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Ask Slashdot: What Stands In the Way of a Truly Solar-Powered Airliner? 590

Posted by Soulskill
from the i-blame-gravity dept.
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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Ask Slashdot: What Stands In the Way of a Truly Solar-Powered Airliner?

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  • Um... (Score:5, Insightful)

    by mbstone (457308) on Tuesday October 30, 2012 @03:53PM (#41821811)

    Clouds?

    • Re:Um... (Score:4, Funny)

      by GeneralTurgidson (2464452) on Tuesday October 30, 2012 @03:55PM (#41821835)
      Heaven takes up a lot of space too.
    • Re:Um... (Score:4, Informative)

      by Naatach (574111) on Tuesday October 30, 2012 @04:00PM (#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... (Score:5, Funny)

        by Motard (1553251) on Tuesday October 30, 2012 @04:04PM (#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... (Score:5, Insightful)

          by roc97007 (608802) on Tuesday October 30, 2012 @04:10PM (#41822131) Journal

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

          • Re:Um... (Score:5, Informative)

            by Capitaine (2026730) on Tuesday October 30, 2012 @05:39PM (#41823897)
            Jet engines are quite inefficient. The main problem being power I would start with props.
            To get an idea of the power needed, just take a regional aircraft, for example an ATR [wikipedia.org] equiped with two PW100 [www.pwc.ca]. That makes roughly 7000kW of energy provided to propellers. Lets suppose you have 100%-efficient electrical motors, and let aside aircraft internal consumption.
            Now this [energysavingtrust.org.uk] paper suggest that high density power solar cells provides about 1kW/sqm. The only challenge is to find 7000sqm of surface exposed to the sun on a 22m long and 24m wide aircraft.

            So far, the only electrical plane that I have been able to see were ultra light aircraft which could barely support they own weight and a pilot. Still a long way until commercial exploitation.
        • Re:Um... (Score:5, Insightful)

          by rtfa-troll (1340807) on Tuesday October 30, 2012 @04:19PM (#41822297)

          But if you had a solar powered jet engine you could chase the sun. And you would never need to waste energy on landing lights.

          Why stop at that? If you had a solar powered transporter you could just go straight from wherever you are to wherever you want to be in two simple steps. In fact, once we can completely ignore basic laws of energy conservation and so on, why not just use a solar powered magic wand and will yourself to already be wherever you want to be?

    • Re:Um... (Score:4, Funny)

      by N0Man74 (1620447) on Tuesday October 30, 2012 @04:32PM (#41822559)

      Clouds?

      Forget clouds. Do you really want to be on a plane in the event that the sun suffers a catastrophic failure and stops shining!? Everyone on that flight will be boned!

    • Re:Um... (Score:5, Informative)

      by Joce640k (829181) on Tuesday October 30, 2012 @04:32PM (#41822567) Homepage

      Clouds?

      I think a bigger problem is that the surface area of an 'airliner' can never provide enough energy to keep it in the air even with 100% conversion efficiency at noon.

      Blimps might work, but they're slow and helium supply is a problem.

      Hydrogen is too scary for passenger blimps. People wouldn't like them even if they had ejectors and parachutes.

      • Re:Um... (Score:5, Insightful)

        by Gorobei (127755) on Tuesday October 30, 2012 @05:08PM (#41823319)

        Clouds?

        I think a bigger problem is that the surface area of an 'airliner' can never provide enough energy to keep it in the air even with 100% conversion efficiency at noon.

        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. Our 747 has approx 1000 sq m top surface, so solar would provide 1% of the power needed even in optimal conditions.

        • Clouds?

          I think a bigger problem is that the surface area of an 'airliner' can never provide enough energy to keep it in the air even with 100% conversion efficiency at noon.

          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. Our 747 has approx 1000 sq m top surface, so solar would provide 1% of the power needed even in optimal conditions.

