You can never have too many options for alternative energy charging choices for the DC system on a boat. Direct Methanol Fuel Cells are an interesting alternative that is worth considering.
A methanol fuel cell combines methanol and oxygen in a reaction chamber that has a membrane that allows larger positively charged hydrogen ions to migrate across, while forcing the associated electrons to form a current flow that can be used or stored by the DC system. It sounds complicated, but the operation of the device is simple, clean, and virtually silent. The by-products, other than electricity, are water vapour, a small amount of heat, and trace amounts of CO2.
The device is commercially available from European electrical distributor, MasterVolt as eFOY; they produce a modest amount of energy (the most productive unit is rated at 210Ah per day), but would be a great complement to solar panels that could produce power during the day and the fuel cell could produce power over the darker hours.
PYS Electrical Technician