. Refineries also operate 24/7 so eliminating 90% of them would tend to shift electrical demand away from peak daytime to a more balanced usage.

Another factor that is rarely considered is the inefficiency and pollution caused by coal plants that can not be turned off and can only be turned down slightly to for off peak lower energy usage. Coal must be used to keep the boilers warm at night to avoid boiler damage. Therefore at night when electrical demand is less the more polluting coal plants will be used rather than the less polluting gas fired power plants. Overall electric vehicles charging at night makes the system more efficient than without them but at some increase in pollution.

The refinery + petrol vehicle (85% x 15% = 13% efficiency ) is about 3 x less efficient than a coal plant plus an electric car ( 40% x 90% = 36%) and the difference is even greater with a gas fired plant plus an electric car (60% x 90% = 54%) (average = 45%) This advantage is somewhat taken up by the more polluting aspects of coal ( about 204 lbs of CO2/1million BTU http://www.eia.gov/coal/production/quarterly/co2_a... ) and by the concerns that burning natural gas produces water vapor and mining natural gas introduces methane into the atmosphere (both more potent GHG sources than CO2. Fracking seems to introduce even more methane (primary component of natural gas) into the atmosphere so some attention must be paid to how the energy is mined, drilled, and transported.

Because the calculations tend to become very complex with many assumptions for variables I am suspect of numbers that attempt to prove or disprove the case for electric cars on the basis of some "exact numbers" for pollution issues alone. What we can say with some confidence is that the EV is by itself a zero emission vehicle and will likely involve from 1/3 to 1/2 the overall pollution (including GHG, spilled liquids and solid waste) of petrol vehicles. When we combine the likely-hood of reduced pollution with the increased security and economic benefits the argument for the EV becomes more compelling.

• 8 years ago

A documentary a few year ago "the future of the car" cited a figure of 25% Co2 emissions for an electric vehicle (charged from a coal fired power source) that is a 75% reduction in emissions compared to a size equivalent gasoline powered car.

While coal is a heavy emitter of Co2 this difference is main down to the efficiently of the electric motor where far less energy is wasted, a gasoline engine waste 75% of it's energy just in generated heat.

As far as I can see Paul H and his claim the two produce the same Co2 emissions are complete fiction, possibly why a blog is used as support. d/dx's number are pretty similar to the documentary, of course if a power source other than coal is used the Co2 emission's are decreased even further.

Trying to use figures that factor in the Co2 released in the manufacturing of the car are pretty irrelevant, given that most of both types of vehicle are the same metals and plastics and glass, the battery of the electric will add a little but that is countered by a much smaller engine using far less metal. I have seen deniers try to use similar arguments when talking about manufacturing emissions of wind and solar as they conveniently forget all the steel and concrete that goes into a coal fired power station.

At the end of the day the simple fact is that cost of energy source relates to energy used and it costs a few dollars to charge and electric vehicle and 50-60 to fill an equivalent gasoline vehicle, admittedly electrics have range issues and to cover the same range as the 50-60 dollar fill, you would have to charge the electric 4-5 times that is still a direct cost of ~10-12 dollar compared to 50-60 a few years of commuting would see that saving as many thousands of dollars in the hip pocket.

Add to that saving the fact that electric motors don't need the care gasoline motors do, no regular services every 3-4 months at what is these days a \$100 dollars or more a service, and the long term saving of an electric are pretty obvious.

Given how much deniers go on about taxes and their hip pocket odd that they seem to dislike electric vehicles so much.

Certainly to those who use their vehicle mostly to commute even if you ignore the Co2 problem completely, an electric vehicle is going to be far cheaper and that will sell a lot of vehicles, that is a genie that is out of it's bottle and no amount of negative and incorrect information from the oil industry will put it back now.

• 4 years ago

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• 8 years ago

A study on the topic was done by Manitoba Hydro with some input from Atomic Energy of Canada (AECL). Manitoba generates >97% of its electricity from renewable hydro. Manitoba Hydro is promoting electric cars because we can run all of the vehicles in Manitoba on surplus capacity at the equivalent of \$0.31/L energy equivalent (\$0.28/L before allowing for 10% battery storage loss). For comparison, the local price of gasoline is \$1.10/L today. Manitoba Hydro wants to use the batteries in idle vehicles as energy storage because such storage will enable the utility to operate more efficiently by storing base load capacity for peak load demand. The vehicle owners would be paid. AECL is interested because nuclear reactors provide base load electricity and are not suited to supply peak load. The Hydro study found that electric cars are more efficient even if the electricity is generated with coal because large generating stations have a higher energy conversion efficiency than internal combustion engines, even after battery losses are taken into account.

Edit: RE ballpark figure 20%, but don't hold me to better than +/-5%. My reference works in the same lab complex. I left a phone message to see if he has the paper on hand and may have better numbers later.

Source(s): This is based on a conversation with an AECL scientist in 2008 that was involved in the study. % reduction not given because I don't want to miss quote.
• paul h
Lv 7
8 years ago

According to the link below, the difference would be around 0.0147kg CO2e/mile less with EV's ...a slight reduction although I imagine there's room to play with the numbers a little.

Multiply 0.0147 times total applicable vehicular miles per year and divide into current total emissions figures for gas or diesel cars/trucks.

