October 28th, 2017 by Christopher Arcus
Tesla is about to reveal its truck, so it’s a good time to consider the range and other requirements. Pack swapping has been considered a possible scenario, but how would that work and how many packs are needed?
Let’s think about pack swap concepts. Truck dispatch can be very complicated for multiple routes and pickups/drop-offs. There is a whole math theory devoted to it, but that is not necessary to consider bulk freight concepts.
How is a truck like a bicycle?
Let’s look at something much simpler and common. High-volume bulk transport dispatch is like a bicycle chain. It’s a continuous belt like a bicycle chain or conveyor belt. Trucks are continually transporting cargo and returning to pick up more. Commodities like grains and bulk items are shipped this way.
The transport vehicles come home empty or occasionally have cargo on return.
Let’s start with a scenario:
Trucks begin at westernmost terminal. Same number of trucks as swap stations. Now trucks start heading east at intervals equal to the transit time between swap stations.
There is a swap at each station along the way with a charged pack ready. The starting terminal has all trucks already charged.
Now the trucks start one at a time in intervals. When the first reaches the first swap station, it picks up one of the packs and drops its pack off.
The first west side swap station has the truck transit time to charge the dropped off pack. For 200 miles, approximately 3 or more hours is plenty of time for charging.
Meanwhile, truck 2 is on its way to swap station 1. Truck 1 is on its way to swap station 2. Truck 1 and 2 arrive at stations 2 and 1 respectively. And so it continues. If all trucks end at the last station, they are ready to continue in the same way back west.
But this scenario has big gaps in transport intervals. It has to wait for trucks to return the full distance before reloading. Let’s assume cargo amounts are much greater than twice the number of trucks, so that all trucks are filled for best economics. This is reasonable for bulk cargo.
The full monty
Imagine instead a full conveyor belt in both directions. Trucks going in both directions at all times.
Now there are N stations and 2N trucks. Every truck arrives at a station at intervals and has a fully charged pack to pick up and a discharged one to drop off.
Trucks at the easternmost and westernmost terminus points can have one truck arrive and leave at the same time. The trucks arriving at the terminus can stay there until they load/unload as long as it is less than the swap station distance travel time.
Swap by hand a new invention?
Perhaps pack swaps are much simpler than imagined. It’s likely that large truck packs will be done in identical smaller sections from below with a lift. In the video below a forklift swaps battery packs. The lift could be a hand truck or a fork lift. Both are easy and economical.
The real deal
Given the pack swap, 200 mile range intervals are enough to operate a full fleet of cargo-carrying trucks continuously. 3000 miles is 15 stations. A major freight company would be able to operate this system economically if electric truck initial cost, swap pack plus maintenance, and charging was equal to ICE truck maintenance and fuel. As the electric truck cost approaches ICE truck costs, the EV becomes more profitable.
There is some consideration for swap station costs, but freight companies often operate repair and maintenance stations at intervals as well. This swap infrastructure cost would have to be considered in the balance, but these stations would be little more than charging stations with some overhead. They need not be much more involved than a charging station, more similar to a gas station rather than a full building. Covered overheads and a locked kiosk with swapping hand trucks might be all that is required. A slightly better arrangement would have a garage and forklift for higher volume and for better protecting packs during charging or for repair in inclement weather.
Truck battery packs could use a flexible combination of pack swap and fast charge to meet a variety of needs.
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