I wonder if it would be OK-ish to build a very lightweight, very long, low powered solar "bus" (or a tram like chain). Just enough to roam around a city at 15-20mph for free.
You'd get enough surface to get ~4kW
I wonder if it would be OK-ish to build a very lightweight, very long, low powered solar "bus" (or a tram like chain). Just enough to roam around a city at 15-20mph for free.
You'd get enough surface to get ~4kW
There have been solar car competitions that colleges have been doing for decades. Here's a YouTube compilation of one that ran last week: https://www.youtube.com/watch?v=ZBin-oXBJzM
I think it can help calibrate people's intuitions about what you can expect out a pure-solar car.
You also need to remember that inside those shells is basically nothing but a driver. No AC, no seats for people beyond the bare minimum. And that's broad daylight. So you need to look at them doing 20-30mph and bear in mind that it's still not comparable to a street-legal sedan of a similar size doing 20-30mph... those cars are essentially as close to "a mobile cardboard box" as the competitors can make them.
You might be able to build something that people would agree is "a bus" that moves with a couple of people on board, but it probably will stop moving once it enters shadow. Anything that we'd call "a bus" is going to need a lot more physical material per unit solar input than those cars have. I'm not sure that even "moves with a couple of people on board" will necessarily end up being faster than those couple of people walking, either. It's effectively impossible to power a vehicle with its own solar footprint in real time. It also ends up difficult to use them to power batteries because having to move the additional mass of the batteries eats up the advantages of being able to gather power for larger periods of time. It's possible, because of course you can hook a car up to solar panels and eventually charge it, but you don't get very many miles-per-day out of it for what fits on the car itself alone if you work the math.
Yup, was just going to link something like that— here's the University of Waterloo's solar car team's vehicles: https://www.uwmidsun.com/our-cars
And even those IIRC don't drive continuously. They drive for part of the day, then park them angled into the sun for the other part of the day to top up the batteries.
It's pretty hard to beat fixed panels + fast charging + parking your vehicle in a garage where it doesn't see the sun anyway (or get super hot).
Thx that was a really awesome video!
Commenting here to encourage other HNers to go watch it. Right now it has under 400 views and no comments.
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.
4kW on a bright sunny day, for a few hours around noon. Even my small EV outputs 100kW when floored, and 4kW doesn't get it very fast.
In direct, unshaded sunlight. Which is the opposite of any significant sized city I’m aware of.
We have trams. We don't need to make worse trams
I suspect the lightweight, and hence low power requirements, are the correct part of the hypothesis. But making the vehicle as big as a bus implicates a lot of weight. Maybe a solar charging cargo bike fairing would have some benefit, but that's an expensive bike and it will tend to get stored indoors.
Well, if you have a fixed route you are not limited by space on the vehicle to put solar on, but can provide electricity via a rail or wire or something and then gather energy on some larger Solarstation or from wind turbines or what else comes to mind.
Then you can reduce rolling resistance by using steel tracks and steel wheels ...
... and oh, you have invented the tram/light rail ;)
(But even with solar you need to finance the construction and maintenance, even the slow vehicle need some ... thus either tax finance or charge fares or mix income)
Maybe an electric assisted pedal bus with a solar roof would make sense.
Very location specific, might do wonders in Cancun or San Francisco or Vegas, not so much in Gatlinburg or Seattle or anywhere where there is not a lot of tourism or where there is a lot of rain or that has a long snowy season.