Toshi
10 kW
an original post by this author on a favorite topic of mine, electric vehicles. the question that this addresses is whether electric cars are actually better for the environment or whether it's half dozen of one, 6 of another when comparing modern gasoline vehicles and battery-electric vehicles such as the Volt or Aptera.
1) http://www.cleanairnet.org/transport/1754/articles-69297_resource_1.pdf is a great paper from the MIT Energy Lab detailing life cycle energy use and greenhouse gas (GHG) emissions for various car technologies. here's the money shot, so to speak:
2) from the above one might conclude that hybrids are a superior option to battery-electric vehicles since their energy use and GHG emissions are comparableâ€â€with lower uncertainty to bootâ€â€and their cost is lower. indeed, i came to this conclusion myself: a Prius might make more environmental sense than a Volt or a Tesla. but before we conclude this let's take a look at the paper's assumptions.
3) what assumptions underlie the above conclusion, that hybrids have equivalent energy and GHG usage and lower cost than battery-electric vehicles?
the first assumption is of 5.1 cent/kWh offpeak electricity (page 2-12 in the paper). this is more expensive than i currently pay in seattle, 3.76 cents/kWh, but this isn't a big deal. the second assumption is of a mix of 52% coal, 28% natural gas, 10% nuclear, 9% renewables, and 1% petroleum in the generation of this electricity (page 2-11). this is a big deal, and i'll discuss it later. the third assumption is of a conventional vehicle design for electric cars, albeit with a reduced weight and a Cd of 0.22, with tank-to-wheels efficiency of about 60% (table 3.4, page 3-24). the final assumption is of battery technology essentially equivalent to lithium-ion.
from the above we see that electric cars are really efficient from the point that electricity is supplied to the battery onwards through driving the thing. the electric car falls on its face due to inefficiency in the areas of electrical production and distribution. again, note the 52% coal in the power generation mix assumption! in the authors words, from page 3-31:
4) do these assumptions and conclusions change based on vehicle type?
the authors make the assumption that the car of the future will be similar to cars of today, just powered by different means. from page 5-2, "we have arbitrarily assumed that the level of amenities, performance, and interior space will remain similar to today’s fleet average car." this isn't necessarily true, however! in particular, the Aptera 2e is a huge departure from the norm:
- it weighs 1800 lbs as opposed to the 3600+ lbs now common in midsize cars
- its CdA (coefficient of drag * frontal area) of 2.11 ft^2 is absolutely tiny compared to a 2004 Prius's figure of 6.24 ft^2 or a Hummer H2's 26.5 ft^2 (! yeah, insane)
- it is designed to use recycled materials, in its interior, for instance, and its carbon shell would be recycled easier, leading to lower energy inputs both in manufacture and eventual disposal
- it is going to average about 96 Watt-hours of electricity usage per mile driven, as compared to 30 Wh/mile that i use on my much smaller, much slower electric bike or about 250 Wh/mile that plug-in Prius conversions tend to use
what do these bits of tech-jargon mean in the big picture? designs like the Aptera can reduce the energy requirements of a car by a factor of 3 compared to a Prius, which in turn is already about twice as efficient as most cars out on the road. multiply those together and you have a vehicle that's nearly an order of magnitude more efficient than some of the gas guzzlers on the road today. (do note that the Aptera design is powertrain agnostic, and indeed might work very well with a catalyzed, small gasoline or diesel engine, not just with a battery pack and electric motor. it'll be offered as an electric only at first, however.)
5) do these assumptions and conclusions change based on region?
NPR published a nice interactive map of the US power grid here: http://www.npr.org/news/graphics/2009/apr/electric-grid/ . also on this map is a summary of state by state electrical power generation. recall from the MIT Energy Lab paper that the greatest inefficiencies with battery-electric vehicles lies not in the vehicles or batteries themselves but rather in power generation and distribution. local, renewable energy is a solution to this problem.
a few interesting states:
nationwide assumptions from the MIT Energy Lab study discussed above:
52% coal
28% natural gas
10% nuclear
9% renewables
1% petroleum
washington
71% hydro(electric)
10% coal
8% gas
8% nuclear
california
47% gas
20% hydro
18% nuclear
7% geothermal
texas
49% gas
37% coal
10% nuclear
west virginia
98% coal
2% hydro
new york
29% nuclear
22% gas
17% hydro
16% oil
vermont
71% nuclear
21% hydro
7% biomass
as you can see the states are all over the map! at one end you have states such as vermont (99% renewable) and washington (79% renewable with an option for individuals like myself to buy credits for 100% renewable), and at the other you have states such as west virginia (2% renewable) and texas (10% renewable).
6) Cliffs Notes, or what does this all mean?
from parts 1 and 2 we see that a rigorous study demonstrates that hybrids and battery-electric vehicles are roughly comparable in terms of lifecycle energy use and greenhouse gas emissions. from parts 3 and 4 we see that radical designs such as the Aptera can reduce energy use by about 60% compared even to a Prius, which is in turn much more efficient than your garden variety car. finally, from part 6 we see that some states have very low rates of renewable power generation while others are very high even today.
in conclusion: whether or not driving an electric car benefits the environment depends on several factors. the first is whether you choose an efficient vehicleâ€â€an Aptera 2e instead of an electric Hummer H2, for instanceâ€â€and the second is where you choose to live. if you live in west virginia chances are that driving a Prius would be a better proposition than stoking your state's coal-fired powerplants all the brighter. if you live in vermont or washington state, on the other hand, going electric might truly be a green proposition indeed.
