Solar Sonex!

[GraemeSmith]

I've just finished some test flights with "solar assist" provided by a "drapable" solar panel that provided between 50 and 120 watts of electricity at a nominal 12v DC (actually regulated at 13.1v).

The idea came to me when I was researching panels for battery maintenance in the tie downs. I saw the Renogy 100 Watt 12 Volt Extremely Flexible Monocrystalline Solar Panel which can be bent in one plane up to 250 degrees. I wondered if one could be made to conform to the wing camber and ordered one to see. Answer - yes it can.

Testing the "drape" and final position

Carefully checking the specs showed a weight of 4lb - which can be reduced to 3.5lb during the wiring process by eliminating the junction boxes. The panel is capable of withstanding extreme wind of up to 2400 Pa. I had to do some fudging of the numbers here - as the manufacturer's assumption is the panel will be terrestrial based - but near as I can tell - allowing for the pressure of air hitting the panel in flight and the vacuum caused by Mr Bernoulli - the "load" on the panel as the aircraft approaches VNe will be in the order of 1078Pa. (If anyone on forum has a better handle on aerodynamic theory and calculations - I'd love a little help here on these numbers).

The panel also has a watertight integrity of IP68 - which is about as good as it gets. Though in breaking and remaking the junction box to reduce its profile and move the wires from the front - to out the back of the panel for putting down through the wing skin - I had to be careful and use 3M 5200 Marine sealer - and I hope I've remade the quality of the seal to the original standard. Time will tell.

For mounting the panel - I "glued" it down to the wing skin using a thin film of silicone sealant to act as both an adhesive and as a cushion between the differing coefficients of expansion between the aluminum wing and the glass fiber panel. I initially put it on the right inner wing where the arm of the extra weight would mimic a passenger slightly and so I could have some confidence the aircraft would remain balanced on the roll axis. This was also the shortest wiring route to the battery on the firewall. Though it was a bear fishing the wiring through the wing. For people thinking of incorporating this idea during build - wiring will be much easier to accomplish while the wing is still being constructed and opened up.

A test flight showed the 100w panel actually contributing 120w on a CAVU day with the sun at better than 30 degrees above the horizon. The panel still managed a very respectable 40w on an overcast day. Enough that I didn't have to manage the battery and alternator nearly as much as normal, could leave both mags on while on the ground and run with lights on while taxiing.

There was no discernible change in aerodynamics - though the panel has a very slight texture to it which might be considered a disadvantage compared to a smooth wing. However I believe I'm seeing a effect similar to a "shark skin" where the texture of a shark's skin holds a layer of still water next to it and allows for smoother boundary transitions into the water it moves through. This effect has been utilized by racing yachts where the bottoms are not polished to a shine but are actually sanded to a matt finish. So I'm thinking I'm getting a similar effect here. I suppose I need a wind tunnel to be sure!

So now what? Well I have 9 more panels on order. The wings will carry a total of 8 and 2 can be draped across the turtle back of the empennage. With 10 total panels on board delivering between 400w and 1200w there will be plenty of power to spare. In addition to being able to run the "normal" ship loads with no concern - I'm thinking that things like electric heat seating will now be possible - which will eliminate all the heartache of trying to heat the cabin with the 80hp Aerovee and ducted hot air. I'm also thinking that I will actually be able to completely eliminate the battery and alternator which will save some 15lb in weight (retaining the backup battery). The 15lb removed will somewhat offset the 45lb total weight of panels, controller and wiring. CG should be unaffected by the 8 panels on the wings but I will need to do a careful W&B to confirm that the battery and alternator coming off the front of the firewall and the 2 panels on the empennage hasn't pushed the plane into an aft CG situation.

(A whole area I have not yet explored would be actually using these panels as the actual top wing skin, eliminating the aluminum and actually getting a weight saving. There would be some issues of rib spacing needing to match the placement of the actual cells in the panel so one was not riveting through a solar cell. Back to my original request for help with my aerodynamic numbers and panel loading before I consider this.)

With the present COVID-19 lockdown there will be plenty of time to work on this - if Amazon would just hurry up with the panels and new controller!

[lakespookie]

I have a few questions,

1. if you were thinking of installing this from the begining i wonder if it would be worth it to instal nutplates on the wing skins and then install these guys with Loctite.
2. Do you have any concerns about how these guys will hold up to percipitation?
3. Given how much power you are producing would it be worth it to intall this or a smaller panel in the open space behind the baggage compartment/tailcone tunnel that is usually left open? Primailiy so you dont have to worry about water etc hitting and damaging the panel or affecting the boundry layer.

[GraemeSmith]

I have a few questions,

1. if you were thinking of installing this from the begining i wonder if it would be worth it to instal nutplates on the wing skins and then install these guys with Loctite.

I'm not the builder. I bought it built

2. Do you have any concerns about how these guys will hold up to percipitation?

Nope - the IP68 rating is effectively as completely waterproof as these things come.

3. Given how much power you are producing would it be worth it to intall this or a smaller panel in the open space behind the baggage compartment/tailcone tunnel that is usually left open? Primailiy so you dont have to worry about water etc hitting and damaging the panel or affecting the boundry layer.

I use the baggage compartment all the time. It would get in the way. And in any event - I'm going to cover the whole of both wings.

[GordonTurner]

Kudos to the experimenter!!!!!

Bizarre but cool idea. Awaiting full report!!!

Gordon

[lakespookie]

Makes sense in regards to the second question i was thinking more in line with the expected pressure rating of the panel given F=ma and the mass of a water droplet is significantly larger that air molecules.

[GraemeSmith]

Makes sense in regards to the second question i was thinking more in line with the expected pressure rating of the panel given F=ma and the mass of a water droplet is significantly larger that air molecules.

Interesting thought. On the ground - irrelevant. Built to take it.

In the air - Well I don't deliberately fly in rain. The surface of the panel is a clear resin which is where it gets its water proofness - I guess (so need to test) that. Perhaps I can set up a pressure washer to mimic flying in rain and see how it fares?

[peter anson]

Don't know how close this is to being practical but you might soon be able wrap your aircraft in solar panels similar to vinyl wrapping. https://www.csiro.au/en/Research/MF/Areas/Innovation/Flex-Electronics/Printed-Solar-Cells

Peter

[GraemeSmith]

Please consider the date of this post before relying on any information in it...

[lakespookie]

Damn you lol

[Bryan Cotton]

Well done!