Solar Questions? Post here and i'll ask my professor and post back answers :)

Turns out a professor friend of mine is BIG into solar. We spent a good 40 minutes talking about it in his office today and flight and stuff.. If you have any questions on Thin Film solar, i will tryo to ask him when i see him again next week. Also, he will be giving me names of a few people who own companies that he knows, so yeah, we might get a discount or two versus buying outright. It's about 100+ for the goods per unit, so this isn't exactly a cheap endeavour, but for an exhaustive flight, it would be a nice thing to have.

Thus far....

we should get 8watts of power per square meter of thin film in a realistic setting. This is for electric planes, obviously. He also suggested compressed air engines? I don't know. my carbon fiber bottles for paintball are light, but i don't think they are THAT light...then again...battery weight...


And please, no flaming or arguing...i'm only trying to help. You can politely disagree, and state your sources on why, but i would rather help than argue moot points. :)

Views: 291

Reply to This

Replies to This Discussion

What would the weight be for the square meter of thin film? Using carbon and carbon/kevlar it is possible to build an extremely light frame to use for this kind of apps. What kind of shape do the panels come in?
It's not true that Wind Power won't work, it's just that it is extremely complicated.

A Sailboat, for example is a lighter-than-x object propelled by the velocity differential between two fluid bodies.

By extension, any object can be motivated by the velocity differential of the same fluid body, provided one can achieve a purchase on parts of the fluid with contrasting velocities. A Kite is a partial example of a airplane powered by the wind - a full example would require two kite in contrasting winds. Such a pair of kites would need aerodynamic control - but there is no fundamental reason why such a pair of kites could not exist, nor why, if they were to exist, they could not derive motivation from the relative movements between their respective adjacent fluidspace.

All the other questions are pedantic - ask the prof about the flight potential of relative air movement; at least its a suitably complicated question...
this is referred to as dynamic soaring the current speed record is like 357 mph
357 mph no power
That's a pretty cool video,
but appears to take advantage of a single uplift. What I describe is the exploitation of two fluid movements simultaneously. Unlike in a sailboat, contrasting flows do not predictably occur close together, so I would expect two flying surfaces connected with a lengthy tether. such a pair could keep aloft and move at any altitude for any length of time, so long as contrasting movements could be found within the proximity of the tether.
no dynamic soaring takes advantage of the slow moving air on the back side of a hill and the fast moving air above the level of the top of the hill, read more here and yes contrasting flowes happen constanly over water . any time you have a mass of air moving over a surface the air close to the surface (turbulant layer) moves much slower then air further away ( laminar layer ) albatros take advantage of the to cross the ocean wile expanding very little energy .
Wind power (fan on nose thing) will work, but adds drag which is proportional to power extracted plus inefficiencies. Good for fast sailplanes. I think you know that you cannot have perpetual motion. NASA did however patent in the 60's a system to extract power from wingtip vorticies using windmills on the wingtips; I believe they outfitted a Piper Warrior with them.

I have been working on making a commercial solar cell unit for powering the R/C receiver and servos only. What I am trying to do is use a PIC to control cell voltage, thus the cell(s) will be at optimal power extraction, and use a MAX1771 chip or similar to output 5V@200mA from a source down to 1.2V so that the cell will provide power even when it is not in the best orientation and a standard small NiMH or LiPo cell can be used to provide backup power.

In order to fly completely on solar power, the goal is to be aware of the aircraft's total power consumption; meaning the aircraft must be designed to be super energy efficient in the areas of aerodynamics, power management, and overall weight. This is the reason I am trying to control cell voltage, aka. minimal cell area required. The aircraft will in no way be a 'screamer', however a HALO design would work perfectly, ie. Helios.

Compressed air or gas has been used in free flight modeling for years. The thing to watch is the cooling of gasses as they are expanded. For compressed air cars, see MDi from France, the tank pressures range from 3000psi on up.

What university are you at? Major?

