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You need to have some idea of how much energy you need. Estimating demand
is a helpful tool and a good place to start in sizing your system. Make a
list of all electrical appliances, DC and AC if an inverter is in your plans.
Note that most AC appliances have their ratings on a tag in the back of the
appliance. They are usually rated for the maximum potential of energy use,
and that the actual operating wattage may be only half as much.
Use the following chart of common household appliances to help estimate your
loads. Note the differences between some appliances and their DC counterparts.
The following format will determine the total amp hours per day used by all
the AC and DC loads in your system:
- If you are going to use an inverter then list all the AC loads, wattage
and hours of use per week. Add up all the watt hours per week to determine
DC watt hours per week:
Appliance Description --- Watts x Hours/Week = Watt Hours/Week
(If an appliance is rated in amps, multiply amps by voltage (120) to find
watts.)
- Multiply your total Watt Hours per Week by 1.10 to correct for
inverter loss. This is your actual DC Watt Hours Per Week.
- Divide your Total DC Watt Hours Per Week by your System Voltage
(12 or 24). This sum is your total Amp Hours per Week used by your
inverter for the AC loads.
- Now list all the DC loads and calculate all the Watt Hours per
Week.
Appliance Descnption --- Watts x Hours/Week = Watt Hours/Week
- Divide your Total DC loads' Watt Hours per Week by System Voltage
(12 or 24). This is the total Amp hours per Week used by DC loads.
- 6. Now, add the total DC and AC Amp Hours per Week. This is the
total Amp Hours per Week used in your system.
- 7. Finally, divide the Total from step 6 by 7 and this will be
the Total Average Amp Hours per Day.
*This final number will be used to estimate the amount of solar modules
needed for your system.
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