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Ask Slashdot: What Stands In the Way of a Truly Solar-Powered Airliner?

Soulskill posted about a year and a half ago | from the i-blame-gravity dept.

Power 590

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?"

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590 comments

Um... (4, Insightful)

mbstone (457308) | about a year and a half ago | (#41821811)

Clouds?

Re:Um... (3, Funny)

GeneralTurgidson (2464452) | about a year and a half ago | (#41821835)

Heaven takes up a lot of space too.

Re:Um... (4, Informative)

Naatach (574111) | about a year and a half ago | (#41821951)

Valid point. A solar powered fleet would limit travel to daylight hours - not just twilight but sun-overhead daylight. East-bound travel would have to start and finish within a short time-span mid-winter. Adding a fuel backup means adding all the infrastructure necessary to convert fuel into motion in addition to electrical systems used for solar energy. By the time you add all that and the fuel, you've exceeded the weight limit that would allow solar-powered flight.

Re:Um... (5, Funny)

Motard (1553251) | about a year and a half ago | (#41822027)

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.

Re:Um... (4, Insightful)

roc97007 (608802) | about a year and a half ago | (#41822131)

I'm pretty sure "solar powered" and "jet engine" do not belong together.

The fastest airplane can't match the 2200 mile (0)

Anonymous Coward | about a year and a half ago | (#41822183)

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.

The fastest airplane can't match the 2200 miles per hour (angular speed) that the Earth rotates and moderate latitudes. You would need a very fast rocket to "follow the sun"

Re:The fastest airplane can't match the 2200 mile (2)

Motard (1553251) | about a year and a half ago | (#41822201)

Yeah, but they're not using *solar* jets.

Also (5, Insightful)

Flounder (42112) | about a year and a half ago | (#41821823)

Night?

And what happens when... (0)

Anonymous Coward | about a year and a half ago | (#41821831)

You try to fly at night, or in cloud-cover?

rain. and clouds (0)

Anonymous Coward | about a year and a half ago | (#41821837)

rain. and clouds

Darkness (0)

Anonymous Coward | about a year and a half ago | (#41821845)

In general Darkness would stand in the way of solar powered anything...

Hybrid... (1)

ilikenwf (1139495) | about a year and a half ago | (#41821849)

Build one that's a hybrid. Solar during the day, electric turbines powered by jet fuel somehow at night.

Re:Hybrid... (0)

Anonymous Coward | about a year and a half ago | (#41821977)

Carrying that fuel is going to require a lot of energy when it is not being used. If a solar plane is going to work, it has to benefit from the lack of fuel weight to make up for the energy difference produced by fuel vs solar energy.

Re:Hybrid... (1)

XaXXon (202882) | about a year and a half ago | (#41821995)

as well as combustion engine weight

Simple : (5, Funny)

Anonymous Coward | about a year and a half ago | (#41821851)

Nothing a good kickstarter campaign cannot solve...

Re:Simple : (-1)

Anonymous Coward | about a year and a half ago | (#41821957)

Kickstarter is a tool of the parasitic venture capitalists. We need a basic income to encourage innovation. The government should eliminate all taxes and just print money and provide everyone with a basic income. The only reason Obamaphone lady hasn't already invented a solar powered airplane is that her welfare check isn't big enough!

Re:Simple : (1)

partyguerrilla (1597357) | about a year and a half ago | (#41822121)

That would ensure we will never see the product in question.

Well (0)

Anonymous Coward | about a year and a half ago | (#41821859)

A prolonged lack of sunlight comes to mind.

A solid grasp of reality? (5, Informative)

Anonymous Coward | about a year and a half ago | (#41821861)

Just saying...

Batteries. (5, Insightful)

sbrown7792 (2027476) | about a year and a half ago | (#41821869)

The capacity and weight as well as power delivery, for taking off (with clouds above) and night flights.

The math doesn't work (5, Informative)

Grayhand (2610049) | about a year and a half ago | (#41821875)

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.

Re:The math doesn't work (2)

SuperMooCow (2739821) | about a year and a half ago | (#41821947)

We'll be facing an energy crisis sooner or later. I say we should ban planes altogether and switch to trains and boats exclusively.

Re:The math doesn't work (4, Insightful)

jesseck (942036) | about a year and a half ago | (#41822043)

Horses are a truly renewable resource- when one wears out, sell it for meat in a foreign country (or maybe our own some day), and buy a new one. Add a buggy, and a whip to go fast, and you are green.

