Green bragging rights: Tesla X vs. Volvo XC90

"Austin" (not his real name) is a neighbor whom I recently had a gentle conversation with after he tried lecturing four kids, including one of mine, on the moral rightness of driving Tesla instead of something with an internal combustion engine like my XC70.

According to the Obama-era site, his Tesla Model X (a small sedan he describes as an SUV) uses about 37 KWH per 100 miles of highway driving, while the newest 325 Volvo XC90 AWD is said to use about 4.5 gallons per 100 miles.

The same site gives the MPGe (miles per gallon equivalent) estimate for the Tesla as 89 and that for the Volvo as 22.  The MPGe metric is supposed to represent the energy use of the vehicle on a tank- or battery-to-wheels basis in terms of the energy available in a gallon of gasoline, but neither the theoretical calculation nor the data provided by the Energy Information Administration translate easily or directly to real-world experience.  My suspicion, in fact, is that the business of comparing apples to oranges, or diesels to electrics, is intrinsically very difficult but that the Energy Information Administration relies on these complexities to discourage unwanted review by the unblessed.

Unsubstantiated MPGe estimates aside, the average gallon of non-ethanol gasoline burnt in an average engine under average American conditions produces about 8,200 grams (18.1 pounds) of CO2, while, again on average, a kilowatt-hour of stored charge derived from coal takes about 1.36 KW of net generation, "costing" about 910 grams of CO2 per KWH at the plant gate for a total of about 1,232 grams per KWH in the battery after losses due to transmission (10%) and charging (18%).

Two notes:

1. The estimated CO2 production for gasoline (8,200 grams/gallon) is reasonable (except that E85 has more emissions because the energy content per unit volume is lower), but the grams/KWH estimate for electricity produced from coal is highly arguable.

Published certainties run from around 453 G/KWH at the low end to about 3,000 G/KWH at the high end.  Much of this is due to real variability in generation technologies and coal, some seems due to special pleading by pro and con coal forces, and some of it seems due to measurement error.  Bottom line: The number I used here, 1,232 G/KWH in the battery, reflects the result of argument among experts and is almost certainly wrong but more probably a bit low than a lot high.

2. The reason electricity produced using solar panels or windmills costs so much more than power from nuclear or coal generation is that the energy and environmental costs of renewables are much higher than for power from other sources.  Thus, a full accounting of the CO2 equivalent for a KWH produced by wind power would produce estimates much higher than those for coal – in fact, a 10MW turbine running at 22% capacity for ten years 100 miles from its customer never returns the energy, mostly from burning coal and used tires, that goes into the steel and concrete needed to bring it online.

Hydro and nuclear are much cleaner than coal, but they constitute a small part of total American power generation, and so, rather than do the extensive research needed to get a real estimate (there are many on the web, most of them absurdly wrong), I've simply assumed the existence of a magical averaging effect – i.e., that all power used to charge Teslas comes from coal.  This is, of course, wrong – but how badly wrong, and in which direction, I don't know.

According to these estimates, therefore, the Model X will "cost the environment" the equivalent of 45,584 (= 1232 x 37) grams per 100 miles, where my 300 HP XC70 will "cost" about 41,000 grams, and the more modern 325HP XC90 SUV will emit about 36,900 grams.  Since both Volvos handily outperform the Tesla on Austin's favorite environmental metric, he can, to put it nicely, go suck it.

More interestingly, the event that seems to have most directly prompted his Tesla devotions was the purchase of new Ford Expedition by one of the other parents.  I think that's a cool super-sized station wagon, but, apparently, it's the devil's own work – except that I'm pretty sure that the only reason it will produce about twice the CO2 the Tesla will on an 87-mile (one-way) day trip to the Castle Mountain ski area is that the Ford will have to tow the Tesla home after a day's exposure to -30 degrees and a 20-MPH breeze leaves it incapable of getting out of the parking lot on its own power.

Did I say that Austin can go suck it?  Good, because I haven't even mentioned the report from the Swedish Environmental Research Institute (Delingpole summary: "Batteries used in a Tesla generate as much CO2 as driving a gasoline-powered car for eight years. And that's before they even come off the production line.") – or why believing that battery degradation estimates developed from experience in Holland apply to the distances, climate, and road variability we have here is going to cost him a bundle.

Paul Murphy, a Canadian, wrote and published The Unix Guide to Defenestration.  Murphy is a 25-year veteran of the I.T. consulting industry, specializing in Unix and Unix-related management issues.