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Solar Planes Aren't the Green Future Of Air Travel (vox.com)
An anonymous reader writes: By any standard, the Solar Impulse 2 is a marvel of engineering. This solar-powered plane didn't use a drop of kerosene on its epic trip across the Pacific Ocean. It's a real testament to how far solar technology has advanced. Unfortunately, for anyone hoping that we'll all be puttering around in solar planes soon -- well, that's pretty unlikely. From a Vox report, "Consider: The Solar Impulse 2 features 17,000 solar cells crammed onto its jumbo jet "size wings, along with four lithium-polymer batteries to store electricity for nighttime. Yet that's still only enough power to carry 2 tons of weight, including a single passenger, at a top speed of just 43 miles per hour. By contrast, a Boeing 747-400 running on jet fuel can transport some 400 people at a time, at top speeds of 570 miles per hour. Unless we see some truly shocking advances in module efficiency, it'll be impossible to cram enough solar panels onto a 747's wings to lift that much weight -- some 370 tons in all. Nor is it enough to load up on batteries charged by solar on the ground, since that would add even more weight to the plane, vastly increasing the energy needed for takeoff. A gallon of jet fuel packs about 15 to 30 times as much energy as a lithium-ion battery of similar weight. That fundamental difference in energy density is a big reason we're unlikely to see large commercial airliners powered by batteries fill the skies."
Having a solar driven plane circle the world is still cool.
A gallon of jet fuel packs about 15 to 30 times as much energy as a lithium-ion battery of similar weight. That fundamental difference in energy density is a big reason we're unlikely to see large commercial airliners powered by batteries fill the skies."
This isn't even the whole story. As a plane flies, it burns fuel, essentially throwing mass out the engines for thrust. Getting lighter allows the plane to climb to a higher altitude where it is more efficient.
Elbonian Air?
Oliver's law of assumed responsibility: If you're seen fixing it, you will be blamed for breaking it.
People are a bit picky about planning travel in advance and getting places on-time.
There are usually thunderstorms daily in the USA, and buses, trains, cars and airplanes go right through that.
Zeppelins have to wait for the storm to pass.
Regardless of Hindenburg, their fate was already sealed.
Grammer Nazis - I mod you "troll" unless you actually add something on-topic. Yes, I know I have mispellings in my sig.
Unless we see some truly shocking advances in module efficiency
It wouldn't work with 100% efficiency, so why would increase in efficiency matter as far as making it practical? What is happening to critical thinking skills?
I think it's pretty apparent that the solar concepts are just concepts. Obviously there's not enough energy output to replace passenger flight.
But the question is, can solar panels on a plane offset the energy consumption enough to make a difference? That's probably also a no, but that's where the question should start.
Keep in mind, some cargo ships have been experimenting with massive kites/sails that help offset the energy needed for their engines:
http://www.skysails.info/english/skysails-marine/skysails-propulsion-for-cargo-ships/
> Unless we see some truly shocking advances in module efficiency, it'll be impossible to cram enough solar panels onto a 747's wings to lift that much weight [...]
Besides that, I strongly suspect there isn't enough power in the form of sunlight falling on a surface the size of a 747's wings to achieve the objective. In other words, it's not just a matter of solar panel efficiency, it's also a matter of total energy available for capture.
Oliver's law of assumed responsibility: If you're seen fixing it, you will be blamed for breaking it.
Batteries, or solar cells, don't make thrust by themselves either. You'd still need the same turbofans, just with heavy electrical windings in the middle rather hollow combustion cavities. Electric motors tend to be quite a bit heavier than empty cavities are, so I'd expect the electric engine to be probably a bit heavier.
You could put a prop on an electric motor. That limits maximum speed, and still electric motors are heavy.
> The fuel system itself
Such as the fuel lines and fittings , the hollow copper tubes? Compare with the copper required to carry thousands of amps safely, with heavy-duty insulation. The fuel line and fittings are probably lighter than electrical lines and fittings capable of transmitting the same amount of power.
> If wing didn't have to carry fuel could it be more efficient?
Wing efficiency is determined by shape and surface smoothness. What's inside doesn't matter, except a snall effectbthat carrying load in the wing is slightly more efficient than carrying the same load inside the fuselage, by eliminating the bending moment on the wing root. Putting solar panels on the SURFACE of the wing, where it's right in the critical boundary layer airstream , is a much bigger design constraint than putting something IN the wing.
