Sweden is testing a semi-truck covered in 100 square meters of solar panels
popsci.com
popsci.com
- the weight a semi-truck is expected to carry vs the surface area available to absorb photons vs motor efficiency. the energy obtainable via the sun exposed surface area available is multiple orders of magnitude lower than the amount of energy required by motors of current or near future efficiency to propel such a vehicle, with typical weight, to the even 1/2 the speed of normal traffic.
- the only way this works is if for some reason the truck is unmoving for long periods of time and has a massive battery system installed that can be charged up while the vehicle is immobile, which drives the cost up a lot, because any truck that's not moving is a capital asset that's losing money.
By the way, you can take advantage of this yourself on long highways by driving close (but safe) to large trucks, driving in their slip stream. It cuts fuel requirements substantially because the truck is doing some of the work of moving the air for you.
One puzzling thing is why trucks aren’t designed to be more aerodynamic, instead of a giant box shape. Anyone got any thoughts on this?
*aside from small things like added friction on bearings, changed tire geometry etc.
Second, those "tapered" add-ons in the back can help a lot to approximate a teardrop shape better given that there are a lot more constraints in general in the front.
This is rolling resistance, it's generally proportional to weight, and it's usually not negligible for heavy vehicles: it can easily make a large fraction of the energy usage of a truck, though at highway speeds it's rare for it to be the majority of it.
Yeah, 200 horsepower's worth.
Wind resistance at semi-truck highway speeds is very significant. Multiply the numbers here[0] by 9.5x to convert from BMW to Semi-Truck (accounts for increase in Cd and frontal area). So semi trucks might take on the order of 180hp at the wheel just to maintain speed. With drivetrain losses you'd need to be generating 200hp.
All this time and I never realised Pixar's Cars has been spreading misleading physics.
Sweden's wholesale electricity prices is ~€32/MWh in July 2023, so this is equivalent to a savings of €256/truck/year. My initial impression is that the juice is not worth the squeeze, but wondering if someone with more context would provide arguments for solar roofs on vehicles.
I know Hyundai (Ioniq 5) and Toyota (Prius) are also offering solar roof options on their cars, so there must be a good reason. The Prius, under ideal sunny conditions, can reasonably get to 1.1KWh/day (or 3.2mi of range), which is nothing to sneeze at, but still relatively small in the large scheme of things.
https://www.motortrend.com/features/the-2023-toyota-prius-pr...
There are two concept cars I know of that can actually get enough power from the solar panels on them to be useful. One of them is the Aptera, which is a no-compromise low energy vehicle. It's tear drop shaped and can only hold two people, so it's going to be a bit niche.
The second is the Lightyear solar electric vehicle, which is shaped a bit more like a standard car but is going to cost luxury car money for an ultra lightweight (read: no soundproofing) car.
And to what advantage? Charge per year doesn't matter, since you're recharging multiple times per year anyway there's no difference between the panels being on the car vs the ground, other than panels on the ground can be directed more optimally and don't add to the weight of the car.
Charge per day matters, and taking a 500 mile trip up to maybe 600 miles (on a perfect sunny day) isn't that big an improvement in practical terms.
Meanwhile, for us mortals: There's something to be said for using solar panels to power aircon/heaters/utilities/etc while the car is stationary outdoors.
Ever been to Sweden. I read somewhere that the sun shines there for half a year, uninterrupted. /s
When you see solar panel mounted on a road/bike path/under train tracks/car/truck you should instantly recognize a scam.
I’m not saying it’s an either/or because you can have both, but it does seem like this is potentially overly complex for minimal gains.
The individual may be minimal but the overall cumulative benefit may be worth it.
a) put solar panels over the truck
b) put solar panels in a fixed spot, where it's easier to use big panels, maintain them, avoid nasty vibrations, and transport the energy to a charger.
In b) you get more energy, even after transferring it to the truck. So you can use the extra energy to power other truck or a home or something, and then avoid burning fossil fuel and then saving the panel.
The option b) is more environmental friendly.
Somewhat related: https://what-if.xkcd.com/17/ Grass is the solar panel of cows.
Oh this is just a regular truck with solar across most of the trailer. That's a lot more area than my first guess.
Of course your best case scenario is only about 400sqft illuminated. Insolation tops out at 100w/sqft and the max efficiency of commercial panels is maybe 22-24%. Doing the math there you get something like 7-10kw which is nowhere near enough to push one of these down the highway.
A normal semi gets maybe 6-8mpg on diesel which means burning 8gal to go 60mi in 1hr. You get about 10hp/gal/hr out of a diesel so that means it takes something like 80hp or 60kw to drive a truck down the road.
It's more then enough to run the climate control, lights, and other cab loads and slow battery drain just a bit. But you'd have to leave the truck to charge for a week in order to drive for a day.
If you can have components with negative load it's all good. Say that 7-10kw / 60kw is 12% to 17% savings. 6-8mpg becomes 6.72-9.36 mpg
Or for laughs one could say every 10th car requires no fuel.
Even if you amortize this cost over several years, and even in climes with more sun, would the economic math work out?