Hi Ann,
Welcome to the forums!
To answer your question you need to know how many watt-hours you need to right-size the system. You've got a great start with a reasonable list of devices. The next step is to determine how many watts each device draws, how many hours per day you'll use it for, and how many days of backup you need.
Sometimes the device will say directly on it how many watts it consumes. If not, watts can be calculated as amps x volts. For example, if a charger says it's 12V at 2 amps, that's 12x2 = 24 watts. Sometimes, especially for things like refrigerators, you can get the information from the manufacturer based on the EnergyStar sticker (there's a
database of devices so you might be able to look it up). If all else fails or you need more precise numbers there are
meters you can measure it with. A refrigerator might consume 160 watts while running, but even though you want it cold for 24 hrs/day, the compressor might only run 7 of those hours.
So, from there you create a table, the
table below is meant to be an example and
has random numbers for the watts column... you'll want to use your actual value for
watts and
number of hours:
Device | Watts | number of hours
needed/day | watt-hours/day |
---|
C-pap machine | 70 | 6 | =6 x 70 = 420 |
fan | 120 | 6 | =120 x 6 = 720 |
frig | 160 | 7 | =160 x 7 = 1120 |
cell | 20 | 1 | =20 x 1 = 20 |
Sum up the right most column, multiply by the number of days backup with no sun. From there you might find these threads useful:
When selecting an inverter keep in mind that inductive loads (like the refrigerator) can have high startup loads, so the inverter you pick must be able handle it's maximum draw for a short period...when you get that far let us know what your top picks are and see if anyone has any advice on them.