1) http://www.cleanairnet.org/transport/1754/articles-69297_resource_1.pdf is a great paper from the MIT Energy Lab detailing life cycle energy use and greenhouse gas (GHG) emissions for various car technologies. here's the money shot, so to speak:
2) from the above one might conclude that hybrids are a superior option to battery-electric vehicles since their energy use and GHG emissions are comparableâ€â€with lower uncertainty to bootâ€â€and their cost is lower. indeed, i came to this conclusion myself: a Prius might make more environmental sense than a Volt or a Tesla. but before we conclude this let's take a look at the paper's assumptions.
3) what assumptions underlie the above conclusion, that hybrids have equivalent energy and GHG usage and lower cost than battery-electric vehicles?
the first assumption is of 5.1 cent/kWh offpeak electricity (page 2-12 in the paper). this is more expensive than i currently pay in seattle, 3.76 cents/kWh, but this isn't a big deal. the second assumption is of a mix of 52% coal, 28% natural gas, 10% nuclear, 9% renewables, and 1% petroleum in the generation of this electricity (page 2-11). this is a big deal, and i'll discuss it later. the third assumption is of a conventional vehicle design for electric cars, albeit with a reduced weight and a Cd of 0.22, with tank-to-wheels efficiency of about 60% (table 3.4, page 3-24). the final assumption is of battery technology essentially equivalent to lithium-ion.
from the above we see that electric cars are really efficient from the point that electricity is supplied to the battery onwards through driving the thing. the electric car falls on its face due to inefficiency in the areas of electrical production and distribution. again, note the 52% coal in the power generation mix assumption! in the authors words, from page 3-31:
4) do these assumptions and conclusions change based on vehicle type?
the authors make the assumption that the car of the future will be similar to cars of today, just powered by different means. from page 5-2, "we have arbitrarily assumed that the level of amenities, performance, and interior space will remain similar to today’s fleet average car." this isn't necessarily true, however! in particular, the Aptera 2e is a huge departure from the norm:
- it weighs 1800 lbs as opposed to the 3600+ lbs now common in midsize cars
- its CdA (coefficient of drag * frontal area) of 2.11 ft^2 is absolutely tiny compared to a 2004 Prius's figure of 6.24 ft^2 or a Hummer H2's 26.5 ft^2 (! yeah, insane)
- it is designed to use recycled materials, in its interior, for instance, and its carbon shell would be recycled easier, leading to lower energy inputs both in manufacture and eventual disposal
- it is going to average about 96 Watt-hours of electricity usage per mile driven, as compared to 30 Wh/mile that i use on my much smaller, much slower electric bike or about 250 Wh/mile that plug-in Prius conversions tend to use
what do these bits of tech-jargon mean in the big picture? designs like the Aptera can reduce the energy requirements of a car by a factor of 3 compared to a Prius, which in turn is already about twice as efficient as most cars out on the road. multiply those together and you have a vehicle that's nearly an order of magnitude more efficient than some of the gas guzzlers on the road today. (do note that the Aptera design is powertrain agnostic, and indeed might work very well with a catalyzed, small gasoline or diesel engine, not just with a battery pack and electric motor. it'll be offered as an electric only at first, however.)
5) do these assumptions and conclusions change based on region?
NPR published a nice interactive map of the US power grid here: http://www.npr.org/news/graphics/2009/apr/electric-grid/ . also on this map is a summary of state by state electrical power generation. recall from the MIT Energy Lab paper that the greatest inefficiencies with battery-electric vehicles lies not in the vehicles or batteries themselves but rather in power generation and distribution. local, renewable energy is a solution to this problem.
a few interesting states:
nationwide assumptions from the MIT Energy Lab study discussed above:
52% coal
28% natural gas
10% nuclear
9% renewables
1% petroleum
washington
71% hydro(electric)
10% coal
8% gas
8% nuclear
california
47% gas
20% hydro
18% nuclear
7% geothermal
texas
49% gas
37% coal
10% nuclear
west virginia
98% coal
2% hydro
new york
29% nuclear
22% gas
17% hydro
16% oil
vermont
71% nuclear
21% hydro
7% biomass
as you can see the states are all over the map! at one end you have states such as vermont (99% renewable) and washington (79% renewable with an option for individuals like myself to buy credits for 100% renewable), and at the other you have states such as west virginia (2% renewable) and texas (10% renewable).
6) Cliffs Notes, or what does this all mean?
from parts 1 and 2 we see that a rigorous study demonstrates that hybrids and battery-electric vehicles are roughly comparable in terms of lifecycle energy use and greenhouse gas emissions. from parts 3 and 4 we see that radical designs such as the Aptera can reduce energy use by about 60% compared even to a Prius, which is in turn much more efficient than your garden variety car. finally, from part 6 we see that some states have very low rates of renewable power generation while others are very high even today.
in conclusion: whether or not driving an electric car benefits the environment depends on several factors. the first is whether you choose an efficient vehicleâ€â€an Aptera 2e instead of an electric Hummer H2, for instanceâ€â€and the second is where you choose to live. if you live in west virginia chances are that driving a Prius would be a better proposition than stoking your state's coal-fired powerplants all the brighter. if you live in vermont or washington state, on the other hand, going electric might truly be a green proposition indeed.
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