Apart from the type of technology involved with any particular type of solar cell, the amount of energy you get out depends on the energy going in, and that is governed by the surface area. 2.5 square inches will probably do next to nothing, 1 volt would not power anything worthwhile even if there was useful current there, which is doubtful.
If you can pile enough of them in series to get more volts, back-up battery charging becomes possible if they can have a very long charge time compared to a short run time.
There are examples of working boats using solar power, but they use quite large solar arrays for the size of boat.
http://www.seacharger.com/ for an ambitious example.