I have bot a few solar panels from taobao for my boat(no problem with custom office so far). They work very well. All you need is to connect the solar panel and the controller with your battery.. A 20W solar battery will be good enough. A normal generator has an output of 1KW (say 50AMP*24V). If you work it for two hour, total power generated is 2KW-Hour. You can get the same power by 100hour of solar panel (20W*100h) this is 20 days of sunshine (assuming 5 hours a day). Normally you only need the solar panel to keep the battery fully charge ( ie you have not run down completely your battery). So a small solar battery will be good enough (2KW-Hour is a lot of power, in fact it is equivalent to total power stored by a N200 battery). The biggest problem I faced so far is to mount it on the boat. It should look good on the deck, and strong enough to stand against the typhoon...
A 20W solar battery typical sold at 300rmb. Another 50rmb to 100rmb for controller and 50 for delivery. Cost around double in Ap Liu Street..