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Solar Panels On Commercial Aircraft  
User currently offlinesolarflyer22 From US Minor Outlying Islands, joined Nov 2009, 1109 posts, RR: 0
Posted (1 year 6 months 3 weeks 6 days 9 hours ago) and read 5732 times:

Solar Impulse has proven its viable to cover horizontal surfaces on a plane, charge some lightweight lithium batteries (non Boeing types) and use the power for something, in their case a propeller.

Can the same be done on a 787/A350 by adding solar panels on the wings and over part of the upper fuselage? The saved power can be used to supplement the APU saving fuel or provide power in flight (in lieu of hydraulics). Regenerative braking can be used to provide further charging.

Before you shoot down my idea, note that panels are lightweight yet strong, probably not much more expensive than aluminium skin cover on a plane. Also, high altitude provides more access to solar energy.

Naturally at night, the engines and APU would provide power. If its weight neutral or close to it, I think it would work and save another 1% in fuel burn.

Solar Impulse FYI:

http://articles.timesofindia.indiati...e-plane-andre-borschberg-zero-fuel

14 replies: All unread, jump to last
 
User currently offlineDLPMMM From United States of America, joined Apr 2005, 3594 posts, RR: 10
Reply 1, posted (1 year 6 months 3 weeks 6 days 8 hours ago) and read 5685 times:

It would probably cost more than 1% in aerodynamic efficiency.

I would suggest you take this to the tech-ops board for further discussion.


User currently offlinePolot From United States of America, joined Jul 2011, 2274 posts, RR: 1
Reply 2, posted (1 year 6 months 3 weeks 6 days 8 hours ago) and read 5652 times:

Quoting solarflyer22 (Thread starter):
probably not much more expensive than aluminium skin cover on a plane.

One that cheap is either very inefficient or doesn't last very long (or both). Boeing actually does a lot of work in this field and has designed some of the best solar cells out there. The fact that they are not on their airplanes is telling.

Edit to add: Thin film solar cells (which I am guessing the Solar Impulse is using) are typically organic compounds or polymers. While that means they are relatively light or flexible, organic or polymer material is terribly inefficient as a solar cell (they don't have broad absorption spectra, meaning they are not absorbing most of the Sun's emission). Note how the Solar Impluse only has the power needs of a small scooter, yet has the wingspan of a 747. Solar cells are nowhere near capable of producing any useful amount of power for a commercial jetliner. The best cells are multijunction. But they are not as lightweight, flexible, and involve using a lot of expensive inorganic material. (Note that I am chemist who doesn't actually do any work with solar cells, but has many friends who do).


[Edited 2013-04-05 20:48:09]

[Edited 2013-04-05 21:00:21]

[Edited 2013-04-05 21:01:25]

User currently offlineN766UA From United States of America, joined Jul 1999, 8313 posts, RR: 23
Reply 3, posted (1 year 6 months 3 weeks 4 days 14 hours ago) and read 4802 times:

The number, size, and weight of solar panels required to make ANY kind of a dent in a passenger liner would be ENORMOUS. You'd be better off flying with solid lead overhead bins.


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User currently offlinesolarflyer22 From US Minor Outlying Islands, joined Nov 2009, 1109 posts, RR: 0
Reply 4, posted (1 year 6 months 3 weeks 4 days 14 hours ago) and read 4734 times:

Yeah Polot makes a great point on the power demands of Solar Impulse. It sounds like this technology is just really really far away. So far away, that you'd probably be better off investing in better engines and composites to save fuel for now.

User currently offlineN766UA From United States of America, joined Jul 1999, 8313 posts, RR: 23
Reply 5, posted (1 year 6 months 3 weeks 4 days 14 hours ago) and read 4715 times:

Quoting solarflyer22 (Reply 4):

Yeah Polot makes a great point on the power demands of Solar Impulse. It sounds like this technology is just really really far away. So far away, that you'd probably be better off investing in better engines and composites to save fuel for now.

Absolutely. It's completely do-able for small things, or like you said for an aircraft with a majorly efficient wing and no payload, but for a passenger-liner, yeah it's a long way off.

You might see them applied as a sort of backup battery or APU or something, though! While they'll NEVER be powerful enough to propel a large passengerliner, they aren't without potential entirely.



