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Solar Impulse Plane Begins Epic Global Flight

Posted by samzenpus on from the as-far-as-the-sun-will-take-us dept.

An anonymous reader sends word that the Solar Impulse 2 airplane has begun its attempt to fly round-the-world powered by nothing but the sun. "A record-breaking attempt to fly around the world in a solar-powered plane has got under way from Abu Dhabi. The aircraft — called Solar Impulse-2 — took off from the Emirate, heading east to Muscat in Oman. Over the next five months, it will skip from continent to continent, crossing both the Pacific and Atlantic oceans in the process. Andre Borschberg was at the controls of the single-seater vehicle as it took off at 07:12 local time (03:12 GMT). He will share the pilot duties in due course with fellow Swiss, Bertrand Piccard. The plan is to stop off at various locations around the globe, to rest and to carry out maintenance, and also to spread a campaigning message about clean technologies."

40 of 65 comments (clear)

  1. Photosynthesis thumbs up! by rmdingler · · Score: 1

    Hopefully the estimates of the plane's traveling capacity aren't as overblown as the articles predictions for solar energy's takeover of hydrocarbons.

    --
    Happiness in intelligent people is the rarest thing I know.

    Ernest Hemingway

    1. Re:Photosynthesis thumbs up! by Anonymous Coward · · Score: 2, Insightful

      Yeah, it's hard to imagine how this technology matters to most aircraft. Don't get me wrong, it's an impressive demonstration of how far you can go on a tiny amount of power, and there are a few applications where it might matter (e.g., high altitude drones). But one look at the amount of power it actually takes to push a commercial airliner (e.g., one Boeing 777 engine produces ~75 megawatts at full throttle) and you realize solar power is completely irrelevant for that application.

      These kinds of articles where it's implied that someday we'll all be flying around in solar-powered planes are silly. It means they haven't done the math. Heck, even if you covered every square metre of a plane with solar cells you couldn't collect enough power. There's not enough there. Even if you charged up batteries from ground sources you couldn't carry enough storage and have the plane get off the ground because of the weight. Even with an order of magnitude improvement of power density you couldn't. The only way that solar could possibly be relevant for air travel is if you used the solar power to generate chemical fuels of some kind, with all the energy losses that conversion implies, and then put that chemical fuel into the plane. Aircraft is the one power demand where we will be using fossil fuels or their chemical equivalent for a long time. Weight, energy storage density, and efficiency matters too much for that application for it to be any other way.

    2. Re:Photosynthesis thumbs up! by Anonymous Coward · · Score: 1

      I wish the pilots well, and it's obviously an interesting project in terms of being an adventure. But to be honest, I don't really see what it's proving in terms of promoting solar power.

      I can see the potential for unmanned solar powered aircraft staying aloft for long durations, but others have already demonstrated the potential for that better, by, you know, building unmanned solar-powered planes that flew for weeks non-stop (QinetiQ Zephyr.

      In terms of piloted aircraft, it actually just shows how bad an option solar power is. I know they're not trying to promote solar as a practical way to power passenger/cargo aircraft, but you can't help but make the comparison. With a bit of fossil fuel power, GlobalFlyer circumnavigated the globe non-stop in less than three days. An A380 could circumnavigate the globe 100 times in the five months these guys will be at it, making one stop per circumnavigation, moving 160000 people and vast amounts of cargo to the other side of the world.

      If you want to promote solar power, I'd say maybe use in a context where it actually looks good next to the alternatives.

    3. Re:Photosynthesis thumbs up! by K.+S.+Kyosuke · · Score: 1

      If you want to promote solar power, I'd say maybe use in a context where it actually looks good next to the alternatives.

      Such as in the context of powering airplanes with synthetic hydrocarbons produced by solar-powered hydrocarbon generators?

      --
      Ezekiel 23:20
    4. Re:Photosynthesis thumbs up! by unrtst · · Score: 1

      With a bit of fossil fuel power, GlobalFlyer circumnavigated the globe non-stop in less than three days. An A380 could circumnavigate the globe 100 times in the five months these guys will be at it, making one stop per circumnavigation, moving 160000 people and vast amounts of cargo to the other side of the world.

