Solar Drone Experiments - How much more battery life do you get by adding solar panels to your quad?

How much more battery life do you get by adding solar panels to your quad?

The setup: (I used a lot of Ian's design for the frame)

APM 2.6

2200 MAH LiPo Battery

15x5.5" Carbon Blades

20 Amp Afro ESC (love the hair)

RCTimer 5010 - 360Kv motors

12mm x 600mm Carbon tubes

2000 Microfarad capacitor

3 Amp Diode

20 Powerfilm RC flexible solar panels

I tried to keep everything as light as possible. The frame is carbon, the solar cells rest on Dollar Tree foam boards.

Each wing has 5 solar panels (7.2 volt / 100 Miliamp) arranged in parallel (7.2 volt / 500 Miliamp total)

I hooked 2 pair of wings in series (14.4 volt) then connected each pair in parallel (1000 Miliamp).

I placed a Diode to the end of the circuit to prevent the battery from feeding the solar array.

I connected the solar array in parallel to the battery so it could assist with the amps needed, then charge the battery a bit while sitting on the ground while I made adjustments.

https://www.youtube.com/watch?v=HjhCrllZ7Tg

I will continue to work on these experiments but from my initial research there is too much surface area on the solar array. Gains made in extra amps were diminished by the extra power required to keep the drone in place against the wind.

-however-

I landed the drone several times for tweaks and checkups. The solar cells really came into play then. It would charge the battery about 0.5 volts each time it landed (it sat in the sun about 15min).

~Daniel~

Digital Wings Drones

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3D Robotics
Comment by Chris Anderson on May 31, 2014 at 6:10pm

This is awesome! But I'll bet that wind is a real issue. I suspect that you'd be better off with fixed wing...

Comment by Rana on May 31, 2014 at 7:14pm

Daniel, hat's off to you for your incredible idea and design. Excellent. Wind will always be creating problem, you have think something different for that.

Comment by Pedals2Paddles on May 31, 2014 at 7:37pm

Unfortunately it is neat but impractical.

Comment by Quadzimodo on May 31, 2014 at 7:42pm

Daniel - I must admit that I had not even considered the idea of placing a solar array on a multirotor to even be feasible.  Your design is an impressive achievement.

Chris and Rana are right that the panels are going to act like great big sails in any sort of wind, and it is very likely that the drag added by the array alone is enough to overcome any assistance the panels are actually adding while you are in the air.  Having the ability to land and charge, however, is a huge advantage with a wide range of applications.

Perhaps it would be worthwhile to allow the panels to fold up during actual flight then unfold after landing.  Maybe with a crude pensioned folding hinge and draw string. Kinda like the way a satellite spreads it's solar array in orbit or a mars rover spreads it's lid once on the ground, just much simpler (maybe just one spring loaded fold per side).

By starting with a configuration that was already incredibly efficient you have given yourself a perfect foundation upon which to build.

There is huge scope to increase solar yield and improve charge efficiency.  For example - you mention that the panels you are using are rated to deliver 7.2VDC@0.1A and that you have 5 per side.  That makes a gross yield of 14.4W (peak). I have done some basic modeling comparing the Flex Solar Cells you are using with the Sunpower cells I am working with for my fixed wing solar project which shows that using virtually the same footprint you could make 82W (peak).

The FSC MP7.2-75 gives up to 0.72W, weighs 17.9g per Watt and costs $25.38USD per Watt (plus shipping) - producing a maximum of 14.4W in the area provided on your solar quad.

The A300 from Sunpower (even B grade) gives 3.42W, weighs 1.84g per Watt and costs $1.17USD per Watt (plus shipping) - producing a maximum of 82W in the area provided on your solar quad.

Charge efficiency and safety can also be greatly improved using one of these to narrow the gap between gross and net yield.  It is just 105g without the case (which is not required as it is not a heatsink) and will provide >96% charge efficiency (if input and output voltage is well matched).

I would be happy to assist you in improving your design in any way I can.


Developer
Comment by Bill Bonney on May 31, 2014 at 8:16pm
The challenge is how to add solar panels in an aerodynamically neutral way with near zero weight. Planes solve the aerodynamic issue (embed them in the wing surface), but what's the impact of the extra weight?

Developer
Comment by Jason Short on May 31, 2014 at 9:32pm

It looks like you've added wings which will create lift and other unwanted aerodynamic effects. Look at umbrellas that are made for high winds. They let the air flow through them with special flaps to prevent big pressure deltas. I'll bet if you punch holes in those the flat surfaces at the right spots you will get wind handling.

Comment by Joshua Ott on May 31, 2014 at 10:35pm

Your design presents a perfect opportunity to implement a passive recovery strategy, in which the craft enters into a spinning helical decent when the power is cut. No need to wait for a chute to deploy and no worry about entanglement with props. Yes, it will be a challenge to get the aero to work in all flight conditions, but that's what engineering is all about. 

Comment by Joshua Ott on May 31, 2014 at 10:47pm

To everyone trying to educate Daniel about the effects of wind: you may want to read his post. It seems that he actually thought this idea through a little bit!

"I will continue to work on these experiments but from my initial research there is too much surface area on the solar array. Gains made in extra amps were diminished by the extra power required to keep the drone in place against the wind."

 

Comment by Julien Dubois on June 1, 2014 at 2:10am

That a funny project but I'm sure you have less autonomy with all these panels than nothing.

Because of extra weight and extra inertia that brings higher motors consumptions to keep the copter horizontal, especially if there is wind.

But, why not for a plane

Comment by Phill Scott on June 1, 2014 at 3:10am

It all depends on how far you want to go.  As a proof of concept, you've done a good job Dan.  You've proved that, in essence, it works.  From now on, its all about refinement, whether that's maximising the potential of the PV panels you use, to making the structure they attach to as efficient as possible.  Unfortunately, with each efficiency you make, the work required to achieve goes up by some power law, so you're going to need to be committed to it by the end.

As I'm sure you already know, the first thing you could look at is a carbon framework for the cells you already have.  You should save weight and improve handling in wind.  After that ,you'll need to start looking at the most shape efficient layout for the PV cells.

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