Re:The math doesn't work (1)

k8to (9046) | about a year and a half ago | (#41822085)

Well, considering that green means a sensible combination of renewable and efficient.. not so much.

Re:The math doesn't work (5, Interesting)

faedle (114018) | about a year and a half ago | (#41822073)

Technically, the "MPG" per passenger mile is lowest on an airplane. A fully loaded Boeing 747-400 gets the equivalent of 91 miles per gallon.

Re:The math doesn't work (1)

Anonymous Coward | about a year and a half ago | (#41822241)

Maybe vs. a car with a single passenger in it, but take a car with 30mpg and 5 passengers, and you've got the equivalent of 150 mpg.

Re:The math doesn't work (0)

BoRegardless (721219) | about a year and a half ago | (#41822141)

I'll be we have a pandemic spread by airliners before we have an energy crisis. Post-pandemic we won't have nearly as much need for energy & a lot of other items.

Size. (5, Informative)

Gordonjcp (186804) | about a year and a half ago | (#41821879)

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.

Re:Size. (5, Interesting)

K. S. Kyosuke (729550) | about a year and a half ago | (#41822039)

You use the energy to synthesize liquid hydrocarbons with high energy density, then you pour them into the airplane...and you have a solar-powered airplane! Come to think of it, all airplanes are solar-powered these days, only the sunlight is of a vintage brand.

Re:Size. (1)

cultiv8 (1660093) | about a year and a half ago | (#41822095)

Hell, I just want a solar-powered cell phone, which they still can't figure out [cleantechnica.com] .

Its (0)

Anonymous Coward | about a year and a half ago | (#41821881)

a simple matter of weight ratios....

Darkness (1)

TechJones (781168) | about a year and a half ago | (#41821883)

In general darkness stands in the way of anything solar powered..

Let's go retro... (4, Interesting)

Flounder (42112) | about a year and a half ago | (#41821885)

I always thought that heavy-lifting solar-powered airships would make excellent replacements for long-haul trucks.

Re:Let's go retro... (1)

ecloud (3022) | about a year and a half ago | (#41822083)

That's a good idea actually. It just takes a lot of space relative to the cargo it can carry, but the sky is big so what the heck. I suppose it's just not going to be fast enough for passenger transport.

Maybe if the envelope was e-ink, you could make it rise by turning it black (to absorb sun) and fall by turning it white. Or use a tether to raise and lower the cargo so that you don't have to completely land in order to "drop-ship" something. Not that it would work so well when the wind is blowing...

Re:Let's go retro... (5, Informative)

gman003 (1693318) | about a year and a half ago | (#41822165)

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".

Ending headlines with question marks, again (4, Insightful)

Gothmolly (148874) | about a year and a half ago | (#41821891)

Dear Slashdot, this is not a highschool paper.

Also, Roland Piquipaille is dead - please stop with the sensationalist, page-hit-generating crap.

Re:Ending headlines with question marks, again (2)

ThatsMyNick (2004126) | about a year and a half ago | (#41821933)

This is Ask Slashdot. If your headline does not end with a question mark, it should not be on Ask Slashdot.

Re:Ending headlines with question marks, again (0)

SuperMooCow (2739821) | about a year and a half ago | (#41821981)

OMG! Roland Piquipaille is dead! STOP THE PRESSES!

Re:Ending headlines with question marks, again (1)

Farmer Tim (530755) | about a year and a half ago | (#41822197)

Why stop them now, when his writing is at its peak?

Re:Ending headlines with question marks, again (2)

TeknoHog (164938) | about a year and a half ago | (#41822051)

The answer is "No", because Betteridge's "law" is the new "correlation is not causation".

Uhhh, I think it is called energy density. (0)

Anonymous Coward | about a year and a half ago | (#41821895)

Find a way to put the energy content of 10,000 pounds of jet fuel into a battery and you will start to see electric airliners.

Physics. (5, Insightful)

Anonymous Coward | about a year and a half ago | (#41821897)

In simple terms, Physics.

physics (1)

zerotorr (729953) | about a year and a half ago | (#41821899)

I'm guessing one of the numerous problems would be surface area to power requirement. I don't think a commercial aircraft could harness enough sun to sustain itself aloft, regardless of the efficiency. Also, batteries are heavy. And night time.

Uh, surface area? (4, Informative)

TWX (665546) | about a year and a half ago | (#41821903)

I don't think that the entire surface area, even with a truly 100% efficient panel, would produce the power needed to propel the aircraft.