      I originally misread the summary, assuming this had to be a non-stop thing, then quickly realized that's not what they said, and the 2 pilots 1 seat stood out a lot too.

      So, I agree... how is this an interesting technical achievement? Given enough time, they could throw a paper airplane around the world, or fly a glider around the world. At this point, "around the world" only seems interesting to me if it's non-stop or human powered (ex. walk around the world).

    5. Re:Photosynthesis thumbs up! by Sarten-X · · Score: 1

      It means they haven't done the math. Heck, even if you covered every square metre of a plane with solar cells you couldn't collect enough power. There's not enough there.

      Let's do the math, then. The specifications of Solar Impulse-2 are available as a starting point.

      At 269.5 square meters of solar cell coverage, and an average power density of 1.35 kW per square meter, the maximum amount of energy the plane can harvest is about 364 kW. Now, we can use two facts to avoid the ugly world of aeronautical engineering (which I don't know): The aircraft has flown under its own power, supplied by four 17.5-horsepower motors. Those motors therefore supply about 13 kW each, for a total of 52 kW of energy required to fly.

      Since 52 kW is far less than the 364 kW the solar cells produce, yes, there is in fact enough power available for collection.

      Even if you charged up batteries from ground sources you couldn't carry enough storage and have the plane get off the ground because of the weight. Even with an order of magnitude improvement of power density you couldn't.

      As noted, the plane has already flown, carrying its lithium batteries with it.

      Weight, energy storage density, and efficiency matters too much for that application for it to be any other way.

      Ah, finally some thermodynamics! Currently, the whole plane needs an efficiency of about 15% to simply fly. After some quick research, it seems most solar cell technologies today run at about 20% efficiency, with new technologies pushing 46%. Going from the 20% point, that means the motors need to be only 75% efficient. A bit more research shows that they're actually reasonably assumed to be around 85% efficient. The plane will fly in bright sunlight just fine under solar power alone.

      Lithium polymer batteries have efficiencies of around 80% to 90%, so going up to a solar cell with 25% efficiency would allow the plane to either charge or fly, but not both. Double the efficiency and you double the capability, so having solar cells that are 50% efficient would allow both charging and flying under ideal conditions. We're getting pretty close to that.

      Throw in some assumptions about duty cycles, allowing the plane to be on the ground for a bit (doubling its charging rate, because it doesn't need to spend energy to fly), and making long trips is feasible in several short hops. Account for an intelligent pilot, using tailwinds and other air currents to reduce the energy needs, and those hops can be made longer.

      A Boeing 777 is designed for speed. If you're not in a hurry, solar power might just be a reasonable option very soon.

      --
      You do not have a moral or legal right to do absolutely anything you want.
    6. Re:Photosynthesis thumbs up! by oobayly · · Score: 1

      There are some difficulties when it comes to scaling aircraft. Very simply:
      Lift = Air_density * Velocity^2 * Coeff_lift * Wing_Area / 2
      Drag = Air_density * Velocity^2 * Coeff_drag * Wing_Area / 2
      Coeff_drag = Parasite_drag + (Coeff_lift^2 / (PI * wing_span_efficiency * wing_aspect_ratio))
      efficiency is a number in the order of 0.85 to 0.9

      So, whilst you only have to increase wing area linearly with mass (or increase speed to the square root of mass), doubling your speed quadruples your drag, and doubling your lift quadruples your lift-induced drag.

      I can't do the numbers at the moment, but it should be quite easy to determine scale at which an electrically powered aircraft is not longer possible (using current technology)

    7. Re:Photosynthesis thumbs up! by brambus · · Score: 1

      A Boeing 777 is designed for speed. If you're not in a hurry, solar power might just be a reasonable option very soon.

