Copper Clad Aluminum Wire
Aluminum wire is 61% as conductive a copper and only 30% of the weight. So for the same amount of conductance it is half the weight. Since weight is an important thing on a solar airplane, this is interesting.
The first problem is that the layer of oxide on aluminum makes it very hard to solder to. We need to connect wires together, so this is a problem.
There are copper clad aluminum wires. The core is aluminum but the outside is copper. This way you get most of the light weight of aluminum but you can still solder to it like copper. Below is a picture:
A bundle of thin strands seem to have a bad reputation for corroding if outdoors. I am hopeful that a single solid core, about 1.5 mm diameter, would last well enough for me. However, I am can't find this on Amazon so far.
There is a place in China that might work.
There are two factors to think about. The first is what percentage of the power would get lost in the wire and would it make sense to have a heavier wire for the overall design. The second question is how hot will the wire get and is there any danger of it melting foam or something. So if 5 watts is lost in the wire, it turns into heat in the wire. That might get the wire hot enough to hurt a foam airplane.
I expect to have two wires running the length of the wing. It would be interesting if it were possible to use these to help with the strength of the wing. If they were under the tape at the top and bottom of the wing it might help with strength. It would be great if the wire could be used both for conducting electricity and as a structural help.