A Solar-Powered Airplane

One of the things I have stated repeatedly is that even as I see the world moving to solar power by necessity, we will always need liquid fuels for long-haul transport and airline travel. Turns out I may have been wrong about the airline travel bit:

Solar Impulse will fly only on solar power

The Solar Impulse project has been broken down in stages to allow for adequate testing and technological advancement. The initial planning stages began in 2003. 2007 and 2008 should see the production of a prototype(s) for testing and the first overnight flights. Then larger prototypes will be introduced in 2009-2010 for longer test flights. The final stage should occur in 2010, when the flight around the world is expected to finally be possible.

Yahoo! News provides video coverage:

Solar Plane Ready for Flight

Amazing. This shifted my paradigm on air travel, which to date has always been that it would require liquid fuels. Of course as is normally the case with new technology, there are caveats. Right now it is still at the simulator stage, and while the stated intent is to eventually be able to fly 300 passengers, per the video this will require “new technologies.” A very interesting story, regardless.

22 thoughts on “A Solar-Powered Airplane”

  1. Photovoltaic airplanes have been around since the ’70s. They’re slow and flimsy. Solar Impulse has never even flown anything to my knowledge, talk of 300 passenger designs is extremely premature. Their website is full of technical errors.

    NASA has done interesting work beaming concentrated lasers up to PV cells on the underside of the wing. You don’t need batteries, but efficiency is awful.

  2. Actually, I suspect you could run a high-altitude IC engined aircraft at a lower altitude if you converted it to use producer gas. That would mean solid fuel, not liquid fuel (and much less range, of course).

  3. If solar energy can be harvested in sufficient quantities to fly passenger airplanes, those same airplanes would be able to run off of a tiny trickle of liquid fuel. Methinks there’s a lot of sleight of hand going on here, and that this is really about powering an airplane off of magic batteries.

    Given that battery size and weight vs. capacity is still such a huge issue for EVs (which don’t need to go airborne), it could only be exponentially more so for air propulsion, I would think.

    Robert, your rigor in analyzing biofuel energy conversion chemistry has inspired me to be much more analytically hard-nosed about the claims within my own industry (solar/batteries). You seem to be going pretty easy on the electrical disciplines these days, though.

  4. Another possibility is airships. Popular Science wrote about the Aeros Aeroscraft (15 Jan 2006):

    “To minimize noise, the aft-mounted propellers will be electric, powered by a renewable source such as hydrogen fuel cells.”

    Latest news is a 210-foot demonstration model has begun final assembly. The main feature of these things is that they’re slow. Anywhere between 130-175 mpg top speed, so would take a full day to cross the Atlantic. Also they depend on helium, which may already be past peak.

    -Laurence Aurbach

  5. Robert, your rigor in analyzing biofuel energy conversion chemistry has inspired me to be much more analytically hard-nosed about the claims within my own industry (solar/batteries). You seem to be going pretty easy on the electrical disciplines these days, though.

    That is of course because it isn’t my discipline. I need people like you to take a close look at these things and if there are issues, to flag them.

    I take all of these claims with a grain of salt. Especially when someone says that it needs “new technology.” New technology is all that stands between me and immortality.

    Regardless, I thought it was an interesting story as I would have never even guessed such a thing was remotely feasible.

    Cheers, RR

  6. Robert,

    I just don’t see how something like a 7E7 will ever fly on solar alone. It’s just too energy intensive.

    Maybe a blimp.

    Or maybe solar could be used to split water for hydrogen production. But there just isn’t enough energy hitting the wings of a real passenger airplane to fly it.

  7. De Vinci portrayed concepts. today some exist in form factors close to sketch.

    who knows?

    ahhh! to have a 1/2 day return pass in 500years. then again NOT!

    in addition to De Vinci, there were also Huxley, et al.

    best to enjoy what we have and wonder.


  8. Here’s an order-of-magnitude check for the giggle test:

    737-800 (162 passengers) has a wing area of 1344 square feet.

    That gets us about 135 kW (peak) of solar panels. You might be able to double that with very good (and expensive) cells and more direct sunlight at altitude.

    From wikipedia, I get the cruising speed, range, and fuel capacity. Taking these together suggests a fuel burn rate of 625 gallons per hour. But burn is much higher on takeoff and landing, and there is a substantial safety factor of extra fuel as well. So let’s go with 500 gallons/hour.

    Jet fuel = 135,000 BTU/gallon
    So estimated cruising burn rate is
    67,500,000 BTU/hour = 19,777 kW

    So we’re about two orders of magnitude off. That’s not as bad as I was expecting, actually, but that’s still a hell of gap to cover. And with airplanes, unlike buildings or even cars, alot of attention has already been paid to removing excess weight and reducing fuel use. So I don’t think we’re going to make up the difference in improved efficiency of vehicle design.

    New technology, indeed. Sounds like magic ponies to me.

  9. You guys are so cynical. I am buying some Flubber at the local Disney store, so I can bounce coast-to-coast without using any gasoline on my new sneakers. Anybody want to have lunch on Kansas City, or dinner in Nova Scotia?

