Proposed Application

System

A teammate and I are working on a design project for an International Baccalaureate class in school. Our proposed problem is whether or not the application of solar cells on various areas of a fuselage of an airplane can help to contribute to it's primary fuel system of petroleum. We were hoping to determine whether or not this integration is a feasible proposition. Naturally, we were hoping to find some expert opinions on this matter because there are lots of facets that we couldn't fathom. A few of which being the actual durability of the solar cells at high altitudes in rough weather, the realistic figures for energy output while in use, the initial capital that would have to be offered up to institute their use, etc. There are a lot of questions we have, and this seemed like a good place to start. Currently, NASA has instituted various gliders powered solely by solar cells, so it's not that ridiculous a notion. So, please feel free to offer opinions and contribute to our knowledge. Thanks.

niel

Re: Proposed Application

i don't think it will do much for reducing the petroleum needs of today's jets. this would be akin to putting a fan on a rocket and may be more of a hindrance than a help. some solar cells can survive those conditions quite well, btw, as we have them in space too, remember?
for jets. they can improve the engines themselves to use less fuel and still perform the task. this is about the best i think we could hope for is for fuel economical engines. do note that everything in a jet is power derived from that same jet engine so conservation in the plane is also a good thing to pursue, but it would contribute little in the overall scheme of things i suspect.

BB.

Re: Proposed Application

You can use a program, such as PV Watts, to figure out how much power you can collect from xx kWatts of solar panel per day/month/year for major portions of the world.

Next, you can research different types/materials used for solar cells... The standard for terrestrial use is Silicon based--"cheap" at $3-$5 per watt (when packaged in weather proof glass panels for mounting on roofs and 25+ year life). You can look at gallium based cells, which can be almost 2x as efficient at collecting sunlight per sq... But they also (IIRC) cost some 10-20x as much as silicon cells (for space use, weight and size of payload vs cost of rocket+fuel cost/benefit ratio).

Running solar panels on an aircraft can have advantages (higher altitude and cold operating conditions increase cell performance).

On the downside, cells are "heavy" and off little in the way of useful energy... Pick some numbers for a back of the envelope calculation for a Boeing 747:

542 sq.meter wing area.

Assume that you collect 1,000 Watts per sq.meter and that around the world, you average ~5 hours of "noon time sun" per day (winter/summer averages). Assume 21% conversion efficiency:

542 sq.meter * 0.21 * 1,000 watts per sqm * 5 hours of sun = 569,100 Watt*Hours per day (569kWhr per day)

A B-747 will hold roughly 63,000 gallons of fuel. Just fuel, in terms of heat content is probably around 40-45kWhrs per gallon.

So, heat content wise:

63,000 gallons of Jet A * 42.5 kWhrs per gallon = 2,667,000 kWhrs of heat worth of fuel...

Assume that a jet engine is ~33% efficient (just a guess--comparisons are difficult as there are other uses for the energy too--such as A/C and aircraft pressurization take significant amounts of energy--so much, that modern airline operations have dramatically reduced the amount of fresh air brought into the cabin over the decades).

2,667,000 kWhrs of heat * 0.33 = 883,600 kWhrs of useful energy.

So, assuming 100% efficiency of solar conversion (may actually be ~50% efficient based on system requirements, less than optimum panel positioning, if stored in batteries for later use, etc.):

569kWhr / 883,600 kWhrs = 0.064% ratio between solar power vs useful fuel load work available of jet fuel...

Without even taking into account the increased weight and costs of "perfect" solar panels, and even if I am off by a factor of 2x in any of my estimates--If you covered the entire wing structure of B-747 with solar panels (ignoring the cabin, and tail structures--you are still only increasing available useful energy for a modern jet airliner by less than 0.1% which will undoubtedly increase fuel costs/reduce payload costs by well more than 0.1% possible fuel efficiency increase.

