best mpg electric cars image
pete
Recently there have been announcements by GM's Chevy dept that It's volt receives some 230 mpg and the Nissan also announced that it's Leaf gets 367 mpg. My question is how does one calculate the mpg rating on an electric car... I thought I'd search online to find a conversion from mile per charge to mpg, but haven't found anything...anyone got an answer?
Answer
GM and then Nissan used the EPA's draft method for calculating an mpg rating from an electric car.
It's a difficult situation, because people are used to seeing a car's efficiency in mpg, but obviously that's not applicable to a car when it's not using gasoline. So what the EPA is doing is figuring out a conversion to translate the amount of energy used by electric cars into an equivalent mpg rating. But they haven't finalized the conversion yet. All they have at this point is a draft, and GM took the draft method, calculated a value for the Volt, and made a big deal about it. Which is kind of lame. Then Nissan one-upped them by using the same calculation for their LEAF.
GM and then Nissan used the EPA's draft method for calculating an mpg rating from an electric car.
It's a difficult situation, because people are used to seeing a car's efficiency in mpg, but obviously that's not applicable to a car when it's not using gasoline. So what the EPA is doing is figuring out a conversion to translate the amount of energy used by electric cars into an equivalent mpg rating. But they haven't finalized the conversion yet. All they have at this point is a draft, and GM took the draft method, calculated a value for the Volt, and made a big deal about it. Which is kind of lame. Then Nissan one-upped them by using the same calculation for their LEAF.
How environmentally friendly is it currently to charge an electric car?
Jeff P
We all know that there is a tremendous benefit to driving a zero-emissions electric vehicle, but that electric charge still comes from a coal fired power plant, in most places.
Can anyone steer me towards any info that shows that, even with the current 20th century methods of mass producing electricity, charging and driving electric cars is more environmentally friendly than normal high mpg gasoline burning cars?
Thanks!
Answer
Electric motors & batteries are much more efficient than combustion engines. Current engines are about 12-20% efficient, whilst electric motors can be 90%+ efficient.
From then it depends on how efficient your power station, grid and batteries are. The latest Economist quotes, per kWh, a combustion engine can drive 1.5-2.5km, a diesel hybrid 3.2km and an electric car up to 6.3km.
Anyhow, the Chevrolet Volt claims to drive 64km on a charge of 8.8kWh:
http://en.wikipedia.org/wiki/Chevrolet_Volt
Or about 0.14kWh/km.
CO2 emissions from a coal power station are somewhere between 900-1300g/kWh. Assuming a relatively new power station it's about 900g:
http://en.wikipedia.org/wiki/Carbon_footprint#Carbon_footprint_for_various_types_of_electricity_production
So a km driven in the Volt on coal powered electricity is just under 125g CO2.
A similar sized car, the UK's Ford Focus Zetex, gets 155g CO2/km. Small cars and hybrids get lower, though.
The UK grid electricity average is about 430g/kWh and in the US it's under 700g. So a Volt in the UK currently gets 60g/km, lower than any marketed petrol or diesel car. In the US it's under 95g.
In France (mostly nuclear) it's something like 15g/km, over 90% lower than the Focus.
CO2 emissions from electricity in many developed nations will probably fall too because of efficiency and global warming concerns.
The UK is planning 30% renewable electricity and a new generation of nuclear power stations, and coal power stations can't be built without capturing part of their carbon.
Electric motors & batteries are much more efficient than combustion engines. Current engines are about 12-20% efficient, whilst electric motors can be 90%+ efficient.
From then it depends on how efficient your power station, grid and batteries are. The latest Economist quotes, per kWh, a combustion engine can drive 1.5-2.5km, a diesel hybrid 3.2km and an electric car up to 6.3km.
Anyhow, the Chevrolet Volt claims to drive 64km on a charge of 8.8kWh:
http://en.wikipedia.org/wiki/Chevrolet_Volt
Or about 0.14kWh/km.
CO2 emissions from a coal power station are somewhere between 900-1300g/kWh. Assuming a relatively new power station it's about 900g:
http://en.wikipedia.org/wiki/Carbon_footprint#Carbon_footprint_for_various_types_of_electricity_production
So a km driven in the Volt on coal powered electricity is just under 125g CO2.
A similar sized car, the UK's Ford Focus Zetex, gets 155g CO2/km. Small cars and hybrids get lower, though.
The UK grid electricity average is about 430g/kWh and in the US it's under 700g. So a Volt in the UK currently gets 60g/km, lower than any marketed petrol or diesel car. In the US it's under 95g.
In France (mostly nuclear) it's something like 15g/km, over 90% lower than the Focus.
CO2 emissions from electricity in many developed nations will probably fall too because of efficiency and global warming concerns.
The UK is planning 30% renewable electricity and a new generation of nuclear power stations, and coal power stations can't be built without capturing part of their carbon.
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Title Post: How do you measure the mpg on an electric motor?
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