So, I guess that you could say that physics gets in the way.

yes, there are solar-powered flying wings. They are not man-rated, they fly very slowly, they are very fragile, and they carry only the most minimal payload/cargo, usually a miniaturized electronics package for a very specific purpose. They're analogous to the folding two-wheel luggage dolly as compared to the crew-cab pickup truck.

Re:Uh, surface area? (1)

ThorGod (456163) | about a year and a half ago | (#41822025)

I'm curious if it's just current efficiency problems (from panels to propellers), or an actual roadblock.

What's the estimated, average solar energy passing through a square foot of area in the sun?

Re:Uh, surface area? (1)

TWX (665546) | about a year and a half ago | (#41822081)

I think that it's an actual roadblock. I'm not strong enough of a student of physics to calculate it, but one could calculate the total energy shining on a surface at any given moment. I expect that quantity of energy will be less than necessary to provide lift.

insufficient energy density (0)

Anonymous Coward | about a year and a half ago | (#41821905)

It takes a lot of power to fly, and fully-loaded planes weigh a lot. So it's hard to imagine solar technology being able to scale to jumbo jets. We'll be lucky to build some sort of way over-sized, ultra-light plane which can carry one person, or several.

Ok, stupidest Ask Slashdot ever (0)

Anonymous Coward | about a year and a half ago | (#41821907)

If you want solar-powered transportation, it won't be an airliner.

You could argue you could convert solar power to another form and use that, but it wouldn't be a solar powered airliner, would it?

Sheesh.

First thoughts... (1)

eexaa (1252378) | about a year and a half ago | (#41821909)

Just first thoughts:

1- energy efficient (which is necessary with low-surface solar-powered stuff) aircrafts are way too slow, much slower than jets. Customers basically don't like spending time sitting in airplane.
2- more people onboard add weight (there should be at least 3 crew people for a commercial flight, plus at least one passenger, sums to twice the largest amount of people I've ever seen on solar-powered plane)
3- more energy needs more surface, which adds both weight and drag.

I hope someone here will be able to apply some kinetics/aerodynamics equations that show those thoughts more accurately.

Answer (2)

pbjones (315127) | about a year and a half ago | (#41821911)

The man with the paddles or flags.

And don't forget... (0)

Anonymous Coward | about a year and a half ago | (#41821917)

Gravity. (mostly)

Solar Cell Efficiency is a big enough problem (0)

Anonymous Coward | about a year and a half ago | (#41821919)

I haven't done any research on this lately, but when I was in school a friend of mine was on the Solar Powered Car team. The car had a top speed of something like 45 mph. If the cells on a small very light car can only produce enough energy to bring it to speeds well below those of a gasoline engine, I can't see even the most expensive available cells over the admittedly larger surface area of the plane producing close to the energy needed to lift a many ton aircraft.

Weight (1)

Brandano (1192819) | about a year and a half ago | (#41821925)

All forms of direct solar power usage have a way too small energy density to be currently considered for a commercial plane.

Physics (1)

MetalliQaZ (539913) | about a year and a half ago | (#41821939)

Forget for a moment that people like to fly at night. There is not nearly enough energy density in sunlight for it to be useful for airlifting hundreds of people or tons of cargo. It's plain physics. The amount of energy needed to stay airborne is X, the amount of energy in sunlight over the area of a plane is Y. X is far larger than Y.

Re:Physics (1)

h4rr4r (612664) | about a year and a half ago | (#41822239)

So reduce X. Hydrogen is pretty light, perhaps it or Helium could be used as some form of "lifting gas", then only forward locomotion would be powered by solar. A solar collector could be used to boil water to turn a turbine and thus spin propellers. This steam airship could one day transport goods and passengers.

Current Solar Powered Aircraft (2)

brit74 (831798) | about a year and a half ago | (#41821941)

I recommend looking at the current solar powered aircraft - they're extremely light, look fragile, and barely carry anything. They generally look like gliders with some efficient propellers. Seems like it's a matter of efficiency and getting enough power from solar panels. I'm also betting they don't travel very fast (commercial aircraft travel above 500 MPH).
http://www.google.com/search?q=solar+power+aircraft [google.com]

Lots of things (1)

NinjaTekNeeks (817385) | about a year and a half ago | (#41821943)

1). Batteries are heavy and not super efficient
2). Night Time flights are out, so are bad weather flights
3). You need a ton of solar panels
4). Solar panels are not that efficient yet

So weight, inefficiency and the fact that the technology isn't there yet.

And (0)

Anonymous Coward | about a year and a half ago | (#41821949)

Gravity.

