Uncle JD’s "famous shortcuts"

I have just attended today a fantastic webinar showcasing a very thorough CO2 lifecycle analysis comparing? BEV Commercial Vehicles with their ICEV counterparts. The depth of analysis, granularity of results, and insights provided far exceed what I have seen in the industry.

The study is certainly well worth what the company is charging to access a complete set of similar studies through a subscription, or just that individual study.

As you would have certainly thought, all the buzz here was on CO2, but the analysis could be done too for NOx and PM (since not all electricity generation is exempt of them), bringing likewise together the different pieces of the puzzle – local, and externalized emissions – acknowledging their different impact on health. To be pertinent, the model should use proper cycles (this is a bit more complicated than for CO2) and include eventual deterioration over time of aftertreatment systems. My assessment is that few people would care for such a study though. Being curious, I have anyway performed a preliminary assessment, and found that indeed, BEV in the USA are likely to emit about 4 times more NOx than new ICEV, EPA27 compliant trucks in the 2030 horizon https://www.dhirubhai.net/posts/jdbonnet_epa-carb-bev-activity-7123793826355322880-mNNf?

Now, for those of us operating on a shoestring – or just thrilled by the idea of getting by themselves one (sorry, yes, just one) result of this lifetime CO2 study – the formula above, applicable to traditional Diesel ICEV, is for you.

Calculating the point at which the initial carbon emissions "debt" linked to the production of the battery of an BEV is "paid back" is not rocket science; following Occam's approach to cut to the chase and involve only those elements that matter, it in fact just requires 3 elements:

• the range the vehicle could reach on 100% battery
• how “dirty” the battery production is (CO2 generated per unit of battery capacity)
• how “inefficient” the ICEV used in the comparison is, compared to the BEV

More precisely, in this formula η is the comparative efficiency of the ICEV in relation to the BEV under the conditions of utilization considered – for example, η is around 40% for well-optimized Class 8 ICEV and BEV; note that this figure must take into account the losses during charging on the BEV side.

Continuing with this example, we could size the battery in a way that it would offer a 400 miles range in the hypothetical case that 100% of its capacity could be used (in practice, we might just get 80-97% of this, but this is a different story not impacting the CO2 breakeven) and associate it with a carbon intensity for battery production of 80 kg CO2 / kWh; the numerator becomes 32,000 miles kg / kWh.

Taking the case in which the (marginal) CO2 content of the electricity drawn for charging would be 0.273 kg CO2 / kWh, the numerator is conversely 0.913 – 0.273 = 0.640; leading to a breakeven in CO2 terms of 32,000 / 0.640 = 50,000 miles.

Now, don’t forget to doublecheck that 50,000 miles does not exceed the life of the battery – but in most case, it is only a fraction of it.

One of the “beauties” of the formula, as you may appreciate, is that the formula seems to sidestep the need to know the energy consumption per mile of both BEV and ICEV involved in the comparison. This is partly true. What happens in fact is that the miles required to reach break-even are homogenous to the amount of CO2 involved in the production of the battery – a quantity itself homogeneous to the capacity of the battery, not the range it confers to the vehicle, times the carbon intensity per unit of capacity of battery – divided by the carbon savings per mile between the BEV and the ICEV. It just happens that this latter quantity is akin to the energy consumption per mile of the BEV times a function representing the difference between the comparative efficiency of the BEV vs. ICEV, and the comparative “dirtiness” of diesel fuel vs. electricity; and that in parallel, the capacity of the battery is equal to the range it confers to the vehicle, times the energy consumption per mile of this vehicle. The energy consumption becoming a factor common to both expressions, it (not so) magically disappears, et voilà!

One last important element: the constant 0.365 must be changed to 0.366 for leap years since the truck would be used one more day in the year. JUST KIDDING!!! This has nothing to do with the number of days in a year but I mentioned this to make it easy to remember; the 0.365 figure is linked to the fact that 1 gallon of Diesel fuel when burnt releases 10.18 kg CO2, and that when accounting for upstream lifecycle impact such as oil extraction, refining, transportation etc. the real impact looks more like 13.74 kg CO2. Bounce this against the fact that the energy content of Diesel fuel is 37.7 kWh / gallon, then 13.74 / 37.7 = 0.365 kg CO2 / kWh, which is our number.

But obviously, comparing a BEV vs. a ICEV running on B20, B100, or R99 / HVO100 would tell a fairly different story, as the 0.365 "constant" will quickly tend to zero with a decreasing fuel carbon intensity, or even ... become negative! But even without going to such extremes, at state level, some pairs fuel x electricity are in fact excellent, while others are terrible. Grid load and TCO allowing, I would certainly go electric in New Hampshire, and opt for a renewable fuel with low carbon intensity in West Virginia.