Basically this is a reasonable idea for transport fuels. Sunlight gives you 1000 W/m², or 160 W/m² at 16% photovoltaic efficiency. A Boeing 777 has a surface area on top of something under 1000 m², and so if you cover it with solar panels, you get 160 kW when the sun is shining directly on it. But its engines produce somewhere between 700 and 1100 kN at a cruising speed of 900 kph, or 250 m/s, which if you work it out means it would need 175–275 MW if the engines are 100% efficient, a bit over 1000 times what it can gather from the sun. (A bit less since it's not running the engines at full power when it's cruising, but a lot more when you take into account that the engines are quite inefficient.)

There are ways you can design the plane to use less power, and Solar Impulse 2 demonstrated that it is in fact possible to fly on solar power alone, but Solar Impulse 2 also took 23 days to go around the world, has a maximum speed of 140 km/h, and has a maximum passenger capacity of 1, rather than a few hundred. Design compromises like these are necessary to lower the power intensity of flight to a solar-feasible level. So, it's likely that liquid-fueled aircraft (the 777 burns kerosene) will continue to have substantial advantages over solar aircraft for the foreseeable future.

The obvious solution is to use some 10⁸ m² of area on the ground — something like a 10 km by 10 km square for each 777 in flight — to generate electricity to produce the liquid fuels for the liquid-fueled aircraft. That sounds like a ridiculous thing to do, building a city-sized solar plant for a single airplane, and today it would be — the photovoltaic modules would cost US$5 billion and installing them would cost another US$5 billion, for a total of US$10 billion. The entire Boeing 777 development cost was only US$5 billion, and each plane sells for US$300M or so. So the cost of the power plant would be something like 30× as high as the cost of the airplanes themselves.

From an exponential point of view, though, that's only 5 doublings. If the price-performance of photovoltaic modules improves by a factor of 2 five times, the power plant falls to the cost of the plane. If PV modules continue dropping in price by 30% per year, as they have been for the last four years or so, that crossover happens in 2028; if they continue dropping in price by 20% per year, as they have been over a somewhat longer period, it happens in 2033. It's only in a scenario where PV modules effectively stop dropping in price where this remains a ridiculous idea.

The same logic applies, but in a weaker form and a nearer crossover, for other challenging transport fuel uses such as ships and trucking.