"Now, lets compare the GHG emissions associated with a PHEV or EV, compared to an HEV or standard gasoline engine vehicle. Using the same assumptions, a PHEV or EV that uses 35 kwh for 100 miles, would produce about 0.2908 kg of CO2e per mile in the Midwest region (using the GHG Protocol's Emissions Standards). This takes into account our region's power plants and the fact that they primarily use natural gas and coal. In comparison to the rest of the country, we are about middle range in terms of emissions produced for electricity. For a standard gasoline vehicle or HEV, the GHG emissions would be 0.3055 kg CO2e per mile. In fact, both vehicles produce approximately the same emissions per mile. Any vehicles that get a gasoline mileage of more than 30.5 mpg would produce the same emissions as a PHEV or EV that gets 35 kwh/100 miles in the Minnesota electric grid region."

http://blogs.mnhs.org/node/97

http://www.renewableenergyworld.com/rea/news/artic...

Transit data ...annual total travel miles for various vehicle modes...up to 2010

http://www.bts.gov/publications/national_transport...

• Anonymous
8 years ago

It depends on where the electricity comes from. If your power comes from coal, buy a small car, and if a diesel engine is available, get one.

The electric car is meant to be used with nuclear power, though it will also work with hydro or geothermal power. If we want to use solar and/or wind power in a big way, we need hydrogen powered cars. Hydrogen can be made whenever the sun shines and/or when the wind blows.

• 8 years ago

I remember Dana saying some time back that current automobile emission account for ~11% of total CO2 emissions. So, probably not a whole lot. It seems to me that the large swaths of land (and subsequent E-cars) powered by coal fire power plants is the bigger problem.

This source states 15% from autos.

http://www.wri.org/publication/content/8468

• 8 years ago

None. If anything the electric car uses power so inefficiently it creates a bigger carbon footprint than a regular car, if you look at it from the power plant to the final usage. Then when the battery goes there is the added problem of disposal. Plus when they crash and burn it only saves funeral costs since it automatically cremates upon impact, but this action creates a lot of GHGs.

• Trevor
Lv 7
8 years ago

The transport sector as a whole contributes 13.5% of all greenhouse gas emissions when measured as a carbon dioxide equivalence (CO2e); in respect of CO2 alone then it’s 17.5%.

This figure of 13.5% / 17.5% can be broken down as:

Road: 9.9% as CO2e / 12.9% of CO2

Air: 1.6% as CO2e / 2.1% of CO2

Rail: 1.4% as CO2e / 1.8% of CO2

Sea: 0.9% as CO2e / 1.2% of CO2

The figure for road transport can be divided almost exactly in half – cars being responsible for half of emissions (4.95% as CO2e / 6.45% of CO2) and commercial vehicles the other half.

1 US gallon of gas = 36.6kWh

1 UK gallon of petrol = 44.0kWh

1 US gallon of diesel = 40.7kWh

1 UK gallon of diesel = 48.9kWh

Conversions from: http://www.convertunits.com/from/gallon/to/kilowat...

Depending just how electricity is generated determines how much CO2 is produced. From coal fired power stations it’s 1.05kg / 2.3 pounds per kWh, from gas fired ones it’s 0.51kg / 1.12 pounds. A 50/50 split would mean 0.78kg / 1.71 lbs per kWh.

The combustion of gasoline produces 3.2 times the mass of CO2 as there is mass of gasoline (it’s typically C8H18 meaning by mass that it’s 87% C and 13% H, atomic weight C = 12 and H = 1, when the C and the H from the C8H18 react with O to make CO2 each C 12 atom becomes a CO2 44 molecule, 44 ÷ 12 x 87% = 3.2)

Combusting 1 US gallon (6.3lbs) = 20.1 lbs of CO2

Combusting 1 UK gallon (3.4kg) = 11.0kg of CO2

Driving 100 miles in a 20mpg car = 5 US gallons = 100.5 lbs of CO2, an electric vehicle would require 183kWh at 1.71 lbs per kWh = 313 lbs of CO2.

Driving 100 miles in a 40 mpg car = 2½ UK gallons = 27.5 kg of CO2, an electric vehicle would require 110kWh at 0.68kg per kWh = 85.8 kg of CO2.

Switching to electrically powered vehicles that rely on electricity generated equally from coal and gas fired power stations increases carbon emissions by about 212%. What this doesn’t take into account is the difference in efficiency between electrically powered and gas powered vehicles, if someone can supply these figures I can do the rest of the calculations.

However, unless the electric vehicle is 3 times as efficient per Joule, then the conventional gasoline vehicle is going to be the less carbon intensive option.

The solution would be to source the electricity for the vehicles from alternative energy sources. If you did that then CO2 per kWh could be as little as 0.013kg, in which case the US vehicle would see emissions drop from 313 pounds to 5 pounds and the UK vehicle drop from 85.8kg to 1.43kg.

With your 50/50 coal/gas split and a 90% switch of cars to electric power, then CO2 emissions increase by 180%. In real terms this is the equivalent of adding an additional 2.7 billion tonnes of CO2 to the atmosphere each year.

If the electricity came from the least polluting sources then the reduction in CO2 emissions annually would be just over 1.5 billion tonnes.

• 8 years ago

None! Going green is currently a joke. To make efficient enough batteries, we create a carbon footprint as large as sticking to fossil fuels. Now figure in the footprint of mining those resources(using fossil fuel) then the source of the energy charging those batteries (80-90 percent fossil) the government subsidizing that worsens the defecit and makes the tax payer poorer, all on a only slightly viable barely efficient crusade. Electric cars have a future but not now.