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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.

  • 1
    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
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To answer your general question: a recent, thorough LCA comparing battery electric vehicles (BEVs), hybrid electric vehicles (HEVs), and plug-in hybrid electric vehicles (PHEVs) to internal combustion engine vehicles (ICEVs) is freely available: "Towards Life Cycle Sustainability Assessment of Alternative Passenger Vehicles".

But to answer your more specific question, I had to dig a bit deeper...


HEV specific components

The HEV components which are not part of a standard 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.

Ignore the powertrain?

The assumption that the powertrain construction for all vehicle types has roughly the same CO2 emissions is based on a comparison of 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:

enter image description here

If this is true of BEVs then it holds even more strongly for HEVs, which would be more similar to a ICEVs.

Battery production emissions by chemistry

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 estimate): 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).

Conclusion

When comparing the carbon emissions from manufacturing of a Prius to an ICE vehicle in a similar class, the most important factor is the battery.

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 battery production are:

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

From the EPA, 8.9 kg of CO2 are released for each gallon of gas consumed.

From FuelEconomy.gov, a new Prius gets 52 mpg, while a new Corola gets 31 mpg. So we can calculate:

(miles)/(miles/gallon)/(kg CO2/gallon) = kg CO2

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

  • with NiMH battery: 315,000 miles / 507,000 km
  • Li-Ion (average): 205,000 miles / 330,000 km
  • Li-Ion (alternate): 110,000 miles / 177,000 km

This is a lot of miles -- farther, in fact, than the standard 100,000 mile battery warranty. There is also a pretty wide range in the figures. However, none of this includes any of the environmental factors besides simply carbon emissions that motivate the decision to purchase an HEV as opposed to an ICE vehicle. Additionally, battery production is both the most carbon intense factor, and the area where technology is advancing the fastest -- meaning all evidence indicates that if they are not already a less carbon intense choice, HEVs soon will be.

  • 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

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