It's an interesting idea. I did some napkin math based on the Solaris Urbino 18 bus. The buses have about 45 square meters of ceiling area (18m by 2.5m). Assuming efficient solar panels you could get 250w/sqm. That works out to 11.25 kwh/hour. The bus advertises with 600km of range with 800kwh of batteries so that is 1.33 kwh/km. Hence it could do ~8km/h on average when it is sunny.
The math does not really work out to a viable product with this bus, but it is not too far off. A city bus that has been purpose-built for low speed in urban areas without other traffic may work as it can make some sacrifices. For instance, since it runs much slower on average it would need smaller engines. It could also use more light-weight material since it won't need to handle high speed collisions. If it is just used for short distances within a city center it could also do away with seats. Lower speed should also lead to lower consumption.
The Solaris Urbino 18 weighs 17.5 tons curb weight. Assuming fuel consumption is pretty linearly related with weight and you could get it down to less than half, you could get a bus with a range of 10 miles per hour of charging. If it drove for 6 hours a day, but got charged for 12, 20 miles on average per hour is possible.
Yeah I wasn't clear enough but I was really thinking about the most limited form of "transportation", low speed, low weight, so minimal frame and no protections really. Basically a string of bus stops on wheels. Maybe an average speed of 13mph would be enough. That's 3 three times the average walking speed.
Why bother? Put the charge station in the bus stop instead. They have a longer runtime to charge and the bus does not have to be slow. Potentially easier to maintain too.
Or even do light rail and electrify the tracks with a solar network wherever you want.
Would that be more interesting with tram because of the low-friction wheels?
I imagine that could be viable in, say, Dubai or some other extremely sunny place ?
Why bother ? Have the solar panels on top of the tram warehouse, use the tram batteries for storage, swap empty ones for full ones when needed. If the solar array is down use the grid. That way you divid points of failure instead of multiplying them
Or... power the tram lines from the grid and feed solar power into the grid somewhere else.
Trams use fixed infrastructure, including overhead power lines. I'm sure they must exist somewhere, but battery-powered trams are not popular.
> I'm sure they must exist somewhere, but battery-powered trams are not popular.
Yes, they do exist. The Alstom Citadis at Rio de Janeiro, which I take often, uses a supercapacitor for small pieces of its route (mostly crossings where the third rail would be damaged too often by vehicle traffic, or be impractical); according to the Wikipedia article (https://en.wikipedia.org/wiki/Alstom_Citadis), the Alstom Citadis at Nice uses batteries for parts of its route (https://www.railway-technology.com/projects/nice-trams/). I'm sure there are others.