Assume that solar panels bolted to an airliner cost $50 per watt (SWAG--forgot to add *21% energy conversion factor)--:

542 sq.meter * 1,000 Watt per sq.meter * 0.21 * $50 per watt = $27,100,000 capital costs

Assume zero maintenance costs and 10 year life (before required stripping of airframe for major rebuild (again SWAG--aka scientific wild ass guess):

$5,690,000 cost / (569kWhrs per day * 365 days per year * 10 years) = $2.74 per kWhr

Note that utilities charge around $0.10 to $0.30 per kWhr in the US.

Assuming 42.5 kWhrs per gallon of Jet A, assume 33% useful work (jet engine efficiency)--even assuming adding 10 year life solar panels to wing area and no negative impact in payload and overall aircraft efficiencies (which is not a reasonable assumption):

42.5 kWhrs * 0.33 * $2.74 per kWhr = $38.50 per gallon break-even Jet A fuel price vs solar.

Questions? Did I do your assignment?

-Bill

PS: Updated using BOLD. Forgot to add 21% efficiency factor when pricing the cost of the gallium solar panels.

mike95490

Re: Proposed Application

Wow B.B. Now I know what a PV encrusted plane looks like when lighting hits it, and goes down in flames.
--
PS Lighting FREQUENTLY hits airliners, and would vaporize any PVs on the skin.

BB.

Re: Proposed Application

Yep... There are static discharge wicks on the trailing edges of jet airliners to try and discharge some of the energy... Also, every hing point on the exterior moving parts (control surfaces, doors, etc.) have a shorting strap to prevent pivot points/bearings from being "spot welded" in position.

To a degree, some of these issues (lightning, hail impact, weight, structural issues, etc.) can be addressed... But, just from a back of the envelope, why would anyone bother if the total energy content available from such a system is less than 0.06% of the energy required for flight.

I did not even bother to go into the fact that you only have some 7 hours of light per day--and the planes fly day and night.

Also, such as system would have to be near 100% maintenance free--a B-747 on international flights flies 18+ hours per 24 hour day (that just amazed me when I was on a tour of the old Pan American facility in San Francisco (SFO) as a young kid.

If people wanted to save energy--on a crowded airport with long waits--towing planes out to the runway with a tug providing ground power would save significant amounts of fuel... I believe I was on an AirBus a decade ago that seem to have shut down the engines and was using its APU to provide power and A/C--and there must have been some sort of hydraulic motor that could taxi the aircraft to the runway (really weird sounds every time we moved). Once we got to first or second in line--could hear the main engines spool up (start?) and used for final taxi to takeoff.

Reminds me of a not-so-funny story from the 1970's when the Airline Management told the pilots to turn off the #1 and #4 engines (IIRC) when taxing in from landing to save fuel... Turns out that it worked very well until one plane need to make several extra stops... Turns out the that hydraulic accumulator was running the brakes only and the last braking required was to stop at the gate--and ended up 10' inside the terminal instead. The #1 and #4 engines ran the A and B hydraulic systems and the fuel saving shutdown was placing the passengers and aircraft at risk because somebody did not understand the whole system.

There is no simple answer/solution on how to save fuel.

-Bill

niel

Re: Proposed Application

the aspect of static and lightning i didn't even think of, but would be a real problem. other problems could also be the extra wing weight and slight deforming on them due to pvs, even if contoured special, causing extra drag or the icing and deicing cycles and any chemicals encountered for deicing.
i think before using pv in a plane that they could provide pedal power for each passenger so as to help(as asinine of a proposal as this would be).
for real pedal power, remember the car on the flintstones cartoon with everybody's feet through the floor of the car?:p too bad we can't get a piggyback ride on a teradactyl.:roll:

homerramirez

Re: Proposed Application

That's a good one Niel, B.B. always stress the importance of generators on any off grid solar power system, so, the air planes already has one, I never seen air plane pasangers trying to read during night fly with candel stiks, ....lol that was a very good one Niel. :cool:

niel

Re: Proposed Application

once in a while my humor is good, usually not though. glad you liked it.:D8)

BB.

Re: Proposed Application

By the way, updated my first post here--I forgot a 21% conversion factor when estimating (guessing) the costs for the B-747 solar panel array.

-Bill