  10. A solar-powered airplane will never be able to carry a significant load, that is unless it uses the Rockwell Retro-Encabulator:


    The key to a solar-powered airplance will be the prefabulated amulite, surmounted by a malleable logarithmic casing in such a way that the two spurving bearings are in a direct line with the pentametric fan.

  11. Thing is, you’re unlikely to power a large commercial aircraft using solar panels on its wings, but why would you want to.

    If long haul passengers were to forgo the bulk of their check in baggage, there is no reason that large carbon fibre cryo tanks couldn’t be placed in the hold to accommodate liquid hydrogen. Said LH could be generated using concentrated solar or PV with electrolysis.

    Running the numbers on the above scenario would give a clearer picture of the ultimate max cost of aviation fuel.

    I have a suspicion that its “only” in the order of 4x current jet fuel prices, which certainly wouldn’t stop me from flying.

    But I haven’t run the numbers as I don’t have good costs for operating industrial scale electrolysis amongst other things.

    Andy K

  12. If you are interested in electric planes then google boeing’s electric aircradt first flown just recently in Spain. This is a fuel cell powered aircraft. But the most interesting one is the Pipistrel Taurus Electro motor glider, from Slovakia.
    This is talking about personal air vehicles rather than high load passenger aircraft. See Cafe Foundation http://cafefoundation.org/v2/main_home.php
    for more on where the technology is, and where it is going.

  13. Airplanes will migrate to liquefied natural gas before liquefied hydrogen. The bulk density of liquid hydrogen is around 80 kg/m^3 compared to about 400 kg/m^3 for methane, so even though the specific impulse of hydrogen is higher it suffers a big drag penalty. Another alternative maybe supercooled propane.

    Also, the electricity requirements to produce enough hydrogen for planes through electrolysis is appalling.

    Also there’s a big difference from an engineering perspective between 20 K and 100 K. Both are cryogens but they are not equivalent.

  14. Taking these together suggests a fuel burn rate of 625 gallons per hour. But burn is much higher on takeoff and landing, and there is a substantial safety factor of extra fuel as well. So let’s go with 500 gallons/hour.

    500 gph at 500 mph implies 1 mpg, pretty amazing for a 175 passenger plane. But then why are fuel costs bankrupting these guys? 1000+ gallons is only $3500 for a typical 2 hour trip. That’s $20/passenger, up from about $10/pasenger a few years ago. Of course it’s a little more than that since most planes aren’t fully loaded, but still it doesn’t sound like a big deal.

  15. Hmmm…if you guys want a non-fossil-fuel technology that could (at least from an engineering point of view) really power an aircraft…I give you…

    the nuclear-powered aircraft.

    As others have noted, there is no way in the world we’re ever going to power a passenger-carrying aircraft on solar cells.

    One application you might see (heck, it might already be in use as the secret replacement for the SR-71 Blackbire), is solar-powered reconnaissance planes, like this

  16. Some of you may have heard of the quantum nucleonic reactor. The air force was very interested in prototyping unmanned craft powered by this energy source as recently as 2003 but since then the topic has largely “gone dark”. I am aware that Boeing was involved at one point as well.

    The physics are described in this University of Texas at Dallas paper titled The Essential Fundamentals of Quantum Nucleonics.

    The essential point is that these halfnium isotopes, when bombarded with x-rays, can emit 60 times the energy input. No, there is no violation of the second law here, as they are releasing energy stored in excited electrons.

    One quote said:

    Nuclear Isomers are an exciting new development in the field of Nuclear physics. They are, essentially, a nuclear storage battery. Just as atoms can have electrons in excited states, atomic nuclei can have nucleons (protons and nuetrons) in excited states as well, but unlike atoms with electrons in excited states, the nucleons can remain in their excited states for extended lengths of time. The excited nucleons can randomly decay on their own, and have representative half-lifes as well. Not all atoms can have stable excited nucleons, and typically larger atoms are more likely to have longer half-lifes of the excited nucleons. But, the theory goes, the nucleons of an atom can be excited to higher energy levels by bombarding them with gamma rays, and then triggered to release their energy on demand by hitting them with lower energy photons, Ultra Violet or X-Rays. These would amount immensely dense energy storage devices, with power densities per unit wieght reaching a theorhetical limit near that of low end fusion reactions!

    Best Batteries – 300 Wh/Kg

    Fuel Cells (aluminum) – 4,000 Wh/kg

    Isomer Nucleonic – 800,000,000 Wh/Kg

    Fusion – 90,000,000,000 Wh/Kg

    This is not a panacea and has its own issues as well. But that is always true of any technology. As always, the issue is not what we can do, but what we will do. As the recent photos of the Phoenix Lander descending into the Martian atmosphere, taken by the Mars Orbiter demonstrate, homo sapiens can do some quite clever things when it decides to do so. The problems come when it decides to trust to chance instead.

  17. Somebody asked why fuel costs are bankrupting airlines.

    The reason is not that fuel costs account for the bulk of your ticket price. Labor and airport fees cost much more from what I have read, although I don’t have a citation for that.

    The trouble is that the business of air travel has razor thin profit margins, so that any increase in the cost of _any_ of their inputs can bankrupt them. One of the reasons Southwest has done well financially is they bet that fuel prices were going to go up and essentially pre-purchased fuel (I imagine by buying call options) for many years to come.

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