The best method that we’ve found is to convert both your power consumption and your power
production into WATT HOURS that way we can compare apples to apples.
Step one is to determine the individual wattage rating for each load/device that you intend to run off
solar. Look on the back of each appliance and try to locate a label which indicates the wattage used by
the appliance, if it doesn’t give you the wattage then it may tell you the amount of volts and amps that
the appliance uses.
Remember volts x amps equal watts. Once you have written down the wattage rating for each
appliance found on the manufacturer’s plaque located on the equipment, you then need to determine
the amount of time each appliance will run during the day.
For example let’s say that you have a television that runs for three and a half hours a day, then write
down 3.5 hours, or let’s say you have a computer that runs for two hours and fifteen minutes, then
write down 2.15 hours, or a microwave that runs for 45 minutes, then write down 0.45 hours.
Next take the wattage rating of each appliance and multiply that by the amount of time it will run, that
will give us the WATT HOUR rating.
For example a television that draws 200 watts and runs for three hours (200 x 3 = 600) will use 600
watt hours, or a toaster that draws 1100 watts and runs for 15 minutes (1100 x .25 = 275) will use a
275 watt hours. Add the up all of the watt-hour ratings for each appliance and that will equal your total
power consumption for each day.
Let’s say that your total power consumption equalled 1200 watt hours per day, then that’s the amount
of solar power you need to produce plus about 10 percent for battery losses. Don’t forget that the
power you produce with solar panels is also a factor of time as well.
So for example let’s say you had a 200 watt solar panel and that panel sat in full sun for seven hours,
than you would have produced 1400 watt hours (200 watts x 7 hours = 1400 watt hours)
Let’s say for example that you only had five hours of full sunlight then five hours times two hundred
watts would only be 1000 watt hours so you would be at a deficit, so you would need to either add
another 40 watts of solar panels or reduce your power consumption by 200 watt hours.