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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?"
Clouds?
Night?
No boom today. Boom tomorrow. There's always a boom tomorrow. - Cmdr. Susan Ivanova
Build one that's a hybrid. Solar during the day, electric turbines powered by jet fuel somehow at night.
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 general darkness stands in the way of anything solar powered..
I always thought that heavy-lifting solar-powered airships would make excellent replacements for long-haul trucks.
No boom today. Boom tomorrow. There's always a boom tomorrow. - Cmdr. Susan Ivanova
Dear Slashdot, this is not a highschool paper.
Also, Roland Piquipaille is dead - please stop with the sensationalist, page-hit-generating crap.
I want to delete my account but Slashdot doesn't allow it.
In simple terms, Physics.
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.
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.
Do not look into laser with remaining eye.
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.
The man with the paddles or flags.
There was an unknown error in the submission.
All forms of direct solar power usage have a way too small energy density to be currently considered for a commercial plane.
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.
"Here Lies Philip J. Fry, named for his uncle, to carry on his spirit"
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
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.
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.
"I don't know, therefore Aliens" Wafflebox1
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.
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.
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.
Is it just my observation, or are there way too many stupid people in the world?
- 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...
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...
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)
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
intellectual property law is philosophically incoherent. it is your moral duty to ignore it or sabotage it
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.
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.
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.
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.
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.
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)
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.
Zeppelins? With solar only (or mostly) required for propulsion, not lift, the power requirements are reduced dramatically. Might be a little slow, though.
Oliver's law of assumed responsibility: If you're seen fixing it, you will be blamed for breaking it.
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).
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.
Yeah, but they're not using *solar* jets.
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.
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.
What do you mean they cut the power? How can they cut the power, man? They're animals!
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.
The sun only puts out about 1.3 kW/m2. A jumbo jet uses more than 100 MW of power, so even at 100% efficiency you'd need something like 100,000 m2 of solar panels.
You could make a huge, low speed flying wing, but if you're going to do that you'd probably be better off with solar powered high-speed rail.
You want to use solar power, on a 100+ton aircraft? OK, lets look at the numbers.
Surface area of the wings of a 747: 510 sq meters.
At 100% efficiency we would get 1KWh per sqr meter.
So, assuming we have these magic perfect solar panels you would need to lift 100+tons with 510KWh.
Simply not enough energy.
For comparison: A 747 uses over 190,000 liters of fuel to go from take off to cruising altitude.
A liter of aviation fuel is 33MJ. That's 6.2 million MJ used over the time from take off to cruise.
A joule is 1 watt per second.
And no, there is no conspiracy keeping solar out of aircraft.
The Kruger Dunning explains most post on
Alternative question: what stands in the way of a solar-powered dirigible? (we'll use helium instead of hydrogen like the Hindenburg did)
Nobody on /. got the correct answer although a couple got close. It all boils down to cost of capital.
There is no reason a solar-glider airfleet, or a solar powered fleet of blimps or whatever could not exist other than the existence of jetfuel powered competitors.
Your competitor rents $100M from the bank and keeps his planes in the air 20 hours out of every 24 hour day and during that 20 hours makes lets say 5 revenue generating flights. So five butts in seats per day or more importantly they sold at least 5 tickets per seat per day (probably a hair more).
You rent $100M from the bank and your planes sit on the ground on average 12 hours per day and you're lucky at the slower speeds involved to get maybe 1 revenue generating flight per day. So you sold one ticket per seat per day. Whoops.
Your competitors gross 5 times the cash you do to pay the bank loan... who cares if 30% of your expenses are fuel or fuel related (engine maint, whatever), leaving you with a mere 70% of previous expense, if you only get to keep 20% of your previous revenue... That's going to ruin your profit margin, in fact you'll be unable to pay the bank back unless or until your competitors go out of business.
The "world" could run on giant solar gliders, or solar powered helium blimps, or whatever, if and only if the cost of capital dropped way more than a factor of 5 and/or ticket prices floated up about 5 times what they are today. Frankly we will inevitably end up there sooner or later, maybe in 20 or 30 years. But its not going to work today.
"Science flies us to the moon. Religion flies us into buildings." - Victor Stenger
Use solar power on the ground to break up water into hydrogen and oxygen. Store hydrogen in liquified form. Burn it for propulsion, where it combines with oxygen and produces water vapor. There are probably still problems, though, as hydrogen doesn't have as much grunt per volume as other fuels. May be practical only for short hops, or may not be practical at all -- would have to do some calculations.
Oliver's law of assumed responsibility: If you're seen fixing it, you will be blamed for breaking it.
Any solar powered device that can't rely on constant direct sunlight needs batteries. In the case of planes they may not be able to generate enough power from solar panels in real time even under ideal conditions. So you need batteries that are charged pre-flight. Batteries are heavy and expensive. And they have limited storage capacity and power output. However there's a lot of research being done to overcome these limitations. Soon your idea may be technically feasible, but right now I think we're not quite there yet.
So I did the math and I'm getting something a lot closer to 1000 miles per hour at the equator. I can't do the math for greater latitudes except to say it approaches 0 mph at the North Pole.
No airplane could support enough collector area to take in enough energy to fly, even at 100% efficiency. Not to mention the problem of flying at night, in cloudy weather, etc.
is it more than just solar cell efficiency that's preventing the creation of a solar-powered airliner?
Short answer: No.
Why do we keep using fossil fuels really (in a non-conspiracy theory world)? Two words: energy density.
