A couple years ago there was an article in multihull magazine by someone who put a solar panel and a lead acid battery pack on a hobie for their electric motor- you may be able to find it in their archives- it will be hard on the gel cell they aren't meant to be deep cycled- as in my computer backup power supply after a few uses they are toast if nearly fully discharged- you need a deep cycle lead acid or a large NIMH or NICAD battery pack- much more expensive than lead acid.