          What if we didn't think about the 747 use-case but focused on the commuter flights. As noted higher up, there are limitations with night flying, clouds, and East-bound travel is restricted. But there sure are a lot of flights that simply go up and down the East or West coast that only fly for 30 minutes to an hour. Or, could a battery last for 30 minutes of flight for a commuter plane?

          • Re:Um... (Score:4, Insightful)

            by Rich0 (548339) on Tuesday October 30, 2012 @06:06PM (#41824289) Homepage

            Ok, let's take a CRJ-200. That consumes 1200 lb/hr of fuel in cruise, or about 170 gal/hr. That's 5MW of power - still a huge amount for a solar plant to generate, and that neglects the power needed to reach cruise altitude which is MUCH higher.

            A little Cessna 172 on 50% power uses 5gal/hr, which is 150kW of power. One of those probably could carry a single passenger and the pilot at typical passenger+baggage limits. If you stretched the thing out into the size of a small airliner using balsa wood you might be able to power it in cruise with top-mounted solar panels, assuming it could be towed up to cruise altitude, still carrying only two people.

            We can't even build solar-powered cars - forget planes with any kind of payload and cruise speed.

        • Aha, but! (Score:5, Funny)

          by SuperKendall (25149) on Tuesday October 30, 2012 @05:14PM (#41823453)

          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.

    • Re:Um... (Score:5, Informative)

      by paiute (550198) on Tuesday October 30, 2012 @04:46PM (#41822865)
      Physics.
      • Yep, physics (Score:5, Informative)

        by Anonymous Coward on Tuesday October 30, 2012 @06:50PM (#41824815)

        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.

    • by mrmeval (662166)

      It already is solar powered. It is organic material created using solar energy that has been further processed over time to be hydrocarbons. All of the energy in this solar system comes from solar. All of the matter in this solar system except hydrogen and maybe some helium comes from stellar processes. Solar cannot be directly used for much on the surface of the earth or close to it which is an airplanes ceiling. We need a storage solution that does not have the costs that coal, oil, gas, solar, wind or ot

  • Also (Score:5, Insightful)

    by Flounder (42112) on Tuesday October 30, 2012 @03:54PM (#41821823)
    Night?
  • Simple : (Score:5, Funny)

    by Anonymous Coward on Tuesday October 30, 2012 @03:55PM (#41821851)

    Nothing a good kickstarter campaign cannot solve...

  • by Anonymous Coward on Tuesday October 30, 2012 @03:56PM (#41821861)

    Just saying...

  • Batteries. (Score:5, Insightful)

    by sbrown7792 (2027476) on Tuesday October 30, 2012 @03:56PM (#41821869)
    The capacity and weight as well as power delivery, for taking off (with clouds above) and night flights.
    • by Ken_g6 (775014)

      Actually, assuming you leave the solar panels on the ground, batteries may be a viable option:

      1. Volta Volare has designed [popsci.com] a small electric-hybrid airplane that should be able to go 200 miles on a charge. Of course, it's not an airliner, but...
      2. Boeing has designed a concept airliner called the Sugar Volt [popsci.com] (video [boeing.com]) that can cruise on battery power alone. It could be built as early as 2035.
  • by Grayhand (2610049) on Tuesday October 30, 2012 @03:57PM (#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.
    • We'll be facing an energy crisis sooner or later. I say we should ban planes altogether and switch to trains and boats exclusively.

    • by Jeng (926980)

      Large aircraft need a dense power source.

      Or to be lighter than air, though being lighter than air on demand would be nice.

    • by Andy Dodd (701)

      Yeah... To my knowledge, there aren't any solar powered aircraft out there that have gone beyond the "research project" phase. I don't think there is a solar-powered aircraft in existence that can carry a human... Right now, the state of the art in solar powered aircraft is "keeps itself in the air with negligible cargo" - the payload limit being, at most, a comms relay and maybe some data collection stuff (airborne camera, etc.). Even that has worked, at best, in a place like Arizona or Hawaii on a goo

  • Size. (Score:5, Informative)

    by Gordonjcp (186804) on Tuesday October 30, 2012 @03:57PM (#41821879) Homepage

    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. (Score:5, Interesting)

      by K. S. Kyosuke (729550) on Tuesday October 30, 2012 @04:05PM (#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.
      • by ZorinLynx (31751)

        "all airplanes are solar-powered these days, only the sunlight is of a vintage brand."

