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Ask Slashdot: What Stands In the Way of a Truly Solar-Powered Airliner?
centre21 writes "I've been reading about solar-powered aircraft all over the Internet, as well as solar power in general. But I'm wondering: is it more than just solar cell efficiency that's preventing the creation of a solar-powered airliner? Conspiracy views aside (which may be valid), it seems to me that if I were running an airline the size of United or American, eliminating the need for jet fuel as a cost would be highly appealing. So, I'm asking: what stands in the way of creating true solar-powered airliners?"
Night?
No boom today. Boom tomorrow. There's always a boom tomorrow. - Cmdr. Susan Ivanova
Nothing a good kickstarter campaign cannot solve...
Just saying...
The capacity and weight as well as power delivery, for taking off (with clouds above) and night flights.
I'm a huge solar fan but to make an aircraft that could carry a 100 or more passengers the surface area would be massive. No current airport could handle a plane that size and it'd never be cost effective. Better to run a plane off biodiesel. Even battery powered makes no sense. Large aircraft need a dense power source.
If you had 100% efficient solar panel, you'd have to make a solar panel the size of a small town to capture enough energy to power a passenger jet.
In simple terms, Physics.
- A 747 consumes 140MW. [ http://en.wikipedia.org/wiki/Orders_of_magnitude_(power) ]
- Nevada Solar One, a 400 acre solar generating station, generates 64MW. [ http://en.wikipedia.org/wiki/Nevada_Solar_One ]
Hmmmm...
But if you had a solar powered jet engine you could chase the sun. And you would never need to waste energy on landing lights.
Actually, that's not a bad idea. Might work better as a replacement for cargo ships, not trucks, though.
With Hydrogen/Helium providing the lift, the engines only have to provide thrust. And cargo rarely needs to go as quickly as people - it currently takes what, weeks, to cross the Pacific? So you can get by with much less power demands.
And you also get much more power to work with. Dirigibles are pretty bulky, lots of surface area, so you have nice big expanses to cover in photovoltaics.
And you even have less potential damage from wave motion or humidity compared to container ships. That might be enough of an advantage for getting electronics from the factory in China to the stores in US/Europe.
Someone get Apple on this - it makes a good stunt, at the very least. "iPhone 7 - now delivered by dirigible".
But if you had a solar powered jet engine you could chase the sun. And you would never need to waste energy on landing lights.
Why stop at that? If you had a solar powered transporter you could just go straight from wherever you are to wherever you want to be in two simple steps. In fact, once we can completely ignore basic laws of energy conservation and so on, why not just use a solar powered magic wand and will yourself to already be wherever you want to be?
=~ s,(.*),<sarcasm>$1</sarcasm>,g if any_point_you_wish();
what stands in the way of creating true solar-powered airliners?
Nothing.
Oh, you meant airplanes? Yea, sorry, can't help you there.
An enigma, wrapped in a riddle, shrouded in bacon and cheese
Aha! So all we need to do is build solar-powered helicopters that sits perfectly still while the Earth rotates under it until you're where you need to be!
Physics.
If Slashdot were chemistry it would look like this:Cadaverine
Let's bring some numbers into this.
According to this page, I can get a cargo container from Shanghai to San Francisco in 18-30 days. That's a distance of roughly 10,000km,
The Hindenburg could reach air speeds of 135km/h. While modern airships could doubtless reach higher speeds, we're also running off solar power here. So let's just run with that 135km/h figure. That gives us about three days to cross the same distance.
For further comparison, a Boeing 747 can make the trip in roughly 11 hours.
So we're beating the container ship by a factor of 6-10, but the jet is beating us by a factor of 6. So we just have to have a price halfway between the two. Unfortunately, that's hard to figure out, because the container ship charges by volume, while the aircraft rates I can find charge by weight. Ultimately, though, it's a moot point, as any figure I can come up with for the costs of running a solar-powered airship will cite work by a certain Dr. M. Y. Ass.
But hey, it might be a good niche to fit into. Faster and safer* than a container ship, but slower than a jet. Someone might be able to find a good use for that.
* Assuming, of course, no Sky Pirates are encountered. Then all bets are off.
I was gonna say night time.
Jet engines are quite inefficient. The main problem being power I would start with props.
To get an idea of the power needed, just take a regional aircraft, for example an ATR equiped with two PW100. That makes roughly 7000kW of energy provided to propellers. Lets suppose you have 100%-efficient electrical motors, and let aside aircraft internal consumption.
Now this paper suggest that high density power solar cells provides about 1kW/sqm. The only challenge is to find 7000sqm of surface exposed to the sun on a 22m long and 24m wide aircraft.
So far, the only electrical plane that I have been able to see were ultra light aircraft which could barely support they own weight and a pilot. Still a long way until commercial exploitation.
That's right.
A 737-300 burns about 5500 lbs/hour at cruise (~2500 kg/hour).
Jet-A contains 43 MJ/kg (lower heating value). So energy to cruise is about 107,500 MJ/hour = 29,800 kWh per hour
The terrestrial solar maximum (insolation on a hot sunny day at noon at the equator) is +/- 1000 watts/m^2. It's actually a bit higher at the equator, and will be higher still at cruising altitude. Call it 2000 watts/m^2.
So, just to maintain cruise speed (which is its most efficient operating mode, vs, say, takeoff or landing) you would need 15,000 m^2 of 100% efficient collector area. (Commercial PV is 15-25% efficient). A 737-300 is about 28m (wingspan) x 33m (length). So even if the airplane were a solid square of 100% efficient collector, it would still be an order of magnitude too small to power the plane at cruise.
The fundamental problem is that people do not understand the relative energy density of fossil fuels relative to renewable sources. Renewable sources are inexhaustible, but they are sparse. Fossil fuels are distilled sunlight - very dense. If solar energy is beer, petroleum is whiskey.
But you could use wind power then.
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