Energy density (1)

Nutria (679911) | about a year and a half ago | (#41821955)

It requires a lot of energy to move an airliner (hell, even a small single-engine plane like the Cessna 150) fast enough to produce wing lift.

Maybe if we had direct photonic -> electrical energy conversion it would work for light aircraft on a sunny day, but no way on an airliner loaded with passengers and cargo.

Clouds? (0)

Anonymous Coward | about a year and a half ago | (#41821969)

It's one thing to build a super light craft with overlong wings that can carry two people and can be flown when optimal conditions present themselves. It's another entirely to build a reliable transit system for hundreds of people and thousands of pounds of luggage per flight. Ignoring cell efficiency and the area required for panels, the weather isn't going to cooperate, and your customers aren't going to care.

If you just had a second set of craft that could do mid-day only, perfect weather flights,

Now, you did say "solar" and not "electric". I'm sure some smart cookie is going to get on here and show how a battery-operated, cell/fuel hybrid backed system would be feasible...

Just my $.02...

Perhaps... (0)

Anonymous Coward | about a year and a half ago | (#41821973)

The laws of physics?

It's a combination of things (1)

Bondolon (1000444) | about a year and a half ago | (#41821975)

Solar Cell efficiency is low, and would likely be ineffective given the limited sun-exposed faces of the aircraft. Using a quantum-dot paint for solar could be viable (they're far more efficient). Secondly, batteries are currently very heavy, which would be a problem. Lightweight, structural batteries would help greatly with that issue. Thirdly, batteries don't really store enough energy currently. Next-generation structural batteries potentially could, but those are some years off. Lastly, the anodes and cathodes of current batteries degrade too quickly. There are upcoming technolgies that can withstand tens of thousands of recharge cycles, but they're all very preliminary. Since planes are expected to have very long life spans, that makes electrical planes currently impractical. Given the above technologies, electrical planes will be very practical within probably 20-30 years. Until then, they are impractical because, logistically speaking, you charge up the plane and, while it's flying, let the solar do all it can to keep the batteries up. The distance the plane can travel, then, is a function of its total stored energy and all of the energy collected from the solar.

Slow (0)

Anonymous Coward | about a year and a half ago | (#41821985)

A solar Flyer would be prop driven, means slow low alt, bumpy flights..

Size (4, Insightful)

sinij (911942) | about a year and a half ago | (#41821989)

Assuming 100% conversion efficiency, zero solar panel weight and an access to ideal tropical daylight during the flight you'd have to have a collector size of a couple football fields to power typical airliner.

Why? It is simply not practical application of technology, you hair-brained hippie.

Propulsion (0)

Anonymous Coward | about a year and a half ago | (#41821991)

It's mainly an issue of propulsion. Currently there are no purely electric propulsion systems that would be able to provide the necessary thrust for an airline sized aircraft.

There are vast fundamental aerodynamic differences between a 2 seat glider (as per the link) and a 100+ seat 737. Combine those with the propulsion requirements of each and a fully electric commercial scale aircraft just doesn't make for a viable alternative.

Re:Propulsion (1)

sinij (911942) | about a year and a half ago | (#41822157)

Not quite. There is no reason why propeller or jet could not be powered by an electric motor. The reason it isn't currently done is that jet fuel has much higher energy density (and as a result significantly less fuel weight required for a trip) than any battery technology. One of the reasons jet fuel is clear winner in weight/energy ratio is that major component of the chemical reaction is plentiful in the atmosphere and you don't need to carry a supply of it.

physics (0)

Anonymous Coward | about a year and a half ago | (#41821997)

Even on a bright cloudless day with 100% conversion of solar light into electricity you still would not be able to collect enough to fly a plane with more than a few people in it. Such a plane would have to be so big that it will be impossible to keep from breaking up.

Re:physics (0)

Anonymous Coward | about a year and a half ago | (#41822117)

Sunlight power density is 120 W/meter^2 and to achieve 5-10 MW requred to fly a plane you need 50,000 - 100,000 square meters of 100% efficient photovoltaics.

Come On?! (0)

Anonymous Coward | about a year and a half ago | (#41821999)

Power to weight ratio. SqFt of solar collector needed. I recommend reading any creditable article on the current prototypes. We might get there at some point but this question is asked in a silly way.

Seriously? (0)

Anonymous Coward | about a year and a half ago | (#41822001)

Seriously, "Conspiracy views aside (which may be valid)"? That statement along speaks volumes...