        Just wanted to let you know that I absolutely love that quote.

        I just tweeted it (with credit given of course).

      • Re:Size. (Score:4, Insightful)

        by gman003 (1693318) on Tuesday October 30, 2012 @05:18PM (#41823519)

        All power is either solar, nuclear, or in one case gravitational.

        Photovoltaic is obviously solar. Any hydrocarbon (oil, gas, peat, even garbage incinerators) is just solar energy gathered by long-dead plants, or just plants in the case of biofuels. Wind is just solar energy heating one area, and we run a dynamo off it. Hydro is like wind, only we're running it off water, not air, being moved around by the sun's energy. Even having a hamster run in a wheel uses solar, as the hamster is powered by plants, which are powered by the sun.

        Nuclear power is obviously nuclear. Geothermal is tapping energy from natural nuclear decay in the Earth's interior.

        The only exception is tidal - pulling the energy of the Moon's orbit. Try as I may, I cannot justify it as nuclear-powered.

        If you want to get technical, you can merge solar and nuclear as well, as the sun is just a Big Thermonuclear Fusion Reactor In The Sky. Or if you want to get technical in a different way, you can rename solar to "fusion" and "nuclear" to "fission", so when we finally get fusion working we can file it properly.

    • by alendit (1454311)

      Sounds unbelievable to me, any numbers to back it up?

      • Re:Size. (Score:5, Informative)

        by Solandri (704621) on Tuesday October 30, 2012 @05:05PM (#41823257)
        Dunno why it would be unbelievable. Solar-powered aircraft [wikipedia.org] have been made. They're ultralight, are covered in solar panels, have practically no payload, and fly at about 20 mph. But if you insist...

        Passenger plane fuel consumption is on the order of 5-7 gallons per mile [airliners.net]. Call it 6 gal/mi.
        Airspeed is about 550 mph, or 0.153 miles per second.
        Fuel consumption is thus (6 gal/mi) * (0.153 mi/s) = 0.918 gal/s.

        Jet fuel has about 35 MJ/L of energy [wikipedia.org], or 132.5 MJ/gal.
        At 0.918 gal/s, that's 121.6 MJ/s or 121.6 megawatts.

        Solar constant [wikipedia.org] in space is about 1361 Watts/m^2. On Earth it's about 750 Watts/m^2.
        Air pressure at 35,000 ft is about 25% that of sea level [engineeringtoolbox.com].
        So figure with only 25% of the atmosphere intercepting sunlight, you get 1208 Watts/m^2 at cruising altitude.

        To generate 121.6 MW with 100% efficient panels producing 1208 Watts/m^2, you need 100,660 m^2, or about a tenth of a square km. A roughly 320x320 meter patch, or about 5-10 city blocks. I suppose a really small town could fit in that area.

        You could quibble about gas turbines only being 40%-50% efficient, but then real-world commercial solar panels are only 15%-20% efficient. And we're ignoring clouds, night, and angle to the sun (all the above assumes the sun is directly overhead). So more realistically you're probably looking anywhere from a quarter of square km to over 1 square km of solar panels needed to propel a passenger plane.
  • Let's go retro... (Score:5, Interesting)

    by Flounder (42112) on Tuesday October 30, 2012 @03:57PM (#41821885)
    I always thought that heavy-lifting solar-powered airships would make excellent replacements for long-haul trucks.
    • Re:Let's go retro... (Score:5, Informative)

      by gman003 (1693318) on Tuesday October 30, 2012 @04:11PM (#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".