Gasoline has a significantly higher energy density than many (most?) explosives. TNT, gunpowder, etc. Compare that to batteries, solar cells, capacitors, whatever, you aren't even anywhere on the same chart. Jet fuel has an even higher energy density than gasoline. On top of that, the best solar cells ever are something like
Think about those solar planes you've seen. Super light weight, incredibly long wings with a super high aspect ratio (wingspan/chord). Often designed to fly at high altitude (above clouds). The kind of wingspan and PV cell area needed for a many-passenger plane would be astronomical. Maybe if PV cells were hyper-efficient, but even then, you can only optimize so much. I highly doubt that completely weightless 100% efficient solar cells completely covering a modern jet in perfectly clear weather at high noon would generate as much power as those jet engines do.
Ze Atomic Device! It iz Ztolen!
Seems to me that submissions are becoming increasingly of the sort the poster could have figured out himself if he had thought about it for 5 minutes. This one might be fun if submitted to xkcd's What If.
"When I first heard Daydream Nation it quite frankly scared the living shit out of me." -- Matthew Stearns
The sun doesn't provide enough energy to go even 200mph with passenger load. Taking off alone would be impossible.
Power to weight is critical in aircraft.
If instead you consider a fairly large airship, with the whole upward surface covered by solar panels, that should produce enough HP to transport as many people as the helium would allow to float. But that would go at less than 100mph, even with the best solar panels demonstrated in labs (40%).
An AirLINER? Like a gigantic tube carrying many tons and tons of people and cargo?
Just think about the size of the solar panels required to generate enough thrust to keep something like that airborne.
Maybe if you use a lighter-than-air craft, like a solar powered airship, then it'd be possible. But for a typical airplane, no way.
He read it on the internet. Seriously, this is what Slashdot is reduced to? Both from a quality of submitter stand point and the fact that it was approved. Sad.
I'll try not to make this boring. I'm a pilot.
Aircraft require a LOT of power to stay up. The most efficient aircraft are gliders. Even they require a lot of power to maintain flight. An airliner burns between 700-900 gallons per hour of fuel. Jet fuel is not the most efficient fossil fuel (gasoline IS more refined) but it still contains a LOT of BTUs.
In simple terms 128,000 BTUs per gallon times 700 gallons means 89 MILLION BTUs per hour of flight. [data sources - wikipedia]
At 429 BTUs per square foot, getting those 89 million BTUs would require 208K square feet per hour, or 3500 square feet per second.
A 737 has half that.
So if there were no such things as clouds.
If there was no such thing as night.
If there was no dropoff on photoelectric cells due to the cold of the upper atmosphere.
If energy delivery was 100% efficient.
Then a solar plane would only be half short on power to ever fly.
E
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
http://en.wikipedia.org/wiki/Energy_density#Common_energy_densities
Jet fuel =~ 44 MJ/kg
Lithium Air Batter =~ 9 MJ/kg
Most fuel consumed by airliners is done while rolling around the airport on the ground. A jet engine burns almost the same amount of fuel at idle as it does while in cruise. To start, older planes should be retrofitted with electric landing gear and engine start should happen at the hold short line when they're #1 for takeoff.
Imagine how much $8.00/gallon jet fuel is burned on the tarmac.
What the hell is electric landing gear? The wheels on the plan are unpowered and spin freely. All of the propulsion for moving around is provided by the engines. You can't keep the engines off until you're on the runway unless you're being towed. Also the engines need to be started using an external device so you'd need to drag that along so that it could spin up the engine and then start it.
"When you sit with a nice girl for two hours, it seems like two minutes. When you sit on a hot stove for two minutes, it
exploring new frontiers in "not even wrong".
Welcome to the Panopticon. Used to be a prison, now it's your home.
In general Darkness would stand in the way of solar powered anything...
Look, let's try to keep Microsoft out of this discussion, OK?
Faster! Faster! Faster would be better!
The problem is physics. Get rid of the laws of physics and it will become not just politically correct and environmentally feel good but possibly possible.
The issue is that while small electric planes can be made they are very different than passenger airliners like a Boeing 747. One difference is the the 747 is a LOT bigger. Being a lot bigger it has to move a lot more mass and push aside a lot more air. As the plane gets bigger and heavier the mass goes up far faster than the available surface area for mounting solar cells.
So, the solution is to do it all backwards. Instead of making bigger solar powered airplanes just make smaller passengers. This would be solved if people were to stop flying in airplanes and instead they sent their fleas, ticks, lice and bacteria to represent them at meetings, sporting events and vacations. The smaller avatar in the form of the flea weighs very little and takes up little space. They also don't complain about inflight service, need as much oxygen, the toilet, stewardesses, etc. This all saves more. Now you have a viable form of solar powered airplanes.
Alternatively consider not flying and not sending your flea bitten representative either. Just telecommute. The internet was invented like, a while ago. No need to waste fuel, materials or time. Go green!
This is why: http://what-if.xkcd.com/17/
There simply isn't enough solar power delivered to the surface of the aircraft, even at 100% conversion efficiency, to move people and luggage using only available sunlight.
Google tells me direct illumination to a surface perpendicular to incoming full intensity sunlight is about 1.4 kW per square meter. Google also tells me that the wing surface area of a 747 is around 5500 square feet. Only half of the 747 wing is directly illuminated by sunlight at any given moment, but the surface of the fuselage could be covered with photocells as well, so 5500 square feet overall is probably a decent estimate for the directly illuminated surface area of the aircraft as a whole. And for hand-wavy purposes lets assume that the entire surface of the 747 is perpendicular to the incoming sunlight (i.e. a planar plane... pun totally intended). And that we have perfectly efficient photocells giving us 100% conversion efficiency. Running the math, this gives us around 715kW under bright direct sunlight, or about 959 horsepower -- the equivalent of 1.5 2012 Ford Shelby GT500's.
