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For simplicity, I will assume that the manufacture of a Prius is essentially the same process as that of a non-hybrid ICE, plus the extra environmental impact required for the hybrid components (battery, electric motor).

Can anyone tell me the amount of carbon emissions attributable specifically to the manufacture of the hybrid components?

I can then calculate how many gallons of gasoline would need to be burned to emit the same amount of carbon as is involved in the manufacture. It then becomes simple to calculate what I really want to know, which is the breakeven point at which the Prius becomes a net positive from a carbon perspective compared to whatever other car. This breakeven point will, of course, vary a bit depending on the MPG of the other car.

I see from some Googling that there is a good deal of information (and misinformation) related to this, although I have yet to find quite the concise answer I'm searching for. I also know that measuring just carbon emissions oversimplifies things a little, as there are other factors at play in the manufacture of the batteries. But it's a reasonably-good starting point.

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    Welcome to Sustainability.SE! There's a similar question here, but not many good answers unfortunately. Also, you may want to edit your question to be about the "what I really want to know" bit, and include your idea of calculating footprint for the hybrid components as a way that might be done. I find the folks here often have better ideas of how to answer my questions than I do! – LShaver Mar 20 '17 at 4:27
  • Thank you for the suggestions. I had seen the discussion you link to and that it suggests looking at LCAs (which is a good idea), but I have not been able to find any of quality. I figured I would focus instead on a single aspect of an LCA (just the carbon) to see if it would be a simpler piece that perhaps someone has info about. – susie derkins Mar 21 '17 at 0:03
  • It is what you want it to be. For example; do you count the gasoline used by the people traveling to work at the manufacturing plant ? – blacksmith37 Mar 26 at 16:05
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Update. In my original answer I inadvertently divided at one point when I should have multiplied -- I found the mistake thanks to comments from Frank and THelper. So here's a new tl;dr:

By mile 4,000 at the latest, total emissions from a hybrid Prius beat emissions from a standard Corolla.


Hybrid electric vehicle (HEV) specific components

The HEV components which are not part of a standard internal combustion engine vehicle (ICEV) include:

  • Electric motors/generators
  • Batteries and/or capacitors
  • Electronics (inverter, controller, charger, etc.)

In "Current hybrid-electric powertrain architectures: Applying empirical design data to life cycle assessment and whole-life cost analysis", the authors group the components and make a few assumptions:

  • Vehicle construction emissions, excluding the traction battery, are equal for all powertrains.
  • Maintenance and disposal (end of life) emissions of all powertrains are equal.

Is ignoring the powertrain a valid assumption?

The assumption that the powertrain construction for all vehicle types has roughly the same CO2 emissions is based on a comparison of battery electric vehicles (BEVs) and ICEVs from "Contribution of Li-Ion Batteries to the Environmental Impact of Electric Vehicles".

Through four different LCA methods (ADP, GWP, CED, and EI 99 H/A) you can see that powertrain (the third pattern from the left) has a similar weight for BEVs and ICEVs:

enter image description here

We can assume that a HEV powertrain would also be roughly the same, as from a component standpoint it splits the difference between the two.

CO2 emissions from battery production

The best data I could find on CO2eq emissions from EV battery production comes from: "Life Cycle Environmental Assessment of Lithium-Ion and Nickel Metal Hydride Batteries for Plug-In Hybrid and Battery Electric Vehicles".

Here are their findings, given as CO2 equivalent emissions per rated watt-hour (Wh) of battery energy capacity:

NiMH:               0.35 kg CO2eq / Wh
Li-Ion (NCM-type):  0.20 kg CO2eq / Wh
Li-Ion (LFP-type):  0.25 kg CO2eq / Wh

These figures match the range found in the report "Life cycle assessment of lithium-ion batteries for plug-in hybrid electric vehicles -- Critical issues" (when scaled from a 10 kWh PHEV battery).

A different report, which is cited (directly or indirectly) in much of the literature on this topic, gives a much lower value for carbon intensity of Li-Ion production:

Li-Ion (alternate): 0.12 kg CO2eq / Wh

From "Life Cycle Assessment of Greenhouse Gas Emissions from Plug-in Hybrid Vehicles: Implications for Policy" (the values themselves are in the supplementary material).

The Toyota Prius HEV comes with either a NiMH or Li-Ion battery bank (from the official spec), with roughly 1.3 kWh capacity (based on a 6.5Ah battery at about 200V - source).

So the resulting emissions for Prius battery production are:

NiMH:               460 kg CO2eq
Li-Ion (average):   300 kg CO2eq
Li-Ion (alternate): 160 kg CO2eq

How far do you have to drive the Prius before it beats the Corolla?

When you drive a Prius off the lot, it has already resulted in emissions of 160 to 460 kg CO2. Per mile, however, it will emit less than a Corolla. So how many miles do you have to drive the Prius before you've emitted less total CO2 than if you'd been driving the Corolla?

From FuelEconomy.gov, a new Prius gets 52 mpg, while a new Corolla gets 31 mpg.

From the EPA, 8.9 kg of CO2 are released for each gallon of gas consumed. So we can calculate the kg CO2eq per mile of each vehicle:

(8.9 kg CO2eq) * 1 / (miles per gallon) = kg CO2eq / mile

Let's call this CO2 per mile or cpm.

Based on the difference in fuel economy, we can then calculate how far you'd have to drive a Prius compared to the Corolla to make up for the CO2 released in the battery production process:

(battery kg CO2eq) / ( Corolla cpm - Prius cpm ) = break-even mile

NiMH battery:       3,967 miles / 6,385 km
Li-Ion (average):   2,587 miles / 4,164 km
Li-Ion (alternate): 1,380 miles / 2,221 km
  • Interesting, but I'm wondering why your outcome is much higher than the calculations discussed in this article. On page 2 they say that "If you assume that both vehicles travel 160,000 miles (257,495 kilometers) over their lifetime, the conventional vehicle requires 6,500 Btu of energy per mile compared to 4,200 Btu per mile for a hybrid." – THelper Mar 24 '17 at 9:04
  • So this would suggest that the break-even point is much lower than 160.000 miles. Those calculations seem to be based on the old Prius, and expectations are that GWP of the new Prius is even lower. – THelper Mar 24 '17 at 9:19
  • @THelper, as with many things in LCA, the numbers are all over the place. The values I cited for kgCO2eq/Wh in battery production are consistent from two different sources (which didn't cite each other). For these variables, the How Stuff Works report cites the Argonne GREET report, which cites personal communication and a Japanese report which isn't online. The new value I added (0.12 kg CO2eq / Wh) agrees with GREET, and is much lower. – LShaver Mar 24 '17 at 14:55
  • Thank you, @LShaver - it is helpful to have the different sources as I am not familiar with where to find which pieces of literature. I now better recognize the value in your original advice re this question (in a comment on 3/20), though I find this answer helpful. It's overly simplistic to expect a neat,tidy answer (e.g. "a HEV becomes better than an ICE after driving 105,000 miles") because of the number of variables and range in estimates, but it's helpful to know that considering only carbon (and likely overestimating break-even), a HEV comes out ahead within a typical driving lifespan. – susie derkins Mar 29 '17 at 18:34
  • Those calculations seem completely off. Let's take the case of the NiMH battery. It adds 460 kg of CO2eq, or as much as the burning of 51.7 gallons of fuel will produce. So the break-even point will occur when the Corolla, driving side by side with the Prius, will have burned 51.7 gallons more fuel than the Prius over the same distance. That point is reached at 3969 miles... – Frank Mar 24 at 23:38

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