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User currently offlineaklrno From United States of America, joined Dec 2010, 954 posts, RR: 0
Reply 6, posted (1 year 6 months 3 weeks 4 days 10 hours ago) and read 4542 times:

In addition to the posts above that point out that this probably doesn't work on the grounds of efficiency, consider the speed at which the aircraft is moving.

Solar panels are relatively flimsy. In order to make them light such as on Solar Impulse, I suspect they are very flimsy. Subject them to a 500 MPH wind and you are asking for trouble. Also at those speeds the slightest bit of increased aerodynamic drag is going to cost some money. Solar power today is going to be limited to very slow aircraft where the drag is less of a problem.

I want to add some solar panels at my house in Reno, but I can get 100MPH winds on a bad day. I haven't seen panels I trust at that speed yet. The windows are made to withstand that wind, but I'm not sure they would survive if a solar panel hit one.


User currently offlineMir From United States of America, joined Jan 2004, 21730 posts, RR: 55
Reply 7, posted (1 year 6 months 3 weeks 4 days 2 hours ago) and read 4332 times:

Quoting Polot (Reply 2):
Note how the Solar Impluse only has the power needs of a small scooter, yet has the wingspan of a 747.

Keep in mind that that's likely a function of aerodynamic needs as much as it is a need for solar panel space.

-Mir



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User currently offliner2rho From Germany, joined Feb 2007, 2695 posts, RR: 1
Reply 8, posted (1 year 6 months 3 weeks 3 days 22 hours ago) and read 4164 times:

Solar Impulse, while an interesting project, is unfortunately creating false expectations/illusions of solar-powered flight.
Solar Impulse is essentially a powered glider - it has the wingspan of an A330 but barely manages to carry one person - that should give you an idea of the power provided by the solar panels. Completely unsuited for practical purposes.

For alternate power sources, fuel cells have a better chance at replacing APU's. And for CO2-neutral flight, 2nd generation biofuels that do not compete with food crops would be the best choice. At best, I could see solar panels as a complementary (not sole) power source on small simple military drones.

P.S. Topic is probably more for Tech/Ops forum


User currently offlinercair1 From United States of America, joined Oct 2009, 1330 posts, RR: 52
Reply 9, posted (1 year 6 months 3 weeks 3 days 21 hours ago) and read 4072 times:
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Two points. If this worked (which I do not think will), you'd have a bit problem with what to do with the energy when the plane is sitting on the ground. You cannot turn off solar cells. They will convert solar energy to electric potential whenever there is light. You can, turn the system "off" but you are only turning off the inverters. There will be dangerous potential around the panels whenever there is light. This is a hazard for a lot of people.

As for how useful - lets try some math - based on thumb in the air guesses. I'm sure there are people out there who can and will point out the big holes in this model - so we can improve on it.

Being very generous - let's say we could find a cell that produces 15 watts/sq ft. This is on the high side - and probably much more than the cells use on Solar Impulse (organic cells are more like 3-5 w/sq ft).

The 787 has a bit over 3501 sq ft of wing area - so lets assume 3000 of it is available for use by the cells.

3000 sq ft * 15 w/sq ft means 45KW at peak - which means "high noon for the a/c"

Now - most models assume 1/2 of that for the "day" average due to various factors like incident angle (an angle of 45 degrees will decrease incident energy to .7 for instance). So - we have 45KW * .5 = 22.5 KW for the generating day - which is considered to be 8am - 4pm. I think we can assume that most planes will fly outside that window - so lets make a guess (based on nothing) that this represents only 66% of the flight time (on average), so drop it by .66 = 14.5KW average.

So - we arrive at 14.5KW on average. In an hour flight - 14.5 KWH

Now - one RR T1000 at takeoff thrust generates 52000 hp or 38480 KW (based on RR statement that each blade generates 800 hp and there are 66 blades - this apparently is only for the bypass). Lets derate this to 40% for average cruise - so about 15,000 KWH per hour flight * 2 (engines) or 30,000 KWH.

So - our solar system, on average, reduces the required load by 0.048% - say .05%.

