What are the carbon emissions from the manufacture of the hybrid components of a Prius?

Question

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.

Answer 1

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.

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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:

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

Answer 2

I was about to post a quick question, trying to figure out the comparison for a Hyundai i30 2018 model vs Prius C, then went down a rabbit hole for a couple of hours.

I'm waaaay out of my depth here, so trying to piece together our situation for two cars we're considering.

The end result (TL;DR) is the Prius C or Prius produce way lower CO2 including battery production than the Hyundai i30, (14.09 Tonnes less).

However, the Prius C is too small for us and Prius is $10k over our budget. So I looked into the cost of offsetting that much CO2 and it came in at $190, if we pay 10X that to make $1900 + a Hyundai i30 is within our budget and reduces our CO2 impact.

This is my thought process and calculations to make a decision about buying an environmentally efficient car.

Our main considerations are buying relatively new (2-3 yrs old), the largest boot size we can get in a tiny car (in case we have kids), spending under 20k (we'll be selling our Subaru for about that much) and environmental efficiency, hence moving from the Subaru.

I love the long post by @LShaver but I feel like you should use CO2 emitted by each vehicle per mile/KM, not per gallon/litre. Because their CO2 efficiency is different.

Is that a fair comment to make? Maybe it ends up being the same, I'm very confused.

The other question I have is I imagine the CO2 emitted when producing batteries will improve over time, so in the 2 years since this post, these calculations might be out of date? But I couldn't find any newer data, after reading 5X technical battery specification PDFS, I gave up.

If I compare them on these data points.

Prius C - 0.9 kWh Nickel-metal hydride - 0.35 kg CO2eq / Wh (Above, I couldn't find a more up to date stat) - 86 g/km (Green Vehicle Guide) - 3.9 l/100 km (Test)

Hyundai i30 Diesel - 157 g/km (Green Vehicle Guide) - 3.8 l/100 km (Test)

Fuel & CO2 stats from this source

Scenario 100,000 km

Prius C - Driving CO2: 100,000 km x 86 g = 8,600,000g = 8.6 Tonnes - Battery: 900 Wh x 0.35 kg CO2eq = 315 kg = 0.315 Tonnes - Total: 8.915 Tonnes

Hyundai i30 Diesel - Driving CO2: 100,000 km x 157 g = 15,700,000g = 15.7 Tonnes - Total: 15.7 Tonnes

Clearly way more in that scenario, and the distance of break even would be very low KMs. The difference in fuel consumption is nominal, 0.1 l/100 km, only adding up to 100L over 100,000 km.

Our scenario: 11,500 km/year for 5 years

Prius C - Driving CO2: 11,500 km x 86 g = 989,000g = 0.99 Tonnes / year x 5 years = 4.95 Tonnes - Battery: 900 Wh x 0.35 kg CO2eq = 315 kg = 0.315 Tonnes - Total: 5.265 Tonnes

Hyundai i30 Diesel - Driving CO2: 11,500 km x 157 g = 1,805,500g = 1.8 Tonnes / year X 5 years = 9.01 Tonnes - Total: 9.01 Tonnes

Also, I feel true life cycle should consider the life after we use it, as someone else will benefit from it's CO2 reduction. Average use is 10.2 years in Australia.

Let's say, it goes for 200,000 km, just double the stats above, obviously it's just going to get better for the Prius C.

Prius C - Driving CO2: 17.2 Tonnes - Battery: 0.315 Tonnes - Total: 17.315 Tonnes

Hyundai i30 Diesel - Driving CO2: 31.4 Tonnes - Total: 31.4 Tonnes

Then I realised the boot size of the Prius C is TINY, so have to consider the latest Gen Prius which is $10-20k more expensive, previous Gen $5-20k, so this is now becoming theoretical....

But looking at the 2nd Generation the battery is 1.310 kWh and CO2 90 g/km , only marginally different, so wont impact the results.

So the question becomes should we spend an additional $5-10k for an older Prius to save 14.085 Tonnes of CO2...

That made me think, what's the cost of offsetting that CO2? (Goes down another Google rabbit hole...) It's really confusing a) if CO2 offsetting is meaningful, and which providers are legitimate.

This government website linked me to a bunch of retailers and half their websites were broken or confusing. http://marketplace.carbonmarketinstitute.org/market-directory/

Whilst these projects may not entirely counteract your own actions or really meet the definition of an “offset”, they are still driving conservation efforts and green research. Carbon offsets are not ideal, but they are an imperfect solution to a complicated problem. At the very least, it remains a mechanism to channel much-needed investment into green energy and conservation. Forbes

This website calculated that many Tonnes costs $130-$190 to offset, which seems very low. Let's say we spend 10X that to really make sure it's offsetting our Hyundai i30 purchase, that's $1300-$1900, well within our budget and hopefully meaningful...?