Thin flexible solar panels

David Kinsell wrote:

Sometimes the current rating given is into a short circuit, so you get
substantially less in practice. I'm sure these particular ratings are for the
panel laid flat, pointing directly into the sun, with no cloud cover. Wrapped
on a fuselage, frequently pointing away from the sun, the average will be a
whole lot less.

These panels are rated at the "maximum power" point; the short circuit
current is higher, of course. In any case, the average will be as you
point out.

So, $120 would buy me 4 panels, which would give me 200 ma at 15+
volts, almost enough keep up with my panel (including the
transponder) over a full day. By "full day", I'm including the time
it's tied out, as it would be at a soaring camp or on a safari, and a
five hour flight.


A full panel these days (with an active transponder) easily draws over 2 amps.

My panel is not so full, apparently, with a radio, 302 vario/recorder,
Aero 1530 PDA, Becker transponder, as it draws about 650 ma while flying
(radio on, but not receiving or transmitting; transponder on mode C).
This will go up next year if I switch to an Ipaq PDA.

The current you'll actually get out of the solar panel would not make a
significant difference.

The $/ma was good enough, that trying a 200 ma set would give me a good
idea of their value, and more could be easily added. The engine doors
would hold over an amp's worth.

You'd be more likely to notice the additional drag
due to the turbulence than you would notice a benefit in the electricals.

At 0.008" thick (slightly thicker than wing tape), and placed on the
engine doors, I wouldn't expect any extra drag.

If 36 AH of batteries (with a generator on your engine) isn't enough, you've
got other problems.

It's enough for probably 3 typical flights (5-6 hours) with new
batteries. The generator doesn't charge at a very high rate, and for the
typical 6-8 minute launch, does little more than replace the starting
draw. I would go longer if a charge was needed, but it's much more
pleasant with the engine off!

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Eric Greenwell
Washington State
USA

Keith W wrote:
But more seriously, would the material of the canopy absorb the frequencies
used by the solar panel - if not, would there be a problem with mounting the
panel inside the 'glass'.

I don't think it is significant, but these particular panels don't have
any specifications that would let you know. The Strobl panels the German
factories supply on their gliders seem to have the similar ratings when
used under a canopy.

Even mounted outside, I suspect that the joint
around the canopy would cause sufficient turbulent layer that the extra
'roughness' would not be noticeable, if the panel were to be mounted behind
the canopy.

These panels are attractive in part because they are very thin (0.008
inches), about the same as wing tape. I"d put them on the engine doors
where the boundary layer is quite thick, but even behind the canopy
might be in a thick enough layer. The further back from the canopy, the
less drag.

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Eric Greenwell
Washington State
USA