      No, a Boeing 777 is built for efficiency and "good enough" speed. High speed rail is already killing short-haul aviation in many places around the world.
      Anyway, let's play this game. How slow is slow enough? The Solar Impulse cruises at 35 knots true airspeed - given upper altitude winds, your actual ground speed might in fact be negative on many days. Just to give you a taster of the energy requirements of "slow" flight (I have the actual manufacturer perf tables): at the lightest loadout (10000 lbs) and lowest and most economical cruise power setting, a 19-passenger Beechcraft 1900D airliner cruises at 25000 feet at 209 KTAS and requires 502 kW of power to do so (2 x 1400 rpm x 1266 lbft). It's surface area is probably less than 1/10 of that of the Solar Impulse. So even assuming 100% efficient power conversion, you're more than an order of magnitude removed. And that's assuming huge concessions to the lightness of the airplane (~3t empty airplane to carry 19 passengers - totally unrealistic), which given current electrical component & battery weight is just pure science fiction.

    8. Re:Photosynthesis thumbs up! by rioki · · Score: 1

      The thing with a solar powered plane is that at theses speeds, I think plane it the wrong design. How about a solar powered airship. You don't need power to keep it flying (almost) and it has a way higher surface area to put solar panels on. Additionally Batteries are almost neglectable, since all you need to do is provide more buoyancy through the balloon.

    9. Re:Photosynthesis thumbs up! by brambus · · Score: 1

      Fully agree here, a solar-powered blimp might actually not be such a bad idea, especially when your goal is primarily loitering for hours on end over something like a race track, or conducting traffic surveillance. However, for transport, especially mid- to long-distance transport, it's a horrible idea. It's akin to placing solar panels on roofs of cars and expecting to be able to use it practically, except much worse due to the much higher drag and power requirements of airplanes.

  2. Two Pilots, One seat by OzPeter · · Score: 1

    This will be one video I will look forward to seeing!

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    I am Slashdot. Are you Slashdot as well?
    1. Re:Two Pilots, One seat by dotancohen · · Score: 1

      This will be one video I will look forward to seeing!

      You just want to see them pull back on the stick, you sicko!

      --
      It is dangerous to be right when the government is wrong.
  3. Pilots by Thanshin · · Score: 1, Funny

    Why carry pilots instead of an AI?

    If it's just for bragging about the capacity for dead weight, they could have chosen other forms for it. Like, a large pig with a funny hat. Or 150Kg worth of penguins.

    1. Re:Pilots by Anonymous Coward · · Score: 1

      Why carry pilots instead of an AI?

      It would obviously run Linux, because without a pilot, windows is unnecessary.....

    2. Re:Pilots by HornWumpus · · Score: 1

      Guess: Legalities as well as PR.

      --
      John McAfee 'It was like that time I hired that Bangkok prostitute; to do my taxes, while I fucked my accountant'
    3. Re:Pilots by oobayly · · Score: 1

      I don't know, I think flying a pig in a hat or 5 emperor penguins would be pretty good bragging rights.

  4. Five months? by DrXym · · Score: 2

    That's a really long time whether it is solar powered or not. If they're waiting for windows as the article says it suggests this plane runs a serious risk of having the crap kicked out of it by the weather when it attempts to fly certain legs.

    1. Re:Five months? by bsDaemon · · Score: 4, Interesting

      When SI1 did the trans-american flight, they had a stop-over at the Smithsonian's Udvar-Hazey annex out near Dulles and I went to go see it. I got to meet Bertrand Picard, which was really cool, got to touch the plane, and it was also a good excuse to go and see the rest of the collection.

      With this aircraft, we're talking about something that has the weight of a car but the wingspan of a commercial long-haul airliner. It is largely constructed out of carbon fiber, and with proportions like this I would assume that sufficiently strong winds could cause it to snap. There are also the stop-overs for educational and marketing purposes (such as spending 3 days at Dulles with the first plane 2 years ago), as well as rest and recuperation time for the pilots. They have a large ground crew, engineering team and marketing team that moves with them. It's kind of like picking up the circus and moving it to a new city and trying to get there in time before your elephants, which are on a different train.