"Hydrocarbon fuel" doesn't necessarily imply "fossil fuel," you know! Synthetic fuels and biofuels are easy sustainability solutions that even work with the infrastructure and aircraft we have now, without the physical impossibility of solar or the political impossibility of nuclear.
"[Regarding the 'cloud,'] ownership was what made America different than Russia." -- Woz
Unfortunately it is impossible. There are hard physical limits on battery energy density.
love is just extroverted narcissism
yeah, this whole airplane thing reminds me of that fool who thought people would have computers in their houses. pfft! how can you fit a giant electromechanical machine that fills a warehouse into your living room? some people, am i right?
Anons need not reply. Questions end with a question mark.
Solar Planes Aren't the Green Future Of Air Travel
I never thought they were. Jeez, why always looking for the negative?
Next: The LHC can't solve global warming.
systemd is Roko's Basilisk.
We also stalled out with SST. Why?
Efficiency. The gains from going 1,200 MPH instead of 600 MPH aren't worth the extra expense. Amdahl's Law -- though aimed at computing -- comes to mind
"I don't know, therefore Aliens" Wafflebox1
Unless we see some truly shocking advances in module efficiency
It wouldn't work with 100% efficiency, so why would increase in efficiency matter as far as making it practical? What is happening to critical thinking skills?
Regarding critical thinking, why couldn't we just use solar panels on the ground to make jet fuel(*)?
Jet fuel in this instance is just an energy carrier, and has a much higher energy density than lithium. While Lithium batteries may be appropriate in some cases (portable devices, ground transportation), for air flight it's more appropriate to use something else.
(*) Or perhaps a biological method such as GM modified algae or a bio-yielding plant. The Wikipedia page of crop yields indicates that Algae can yield 80,000 kg/ha/yr, with "ha" being the area of a square 100 meters on a side.
A quick calculation shows that a 747 holds around 183,000 kg of fuel, so 3ha of open-pond algae could supply enough fuel for one tank each year.
Anyone who has driven across the "great basin" and other nearby sections of the US (western part of Utah, Nevada, parts of Arizona) knows that we have lots and lots of unused area that gets a lot of sunlight, and water is generally available from wells.
It seems reasonable that we could put up large solar and wind installations in these places, generate biodiesel and other organics, then ship them by tanker truck to where they are needed.
About 11 million gallons of fuel used in the US for aviation annually, that's 31 million kg, which requires 387 of those 10m x 10m algae pools(*).
At roughly $5 per gallon, the output of such an installation would be worth $55 million per year.
This seems like a futuristic prediction, but it makes sense.
Once the price of fuel goes up, this sort of installation may not be far in our future.
(*) This seems low. Have I dropped a digit somewhere?
To slashdot's new masters: your readers aren't so ignorant that we think that Solar Impulse 2 means we'll be seeing solar powered 747s. Sheesh.
Post may contain irony: discontinue use if experiencing mood swings, nausea or elevated blood pressure.
... progress is made by refining the process ...
Yes, and the bias against internal combustion and jets and the bias towards solar are causing people to miss a major piece of that process. The fuel. There is nothing wrong with internal combustion and jets, the problem is only their current petroleum based fuels. Switch to bio fuels that are carbon neutral and we have no problem. Carbon is not the problem if it is taken from and returned to the current environment, as with bio fuels. Carbon is only a problem when we mine ancient sequestered carbon and reintroduce it to the current environment, as with petroleum.
Liquid fuels have incredible energy density. We would probably need a Back-to-the-Future-like "Mr Fusion" reactor, not improved batteries, to make electrically powered fixed/rotary wing aircraft practical.
Synthetic fuels may be easy but fossil fuels are so cheap that they can't compete. A carbon tax would level the playing field.
So would passing peak petroleum production, which we may have already done.
So would national security concerns about foreign petroleum supply lines. Note the military has had jets flying on biofuels since 2010. They can justify the higher cost with more secure supply lines. Satisfying the military's need for jet fuel, or a large part of it, can jump start the biofuel generation infrastructure and bring costs down.