+ What is the current efficiency of a solar cell?

According to the U.S. National Renewable Energy Laboratory, the current maximum efficiency that is achieved in the lab is at around 47.1%. That means that such a solar panel could (theoretically) deliver 471 watts of power when it is irradiated with 1000 watt. Currently most commercially available solar panels give you an efficiency of around 15-20%, or about 250 watts in North-Western Europe.

+ How much surface area do you need to generate 1MW of solar power?

Assuming 1 MW peak and an average efficiency of 250W per m2 as described above, one would need approximately 4000 m2. That is an area of roughly 60 by 60 meters, or a circle with a radius of about 35 meters. Such solutions would be feasible for large working class vessels or close to an offshore platform, but not for sailing vessels.

Feasible surfaces for these vessels would most likely be in the form of strips. Assuming a usable freeboard in the order of 10 meters, one would need a length of 400 meters to obtain 1 MW of peak power. Though the circumference of large container vessels (and other parts of the deck) could possibly provide such an area, the yield would become lower than 1 MW as one part of the vessel would not receive full sunlight. Nonetheless, these back of the hand calculations show that several hundreds of kW of power could be generated by solar on large vessels. This is especially the case when paintable (perovskite) solar PV comes on the market, which is unfortunately still in its infancy.