I'm no battery or solar tech, but try to just use basic logic and common sense! We barely have electric cars that are viable, with the best having ranges in the 300mi vicinity. Cars consume FAR less energy to move than aircraft do. Therefore, you're going to see long range electric cars well before aircraft. The energy density of fossil-fuels is outstanding, which is why they continue to be used. The cost of battery technology is high and the size/weight is great, which is what limits the range and performance of electric vehicles.

What stands in the way isn't some imaginary evil cabal, it's technology - and it's years if not decades off. It will happen at some point because energy is fundamental to so much of what we do, and material sciences is moving in leaps and bounds so battery tech is really evolving.

But you still need two things to make this happen - first, a usable electric plane, by usable, I mean one that flies for more than a couple minutes. Next you need solar cells with super high efficiency - enough that it's somehow able to recharge the super batteries that would be necessary.

I hope the original poster was a child or at very least fairly young, otherwise it's a sad commentary on the problem solving and reasoning skills of 'average' person...

Physics? (4, Informative)

Overzeetop (214511) | about a year and a half ago | (#41822007)

Physics, mostly. Take 1200W/m^2, then imagine the upper surface area biggest plane you can practically create - that'd be ~1200m2 for a 787 dreamliner, or 1.44MW. That's the limit of power you will have on a sunny day with 100% efficient solar panels. Buy really expensive cells, and divide that number by 5. Then multiply by 0.7 for really efficient conversion to a form you can use. Your now at 202kW, or 271HP. That's probably around 10% of the cruising HP of an actual jetliner.

Assuming that actually works...
Speed - you're probably looking at a prop or fan flying at maximum efficiency, which probably means relatively slow.
Overall cost efficiency - solar panels cost, in power, as much or more than the electricity used to make them.

Re:Physics? (0)

Anonymous Coward | about a year and a half ago | (#41822225)

Physics, mostly. Take 1200W/m^2, then imagine the upper surface area biggest plane you can practically create - that'd be ~1200m2 for a 787 dreamliner, or 1.44MW. That's the limit of power you will have on a sunny day with 100% efficient solar panels. Buy really expensive cells, and divide that number by 5. Then multiply by 0.7 for really efficient conversion to a form you can use. Your now at 202kW, or 271HP. That's probably around 10% of the cruising HP of an actual jetliner.

Assuming that actually works...
Speed - you're probably looking at a prop or fan flying at maximum efficiency, which probably means relatively slow.
Overall cost efficiency - solar panels cost, in power, as much or more than the electricity used to make them.

I'm pretty sure everything but game consoles cost more than the energy to make them costs.

loitering vs 500mph (0)

Anonymous Coward | about a year and a half ago | (#41822047)

Energy density in solar power is pretty low. Current solar-powered airplanes do only slightly more than loiter.

Paying customers expect to travel about 500 miles an hour. Even with theoretical 100% solar energy conversion, no solar plane will come close to that.

The weight of batteries (0)

Anonymous Coward | about a year and a half ago | (#41822049)

You'd need a heck of a lot of batteries to hold sufficient power for a plane. I suspect these would simply weigh too much with today's battery tech.

just my opinion (1)

mardicas (1786618) | about a year and a half ago | (#41822055)

It would make more sense to me to build tehse large solar panels to the airports themselves, since they use up quite a lot of surface area already. Produce H2 from the electricity and use it as a fuel to power the planes. Burning it will produce only water. "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. " it is the opposite, without the need for fuel there would be no war, no profit to military corporations and oil companies...

Solar powering devices (1)

wiegeabo (2575169) | about a year and a half ago | (#41822057)

The one thing you could do to save on fuel is possibly power the non-essential technology from solar. The tv's, sound system, charging stations, satellite phones, and the like. You probably wouldn't see huge tonnages of fuel saved per flight. But over the course of a year, with all of their planes, it would probably add up to a noticeable savings for airlines and pay for itself in relatively little time.

And if it's night, the plane isn't above cloud cover, or there's an issue with the solar system, it should be a simple matter of automatically switching back to standard power. (I'd assume the planes wouldn't carry batteries due to extra weight)

weight. power (1)

circletimessquare (444983) | about a year and a half ago | (#41822063)

even the best tech theoretically, if you consider the maximum power possible you can get from sunlight over a given area, would have to be supported by some sort of scaffolding that, again, with the best strength to weight ratio we think we could get, would still not be enough to get it off the ground

but you can still do solar powered aircraft: biofuel

this, or so I heard (1)

NoiseCounsellor (2668963) | about a year and a half ago | (#41822065)

If solar-powered cars remain fiction because their surface area is insufficient to harness the power needed to perform in a way comparable to your current average car, I doubt very much that commercially viable air travel would be possible for the exact same reason. Also, for any moving object, realining the panels needs to be a little quicker than one rotation in twenty-four hours, unless you're perfectly satisfied with about half of them not being exposed to the sun at any given time, depending on the way you're traveling.

