People have looked at it, but I think the general consensus is that there's not enough surface area on the airframe to generate enough electricity to make a significant impact.
Depending on the exact motor+prop setup, peak draw of between 200-400W is pretty common for fixed wings in the 1.5-2M wingspan range, and cruise is often around half of that.
Depending on the exact motor+prop setup, peak draw of between 200-400W is pretty common for fixed wings in the 1.5-2M wingspan range, and cruise is often around half of that.