Updated
9/3/15

John Drake Services, Inc.
1427 E. 68th Street
Long Beach, CA 90805

voice line
(562) 423-4879
electricity from the sun by John Drake II     |     home
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Power Needs Worksheet
This work sheet can be used for both full timealternative energy systems
and back up power systems.

To determine how much power you need to produce, please print out
and use this work sheet to find out how much power you will be using.  
Description of A.C.
loads run by inverter
Load
wattage
Note # 1
Hours per
day used
Total watt
hours per
day used
Total watt
hours per
week used
X
=
X 7
=
X
=
X 7
=
X
=
X 7
=
X
=
X 7
=
X
=
X 7
=
X
=
X 7
=
X
=
X 7
=
X
=
X 7
=
X
=
X 7
=
X
=
X 7
=
Note # 1 - Wattage of appliances can usually be determined from the tag on the back of the appliance or from the owner's manual. If an appliance is rated in amps, mulitply amps by the voltage that is used by the appliance (120 or 240 volts a.c.) to find the watts.
Total watt hours per week of all A.C. loads
       =

    Multiply By
 1.25
Row # 1
To get watt hours per week used, corrected for battery, inverter and power source / wiring   losses

       =
Description of D.C. loads
Load wattage
Note # 2


Hours per day used
Total watt hours per day used
Total watt hours per week used
X
=
X 7
=
X
=
X 7
=
X
=
X 7
=
X
=
X 7
=
X
=
X 7
=
X
=
X 7
=
X
=
X 7
=
X
=
X 7
=
X
=
X 7
=
X
=
X 7
=
Note # 2 - Since most d.c. loads are rated in amps, multiply the amp rating of the load by the voltage it uses (12, 24 or 48 volts d.c.) to come up with the wattage.  
Total watt hours per week of all d.c. loads
        =
    Multiply By
  1.125
Row # 2
To get watt hours per week used, corrected for battery and source / wiring losses


        =
Note # 3 - These figures do not take into account the days of rain or overcast                 conditions where a photovoltaic system
will be relying on battery storage only. The same holds true with a wind or hydro system where the wind is calm or the water flow is reduced or stopped.  
Add Row # 1 and Row # 2 to get the weekly amount of wattage your source needs to produce, please see Note # 3


      =

Note # 4 -To find the weekly amp hours that the source needs to produce, take
                  the total d.c. watt hours and divide by the system voltage (12,24,or
                  48 volts d.c.).     hours and divide by the system voltage (12,24,or
                  48 volts d.c.).