One tip about solar panels... they have ( as Nigel points out ) very different spec sheet to real world values. Also, panels will typically output a much higher voltage when new, than after in use for a period of time. For example, the large 64 Watt panels I use at work generate up to 23 Volts when new, open circuit, and after in service for a few months, level out around 20 Volts open circuit, 16.5 or so at design load. Better manufacturers are upfront about this, and have derating curves for output versus load, temperature, etc.
Also, some panels are not very shadow tolerant, with the output varying by massive amounts during partial shadow of the panel.
I would do some experiments with your panel before comitting to any design.