It all depends on the parameters that you are after. Big without speed has already been done; see Facebook's 747 sized solar powered aircraft http://www.thever

It all depends on the parameters that you are after. Big without speed has already been done; see Facebook's 747 sized solar powered aircraft http://www.theverge.com/2015/7/30/9074925/facebook-aquila-solar-internet-plane http://www.theverge.com/2015/7/30/9074925/facebook-aquila-so... The issue is the amount of energy that you need to reach the speed of your average jet. Just to put it in perspective jet fuel has a theoretical specific energy somewhere over 10,000 Wh/kg, compared to all of the options the author was exploring being well below 1000 Wh/kg