Each engine of a 747 generates around 15,000 horsepower at cruise, and around 30,000 at takeoff, and a 747 has four engines. So you need around 125 times the power generated by a perfectly efficient perfectly illuminated solar-powered 747 to get said plane off the ground, and around 65 times the power for cruising. And then you could only fly it in the middle of the day near the equator.
Cyrano de Maniac
Weight - solar cells add weight. The huge electric motors to generate >10,000 horsepower would weigh a lot.
Nighttime - they'd sit on the ground all night.
Density of solar power - ~1 KW per square meter at the earth's surface, ~750 watts per horsepower to get 10,000 horsepower you'd need a square array ~85 meters on a side. That assumes 100% efficiency of cells and motors.
Not happening any time soon.
The fact that this question is even being asked shows how poorly people understand the practicalities of solar power. Cover something with PV cells and you've got power. Problem solved, right?
There are two problems here. First, small-scale solar power generation is just not very efficient. If you spend a lot of money and cover your roof with PV cells, not only will you not make back your cost, you probably won't even prevent enough greenhouse gas emissions to offset those emited by manufacturing and installation
Second is storage. There's just no way to store electrical energy that comes even close to the energy storage provided by hydrocarbons. And you have to have storage, because you can't count on the sun being out when you need juice.
These problems can be solved but without some fundamental breakthroughs they can't be solved on a small scale. So the future of solar power is huge generation and storage facilities, not vehicles covered with solar cells,
And you need to solve all of those problems (and many more) for multiple engines. Who operates single engine commercial passenger planes? Nobody. (I doubt one could even get FAA certification.) It'll likely be decades before anyone even makes the solar powered equivalent of a high-wing Cessna capable of carrying the typical four-passenger load that private planes easily handle now let alone a multi-engine commercial passenger plane.
Has anyone done the math for what the power output of a Cessna-sized wing covered with current technology solar panels would be? Are there any electric motors capable of translating that electrical output into sufficient lift to even get such a plane off the ground on a sunny day? If not, how big would such a wing need to be to get you enough power to get the plane off the ground? How maneuverable would the plane be with the gigantic wing that will likely be needed? I suspect that solar power may never be practical for use in aviation -- at least commercial aviation. Now I wouldn't bet against some EAA member concocting something that could be flown at Oshkosh. (But I would bet against their being able to fly it to and from the event.)
CUR ALLOC 20195.....5804M
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!
and the number of European or African sparrows you can capture.
SJW: a person who perceives an injustice, and while correcting it, commits a greater injustice.
That's a good thing, since your speed will be 0 mph between appropriate solstices at each pole, due to poor or no sunlight.
A solar Flyer would be prop driven, means slow low alt, bumpy flights..
Not at all. Sitting on the runway, perfectly still, would be a very smooth ride.
Faster! Faster! Faster would be better!
Use the Sun's energy to vaporize water to ultra-high pressure steam that is then directed as thrust and everything else works like a petrol jet engine?
Or use the Sun's energy to separate water into hydrogen and Oxygen and then burn them both in a modified petrol jet engine?
Wild ideas?!? Absolutely! But that's what we need. Let's think outrageously and go from there.
Sure, but the weight to energy ratio of either of these solutions would be prohibitive, unless you're talking airship instead of airplane, and maybe not even then. You'd have to do the energy collection on the ground and then somehow get it into the airplane. Something like a hydrogen plant on the ground that produces liquified hydrogen which is then used for fuel. (Which may still not work because even liquified hydrogen has much less energy per volume than jet fuel.)
As to using heat to vaporized water... unless your hydrogen fusion source is very local (as opposed to 92M miles away) I don't think you'll ever approach enough thrust to be noticeable. Heinlein used to write about torch ships that were propelled by superheated seawater, but the heat source was a nuclear fusion reactor in the vehicle.
Niven wrote about a lifting body propelled by air compressed to nearly-degenerate matter, but I don't know if the math works out for that one either.
Some "solutions" (like a steam powered airplane using a solar collector) aren't worth trying because they just don't pencil out. Heavier than air craft need a lot of energy to stay airborne and move about, and replacements for jet fuel have to have at least vaguely similar energy density.
Oliver's law of assumed responsibility: If you're seen fixing it, you will be blamed for breaking it.
Sanity? Reality? The laws of physics?
1. Lift
2. Weight
3. Thrust
4. Drag
I'm sorry, but your opinion seems to be wrong.
The most you can hope to get out of direct sunlight is 1.2 kw per m2, but more likely it's going to be 1 kw per m2.
The wing area is 510 square meters. Let's say that that you will cover just the wings with solar panels. Figuring 1 kw per m2, that's 510 kw, which is I'm estimating is close to 600 hp. I think you need more than 50 times that to operate a 747. Consider a DC-6 flew with nearly 10,000 hp and it's much smaller and slower than a 747.
That was the turning point of my life--I went from negative zero to positive zero.
Even if you had 100% conversion efficiency and no clouds, there's just not enough energy in the sunlight hitting a plane to lift it up and fly it with anything but a trivial payload, unless of course, you had a few 10s of thousand square feet for energy input. No problem with takeoff there, surely.
BUT, what you could do is mount solar panels on a large flattened hydrogen blimp and you're more or less on your way. You can even replenish the hydrogen from water if needs be. Slow, but functional.
Please do not read this sig. Thank you.
Truthfully, I think the only viable solar powered option is a huge giant blimp wing semi-dirigible. And that having a light weight spray on solar conductor.
Actually, that's not a bad idea. Might work better as a replacement for cargo ships
Boy oh boy, this is where industry knowledge separates the men from the boys. I just worked a file for a ship that had 180 million cargo pounds handled at one port, and it can carry about 250 million. There are also ships almost twice its size in operation today, and these are on a weekly rotation all over the world. There's some interesting calculations here for the mathematically inclined on how big the blimp would need to be. On the bright side, the bouyancy needed to airlift that kind of weight might solve our albedo issues though, what with the entire ocean being blotted out by blimps an all :)
What Stands In the Way of a Truly Solar-Powered Airliner?