Air Ship (4, Insightful)

waimate (147056) | about a year and a half ago | (#41822075)

A solar powered air ship is probably more the go. Greater surface area, less power required. But it would need to fly above the weather, and the low speed combined with daylight operation would yield a very low range. Probably in the same category as a solar powered submarine.

A Solar Eclipse... (0)

Anonymous Coward | about a year and a half ago | (#41822077)

... The Moon can get in the way at the most inconvenient times.

You mean, other than power to weight ratio? (0)

Anonymous Coward | about a year and a half ago | (#41822091)

Nothing.

Unless you are also counting the cost of all that carbon and solar cells.

Are you for real? (0)

Anonymous Coward | about a year and a half ago | (#41822101)

Conspiracy views aside (which may be valid)

You know, if I could, I'd punch you into paralysis.

This has to be one of the most stupid "Ask Slashdot" posts I've ever seen... and that, frankly, takes some doing.

it's the solar power flux (0)

Anonymous Coward | about a year and a half ago | (#41822125)

You're kidding, right?

Power consumption of a 787: ~200 MW (estimated from 787 range, cruise speed, and fuel capacity)
http://pilotjohn.com/sizing-up-the-boeing-787-dreamliner-and-the-airbus-a380/
http://en.wikipedia.org/wiki/Aviation_fuel#Energy_content

Power incident on a *DISK* of the same size as the 787, on the equator at high noon w/o atmo: ~3.5 MW.
http://en.wikipedia.org/wiki/Boeing_787_Dreamliner
http://en.wikipedia.org/wiki/Solar_constant

Not even close...

It's about power (1)

QuasiEvil (74356) | about a year and a half ago | (#41822133)

Quite frankly, solar energy isn't that dense (only a couple kW per square meter) and aircraft require a tremendous amount of power to actually be able to move useful loads at useful speeds. Jet engines are usually rated in pounds of thrust, which I'm too lazy to go find the thrust-speed-altitude relationship to convert that to power. A number I could find was that a single C-130 turboprop engine is rated at about 3.3MW of output. So with four of them for one of these cargo haulers, that's about 13MW of power. Even assuming 100% conversion efficiency and 3 kW/m^2 at cruising altitude (it's roughly 1kW/m^2 at sea level, and 1.5kW/m^2 at 6000 feet, so this is probably close or a bit generous), you'd need 4333 square meters to collect enough power. The wingspan of a C-130 is 40 meters, so you've basically only got at most maybe 160 square meters of collecting area on the wings. And that's at 100% efficiency. Now consider that the overall system efficiency for photovoltaics would be around 10%, and that you'd need storage so you could take off, land, fly in the dark, and fly through clouds, and you've created something about the size of that flying quad-copter fortress from Avengers without all the actual coolness (or, say, adequate lift).

Nothing beats good old liquid hydrocarbons as fuel sources in terms of flexiblity and energy density.

Energy density (0)

Anonymous Coward | about a year and a half ago | (#41822135)

Energy density of solar radiation. Even with 100% efficient solar conversion you would be orders of magnitude behind the needed energy for commercial flights.

Unfeasible (0)

Anonymous Coward | about a year and a half ago | (#41822139)

I appreciate the sentiment, but the scaling here is all wrong for that to work. Solar capture is based upon the surface area, and fuel requirements will be based on the volume (assuming an average density of humans, which we're not going to budge much), making solar increasingly miniscule an energy source as the size goes up.

And if you're not talking about solar as an on demand power source, but a power bank, you're really talking about a battery issue. If we had the kind of batteries to support that, we'd then just charge them on the ground.

Aside from a low power source for small autonomous vehicles, solar is not a place to look for large scale flight. I doubt even max efficiency capture of light on whole surface would be enough, though I'm too lazy to calculate it at the moment.

Aviation regulation? (1)

Kwyj1b0 (2757125) | about a year and a half ago | (#41822161)

I am not sure, but doesn't any new technology require a long period of testing before getting certified as air-worthy?

I raise this point not because I am against regulations (I think certain bodies like the FAA are necessary), but because those will play a role in any new technology (not only solar). If someone came up with a much more efficient engine/turbine, could those be integrated into a new plane right away?

