Li-ion battery&#x27;s are 0.265 kWh per kg.  Over a 2 hour flight the lightest thin film solar cells produce 12kWh.  Battery&#x27;s might be improving but not 50x as good. 
See 6w per gram: 
<a href="http:&#x2F;&#x2F;news.mit.edu&#x2F;2016&#x2F;ultrathin-flexible-solar-cells-0226" rel="nofollow">http:&#x2F;&#x2F;news.mit.edu&#x2F;2016&#x2F;ultrathin-flexible-solar-cells-0226</a><p>You would probably want a thicker coating to protect the cell, but in 50 years solar can add very minimal weight.