Gravity?! :p
A typical trans-country flight in a Boeing 767 uses around 50,000 lbs of fuel or around 7500 gallons.
Each gallon of jet fuel contains 34 KWh of energy, so the 5 hour flight uses 255KWh worth of fuel.
A jet engine is only around 35% efficient, so 89,250kWh of energy is needed to power the plane for the 5 hour trip
Assuming your electrical drivetrain is 100% efficient, you need "only" an average of 18,000kW to power the plane. In full sun, during the peak of the day, you'll get around 1300W/m^2 of solar power, let's use 75% efficient solar cells (which do not exist) and assume 1kW/m^2 of usable power.
So, your mythical solar powered jetliner will need 18,000 m^2 of surface area as long as you don't mind flying only in peak sun.
A B747 is around 80m long with a 70m wingspan. If you constructed a huge rectangular solar array above the plane that's as long and as wide as the plane, you'd have 5600 square meters, you'd need at least 3 of these giant solar arrays to power the plane (ignoring the extra drag caused by the huge solar array).
This only looks at average power and ignores the huge amount of power used in takeoff to get up to cruising altitude, for that you'll need some pretty serious batteries or other power source (fuel cells?). I'd like to see what the numbers look like if you use conventional jet engines (or even something more like one-time-use JATO rockets) to take off and get up to cruising altitude and wanted to rely on solar for the rest of the trip.
Strange that it didn't seem to occur to people here in what is ostensibly nerd land. Very strange. Disturbing, even.
I'm pretty sure you are right... the earth is almost 25,000 miles in circumference, and rotates once in 24 hours, which comes out to just over 1000mph at the equator.
...I just came for the free beer.
.... and the solar powered black helicopters have been sent on account of your asking too many questions.
Have gnu, will travel.
The question is a good one, but you're looking at the wrong renewable energy source. Planes move fast right? Why not harness the speed of the wind rushing by the plane with a wind turbine? You could put two turbines on the back of each wing for a total of four turbines!!!! Imagine the energy creation potential! Suck that energy from the turbines into battery banks, and then use that energy to power the 4 propellers on the front of the wings. I think I've just invented propetual motion!!! Damn skippy!
How about use wind to power the engine. Say use the turbine to generate the power to power the turbine... wait a minute.
Assuming that the solar irradiance you get on top of the atmosphere is 1360W/m2, 1 square meter worth of solar panel with 20% efficiency (e.g. the best SunPower crystalline silicon modules) would generate 270W of electricity.
Airbus claims that the A380 consumes 3l/100km.passenger of fuel. At Mach 0.85 (~250m/s at 10km altitude), this represents 27l/h.passenger.
Assuming 10kWh/l of fuel energy content and 50% efficiency of the turbofans (pulled out of my ...), that amounts to 135kW of mechanical power needed for every single passenger.
Assuming an electrical motor with 100% efficiency, you would need 500m2 of solar panels for every passenger to generate the required electricity, but only during the day.
The plane from TFA seems to have 200m2 of solar panels with 12% efficiency. It can get away with it because it is much lighter and flights much slower.
Conclusion : The orders of magnitude just don't match, even with 100% efficiency => Commercial flights as we know them & photovoltaics are incompatible.
Next "Ask slashdot" : Can I fart hard enough to reach the moon?
What stands in the way of a solar powered airliner? Power! There are 745 watts per horsepower, no matter how you slice it. Look at the horsepower generated by a jet engine, and multiply by 745. That's how many watts you need. Pursuing electrically powered vehicles, especially airplanes, reflects a lack of understanding of basic physics, and a misguided attempt to solve a problem. Pursue something believable and useful, like perpetual motion.
Presumably you're ok with the solar tech not actually being onboard the aircraft. The aircraft would still store the energy as energy-dense hydrocarbons (not lead batteries with wings) but on the opposite end of the airport from where they pump in the fuel you've got fields of solar panels and some kind of conversion system that binds the energy in the form of conventional jet fuel (kerosene/paraffin). The generation is totally asynchronous and buffered, and it's ok if sometimes it takes 4 hours to generate enough fuel for 2 hours of flight, as long as every month/week/day (whatever your buffer size) you make as much fuel as you burn.
In that case, I think the barrier is either that it currently costs too much (fuel made this way is expensive), or that jet fuel from fossil sources is subsidized (e.g. taxpayers provide security for oil tankers). Wouldn't surprise me if it's a combination of the two factors.
When you solve this, you'll probably have solar-powered everything, not just aircraft.
As copyright owner of this comment, I authorize everyone to defeat any technological measure which limits access to it.
let's say it's high noon and you have a plane with every outside surface covered with solar cells.
Now a 747-400 has a wing area of around 6000 square feet.
Full sunlight falling on 6000 square feet, or about 666 square yards, generates about 100,000 watts.
There are 746 watts per horsepower, so you have about 134 horsepower to work with.
Unfortunately a 747-400 needs about 80,000 horses just to stay in the air.
We are only about a factor of 600 short on the horsepower front.
As soon as we can make bacteria or algae that poop out jet fuel, we'll have it.
Yep. approx 30 kWh per gallon of fuel, a 747 is burning approx 1 gal/second, so 100K kW (3600x30) needed. Solar gives us approx 1kW / square meter, so we need about 100K square meters of solar panels on our 747
But you forget that as you have to increase surface area for more energy, you also get more wingspan, reducing the need for energy!
By my calculations* the new needs cross over each other at around a wingspan of 200K square meters of solar panel with 10K kW provided. Simple!
