Battery Swap for Electric Trucks Adds Only ~30% Extra Battery Overhead, Janus Electric Says

When I wrote an article a while ago about Janus Electric, an electric truck company in Australia that featured diesel semi electric conversions and battery swap, I put it away in my mind, until I happened upon an interview with Janus CEO Ben Hutt. The interviewer asked how much extra battery overhead there was for operating the trucks as a fleet in swap mode. He replied that it was about 30%. Janus would know, since they set up or operate heavy truck freight corridors. It turns out, I did calculations about that long ago that showed how this neat trick happens.

At first when I examined truck swap operations, I used a concept of unit charging transaction, the most basic element of battery replenishment. Over time, I drew illustrations of unit transaction to depict how they worked and how those unit cells expanded. If a picture is worth a thousand words, it is also a great way to see how something works, and show the math pictorially. When I came upon the Janus CEO quotation, I instantly remembered a concept I wrote about in a little article I called “EV Station & Charger Planning.” Let’s illustrate by comparing the simplest unit transaction and how it scales. This is an analysis with no waiting. Each expansion works by superposition of methods. Let’s do it by pictures. This is what a unit transaction looks like:

To get the unit transaction extended over longer distances we can do something I call chain staging. By starting each truck at the proper interval, all trucks are staged so that there is one truck en route between stations. I call this chain staging, because it looks like a chain. There is only one truck between swap stations with mobile battery, and one swap battery in the station slowly charging up. We can illustrate by chaining unit transactions together — see Figure 2.

Notice that this concept works in both directions. We can reverse the picture, showing trucks going back the other way. It is easy to understand how we can make a system of stations connecting two end points at any arbitrary distance. The ratio of batteries, trucks, and stations is the same as the unit transaction. You might call this a chain loop. It makes sense, because trucks are always going from pickup to destination and dropoff, then return. See how easy it is to figure out scaling in Figure 3?

If vehicle travel starts are staged, then we can have only one truck en route, and a swap battery at every station. In this manner, we can string trip starts so that one truck is always en route to the next station and there is always one mobile and one swap battery for every truck. Scaling is easy.

Next, we can use route stuffing. Instead of one truck between stations, we have a different number chosen en route.  If we choose three, then we can see there will always be three trucks with mobile batteries and one swap battery. In the interval between trucks en route, the battery pack can charge, and then the truck gets a fresh pack and leaves another to charge. This minimizes the number of batteries used and peak power demand. This is where we see how Janus can have a battery overhead of just 33% for swap, with route stuffing 3 trucks en route in the Figure 4 illustration.

The article shows how truck shipments can expand in pulses, with more than one truck dispatched at the same time. Fleet cargo volume can expand in a programmed way using this. The effect of multiple simultaneous departures is shown in Figure 5.

Batteries can swap in 4 minutes, and arrivals will service accordingly. In reality, for example, for a four-truck arrival, all trucks are served by 16 minutes, and any subsequent swaps would have no waits because arrivals would stagger every 4 minutes. The time interval between pulses of trucks may be larger than the multiple truck swap time.

The size of mobile battery packs can be reduced to increase load capacity. How this works is shown in the illustration. Stations at half distance intervals cut battery size in half. The total amount of system battery is the same, but mobile battery size halves and truck load-carrying capability increases, as shown in Figure 6.

Finally, unit transaction concepts easily show and compare systems’ peak power demand and energy requirements. Graphical analysis shows how battery swapping works, how it expands as need requires, and how to minimize grid peak power demand and swap station battery overhead in a flexible, predictable way.

Conclusion

Unit transaction illustrations are a helpful way to visualize electric vehicle battery replenishment needs. Trucks can operate with as little battery swap infrastructure overhead as one-third the amount of batteries on trucks. Graphical illustration easily shows how freight system operations can minimize peak grid power demands, battery requirements, and system capital costs using concepts like trip start staging, route stuffing, and multiple departures. These illustrations make it easy to plan initial operations and expansion, and analyze capital and operating costs. In electric freight systems, it pays to organize and coordinate shipping in a continuous chain, a match for freight corridors between ports and large warehouses, mines, and other concentrated freight corridor destinations. You don’t need one swap battery for every truck. By using route stuffing, system battery infrastructure needs can be reduced to a fraction of mobile battery requirements. Further illustration can show how other strategies match warehouse-to-distribution needs at retail centers and system granularity matches local delivery needs at every level and route length. There are further concepts to explore for remote station operations.