Not sure if by "converting" you mean retrofitting old buses or replacing diesel buses with new electric buses. If it's the former definition, it's non-trivial from a safety and engineering standpoint to integrate a high-voltage, high-energy battery system into an old bus and expect to realize a decent ROI. Those old clunkers are not designed with an electric powertrain nor efficiency (i.e. they're heavy and have have drag coefficients) in mind. Furthermore, safety is paramount in most bus operations, and a lot of thought needs to go into mitigating thermal runaway or other catastrophic failure modes with systems of that voltage (100s of V) and energy (300kWh+). Depending on the existing bus system that the battery needs to be integrated into, this can be challenging and sometimes infeasible.

I say all of this more to make the argument that rather than retrofit old buses, in my opinion it makes more sense to outright replace them. Right now Proterra is the largest domestic producer of pure electric buses. They compete on most contracts with BYD in China, and New Flyer in Canada. Behind BYD and the government, the electric bus market in China has absolutely exploded over the last several years. Proterra is anticipating high growth in the U.S. market as well and just launched a new factory in LA last month [2].

[1]https://www.proterra.com [2]https://www.forbes.com/sites/alanohnsman/2017/07/26/proterra...

Seriously?

While aerodynamic teardrops are most efficient that means nothing if the up front cost is prohibitive.

Also, efficiency and a box that's strong enough to appease the "think of the children" types are very much at odds with each other.

For a bus with low mile requirements some boxes to hold batteries and a big DC motor where the engine goes would work fine.

The "scaled up golf cart" architecture works well if the route does not change and is very cheap to implement.

The upfront cost is no longer prohibitive with all-electric buses realizing savings in the form of reduced maintenance and fuel costs that exceed the initial investment discrepancy [1-2].

On your second point, a bus doesn't necessarily have to have a heavy steel frame for it to be safe. There are plenty of lighter weight (e.g. composite/carbon fiber) solutions which don't sacrifice safety.

Sure, if the mileage requirements are low then there's definitely a cost-effective retrofit solution. But if you're a company already building a full electric bus and investing a lot of R&D into the pack design anyway, then you could probably just sell battery solutions to school bus companies as another revenue stream. I'd wager, though, that the larger addressable market is customers looking for new electric buses for longer routes.

[1]http://www.columbia.edu/~ja3041/Electric%20Bus%20Analysis%20... [2]https://www.nrel.gov/docs/fy16osti/65274.pdf

I would argue that efficiency is more important in a school bus than safety.

Buses are designed for many years of service with long-lived and easy to replace parts. On the safety front they are painted yellow and have some lights. That's pretty much it. They don't even have seat belts.

It looks to me like efficiency trumps safety in this case.

It is reasonable to assume that safety is the primary concern for school buses. There are are a lot of safety standards.

"Pursuant to these requirements, federal safety regulations applicable to bus manufacturers have been developed. There are a total of 37 federal motor vehicle safety standards that apply to school buses. Many of these also apply to other types of motor vehicles, but several (among them standards 131, 220, 221, and 222) are written specifically for school buses."[1]

As for seatbelts,

"Large school buses are heavier and distribute crash forces differently than passenger cars and light trucks do. Because of these differences, bus passengers experience much less crash force than those in passenger cars, light trucks and vans."[2]

It seems that even weight[3] is a safety consideration.

[1] https://www.cga.ct.gov/2004/rpt/2004-R-0730.htm [2] https://www.nhtsa.gov/road-safety/school-buses [3] http://www.americanschoolbuscouncil.org/love-the-bus/educato...

Additionally there are different rules for school bus drivers, for example even small school busses are forbidden from turning right on red.

I can't speak on behalf of everyone, but my mother has been a school bus driver for the past 20 years. I'm not so sure I would consider the runs short. She drives at least 8 hours a day, with a break in the middle. There isn't much extra space in her bus for batteries.

In addition, the lifetime of a bus isn't measured in the same way cars are. They are purchased once a decade, never retrofitted, and not every bus is replaced with that purchase. With that in mind it will probably be another 2 sales cycles before we see any.

I was thinking underneath the bus was the perfect space for battery packs. Once you remove the gas tank and exhaust etc there would be plenty of room.

You need to add a much strong suspension system as well, that implies more wheels.

I'm not saying it can't be done, just that it is harder than it looks.

Busses are typically MDT chassis that are spe-d out very lightly and even then they pretty much never run anywhere near their GVW (whereas every other commercial vehicle is near, at or over the GVW basically all the time). A box truck for hauling baked goods is about the only thing that's going to be spec'd out lighter.

An extra few thousand pounds would not be a problem for a full sized school bus.

And think of the cost. Diesel is cheap, buses stay in service for years and it takes just a few minutes to refuel. You’d need hundreds of charging stations for every school district. Instead of just a few fuel pumps. It would cost literally 10s of billions to convert all school buses for a marginal cost benefit.

School buses also have secondary uses as evacuation vehicles so relying on electric isn’t a secure option. Hurricane Katrina, for example, used hundreds of buses for evacuations and it would have been extremely difficult to charge a bunch of buses off generators.

As with everything else, time and money. Most schools don't have the funds to replace their fleet of buses because of (the next big thing) and will have to do it as the old ones die off. Add to that the higher cost of electric vehicles and it doesn't look as immediately appealing.

Likely for the same reason Tesla was really, really expensive until now and is just reasonably expensive now with model 3. The initial investment plus extra funds to build charging infrastructure is likely the reason why we cannot have it yet. Also, if you think about it, each school bus might not be driving enough miles to make up for the cost of conversion.

My guess is risk is part of the answer. They don't have a huge budget, and it could be pretty financially disastrous to them if the experiment fails. And this has worked for them for 50+ years so there's no pressing need to change it.

Also, school districts are in the business of education, not transportation, so they may not see themselves as the people who should be leading in this area. If someone else (transit agency, airport shuttle company, etc.) tries something and proves that it works long term, they may then feel comfortable following along, but as far as I know, that hasn't happened yet because by definition it takes a long time to prove that.

Unfortunately, busses in many metropolitan areas run on staggered schedules. It's why middle school starts at 7:20am while grade school starts at 8:10 in some cities.

A typical service day for a school bus can be pretty packed.

Where I live (not USA) the bus company uses those same buses for other purposes through the day. So recharging them fast is very important.

Newer London buses are all hybrid and there are some electric as well I think?

Ask Bluebird; they have the market cornered. My guess is they have no need to innovate, so they do not.

They have just announced electric buses last month [0]. They also have CNG and propane powered models.

[0] https://www.blue-bird.com/blue-bird/Press-Releases/Blue-Bird...