* Calculations actually made up figures for humorous effect, writer does not guarantee a 747 with 200K square foot wingspan will fly or not collapse in on itself.
"There is more worth loving than we have strength to love." - Brian Jay Stanley
You're talking about taking the primary element of powered flight -- the engines -- and totally changing their internals. Better or worse or same doesn't matter. To do it, not only is the actual innovation required, but you've also got to go through the entire gamut of certification from the start. And I'll bet that there aren't any firm official certification requirements for such engines on commercial flights. Which means that anything you do requires the enormous risk of maybe the FAA or other body simply won't accept it.
That's not to say that current engines are perfect by any means. But they exist, can be certified, we all know what it takes to get them certified, and there are no business mysteries.
Since we're talking about millions and billions of dollars in research and development, that's a big risk to take just to end at a pseudo-government body simply saying no.
It can come down to something as stupid as: we can't measure the amount of exhaust, so you don't pass -- even if the reason is that there is too little to measure.
You just need to fly it out of the also-rotating atmosphere...
There are two basic problems with a solar powered aircraft. First is energy creation. As many posters have pointed out, given the available surface area of a aircraft, even with ideal (perfect) solar panels, you would not be able to get close to producing the amount of energy necessary to keep the aircraft in the air. Second is energy storage. Since a solar powered aircraft can not generate enough energy during flight, it will have to have some form of energy storage. Currently the "best" option for storing energy in electric form is a battery. Currently batteries store so little energy per pound that it would be more accurate to call a solar / electric / battery powered vehicle a train then an airplane because it will weigh so much that it will never get off the ground. To get an idea of how abysmal batteries are, see wikipedia: http://en.wikipedia.org/wiki/Energy_density Pay special attention to the graph. I don't work for Exxon, or anybody else that might benefit from continuing to burn fossil fuels. I just took a few physics classes in college. The basic math I picked up about how the world works in those classes informs me that a conspiracy among oil barons or power brokers is completely unnecessary since those bastard scientists have already "written" the laws of nature to ensure that most of our transportation energy needs can only practically be solved by fossil fuels given the current technological landscape.
You're going to have to change your signature. George is selling Lucasfilms to Disney.
Yes, I read that. But if Disney makes a watchable Star Wars film without Lucas, that'll prove the rule, won't it?
Oliver's law of assumed responsibility: If you're seen fixing it, you will be blamed for breaking it.
I thought he was talking about the combined forces of Microsoft, Apple, the RIAA, and the MPAA.
I see few of those who thinks a little broader - that the question is not about panels on aircraft, but solar powered aircraft The practical approach might be to use satellite solar power, beamed with lasers http://en.wikipedia.org/wiki/Space-based_solar_power to aircraft. In fact for aircraft in flight there could be less obstacles than for any place on earth, so beaming solar power to aircraft might be a closer aim, than beaming solar power to earth stations. Thus - 24 hours flight, the only catch - to have enough power to get out of clouds ( usually they do not obstruct much of sun light below 10 000 meters ) and then the whole flight might be powered by solar power
164 Watts per Square meter is all you will get from the sun. THIS is the number 1 reason why you will never ever see a Solar powered airliner.
Do not look at laser with remaining good eye.
To inject some math into the discussion:
ThrustToKeepFlying = FlyingMass / LiftToDragRatio
PowerToKeepFlying = ThrustToKeepFlying * Velocity = Velocity * FlyingMass / LiftToDragRatio
Typically LiftToDragRatio is about 20 or so. Airplanes don't really make sense unless they are faster than other vehicles, so Velocity needs to be 100-300 m/s. (Typically, jets fly just under Mach 1, where they have the least drag/greatest power)
FlyingMass = AircraftMass + PayloadMass + EngineMass + PowersourceMass
Since we are using unobtainium to build our aircraft, it doesn't weigh anything. And we'll just say that we can fly arbitrarily large airplanes for a single passenger, so PayloadMass is essentially zero as well.
The best solar cells are about 300W/kg (http://en.wikipedia.org/wiki/Solar_panels_on_spacecraft), and the best electric engines are about 6 kW/kg. So
FlyingMass = OtherStuff + PowerToKeepFlying / 300 + PowerToKeepFlying / 6000 = OtherStuff + 0.0035 * PowerToKeepFlying
FlyingMass = OtherStuff + 0.0035 * ( 300 * FlyingMass / 20 )
FlyingMass = OtherStuff + 0.0525 * FlyingMass
OtherStuff = 0.9475 * FlyingMass
So this says that as long as your airplane and payload are under about 95% of the engine / power source mass, it is at least possible. Structures that light are not really an issue - the real issue is only flying during the day and in good weather. (And, of course, it would cost an arm and a leg!)
while (sig==sig) sig=!sig;
In principle, beamed power to power airliners is not impossible.
Tricky - certaintly.
http://authors.library.caltech.edu/3303/1/PARaipcp04a.pdf for example is a paper on doing this for vehicles to launch into orbit.
However, airliners are rather easier in some ways.
The 275 megawatts needed to boost the space vehicle are moderately less for the airliner, a 10m diameter, not 3m beam receptor is plausible for aircraft, making the frequency and/or dishes lots easier.
Range could also be considerably lower than the assumed 150km.
In use, it would involve multiple chains of dish stations, and microwave transmitters, perhaps 90km apart.
On the plus side, this can save _lots_ of power, as the airliners have to carry almost no fuel. (some for emergencies perhaps)
Current solar panels wouldn't work due to weight, but you could imagine the roll-to-roll printed photovoltaics that have been talked about being doable.
A) Please get into the habit of using metric.
[energy provided by sun to earth] 1KW per sqr Meter on the earth [surface]
Now that's a nice coincidence! (Speaking about the metric system...)