      • by vlm (69642) on Tuesday October 30, 2012 @04:30PM (#41822499)

        And cargo rarely needs to go as quickly as people

        Bzzzzt

        You can BS passengers into paying much more because you have comfier seats or serve cookies or have non-stop / non-transfer flights to their home town or some goofy "air miles" deal. None of which cost much but people will pay thru the nose for... nearly pure profit.

        Cargo doesn't care. You've got a $1M/month mortgage to pay on that $100M plane and the ONLY thing that matters is making as many trips as possible to haul cargo to make that payment. You go quick you make tons of profit and pay your mortgage. You glide around like drunken seagull and make one revenue generating glide per week, the plane gets repo'd.

        Even worse, its always going to cost more to fly than swim in a boat or drive a truck. Some cargo is time sensitive enough that they'll pay 50 times as much to go 5 times as fast as a semi trailer. But there's no way in hell they'll pay 50 times as much to go slower than the alternatives.

        • Re:Let's go retro... (Score:5, Interesting)

          by gman003 (1693318) on Tuesday October 30, 2012 @04:49PM (#41822939)

          Let's bring some numbers into this.

          According to this page [alibaba.com], I can get a cargo container from Shanghai to San Francisco in 18-30 days. That's a distance of roughly 10,000km [wolframalpha.com],

          The Hindenburg could reach air speeds of 135km/h. While modern airships could doubtless reach higher speeds, we're also running off solar power here. So let's just run with that 135km/h figure. That gives us about three days to cross the same distance.

          For further comparison, a Boeing 747 can make the trip in roughly 11 hours.

          So we're beating the container ship by a factor of 6-10, but the jet is beating us by a factor of 6. So we just have to have a price halfway between the two. Unfortunately, that's hard to figure out, because the container ship charges by volume, while the aircraft rates I can find charge by weight. Ultimately, though, it's a moot point, as any figure I can come up with for the costs of running a solar-powered airship will cite work by a certain Dr. M. Y. Ass.

          But hey, it might be a good niche to fit into. Faster and safer* than a container ship, but slower than a jet. Someone might be able to find a good use for that.

          * Assuming, of course, no Sky Pirates are encountered. Then all bets are off.

          • by NetFusion (86828)
            The bigger payoff is in improving the energy efficiencies of existing models then trying to create new ones. Moving cargo by ship takes advantage of the density difference between water and air for buoyancy and reduced friction of heavy loads. When we talk about where you can place 5 to 10 square city block of solar panels on a moving object, a container ship comes to mind. Add to that things like giant kites to take advantage of free wind power [earthtechling.com] and air lubrication of the hulls [mhi.co.jp]. We need that kind of
      • Big Numbers time (Score:5, Insightful)

        by PPalmgren (1009823) on Tuesday October 30, 2012 @04:47PM (#41822881)

        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 :)

  • by Gothmolly (148874) on Tuesday October 30, 2012 @03:58PM (#41821891)

    Dear Slashdot, this is not a highschool paper.

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

  • Physics. (Score:5, Insightful)

    by Anonymous Coward on Tuesday October 30, 2012 @03:58PM (#41821897)

    In simple terms, Physics.

  • Uh, surface area? (Score:5, Informative)

    by TWX (665546) on Tuesday October 30, 2012 @03:58PM (#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.
    • by ThorGod (456163)

      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?

      • by TWX (665546)
        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.
      • Re:Uh, surface area? (Score:4, Informative)

        by geekoid (135745) <dadinportland AT yahoo DOT com> on Tuesday October 30, 2012 @04:21PM (#41822335) Homepage Journal

        A) Please get into the habit of using metric. Pretty please? we look like the scientific laughing stock.
        B) It's not the energy passing through a sqr meter of the sun, it's how much of that energy is there in a sqr meter on earth. Unless you are planning on flying a meter above the surface of the sun~

        1KW per sqr Meter on the earth. Altitude will change that, but not nearly enough.

