DC Ceiling Fan - will it work?

erase bogus equation and below had 300 Watt fan. All wrong.

Different DC Fan Mfg... One vendor/model suggested used 18 Watts on maximum--That would be a much nicer fit for your system (although, these fans are not cheap):

http://forum.solar-electric.com/discussion/350028/ceiling-fans

You did not let us know the size of your battery bank and other loads--That is also important in this set of questions (and your feelings about using a genset to "help").

-Bill

And I read too  quickly and mixed the 30 watt fan.

Not my day today.

-Bill

I put words (and feet) into my own mouth--Thank you very much Estragon.

Anyway, there are several ways to approach a system. The "best" is to estimate you loads (and how many days of "no sun"/generator usage are acceptable, and such) then define your battery bank. Next, define the solar array to both "keep the battery bank happy" and keep up with your daily loads (two different calculations).

Or, we start with your system and see how much useful energy we can get out of it. Since you have 2x golf cart batteries and 300 Watts of panel...

With your battery bank, the usual "optimum" is 2 days of stored energy and 50% maximum discharge. For a "golf cart" bank, that would be around:

• 200 AH * 12 volts * 1/2 days storage * 0.50 maximum discharge = 600 Watts of stored energy per day

So, your 30 watt fan would run about 20 hours on the battery bank for two days.

Or, if you have other loads... Say (just throwing some generic numbers out there):

• 30 Watt fan * 10 hours = 300 WH per day
• 20 Watts lights * 5 hours = 100 WH
• 30 Watt laptop computer * 6 hours per day = 180 Watts
• Total = ~580 WH per day from your GC battery bank

And for the solar panels... We suggest around 5% to 13% rate of charge. 5% can work for a weekend/summer cabin. And 10%+ works well for a full time cabin/home (~9 months per year solar + backup genset for winter weather):

• 200 AH * 14.5 volts charging * 1/0.77 panel+controller deratings * 0.05 rate of charge = 188 Watt array minimum
  
• 200 AH * 14.5 volts charging * 1/0.77 panel+controller deratings * 0.10 rate of charge = 377 Watt array nominal
  
• 200 AH * 14.5 volts charging * 1/0.77 panel+controller deratings * 0.13 rate of charge = 490 Watt array "cost effective" maximum
  

Your 300 Watt array is not bad for a seasonal cabin. And based on hours of sun per day for a fixed array near Lawrence Kansas:
http://www.solarelectricityhandbook.com/solar-irradiance.html

Topeka
Average Solar Insolation figures

Measured in kWh/m2/day onto a solar panel set at a 51° angle from vertical:
(For best year-round performance)

Jan	Feb	Mar	Apr	May	Jun
3.57	3.75	4.66	4.89	5.16	5.41
Jul	Aug	Sep	Oct	Nov	Dec
5.70	5.36	5.33	4.64	3.61	3.36

Toss out the bottom three months (generator assist), you can expect (long term average) solar power per day of:

• 300 Watt array * 0.52 off grid AC system eff * 3.75 hours of sun (February break even month) = 585 Watt*Hours of solar (February average)

If you use the cabin  mostly during "summer", a minimum of 5.0 hours of sun would give you:

• 300 Watt array * 0.52 off grid AC system eff * 5.0 hours of sun = 780 WH per day from solar (May-September)
  

500 WH per day is sort of the minimum that would work for a cabin... And 1,000 WH per day works very well (unless you add a refrigerator, well pump, washing machine).

Does this look like such a system can meet your needs?

-Bill