A few things:
1. AWESOME, by the way, going off grid. Thats one of my dreams.
2. I've been poking around welding since I was in middle school - dad got a small 120v flux core machine for smaller tasks and I inherited it later (more like borrowed it for the past 15 years, but they moved and he hasn't had any use for it anyway). Now I have 2x stick machines - an old transformer (round top lincoln idealarc 250, AC/DC) and a small/light/portable inverter (Everlast Powerarc 210STL, does DC tig also). If I were to give any advice to a newcomer to welding it would be to start with stick welding. On top of that I would highly recommend an old transformer machine that does both AC and DC - DC is more versatile. The old machines that have infinitely variable current adjustment are ideal especially for lighter welding - you can finesse the current and in some cases 5 amps makes all the difference in the world. You can't do that with a machine like an AC225 that has switched taps as opposed to being infinitely variable. For heavier welding it doesn't make as big of a difference, but on the light stuff it is a godsend.
3. You are not going to weld those containers on alternative energy. So get that out of your head about using the inverters. Though, I understand where you are coming from. I've studied alternative energy - that is one of my on-going hobbies also. We have cabins in the boonies that are actually on-grid that I have been studying on how to get off-grid. If we can replace the electric water heater with gas (and can get a sufficient gas supply) then that will allow alternative energy to work but it would still take a lot of combined solar and wind power (plus battery storage). As you well know if you are truly off-grid - you can not plan your existence on the "ideal" conditions all the time for either solar or wind. You have to plan for production in less-than-ideal conditions and have the capacity to store power that is surplus when you CAN generate it so that it is there for when you CAN NOT generate it (cloudy days with no wind for example). Then on top of all of that you need generators still because there might come a time when conditions just suck and you don't have enough battery capacity to get you through, or there is a failure somewhere in the system and you loose power from your batteries, inverters, or both, entirely.
So add in the power requirement of trying to weld as you are questioning in to all of the above considerations with alternative energy - aint' gon' happn'.
By the way.... There are 15kw and 18kw split phase power inverters available, if you were not already aware. They are made by Sigineer. I have had their 15kw on my "radar" for a while now and noticed they just came out with an 18kw version this season too. They will run your traditional split phase 120/240v AC power systems. They state that the running wattage is the label 15/18k and the "starting wattage" is 3x that. I am not sure if I buy that, but there is a youtube video of a guy at an off-grid property that powers a large air compressor off of one of the 15kw units. That is about as hard of a starting load as there is. I'd say thats even harder to start than a normal household AC unit.
Link to a page where you can source the inverters in the US:
http://store.evtv.me/products.php?cat=4
4. You need to watch your input amps for what ever welder you get, if it is not an engine drive you will have to have power available to run it. Most inverter welders require less than 5% THD (total harmonic distortion). Not all generators are created equal. There are generators out there that will give you the power you need, but the power they produce is pretty trashy. Harmonic distortion will destroy sensitive electronics, and unfortunately the "brains" in inverter welders generally are considered "sensitive electronics". As far as the amperage goes - you want the amperage that the welder draws at your intended welding amperage setting to be within the RUNNING wattage of a generator, not the STARTING or PEAK wattage. Say the welder pulls 55 amps from the supply when welding at 250 amps - the welding voltage is less than the line voltage, so that is how the welding current is higher, if you didn't already figure the math on that one.
Wait a minute.... Did I just mix up watts and amps? If you caught that - good. You need to understand the difference because generator manufacturers will not always be truthful about the ratings on their generators. And most of the time generators are plastered on the side with..... Wattage. So and so manufacturer may sell a 10kw, 15kw, and 18kw "model" of what appears to be a similar generator. There are two things you need to dig to find on those generators:
1. Rated running AMPERAGE (on 240v, not 120v)
2. MLCB (main line circuit breaker) size
Take the Generac GP15000E for example. On the label it is a 15kw running/22.5kw starting/surge unit. What size is the biggest breaker on it? 50 amps. 50 x 240 is 12,000 watts. If you had a load that max'ed out the 22.5kw (or 93.75 amps) - where do you pull it from? Answer - you dont. They combine the power you can draw from multiple outlets, not one. So if you have one device that requires all the units' power you are SOL.'
Moral of the example and the long post - watch your numbers and understand them. You want to have sufficient power and not set yourself up for disappointment.
Last note - yea, engine drives might seem like expensive options but if you have your power requirements otherwise met - an engine drive is a whole world of freedom. Only run the engine when you need the power. Additionally - Miller makes dual AC/DC engine drives that will serve as a legitimate AC power generator. Lincoln, to the best of my knowledge, never produced one. Theirs are all DC so you can't use them for conventional AC power. There are some mods/upgrades people may have done to get some AC power, but I think the easiest route to go with them and AC is to run an inverter off the starter battery. That doesn't really count, in my book, for "AC output" because it isn't coming from the main alternator like the welding power is. Yeah for some drilling or grinding in between welding it might work, but not if you're trying to power your house or do other fabrication stuff. That's where the Miller engine drives might be the way to go there.
Good luck and keep us posted on your project. It sounds really cool. If you're going to learn any welding process I say start with stick. Its a much more versatile process and I wish we had stick all these years and didn't start off on flux core.
