It seems to me that the primary disadvantage of solar energy is its reliability on daytime, nice weather and high UV levels. However, there are so many applications where solar would benefit the world regardless of this, so I guess in these cases it's just the cost? But surely the cost of investment would eventually be repaid in energy savings?
For example, in my mind it makes absolute sense to put solar panels on ships. The roof of the bridge on most ships is empty space, and could easily accommodate solar paneling. This could help to power the ship's electronic systems, with the engine providing backup electricity when needed. I think the investment would be very small when you consider a container ship costs hundreds of millions of pounds, and solar panels just a few thousand. Not only would the panels pay for themselves, but it would be gold PR. So, what are the disadvantages that are stopping solar power being utilised in more applications like this?