FWIW, 1l water = 10cmx10cmx10 cm = 1kg (or 1mx1mx1m water = 1 ton) is not a coincidence.
Neither is 1 W = 1 kg * m / sÂ
The problem is not "Airplanes are not solar powered!" the problem is "Moving large numbers of people and cargo around at almost Mach 1 is pretty energy intensive".
If you're seriously interested in what engineers are actually doing about this problem, start reading about NASA's SUGAR research:
http://www.nasa.gov/topics/aeronautics/features/future_airplanes.html
I can't help you with your conspiracy theories. Anybody who could make such an airplane as you imagine would become instantly, vastly, wealthy.
Why yes, I AM a rocket scientist!
All of the energy stored in hydrocarbon fuels is originally solar. In that sense, airliners are currently powered by solar energy.
Something like a hydrogen plant on the ground that produces liquified hydrogen which is then used for fuel.
The on-the-ground solar power collection mechanism that's currently most workable is algae. We've already had 747s fly on fuel produced from algae and algae are much more efficient than solar panels at harvesting energy from the sun. From what I've read, the only reason algae-based fuel isn't used commercially today is cost.
Generating power on the plane is dumb even with perfect technology. The laws of physics just aren't your friend on this issue. That said, laws of physics have no problem with high density batteries storing enough power to take a plane from point A to point B. The only issue then is generating enough power ground side to power them up between stops. And that's not a big deal.
So... batteries.
I've decided to stop wasting my time responding to AC trolls/sockpuppets... so if you want a response from me... login.
Nah, the SR-71 used to outrun the Earth's rotation. As others noted, recheck your math.
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.
Trains are among the most energy efficient mass transit vehicles. Followed by cars/buses, and then airlines.
Trying to build a solar powered airline right now would be like trying to build a 3GHz quad core laptop in 1970. Start with a solar train or bus. Train would probably be best, since it's my understanding that even many 'diesel' trains are really electric -- they just used the diesel to run a generator.
As a note, the 1kW/m2 is the total incident energy for a surface perpendicular to the Sun's rays at sea level on a clear day. http://en.wikipedia.org/wiki/Insolation Currently, the most efficient "research" solar cells are: 44% efficient per this chart: http://upload.wikimedia.org/wikipedia/commons/5/52/PVeff(rev121015b).jpg As such, we're even worse off then your helpful calculation shows. With current energy needs for flight, we simply aren't there for any large scale system.
To inject some math into the discussion:
ThrustToKeepFlying = FlyingMass / LiftToDragRatio
PowerToKeepFlying = ThrustToKeepFlying * Velocity = Velocity * FlyingMass / LiftToDragRatio
Um, math is nice, but it needs to be applied to the physics of the situation.
In your first equation, you claim an equality between thrust and mass. They don't even have the same units.
Your second equation just compounds the problem.
Ummm, didn't Buckminster Fuller run some numbers on spherical cities made of glass and steel greater than a mile in diameter which floated on the atmosphere with just the slight solar gain through the glass? They would have had a problem staying aloft at night, but it seems that if you make a glass sphere large enough the skin weight is trumped by the enclosed atmosphere temperature.
I recall someone at a Space Studies Institute conference suggesting this idea. You collect the solar power in space via a solar space satellite, and then you focus it on the aircraft (either as a laser beam or as microwaves).
http://en.wikipedia.org/wiki/Space-based_solar_power
Presumably you could do the same from the ground as well perhaps. Think of this as a variation of laser launching systems where a small capsule rides a laser beam into space (perhaps with the beam ablating some layer at the bottom which serves as propellant).
A 21st century issue: the irony of technologies of abundance in the hands of those still thinking in terms of scarcity.
Fixed wing and foil and prop and rotor are out, the engineers who push those designs are all paid stooges for Big Oil. How about... solar powered flapping machines? We could graft an iguana onto the end of bird. The bird has the right equipment to fly, and iguanas spend most of the day basking in the sunlight. I'll bet iguanas have an incredible amount of stored solar energy.
<blink>down the rabbit hole</blink>
Photons will go out of style in coming decades, as they start to piss people off by becoming too few or too numerous. The future is neutrinos. Just switch from catching solar photons to solar neutrinos. We have no excuses.
First of all they have millions of times more energy per particle than these little photons that barely get through the atmosphere much less the earth. Anytime at night, a certain number of neutrinos will still go straight through the earth and emerge from the ground on parallel paths aimed directly at your jet in the stratosphere. And there are three different kinds of neutrinos to choose from. I could believe not being able to harness one or two, but all three? Come on. I don't believe it. Let's get real. Let's get off our butts and get to work. Here is my five point plan:
Now some of you are going to say this is impossible, and pull a bunch of numbers out of your ass including a neutrino flux that is one third of its true value. If you insist on incorrect numbers to start then I will say haha those numbers are stupid.
I put a little thought into the airship idea, and even something like the Hindenburg, covered with solar panels, but the end result will just be that they cannot move fast enough to make air travel suitable to today's needs.
Is that a roll of dimes in your pocket or are you happy to see me?
This question deserves an serious answer, which requires serious thought. Which I don't have time or caffeine level for right now, so answer as per subject.
If my comment didn't sound as good in your head as it did in mine, then I guess we all know who's to blame
Well yes and no. You don't care as much about the Mass, you care about gravity, i.e. downward acceleration. That *is* essentially Thrust, just in the wrong direction. His equation where he divides the FlyingMass by the LiftToDragRatio accommodates that issue seamlessly.
---jstlook ---For that is the way of Elves, for they say both yes AND no, and mean every word of it. --- J.R.R.T.
Physics.