Assuming the fuel to electricity path of the engines and generators is 20% efficient (I have no idea), we reduced fuel flow by 0.24%

Okay- is a .24% fuel reduction worth the certification difficulty - and what impact will it have on the efficiency of the wing.

And where did I go wrong in this back of the napkin calculation?



rcair1
User currently offlineaklrno From United States of America, joined Dec 2010, 954 posts, RR: 0
Reply 10, posted (1 year 6 months 3 weeks 3 days 12 hours ago) and read 3807 times:

I might have approached this from a different direction. How much fuel is required to generate that much energy? In Nevada, I pay about $0.11 per KWH. 14.5 KWH costs me about $1.60. That power is generated from natural gas and delivered to my house. I think that $1.60 currently buys about 2 or 3 pounds of Jet A. It would be hard to justify the weight and expense of solar cells for that.

A few weeks ago I was corralled into judging a business plan competition. Energy generating schemes were a popular topic. As the only technical person on the panel (among mostly accountants and other business types) I was the only one who tried to quantify some of the proposals technically. After eliminating the perpetual motion schemes I found some which required an investment of several hundred thousand dollars to generate about one dollar's worth of electricity a day. They were often very clever, but it's really hard to beat the price of natural gas today. Jet A may be more expensive, but for what it does it is a bargain. For comparison, I've seen people pay as much or more for bottled water.


User currently offlineAesma From France, joined Nov 2009, 6747 posts, RR: 12
Reply 11, posted (1 year 6 months 3 weeks 2 days 20 hours ago) and read 3628 times:

Electric planes are coming, but first in the GA world. Electric motorgliders are already proven (Antares 20E). Solar panels on composite airframes (common in modern GA planes, gliders, and now airliners) are a problem, because of the heat generated that glues don't like. In the context of GA it will probably make more sense to cover the hangars with panels to charge the planes/gliders. I think the Antares 20E has an optional solar panel on its trailer to top it up during the week.


New Technology is the name we give to stuff that doesn't work yet. Douglas Adams
User currently offlineWingedMigrator From United States of America, joined Oct 2005, 2225 posts, RR: 56
Reply 12, posted (1 year 6 months 3 weeks 1 day 9 hours ago) and read 3423 times:

Quoting rcair1 (Reply 9):
They will convert solar energy to electric potential whenever there is light. You can, turn the system "off" but you are only turning off the inverters. There will be dangerous potential around the panels whenever there is light. This is a hazard for a lot of people.

A battery will convert chemical energy to an electric potential so long as it is charged. You can turn the system "off", but there will be dangerous potential around the battery whenever it is charged. This is a hazard for a lot of people.

That's why they invented "switch" technology.

 


User currently offlineRoseflyer From United States of America, joined Feb 2004, 9670 posts, RR: 52
Reply 13, posted (1 year 6 months 3 weeks 23 hours ago) and read 3324 times:

The benefit from solar cells would be saving weight in the form of batteries, or lowering the shaft power taken off the gearbox from the engine, which would improve engine efficiency.

The problem I see is that the airplane has to work in all environments, including night. That would eliminate the weight savings from batteries, since you get no solar power at night. As for engine efficiency, airplanes are not designed to the maximum limit of electrical power. There is a lot of power In an airplane and a lot of demand. Inconsistent solar power doesn't help an airplane much in steady state cruise.

Quoting Polot (Reply 2):
One that cheap is either very inefficient or doesn't last very long (or both). Boeing actually does a lot of work in this field and has designed some of the best solar cells out there. The fact that they are not on their airplanes is telling.

You are right. The Boeing research labs in Huntington Beach for satellite technology produce some of the most advanced solar cells in Existence, so if there is opportunity, Boeing does have the knowledge.



If you have never designed an airplane part before, let the real designers do the work!
User currently offlinercair1 From United States of America, joined Oct 2009, 1330 posts, RR: 52
Reply 14, posted (1 year 6 months 3 weeks 23 hours ago) and read 3313 times:
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Quoting WingedMigrator (Reply 12):
That's why they invented "switch" technology.

Cute.
A battery is a localized source and you can put 1 switch there. A solar array is distributed and you'd have to put a switch at each panel. Possible? Maybe. Practical, no. But none of this makes any sense anyway so....



rcair1
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