[limitedfrom]

> “They have more energy in each bus than they need to do their route, so there’s always an ample amount left over,” said Rudi Halbright, product manager of V2G integration at Pacific Gas and Electric Company, the utility that’s partnered with Zum and Oakland Unified for the new system.

This just sounds like the batteries are oversized for the application and they're carrying unnecessary weight around all day. Consumer EVs are doing this to an insane degree all day for "range anxiety", but I can't help but think that well defined space like school buses could be sized much closer to the true requirements.

[Gigachad]

The buses will all have different length routes, you aren’t going to custom build a bus for a single route and then have it be impossible to reassign later. The batteries will also degrade over time so you wouldn’t want them left completely useless when they degrade 1% and can now no longer complete the route.

[limitedfrom]

To some extent, definitely. But I'd like to think that

1) School districts could buy a mixture of different ranged buses to fit their needs. After all, airlines have a mixture of planes in the fleet for different range / needs and not just have all the fleet be the largest / longest range model, and

2) The manufacturer offers range conversions later since it's a more commercial use than consumer EVs, especially when they want to sell it to different school districts. They probably need to do battery swaps when batteries degrade beyond a certain degree anyway.

Carrying additional capacity takes a lot of material (that could be used for other batteries especially) and energy. I get that it's convenient, but I hope folks put a little care into it than just put large batteries everywhere.

[schimmy_changa]

Perhaps, but there's a reason that anyone in supply chain or logistics tries to standardize on the fewest SKUs as possible. Planes are a special case because weight _really_ matters and thus it's worth the loss of standardization.

Imagine the nightmare of what happens when a driver grabs the wrong bus and is several miles along their route before they notice. Do they return to the school? Do they get as many kids as they can before they run out of charge while a dispatcher furiously tries to coordinate a place within range but still further along the route to send a whole new bus to switch the kids onto? What happens when the driver who's bus got taken drives off in ANOTHER driver's bus, perhaps with the same results cascading onwards?

Currently you have to balance drivers, bus capacity, and bus breakdowns/availability, but you don't have to manage bus charge because the gas range is large enough and the driver can quickly top up if needed. Adding another dimension of complexity into it likely isn't worth it compared to the cost of having a somewhat larger battery.

[limitedfrom]

City buses in many districts are tied to their operator's licenses, displayed somewhere in the buses; same with taxis in most places I've been (prior to proliferation of ride shares). Not that they need to be tied to a vehicle necessarily, but I don't see why you think school bus drivers wouldn't be capable of getting into correct vehicles nor why that should be how a district picks a fleet of buses.

Also, for the SFMTA[0] as an example, different routes use different vehicles depending on the size & route & electrification. It doesn't have to be air travel to want a few varieties to fit all the needs.

Here are some stats[1, page 3]: An average school bus route is 32 miles, with max observed being 127 miles (and this is most likely a very rural route, not like the Oakland example here; in fact, here's an average of student distances for Oakland[2]). Given such a long time period between school start and end times, I expect most of these to be able to be charged between the two shifts with the exception of some field trips.

If you look at the Zum website, their buses are capable of 155 miles[3]. I suspect this was designed to fit the highest range case described in the paper, but almost 5x the average route distance. For most non-rural school districts, even if you account for some detours and faulty charging even, x2 (or x3, sure) seems reasonable to keep as the majority of the fleet. And perhaps you can keep a few of the largest range ones if the school regularly has field trips in that range.

For what it's worth, ETOPS regulations are interesting look for how aviation deals with failure modes for range/routing. Assuming failures are rare, the idea is to ensure the planes have enough to get to safety, not just put as much range as possible on all the planes.

[0] https://en.wikipedia.org/wiki/San_Francisco_Municipal_Railwa... [1] https://www.nrel.gov/docs/fy14osti/60068.pdf [2] https://gopublicschoolsoakland.org/wp-content/uploads/2016/0... [3] https://www.ridezum.com/blog/electric-school-buses-the-benef...

[superb_dev]

Also having extra range is handy for sudden route changes, like a road closure or a train. In my home town it was a pretty long detour if you needed to get around the train

[bastawhiz]

Or a field trip! Or a sports game on the other side of the state!

[bastawhiz]

> the largest / longest range model

Nothing has suggested that they are.

You're also neglecting the eventuality where the moment a district needs more buses with a minimum range above some threshold, they need to sell some buses (probably at a significant loss) and buy more new buses. And those new buses need to be compatible with all of the existing systems.

You don't want a fleet of twenty vehicles that need eight different sets of parts. You want a fairly uniform fleet.

[limitedfrom]

I did not suggest that they have twenty vehicles either. I replied on a different post, but an average school bus route in the US is about 32 mi[0]. Zum buses are capable of 155 mi[1]. Given their "up to" language, I'd like to think that they actually offer smaller battery capacities as well, but especially for a non-rural district like Oakland[2], if one were to carry 155 mi range for a typically 32 mi or less route, it would be quite an overkill.

One can have a few 155 mi range vehicles for field trips, sports games, etc. but the majority of the fleet can be much smaller for every day uses.

[0] https://www.nrel.gov/docs/fy14osti/60068.pdf [1] https://www.ridezum.com/blog/electric-school-buses-the-benef... [2] https://gopublicschoolsoakland.org/wp-content/uploads/2016/0...

[dgoldstein0]

Not necessarily. The battery may be able to provide power to the grid when it's low and does not enough power to drive the bus. The bus probably requires some minimum voltage to move and a bit more to be able to climb hills. And of course you don't want to run out of power so more buffer for that. So it's not unimaginable a bus could be near empty for the purposes of driving the route but have useful juice to give the grid. Fair question would be how such discharging affects battery lifespan

[dangus]

I disagree with you here.

It’s not just range anxiety. You need to have extra capacity for cold weather and degradation over time.

If I have a car with a 300 mile range, and it’s 0 degrees outside, now I’ve lost a solid chunk of range, I’m down to the low 200’s

Then, if the car is 15 years old, I’ve lost another 10-20% of battery capacity.

But I also need to stay below 80% charge or I’ll double my charge time, so really I only want to operate between 5-80% on a road trip.

Now I have to charge every two hours of driving or maybe even less.

Compound that more if I need to tow something, put a kayak on the roof, put a bike on the back, etc.

So if I’m starting from an EV that has a more reasonably sized battery pack delivering 150 miles of range, well, maybe I can tolerate that but not in the winter 10-15 years from now.

Of course this discussion isn’t extremely relevant to school buses.