There's not enough energy in sunlight to push a plane. If you'll pardon some algebra:
Drag force on plane = (1/2) Cd * air density * wing area * speed^2
where Cd is the drag coefficient, which is fairly constant (about 0.03) for typical aircraft ranging from Cessnas to 747s.
Power needed to push through the air = Drag force * speed
Let's suppose the wings are entirely covered with solar panels, producing power:
Solar power = wing area * solar intensity
Suppose these panels are 100% efficient, and the electric engines are 100% efficient too: then solar power in = drag power out.
wing area * solar intensity = (1/2) Cd * air density * wing area * speed^3
Good news: wing area cancels out. It doesn't matter how big our plane is. Solve for speed:
speed = (2 solar intensity / (Cd * air density)^(1/3)
For a typical high-altitude airliner flying at 30,000 ft in daylight in mid-latitudes,
solar intensity = 300 W/m2
Cd = 0.03
air density = 0.4
speed = 37 m/s (or about 80 mph).
Bad news: your plane can go no faster than highway speed. You might as well drive. Worse news: at this altitude, at this speed, your airplane is sure to stall. To maintain enough lift to stay in the air, you're going to have to fly at low altitude. Where the air density is greater. And you're beneath the clouds. Crap.
Flying near sea level, let's suppose
solar intensity = 250 W/m2
air density = 1.3
our equation gives a top speed of 23 m/s, or 50 mph. Still tough to design a cargo plane that can stay aloft at that speed, and once again, you're definitely better off driving.
Keep in mind that I assumed absolutely perfect solar cells and engines, which are impossible. And you can't fly at night. Or at high latitude. And if it gets too cloudy you'll crash. And...
Here is a snippet from:
http://www.inference.phy.cam.ac.uk/withouthotair/cC/page_269.shtml
What are the fundamental limits of travel by flying? Does the physics of
flight require an unavoidable use of a certain amount of energy, per ton,
per kilometre flown? What’s the maximum distance a 300-ton Boeing 747
can fly? What about a 1-kg bar-tailed godwit or a 100-gram Arctic tern?
Just as Chapter 3, in which we estimated consumption by cars, was
followed by Chapter A, offering a model of where the energy goes in cars,
this chapter fills out Chapter 5, discussing where the energy goes in planes.
The only physics required is Newton’s laws of motion, which I’ll describe
when they’re needed.
This discussion will allow us to answer questions such as “would air
travel consume much less energy if we travelled in slower propellor-driven
planes?” There’s a lot of equations ahead: I hope you enjoy them!
The best solar cells are about 300W/kg (http://en.wikipedia.org/wiki/Solar_panels_on_spacecraft), and the best electric engines are about 6 kW/kg. So
Unfortunately the exposed surface area of solar panels scales directly with mass, unlike jet engines. To match two 6kW jet engines you would need 40000 m^2 (best case scenario) of solar panels. That would add just a bit of drag.
I would be quite embarrassed to have asked this on slashdot. Next up: why doesn't magic work?
For every expert, there is an equal and opposite expert. - Arthur C. Clarke
Without broadcasting the power to the airliner from a couple square miles of battery-backed array, so the airliner doesn't need to carry the weight of the power source, it's not going to work.
we have the material to build football field sized wings with no weight or structural integrity issues?
the slow speed doesn't mean a stall and dropping out of the sky?
i don't think you are correct
intellectual property law is philosophically incoherent. it is your moral duty to ignore it or sabotage it
What's wrong with going, quite literally, ballistic? Collect solar energy any way you want (PV, wind, biomass burning, etc), then use it to launch a projectile with steering fins and a landing parachute on a ballistic trajectory to the destination. I'd have to run some numbers on that one to figure out how fast one would be wasting energy in lower atmosphere, though.
A successful API design takes a mixture of software design and pedagogy.
That's no problem at all using unobtainium, of course!
Actually, my math is off by a factor of 10 - I didn't convert kg to N correctly. The corrected result is:
FlyingMass = OtherStuff + 0.525 * FlyingMass
So your aircraft has to be half solar cells, roughly speaking. And, yes, the solar cell area is a bit on the large size...
while (sig==sig) sig=!sig;
Well, there are applications for very slow airplanes, such as if you really care about altitude or the terrain below is impassible. IIRC, high altitude drone aircraft have been suggested for Venus and Mars probes. The former, because we can't send anything to the surface and have it survive for long, the latter just to get better observations of the ground than we do with satellites. And in both cases you'd want them to be solar or nuclear powered since conventional fuel would run out too fast and there may not be anything convenient to use as an oxidizer.
-- This and all my posts are in the public domain. I am a lawyer. I am not your lawyer, and this is not legal advice.
Does something powered by a fuel generated by the energy of the sun (hydrogen or biofuels) count? Generally aircraft want to carry as little as possible. So any "solar" solution needs to separate energy capture from consumption. You want to do the first on the ground and store it in a high energy, low weight, low volume form where the energy is easily extracted. Combustion is great because one half of the chemical equation (Oxygen) isn't even carried.
I mean at least partially as gasoline is essentially a plant derived product and a plants main power source is light from the sun ergo Gasoline is solar energy :)
Build a Man a Fire, and He'll Be Warm for a Day. Set a Man on Fire, and He'll Be Warm for the Rest of His Life.
There's an assumption here that the Solar Panels / Collectors need to be placed on the aircraft itself. That would appear to be impractical. How about putting the solar array in _orbit_, and beaming down the power via Microwave power transmission or some such technology? This would solve the issue of night flight, as an orbital power grid could move energy to areas not shadowed by the earth. Clouds shouldn't a problem either.
The weight of the average American passenger.
/awkardly raises own hand
Break-even on PVs is more like 5 years for the average American family. Most families own homes for 30 years.
Please stop the FUD. It keeps us poor and dependent.