      That said, it's one of the coolest things I've ever gotten to see in person, and Bertrand Picard is an amazing guy, from an amazing family. His grandfather was a high-altitude balloonist and scientist who inspired Professor Calculus in Tin-Tin. His father went with Challenger Deep to the bottom of the Marianas Trench. His uncle was also an explorer, Jean Picard, after whom Jean-Luc Picard of Star Trek was named. The idea for this plane came about after nearly running out of fuel during an around-the-world balloon flight in the 1990s.

      Whether we'll be seeing solar air transport on a commercial level in my lifetime or not, they're definitely attacking various engineering, scientific and social problems in a high-profile way.

    2. Re:Five months? by brambus · · Score: 2

      Whether we'll be seeing solar air transport on a commercial level in my lifetime or not, they're definitely attacking various engineering, scientific and social problems in a high-profile way.

      I love the forward thinking and positive view of technology including solar power, but there's no way there are ever going to be purely *directly* solar powered commercial airplanes in the future. The power requirements are just so far removed from being able to fly at anywhere near the speeds you may want to travel at to make it a viable mode of transport. Just to give you a taste of the energy requirements needed for air travel, let's have a look at a modern airliner, .e.g a Boeing 777-200LR. From experience, I can tell you that its engines run at about 40-45% of maximum rated sea level thrust in cruise at a speed of about M0.84, which at 35000 ft pressure altitude comes to around 480 knots true air speed or about 250m/s. Max sea level thrust on the GE90-115B is ~500 kN, so at say 40% thrust those engines are producing about 400 kN total. As you know, work = force x distance and since power = work / time, the power consumption required, just to keep the airplane in cruise is 400000 x 250, or about 100MW. Now assuming even a 100% efficient solar panel (about 1kW/m^2), you'd need about 100000 square meters of panel, or about a third of a kilometer on a side. Meanwhile, the actual top-down looking surface area of a 777 is approximately 2 orders of magnitude less than that. And any increase in surface area beyond that dramatically increases drag and the resulting energy requirements. And that's with a hypothetical 100% efficient solar panel (in actual fact, best lab results are about 35-40% efficient). Put simply, even from first principles, the idea of a solar-powered commercial airplane is just a non-starter.

    3. Re:Five months? by bsDaemon · · Score: 1

      This plane is really battery powered; the solar cells charge the batteries and take in enough over the course of the day to power the batteries over night. The plane could stay aloft indefinitely, if it weren't for the pilot's biological needs.

      I agree that a 'solar powered' commercial airliner isn't realistic. however we very well may see some 'hybrid' type of aircraft in the future where large portions of the electricity necessary to run non-propulsion systems is provided by solar-rechargeable batteries (if that isn't a thing already... i'm not an aeronautical engineer, though I do come from a long line of pilots). Applying solar power to other methods of transportation could be the next experiment.

      Sometimes stuff like this is just cool on its face regardless of practical applications in industry.

    4. Re:Five months? by brambus · · Score: 1

      I know they charge during the day and use that to run during the night, however, that's not really addressing the basic power requirement problem.
      I'm glad to see you acknowledge that this is probably not realistic to power an airliner and I'm sorry to put a dampening on your hopes for this being used to power on-board systems. The electrical draw in an airplane is minuscule compared to the mechanical load of just moving the airplane through the air. As I've calculated, the 777 requires about 100 MW of power to cruise. I'd be surprised if the electrical load was anything more than 1/1000 of that (100 kW) - pretty much a drop in a bucket when it comes to the engines. A much higher load, in fact, are things like bleed air (used to pressurize the cabin, among other things) and anti-ice systems. The electrical load is in fact so small, that modern commercial airliners have a thing called a RAT (Ram Air Turbine), a miniature windmill electrical generator, that serves as a backup should all on-board power generation fail (which is triple-redundant in the 777) and is capable of providing several kW worth of last-resort backup power for things like avionics, electrical hydraulic pumps and emergency lighting.

    5. Re:Five months? by SillyHamster · · Score: 1

      Put simply, even from first principles, the idea of a solar-powered commercial airplane is just a non-starter.

      And you haven't even touched on the safety/risk aspects of relying on "fuel as you get it from daylight" to transport commercial quantities of people.

      At best, a "solar-powered" plane will be an electrical battery/cap-powered plane that is charged with solar-panels.