I once heard that the requirements are (fortunately) stringent, and that aircrafts still use old (and highly tested) algorithms and computers, instead of the latest technology.

One thing.... (0)

Anonymous Coward | about a year and a half ago | (#41822163)

Batteries are heavy, and it would take a lot of them. Perhaps a hybrid when they invent more light weight storage all things considered.

Low solar efficiency, and low fuel cell efficiency (1)

aurizon (122550) | about a year and a half ago | (#41822173)

Right now we gather about 20% of the suns energy, so if we had large solar banks making electricity that was used to power hydrogen generation, the resultant hydrogen being stored in hydrides or as liquid H2 in super-insulated hydrogen tanks, with which we run turbo-jets with the atmospheric oxygen. The Oxygen from the earlier electrolysis we sell locally. If we had high efficiency fuel cells and high power electric motors we MAY be able to make that work after 20 years of research
As it sits, 20% is too low an efficiency. If we could get it up to 40% through various stratagems and research, we would cut the hydrogen cost greatly.
The super insulated fuel tanks also need to be lighter as well. They are heavy now, but not as heavy as compressed hydrogen gas tanks would be. Liquid = lots cheaper.
This would be indirect solar powered airflight.

With direct solar power = no hope with heavier than air. The fragile demonstrators are almost useless for real cargo or passenger use. Zeppelins can work, but have restrictions on the air they can fly through - they are quite fragile, but even zeppelins are marginal even at 40% solar cells (we are now maxed out at ~~34% on the best cells)

Not fast enough (1)

rasmusbr (2186518) | about a year and a half ago | (#41822175)

Commercial transport is all about speed (up to a point). An electric plane would be significantly slower than a jet and a slower plane will produce fewer passenger miles per unit of time, which means it will take longer to produce the number of passenger miles needed to pay back the purchasing cost of the plane. Pilots and flight attendants are also about as productive as the plane is fast. In other words if you downgrade to a slower plane you need to pay for more labor to produce the same number of passenger miles. Also, passengers will not be willing to pay as much for a slow flight as they would for a faster flight all else being equal.

The fuel cost only amounts to something like a third of the cost of a typical ticket on a low cost airline, which means that the best the electric plane could do if it was as fast as a jet (which it wouldn't be) would be to cut the price by a third, so it's not like it would be revolutionary.

I think one could imagine a solar powered military drone, either heavier than air or lighter than air, that could stay airborne for weeks or months at a time and function as a sort of poor man's satellite which would be effective against Talibans and pirates and anyone else who doesn't have access to high altitude anti-aircraft missiles. I don't know why the US military or some other military dealing with guerrilla adversaries hasn't tried that.

How about... (1)

roc97007 (608802) | about a year and a half ago | (#41822179)

Zeppelins? With solar only (or mostly) required for propulsion, not lift, the power requirements are reduced dramatically. Might be a little slow, though.

power (0)

Anonymous Coward | about a year and a half ago | (#41822181)

It's easy to calculate how much energy an airliner requires, take the jet engines and look at the output, this is how much power they require, look at the size of the aircraft divde the surface area by two (just the bits that look up) and divide into the engine output, so you have KW/per Sq M, assuming 100% conversion from the solar cells, look energy from the sun, if it's greater than the requirements , all systems go , if no it's no go.

I have my suspicions that even with really big planes it won't fly.

Reality (2)

onyxruby (118189) | about a year and a half ago | (#41822191)

As much as we can try to legislate and wish technology into existence, you have to let things run their course. The hard politically incorrect reality is that things like battery technology and solar panel technology are years away from being production ready.

By way of point look at where they are actually being used in alternative fuel vehicles like the Fiskar Kharma. The car has a small solar panel on the roof and a battery to run the vehicle. Since it doesn't carry passengers for hire it has far lower requirements for regulatory purposes than a plane. It is made by a company that in principal is fully dedicated to having vehicles that don't run on fossil fuels. I think you can safely say they are not in on any conspiracy theories your tinfoil hatters can come up with.

The solar panel on this car is rated only for minimal charging for accessories and to help keep the battery from going completely flat (it is very expensive if this happens to your Tesla). The car still has trouble with batteries catching fire which led to a recall not that long ago. It's a beautiful car that is the bleeding edge of technology and arguably was produced before it was ready.