  • 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 wi

  • by pbjones (315127) on Tuesday October 30, 2012 @03:58PM (#41821911)

    The man with the paddles or flags.

  • 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.

  • by brit74 (831798) on Tuesday October 30, 2012 @04:00PM (#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]
  • 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.

  • Size (Score:5, Insightful)

    by sinij (911942) on Tuesday October 30, 2012 @04:02PM (#41821989) Journal
    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? (Score:5, Informative)

    by Overzeetop (214511) on Tuesday October 30, 2012 @04:03PM (#41822007) Journal

    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.

  • power requirements (Score:5, Informative)

    by goertzenator (878548) on Tuesday October 30, 2012 @04:04PM (#41822023)
    - A 747 consumes 140MW. [ http://en.wikipedia.org/wiki/Orders_of_magnitude_(power) [wikipedia.org] ]
    - Nevada Solar One, a 400 acre solar generating station, generates 64MW. [ http://en.wikipedia.org/wiki/Nevada_Solar_One [wikipedia.org] ]
    Hmmmm...
  • 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

  • Air Ship (Score:5, Insightful)

    by waimate (147056) on Tuesday October 30, 2012 @04:07PM (#41822075) Homepage

    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.

  • by onyxruby (118189) <onyxruby@@@comcast...net> on Tuesday October 30, 2012 @04:13PM (#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).

  • Short Answer (Score:5, Interesting)

    by CanHasDIY (1672858) on Tuesday October 30, 2012 @04:25PM (#41822413) Homepage Journal

    what stands in the way of creating true solar-powered airliners?

    Nothing. [solarship.com]

    Oh, you meant airplanes? Yea, sorry, can't help you there.

  • Green Cows (Score:4, Informative)

    by Cyrano de Maniac (60961) on Tuesday October 30, 2012 @04:30PM (#41822517)

    This is why: http://what-if.xkcd.com/17/ [xkcd.com]

    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.

  • Some basic literacy (Score:3, Informative)

    by fm6 (162816) on Tuesday October 30, 2012 @04:32PM (#41822549) Homepage Journal

    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,

    • by djh101010 (656795)

      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

      Really? That's odd, because, I went live with a 3KW solar array a month ago. In that month, I've produced 459KWh. This gets sold to the electric company at retail, which is $.25/KWh during the week and $.12KWh on weekends. So, (5/7*459*.25)+(2/7*459*.12)= $81.96+$15.74=$97.70 per month. The array cost me $4.00/watt, installed, so, $12,000. There is a 30% federal tax rebate, which brings my cost down to $8400. Plus a $1400 state "focus on energy" grant, which brings my cost to $7000. So, assuming thi

  • by pr0t0 (216378) on Tuesday October 30, 2012 @04:38PM (#41822685)

    1. Lift
    2. Weight
    3. Thrust
    4. Drag

  • by PortHaven (242123) on Tuesday October 30, 2012 @04:46PM (#41822873) Homepage

    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.

  • by hawguy (1600213) on Tuesday October 30, 2012 @04:49PM (#41822931)

    A typical trans-country flight in a Boeing 767 uses around 50,000 lbs of fuel [alliedpilots.org] or around 7500 gallons.

    Each gallon of jet fuel contains 34 KWh of energy [wikipedia.org], 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.

  • by Lumpy (12016) on Tuesday October 30, 2012 @05:36PM (#41823843) Homepage

    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.

  • by queazocotal (915608) on Tuesday October 30, 2012 @05:49PM (#41824029)

    In principle, beamed power to power airliners is not impossible.
    Tricky - certaintly.
    http://authors.library.caltech.edu/3303/1/PARaipcp04a.pdf [caltech.edu] 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)

  • 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 [nasa.gov]

    I can't help you with your conspiracy theories. Anybody who could make such an airplane as you imagine would become instantly, vastly, wealthy.

  • by goodmanj (234846) on Tuesday October 30, 2012 @09:11PM (#41826085)

    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...

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