      It is hilarious and tragic that an AC response accuses you of not having enough imagination. The sad thing is that he is the one who is not using his imagination to consider the costs, challenges, and risks.

    6. Re:Five months? by brambus · · Score: 1

      Oh yeah, the safety is a whole other matter :) The reason I took it from a physics angle is that if the basic physics isn't there, we don't even need to consider the question of safety and risks (which are, to a much larger degree, qualitative). It'd be like discussing the safety implications of intergalactic wormhole transportation technology.

    7. Re:Five months? by brambus · · Score: 1

      Just as well not everyone is as limited in their imagination as you.

      Please do give me a call when your imagination figures out a way to break the laws of physics. There's no problem with having your head in the clouds, as long as your feet are firmly on the ground. No amount of inventive imagination is going to let you circumvent things like conservation of energy.

  5. Solar constant is 1kW/m^2. No way around that. by renergy · · Score: 4, Interesting

    Given the solar constant, i.e. the fact that there is at most 1kW per square meter of solar irradiation, there is no way this kind of planes could be used to air transport as we know it. To make the plane more powerful, way too much wing area would be needed, which would in turn reduce the speed etc. So, unfortunatelly, planes powered directly with photovoltaic panels will always be very limited in the weight they can carry. There are still applications for such kind of planes, though. (the 1kW/m^2 corresponds to a clear sky, the plane perpendicular to the impinging fotons, near the equator around noon, so the sun rays go almost perpendicularly through the atmosphere AM1.0 spectrum - simply the most favorable conditions). Photovoltaics (on a large area) powering the synthesization of hydrocarbons for conventional airplanes, renewably from air CO2 and water - that's completely different story. But it is not what this project is about.

    1. Re:Solar constant is 1kW/m^2. No way around that. by schlachter · · Score: 1

      surveillance
      disaster monitoring
      coms relay / internet
      electronic warfare / jamming / decoys

      --
      My God can beat up your God. Just kidding...don't take offense. I know there's no God.
    2. Re:Solar constant is 1kW/m^2. No way around that. by AmiMoJo · · Score: 1

      Solar aircraft could be a whole new class of bird that replaces some of the functionality of satellites. Much, much cheaper to build and launch, can stay up almost indefinitely and then be easily retrieved for maintenance. Think wireless communications, from "sat" phones to mobile broadcasting to wireless internet. Could be useful for surveillance applications too, e.g. deploying at high altitude over interesting areas at a price that is affordable for charities and other NGOs working on the ground.

      --
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    3. Re:Solar constant is 1kW/m^2. No way around that. by HBI · · Score: 1

      How about a solar powered rigid airship? That always seemed a lot more likely than a fixed-wing aircraft.

      --
      HBI's Law: Frequency of calling others Nazis is directly correlated with the likelihood of the accuser being Communist.
    4. Re:Solar constant is 1kW/m^2. No way around that. by brambus · · Score: 1

      If the Solar Impulse project is anything to go by, it's hopelessly dependent on good weather to be able to sustain flight. For example, if you were dealing with aviation on a regular basis, you'd know that there are these things called "upper altitude winds" which regularly reach speeds in excess of 100kts even at fairly low altitudes (~10000-15000 ft) and given that the Solar Impulse's cruise speed is around 35 kts, it'd simply get blown all around the place, almost like a balloon. At that point, you might as well just junk the idea of heavier than air flight and just stick your comms antennas on a solar-powered blimp. And given the atrocious coverage such a system would provide vs. space satellites, means you'd need probably like tens of thousands of those in constant upkeep, just to give you decent coverage. For global "satcom" phone coverage, it's much easier to just launch 20-30 small polar orbit satellites, which are on stable orbits and give you global coverage at the same time - and we've already done that. For internet access and broadcasting, just build radio masts, which are cheap as heck and require almost no maintenance, or a couple of high-power GEO satellites to cover a whole continent - and we've already done that too. And as for NGOs and high-altitude surveillance, what you want is a blimp, not an airplane.
      Put simply, solar-powered airplanes are a solution in search of a problem.

