It comes down to energy density.

That setup (charging where the buses go at the end of the day) requires the buses have enough battery to go their entire day on one charge. But then, that restricts the ability to take a just-now-ending-service bus that's out on the road, and redeploy it to fill in for a bus that is running late, or a bus that has broken down.

(I have seen this happen: I have seen a VTA "Rapid" 522 bus, just about to go in-service at the start of its route, switch to "Not in Service" and leave without picking anyone up. When I called in to report the weirdness, the agent on the other end checked and told me that an Express bus nearby had broken down. That was the right call: The Raid bus was closer, and the Rapid schedule frequent enough to absorb the loss.)

So ideally, you would want charging points to be available where buses sit during the day. That is at least at one end of the route. It can be done, it just takes more infrastructure.

> I assume it's already got a diesel pump of some sort to feed the buses since you don't exactly see city buses at normal gas stations.

While I was an undergrad at Ohio State, I drove 35- and 40-foot buses for CABS (the campus bus service). We did indeed have a diesel tank and pump on-site. But occasionally it would break down. When that happened, we would indeed use a normal gas station! All of the nearby gas stations with diesel pumps were evaluated for bus access.

I wonder if you could get away with charging most of the buses by having overhead lines in heavy bus traffic areas to power and charge the buses during a portion of the route before having them return to full battery usage. This might also simplify overhead line deployment as there are some areas that are poorly suited for lines - line deployment could be focused on easy to service and deploy areas.

There are at least charging stations for buses.

For example: https://www.oppcharge.org/ https://www.heliox.nl/

What I would really like to see are small self-driving battery powered trams. (Seems like large "bi-mode" human operated ones already exists).

I thought the same too, to the point that maybe even lead acid batteries could work. Unfortunately, buses still care somewhat about weight--from a 2005 report: https://www.transit.dot.gov/sites/fta.dot.gov/files/Electric...

> Consequently, powering a full-size bus would require a battery pack that is unacceptably large and heavy, as well as too costly to make a battery-electric bus commercially competitive.

Of course, the energy density of lithium may change things!

I can't speak for the relative costs but adding a bigger battery adds cost, it also adds weight which increases the motor size you need, further increasing costs, it also increases wear and tear on the road.

Also the article mentioned $1.5million for infrastructure to charge 20 buses. Ideally you'd want that running 24/7, not lying dormant for 16 hours a day.

And lastly, you're adding a massive single point of failure. What if the power goes out overnight? Suddenly you don't have any buses the next day.

Ps I like the idea of buses going to sleep at night :)

Why would it increase the motor size significantly? Even low voltage electric motors have insane torque compared to fossil fuel engines.

Well its like the tyranny of the rocket equation. Yes the size increase isnt linear, but it isn't a free lunch either.

Don't forget, once you've added an extra tonne of batteries your suspension and chassis need upgrading (ie get heavier) to compensate, so you need to add more batteries to compensate....

One issue that the article highlighted was that if you do that you might need a significant grid upgrade to handle a large number of buses charging simultaneously. If the charging stations are spread out over the city the grid probably doesn't need to be upgraded.