# Posted: 4 Oct 2010 16:06
Unfortunately there just isn't enough here to help you, but here at least is the process.
make a list of what you want to run and how for how long for a typical day, then actually find the item and read how many watts it eats. Multiply the numbers together to get a Watt-hour value. If a device lists "amps", multiply that number by your system voltage (120 in the US) to get watts. You should have several lines like this:
Light (60w equivelent, CFL), 13W, 4 hour, 52Wh
Now to size your system. Add up the W column of all devices that you want on at the same time. Multiply by 1.2 to be safe, and that is the size of the inverter you need. Sum up the Wh column and this is the amount of energy you need.
For true off grid, you'll want to size a battery to last a week, and average out solar or wind on a daily basis. So, if I ended up with 1000 Wh per day, for full time living, I would want (W / Battery Voltage, 12V for example) 1000Wh * 7 (days per week occupied) / 12 = 583Ah Hr. That's 6 good Deep Cycle marine batteries.
For the source, let's do solar. Call the place where you want to get your panels and ask them what your "Peak Solar Hours" are in the winter (lowest number of the year). For my area in far north eastern illinois, I get 2.5 in the darkest days of winter, that means I need 1000Wh / 2.5 = 400 watts of solar panels. Again I would multiply by 1.2 for a bit of a safety margin and 500 watts of panels.
I know that is a lot, but I hope that helps.