For about 200 miles until it ran out of fuel.
If you think someone isn't free to have a different definition of "freedom" you may be a tyrant.
I work in the solar industry. The average PV is about 20% efficient sometimes you get up around 30% if you pay out the nose for a satellite. Until there is a higher output you won’t see them moving anything heavy..
No good deed goes unpunished.
The atmosphere isn't what is causing you to match ground speed, it's your own momentum which was transferred from the ground. You'd just end up in an unstable orbit around the planet. That is, if you'd manage to fly an air propelled craft out of the atmosphere.
Also: WOOSH !
Earth circumfrence: ~24000 miles.
Earth rotation rate: 24 hours
Math: ~1000mph rotation rate.
Who taught you math? But let's just assume you're right for the sake really crushing your post.
SR-71 (and related family): Maximum (unclassified) speed: > 2200 mph. They outran the sun regularly. And the aircraft was never really bottomed out due to safety concerns.
MiG-25: >2100 mph. Developed to catch the XB-70. which us to...
XB-70: >2000 mph
And there's others as well. So you also dont know your planes.
The guy who said the election was rigged won the presidency with the second-most votes.
Um no. You dont know what you're talking about.
They cruised at that speed. It was the first "supercruise" aircraft. Reason being the engines (still largely classified as to their internals) were actually much more efficient at that speed. Range was in excess of 3000 miles, at speed (official range is less, but like many things about the blackbird, the "official" numbers dont match up with what the aircraft actually did in operation).
(http://en.wikipedia.org/wiki/Lockheed_SR-71_Blackbird#Records)
1.Los Angeles, CA to Washington, D.C., distance 2,299.7 miles (3,701.0 km), average speed 2,144.8 miles per hour (3,451.7 km/h), and an elapsed time of 64 minutes 20 seconds.[75]
2.West Coast to East Coast, distance 2,404 miles (3,869 km), average speed 2,124.5 miles per hour (3,419.1 km/h), and an elapsed time of 67 minutes 54 seconds.
Far far >200 miles.
there's also the 15000 miles in 10 hours record. The London to New York run at 1600mph. And the classified sorties made over the Soviet Union, the middle east, and vietnam, where they actually outran missles.
The guy who said the election was rigged won the presidency with the second-most votes.
We need to increase the power output of the sun. Side effects: negligable.
Alas, reality stands in the way of pipe dreams.
I haven't thought of anything clever to put here, but then again most of you haven't either.
.... she is bigger than a plane.
Life takes interesting turns, but the most interest is when you're off the beaten path.
I think perhaps most people are looking at this the wrong way round.
Very small aircraft are already flying great distances using ground-charged batteries plus solar power. The issue shouldn't be "how do we build a 300-seat version", but "how do we make it possible for everyone to take small planes".
The challenges then become fundamentally different:
However, there are potentially some huge benefits (beyond the energy savings):
I'm not up to solving 1, 2 and 3 above, but my suspicion is that ICT-based solutions are getting closer, i.e. more heavily computer-assisted flight and air traffic control, better weather monitoring and comms so that planes can be routed or grounded as necessary.
Intercontinental travel is still difficult from a safety perspective, because a forced landing at sea would be much more dangerous than on land (gliders like the one in the article would be very capable of ground-based landing even if all power had failed). Maybe large oil-rig-like touch-and-go points along the route could do the job, adding some safety as well as doing more efficient plugged-in recharging.
As for improving the planes themselves, what about a ground-based accelerator, so they're at flight velocity before take off? Isn't take-off itself one of the biggest energy drains?
Where is my flying car?
Last I checked, air expands when heated, so your lasers would need to point downwards. Secondly, air is pretty poor at absorbing EM radiation so you'd not be able to generate a "hot zone", you'd just heat up air in the line of your beam For a long way. Third, the amount of power you'd need would be astronomical (unless you trapped the hot air in a balloon for lift, which has been figured out for a while now).
(Which may still not work because even liquified hydrogen has much less energy per volume than jet fuel.
uhm http://en.wikipedia.org/wiki/Energy_density#Energy_density_in_energy_storage_and_in_fuel
Hydrogen (compressed at 700 bar) 123Mj/kg
Jet fuel 43Mj/kg
VOLUME
Oliver's law of assumed responsibility: If you're seen fixing it, you will be blamed for breaking it.
It takes a 777 airliner 18,000MJ to move 1 person 7800 miles at .85 times the speed of sound(assuming a full airliner of 400 people) using jet fuel. say in about a 12-14 hour flight. So take that as a 'standard', you'd need a solar array that can gather that much energy. For a basic 130W solar panel you'd need 3200(60" x 30") of them for each passenger on that plane. That's about 42,000 square feet or about 3/4 of a football field for each passenger.
(Which may still not work because even liquified hydrogen has much less energy per volume than jet fuel.)
On the other hand, in its gaseous form you can use it to generate as much lift as you like without even burning it...
There will still be graphics overkill. There will also be actors "acting" and a plot that might make sense outside King George's skull.
I love vegetarians - some of my favorite foods are vegetarians.
There will still be graphics overkill. There will also be actors "acting" and a plot that might make sense outside King George's skull.
You may very well be right. In that case, I will decline to see it, and I have lost nothing.
Oliver's law of assumed responsibility: If you're seen fixing it, you will be blamed for breaking it.
Which goes back to the airship concept. The problem there is that although airships can have huge lifting capability, they tend to be slow. And people still remember the Hindenburg.
Oliver's law of assumed responsibility: If you're seen fixing it, you will be blamed for breaking it.
Gravity! Electricity will never have the raw power to compare with fossil fuels
More theoretically tractable, if nothing else.
You want the truthiness? You can't handle the truthiness!