I just installed AC units at home that move around 2500 W of heat energy (in and out, heating and cooling), at about 800 W energy consumption. If one of those

I just installed AC units at home that move around 2500 W of heat energy (in and out, heating and cooling), at about 800 W energy consumption. If one of those units is enough for the bus, and it's on 30% of the time that would mean around 250 W per hour power requirement, resulting in 6 kWh over the day. In a reasonably sunny environment, solar panels can get 100 W per square meter. Let's say there are around 15 sqm available on the roof, yielding a total of about 12 kWh over the day - that's assuming around 8 hours of sun. If that doesn't work out due to latitude, it would be relatively easy to design panels that can be unfolded, providing extra area and serving as an extensible roof at the same time. If batteries and inverter don't swallow more than 50% of that yield, it should be enough to drive a normal AC, lighting, and a laptop, maybe even a small fridge. You'd need a backup stove for the winter though.