Re: Help with a simple question
You need to know how much power the fan will draw... Say it draws 2 amps at 12 volts DC...
So, at a minimum, you would want a 24 watt panel for this mythical fan. And picking the panel, you would want a crystalline silicon panel (not an amorphous panel). A crystalline panel will be about 1/2 the square inches as a amorphous panel.
A typical 30 watt 12 volt panel will cost around $230 (plus shipping and handling--and I am sure you can find specials for less). Such a panel will be 16"x26" and weigh 8.5 lbs (includes an aluminum frame).
You can use a smaller fan and get a smaller panel.
Also, there are "flexible" amorphous panels that will be larger in square inches--but are not as easy to break (a glass panel is like trying to carry a sheet of glass in an aluminum frame--very easy to break).
Lastly, as a warning... 12 volt panels are typically around 17 volts Vmp (voltage maximum power)--So, the average solar panel will be outputting higher than 12 volts to the motor... The motor may run fast and wear out sooner. Probably not an issue for a "beach fan"--but if you want it to be reliable, you may need to monitor the current and voltage between the panel and the fan to make sure everything is OK.
20x BP 4175B panels (replacement) + Xantrex GT 3.3 inverter for 3kW Grid Tied system + Honda eu2000i Inverter/Generator for emergency backup.