If they are having this level of problems with a car, just imagine the hurdles that need to be overcome with an airplane. Your weight to thrust ratio is much, much more critical on a jet or plane than a car. Your fire that burned down a garage could instead burn alive hundreds of people. You have regulations from all over the world to pass and they can take years for certification to clear.

Carbon fiber is just now hitting the market with the Boeing dreamliner, yet it's been in consumer cars for at least a decade and military jets for even longer. It will likely be decades before the technology /could/ power something like a commercial aircraft. It will then take at least another decade after that for it be proven well enough to be considered for passenger use. If you want to get real about energy usage for commercial aviation that help with finding fuels that can be used at a commercial scale (algae etc).

The problem is physics (1)

Anonymous Coward | about a year and a half ago | (#41822193)

Physics stands in the way. You're forgetting that, at any particular distance from the sun, there is only a finite amount of power per square area. This is called the solar constant, and at 1 AU it is about 1.36 kilowatts per square meter (taken from wikipedia). So even if you coated the entire surface of an aircraft with solar cells, and even if we go ahead and assume these cells are 100% efficient (a huge concession, given current solar cells are like 20-30% efficient), there is still a very limited amount of power being generated. My (very rough) estimates put the surface area of the top half of a 747 at 1000-2000 square meters, which means you'd be generating 1360-2720 kilowatts. That's 1823-3646 horsepower, if it's easier to imagine. Now consider that a 747 consumes 100-150 megawatts of power, 100 times what we're getting from our best-case scenario with solar cells. It's not even close. No amount of tweaking the numbers is going to make up 2 orders of magnitude.

Solar power only is viable when you have huge amounts of surface area to cover.

Electric, short-haul planes are feasible. (1)

mschaffer (97223) | about a year and a half ago | (#41822211)

Electric, short-haul planes are feasible. It will really be dependent on the amount of electricity that can be stored by on-board batteries.
Due to the limited surface area available, it may be faster to take a solar-powered bus or car. After all, ground vehicles do not need to produce lift and can travel at a slower pace.

Physics (0)

Anonymous Coward | about a year and a half ago | (#41822223)

Pushing a hundred butts through the atmosphere at 500 mph takes well over 10,000 thousand horsepower. If you somehow collected every last eV of solar energy incident on an airliner during flight, or even for many days before a flight (given some magical storage device that doesn't weigh more than the plane) you wouldn't have more than a fraction of that.

Maybe you could stick some lightweight thin-film solar panels on the fuselage to run the bathroom fans or something, if that makes you feel better. Be sure to source those from China.

Change the culture (0)

Anonymous Coward | about a year and a half ago | (#41822231)

Why be in such a rush to go every where? Biological Units have provided travel for 1000s of years, between horses, oxen, and donkeys. Feet have served well too, but that might cut into the lifestyle of fat and lazy.

Power Availability (1)

devnullkac (223246) | about a year and a half ago | (#41822243)

Airlines need to be extremely flexible and solar powered operations could only be conducted during daylight hours. In addition, unless there was a lot of excess capacity in the generated power, they likely could not operate near dawn or dusk or in cloudy conditions.

A lot of things (1)

Anonymous Coward | about a year and a half ago | (#41822251)

Manufacturing - You would likely need to coat all surfaces in panels while in an aerodynamically friendly profile. This would be a manufacturing nightmare - composites are only starting to make significant appearances in aircraft with the A380 and B787.
Weight - I don't know the specific weights per square foot for panels but you'd have to add that weight to all surfaces. I also doubt that they can be used in load bearing so you'd need extra structure. Add in batteries for some level of storage.
Efficiency - I don't believe energy density is remotely close to that of jet A. It takes a lot of energy to fly at Mach 0.80.
Life cycle cost - Aircraft go through routine maintenance and solar panels degrade over time. One of the challenges will be in designing an aircraft such that panels can be easily replaced without just popping off if they were damaged. And this would have to be done quickly. Engine maintenance is quick - put in a new stage/turbine/compressor where needed.
Continued improvements in existing technology - A320neo and B737Max are looking at 15-20% reductions in fuel burn from existing versions. Engine technology will continue to develop and make the competition with solar even more difficult.
Alternative fuel research - Research is being heavily conducted into alternative fuel sources. This is largely for environmental reasons but cost concerns are equally valid.

Obviously, it's not impossible as we have things like NASA's Helios (which failed for other reasons). But these are smaller aircraft that are working to build the technology beyond demonstrators. I would speculate that solar powered aircraft (if they become viable) to not exist in large scale for another 50 years as both Boeing and Airbus have largely committed their product lines for the coming decades.

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