The Louisiana Solar Energy Society is an
educational organization formed to promote the
use of solar energy and to share information
on the subject between its members and the

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Want to estimate your load?

Follow the example below and make your own chart:

  APPLIANCE  WATTS X HRS/DAY =WATT-HRS/DAY                         

20"  Color TV             60 w         x         4    =                    240
Computer                   120 w       x          3    =                    360
4 -15w fluorescent lights 60 w      x          3    =                    180

SUBTOTAL OF AC LOADS ABOVE                                     780
15%  INVERTER ALLOWANCE                                           117
TOTAL AVERAGE DAILY LOADS                                        897

So how many Panels?
So how many watts of solar panels do you need?   That's easy.  If you have 5 hours of sun (that's what we average in Louisiana) than you need about 180 watts for the loads above (897 divided by 5 is about 180).  So you need 3 - 60 watt panels, or 2 - 90 watt panels. 

Now how many Batteries?
So how many batteries do you need to operate this system independent of the grid?  Also easy!  If you want to go 3 days without sun and only use the batteries half-way down, (900 x 3 x 2 = 5400)  You will need 5400 watt-hours of storage.  Typical 6 volt batteries hold 220 amp/hours or 1320 watt-hours each (for a 12 volt inverter you'll need to buy in groups of two's).   So 5400 divided by 1320 is about 4 so you would need 4 groups of 2 or 8 batteries.  It's a good idea to size your system with this reserve.