I am a 4th year aerospace engineering major at CalPoly ( I also do a lot of Electric Vehicle development and work at BatteriesPlus ( so I know my batteries. Most of the stuff I have done is High G capable sensing and data circuit integration for high power amateur rocketry.
i am not suggesting to attach an electric turbine to power an airplane , that is just silly . but however there are all kinds of examples of non powered flight . these aircraft extract there energy from wind and or solar (thermal) that is what i what mean by wind powered . when i think airplane power i think " the energy that moves it forward "
so yes a solar panel to power servos etc but the main motive force could come from wind . as can be demonstrated with many examples both natural and man made. any way back to the main subject of this post,
8watts ?that is extremely small.Genesis , i think a good question for the prof would be this , how much power is contained in a meter^2 of sunlight say @ sea lvl on a clear day with the sun directly over head ? this should give every one a good idea of the limitations of direct solar power. I say direct because after all a thermal sailplane derives its power from the sun it just has a whole lot more meters^2 of collection area.
ps Alex have you seen this?
within the atmosphere you should be able to get 1000 W/m^2 on the surface. With photovoltaics that would be around 150 W/m^2. That's why a heat engine at carnot efficiency (ie. Stirling cycles) would be more efficient at this point in time.
the lvboost is basically the maxim 1771 or similar chip covered in a green heat sink and mounted. You can purchase that IC for less than $1. A better circuit will use two IC's thus creating a jump started unit that can operate down to 0.8V; see Application Note 1029 on (

I intend not only to convert the lower voltages of the more efficient cells to 5V but to control the power draw from the cell such that it is at its most efficient point on the I-V curve through the use of a PIC microprocessor and a rechargable battery as storage. Thus i will pull power from or dump energy to the battery to control the voltage on the cell therefore keeping the cell at the point of max energy output. It's similar to governing the speed of a diesel to the rpm of max torque or HP and using gears or a controllable pitch propeller in marine apps to access the full range of torque or HP available. See page 4 of (
As an investigative exercise a few years ago I looked into building a solar powered plane that could autonomously fly around the world.

Unfortunately I found the construction of such an aircraft is not possible with current COTS technologies at the time. There are two factors that are preventing the creation of such an aircraft. The first is energy storage technology. Data on Li-S battery technology would indicate that it may be able to provide enough storage for multiple over night flights but current battery technologies lack the power to weight ratio required for such a mission. Super capacitors also provide interesting performance charachteristics. The second factor are solar cell efficiencies.

As far as solar technologies go, thin film has an atrocious efficiency rate. The best cell available (that I found) is produced by sun power. Boeing, and most recently NASA have demonstrated cells with a 40% conversion rate. Sun power advertises a 21% conversion rate for their cells. Somewhere I have some estimates on output of these panels when configured for a small aircraft wing.

Certainly thin film is interesting from a weight and ease of fabircation perspective, but 8 W/m^2 is nothing to an electric motor.

Compressed air is interesting, anyone have the energy density of compressed air at various pressures?
for compressed air; you can use the equation for determining the hp for the compression of air to estimate the hp coming from air for a single stage adiabatic expander. see

Of course bear in mind the inefficiencies of single stage expansion and the practicalities of multistage decompression/expansion in terms of size and weight. Like MDi in France (, some kind of heat transfer system to warm the expanding air is necessary. Turbines can reduce size and weight but the mass flow of air is horrendous. Practically you are looking at tank pressures from 2500psig on up. Two ways to do this are to 1) get a scuba tank compressor or 2) cool the tank while using a standard compressor thus when warmed the pressure will rise. Make sure, of course, the dryness of the air which will affect performance and durability of the system.

It may be a better option to isothermically expand the air by extracting torque rather than HP. Similar to the old free flight CO2 model airplanes from the 50's you may end up with a small bore and stroke with a large diameter propellor.

Maxwell Technologies supercapacitors are really cool since they weigh as much as NiMh cells (BoostCap series) but the energy storage is even less than the NiCd chemistry. I am working on, in my personal electric scooter, to use a lithium pack from superdroidrobots in combination with a supercapacitor pack for the best compromise. The cost is the limiting factor for me currently.
8 watts/m^2? At noon that would mean less than 0,9% efficiency - atleast according to the graph at: . In their SkySailor project they got 84-90 watts from about 0,5 m^2 of panels. My EZG uses about 40 watts on average during a flight with camera so I could easily acheive sustained flight (during day time) if I could afford the panels since EZG has 0,41m^2 of wing surface area...... although they probably used some super efficient solar modules..

BTW: I can't remember which university it was but anyways: some university (in Finalnd?) is developing printable electronics and solar cells.. Think about that: solar cells printed directly onto your RC!

Reply to Discussion



Season Two of the Trust Time Trial (T3) Contest 
A list of all T3 contests is here. The current round, the Vertical Horizontal one, is here

© 2020   Created by Chris Anderson.   Powered by

Badges  |  Report an Issue  |  Terms of Service