Ain't gonna happen! Unless the solar power comes from a large, and I mean parking lot size, array of PV panels, there's simply insufficient power that can be generated by a single bus to power itself. For example, I have 2kW of solar on my bus roof which occupies 22 feet of roof length, so if I were to cover the whole darn roof with panels I could conceivably have about 4kW of panels there. (Never mind that it would look really hokey and be very unaerodynamic.) 4kW of panels can charge about 2000aH of 12V batteries at about their maximum 13% charge rate for FLA batteries (you'd want to charge the on-board batteries as quickly as possible). 2000aH at a nominal 12V is about 24kWH. One horsepower is 746 watts, so therefore you could theoretically get about 32 HP for one hour. In practice you shouldn't discharge FLA below 50%, so that halves the usable power to about 16 HP. Where am I going to go with 16 HP? Heck, my 42MT starter motor is 10 HP, and that will hardly move a 27,000 pound bus at all, even on level ground.
In a nutshell, self-contained solar is good for house loads except resistive heating, but as a way to move the bus it's a non-starter.
One thing I wondered about in that article - why is a bus being used at all to move just one or two special-needs children? Why not use a high-roof minivan with wheelchair lift?
Some years ago Blue Bird had some battery school buses, including one used at Beaumont CA. That experiment didn't work out too well, and Beaumont's was sold off for scrap after a few years. Presumably it was charged from the grid; one could charge such buses from a dispersed non-local solar farm or any renewable energy source such as wind power, so it would the be possible to reduce carbon footprint that way. Ironically, Beaumont is not far from the huge windfarm at the Banning Pass just west of Palm Springs - I wonder if their electric bus used any power generated that way?