    5. Re:Solar constant is 1kW/m^2. No way around that. by blue+trane · · Score: 1

      There is a way around 1kw/m^2: multiple exciton generation. One photon generates more than one electron so current is more than the incoming light generates without the MEG techniques. The 1kw/m^2 value is based on one photon-one electron.

      Wikipedia says:

      "Note that in the event of multiple exciton generation (MEG), quantum efficiencies of greater than 100% may be achieved since the incident photons have more than twice the band gap energy and can create two or more electron-hole pairs per incident photon."

      Keep increasing the generated electron-hole pairs per photon, and you get an efficiency over 100%. Sorry, Kelvin!

    6. Re:Solar constant is 1kW/m^2. No way around that. by renergy · · Score: 1

      No, there is not. You are mixing the number of particles and the energy they have. You can get more free electrons than incident photons - this is really what the Quantum efficiency is about, QE = [number of electrons]/[number of incident photons]. But those "more electrons" would be at a lower energy level, which translates to lower open circuit voltage of the cell. The overall energy of the pair of electrons would still be lower than the energy of the photon that kicked them to the conduction band, i.e. the efficiency would still be (way) below 100%. Sorry pal, energy conservation holds.

  6. Spectacular success or spectacular failure by thebes · · Score: 1

    Mouse: What does it mean?
    Switch: It doesn't mean anything.
    Cypher: Everyone falls the first time.

  7. Re:Should succeed by ChrisMaple · · Score: 1

    Warmer is worse. The air is thinner and the voltage from the cells is reduced.

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  8. popularize idea, not have solar airplanes by Anonymous Coward · · Score: 4, Interesting

    I think that the effort isn't about "solar powered airplanes", since, as pointed out above, 1kW/square meter just doesn't do it. It's more about "expanding the possible" by doing something unusual. There's significant value in doing something challenging.. or do you sit at home and say, "well, it's theoretically possible to go to the North Pole on foot. I can read lots of books and figure out how to do it, theoretically. So, that problem's solved. Next...."

    How many people will be inspired by the idea in general: yes, you can do cool stuff with solar power. Some will be impractical (cargo planes with solar cells), but maybe, as someone does the calculations to show that it's impractical, they'll get an appreciation for what *is* practical (dirigibles using solar power for propulsion, but not lift, if we want to stay in aviation) , and then, they'll go out and say, let's go do that. Or, for that matter, they may not go solar power at all, but you've planted the seed of curiosity in someone

    Let's not forget, too, that at least one of the pilots is an adventurer (he's already done a non-stop around the world balloon flight) from a family of adventurers (August in balloons, Jacques to the bottom of Challenger deep)

  9. why not a standard glider? by Anonymous Coward · · Score: 1

    If this trip is over months with stops in the middle, why not use a standard glider, which in skilled hands can fly thousands of km without stopping? All gliders are solar powered.

    1. Re:why not a standard glider? by LeadSongDog · · Score: 1

      Transpacific glider? I wanna see that!

      --
      Oh, I'm sorry sir, I thought you were referring to me, Mr. Wensleydale.
    2. Re:why not a standard glider? by Deadstick · · Score: 1

      The problem is what's between the islands. You need thermal lift to fly long distances in a glider, and there's precious little of that over open water. And for every successful flight of 1000+ km, there are plenty that had to be abandoned partway.

  10. Re:Why East? by jklovanc · · Score: 2

    The jet stream goes east west. Get high enough and one get a boost in speed.

  11. Carbon Footprint by jklovanc · · Score: 1

    While the mission will be run out of a control room in Monaco, a group of engineers will follow the plane around the globe. They have a mobile hangar to house the plane when it is not in the air.

    I wonder how big the carbon footprint of the support team is. I bet it is at least a few times as big as the carbon saved by the aircraft.

  12. Re:So when will you invent time travel by blue+trane · · Score: 1

    It was absolutely certain to Lord Kelvin that heavier-than-air flying machines would never happen. Then it did, but he had died a year before. So I guess he was right, in a way, for himself; but not for the rest of us.