Does electrifying trucks make sense if the trucks are electrified?
When we looked at whether full size tractor trailers (semi trucks) could be electrified (here), the point was raised that automated trucks may change the picture a great deal. The trucks may use lower speeds, different routes, and won’t be limited by daily driving range (except by their fuel).
What Would Really Change?
For starters, we wouldn’t need nearly as big a battery. Our big battery was selected to give our human driver a full day of driving range. Ideally, the truck would then recharge while the driver does. Our automated truck could charge much more frequently. Even if it loses time for charging, it won’t lose time for sleep.
How Big Will Our Battery Be?
Let’s say we want our trucks to recharge every 100 miles. That’s long enough that recharge stations could be on the outskirts of most urban areas where they’d be cheaper to construct but not so far apart that our trucks would need massive batteries. Odds are, the batteries will cost more than these stations.
To get that range, we’ll pick a battery size that will give us about 120 miles of ideal range. That will give us some cushion in case of range reducing emergency braking. We won’t need to worry about the climate because only human drivers need climate control.
118 (miles) × 51.83 (ton) ÷ 5.13 (((ton) × (mile)) ÷ (kWh)) = 1,200 (kWh)
For the record, I had to actually calculate that in reverse (given the kWh, find the range). That is why the end number is even. It’s also how I knew the tonnage of the batteries for the above calculation.
Some trucks may require range reducing climate control for their cargo. We’ll revisit that if the rest of the idea seems workable.
- How long would it take to charge an electric truck?
Let’s say we’re using a beefy level 2 charger that is available for modern electric cars to charge our trucks. At least some of those can use up to 32 AMPS and 240 volts. How many kWh can each charger provide per hour?
(32 (amp) × 240 (volt)) ÷ (1000 (((amp) × (watt)) ÷ (kW)) × 1 (hour)) = 7.68 kWh
That’s not looking promising. Charging our 1,200 kWh truck is going to take 156 hours. This is not comparable to a good night’s rest.
1,200 (kWh) ÷ 7.68 ((kWh) ÷ (hour)) = 156.25 (hour)
So This Won’t Work?
Despite not being comparable to a driver resting, like most problems this one can be solved by throwing money at it.
A Better Better Place
The slow charging times of electric vehicle batteries is one of their key weaknesses. Tesla tries to overcome that with their super chargers. Better Place tried to overcome the problem by creating stations (like gas stations) where consumers would drive up and have their drained battery replaced with a charged battery. That swap could take an amount of time comparable to a gas fill-up and the swap station would then charge the drained battery to insert into another vehicle.
If you read the history you’ll find that plan didn’t work out for Better Place. However, our dynamic will be a little different. We’re not working with people, we’re working with autonomous trucks. I’ll go on the record as saying people are the most unpredictable part of any business venture.
So, let’s take that idea and presume that we’ll simply have a wide network of truck battery swap stations. Every hundred miles or so, a truck will drive in to have it’s battery replaced with a fully charged unit and continue uninterruped.
How Many Batteries?
Now we have a new problem to solve. How many swappable batteries (at a minimum) would each truck need to have in order to achieve the target driving range?
As was pointed out, these trucks could operate on very different patterns than modern trucks. Let’s say our automated electric truck has an average driving speed of 35 miles per hour. That would mean it would take at least 2.7 hours before it reaches the next battery swap station.
100 (mile) ÷ 35 ((mile) ÷ (hour)) = 2.7 (hour)
That means our truck needs access to a fully charged battery every 2.7 hours. To meet those requirements, we’d need at least 58 batteries containing 1,200 kWh per truck.
156.25 (hour) ÷ 2.7 (hour) = 57.5
If you see the quoted average speed of 35 miles per hour, and think that’ll be inadequate for an autonomous truck, you’d be wrong. If it was simply doing long distance hauls, that truck would have a range of 840 miles per day, which is quite a bit longer than the 300 to 500 mile quoted distances of driving ranges we had found before.
Unfortunately, Batteries are Expensive
Since our pretend batteries cost $100 per kWh, we can easily see that each 1,200 kWh battery costs $120,000. Getting 58 of these per truck would mean each autonomous electric truck would need $7,000,000 in batteries.
120,000 ($) × 57.54 = 6,904,247 ($)
And that’s just one truck. If we wanted to electrify all ~1.9 million trucks in the US, it’d cost about 13 trillion dollars.
6,904,247 ($) × 1,866,667 = 12,887,927,350,427 ($)
Are Batteries Expensive Compared to People?
The average truck driver has a salary of about $41,500. That means it would take about 166 years of savings on driver salary to equal the cost of our batteries. That’s well above the useful life of the batteries, so it’s safe to say there is no break-even that grants batteries an advantage here.
6,904,247 ($) ÷ 41,500 (($) ÷ (year)) = 166 (year)
So…the Idea Won’t Work?
Not as I’ve laid it out here. That’s not to say that it couldn’t work. To take this idea and make it attractive, trucks would need to be broken into categories.
Long distance haulers would behave like we quoted above and would be tremendously expensive to power – despite having fantastic range and overall speed.
Local trucks could be used for making deliveries to stores and such). These would have more modest range requirements and wouldn’t run continuously. That would make these far more attractive (albeit, they still may not be cost effective).
A Better Bettter Idea
This reinforces what we calculated before. Batteries simply don’t have enough energy density for commercial use. It’d be far wiser to power the commercial infrastructure (including trucks) with hydrogen.