One other thing to consider....
And this is from personal experience; if you try to run a 250A welder off a 4kva sine wave generator (even with the welder turned right down) the generator will have a conniption and stall.
If you try it several times, lowering the demand on the generator by turning the welder down further still in an attempt to find a level where it might actually work, you will likely burn out the electronics in the generator.
A solar inverter like this, however:
http://www.ebay.com.au/itm/NEW-18000...fe31b06&_uhb=1
Will run a circular saw, fridge and air conditioner all at the same time and be at less than 50% of its real continuous load capacity. (17% of its peak)
You of course have to have the battery (or solar) capacity to keep up with it if you intend to do that for any length of time, but that isn't as difficult as you might think.
The essence of the message here is that solar inverters are commonly designed to handle instantaneous power loads 3x their continuous ratings. (even the units manufactured in china) and don't be surprised if a generator karks it when a load 1/3rd its rated capacity is suddenly dumped on it. Generators by Honda, Yamaha, etc, fair only marginally better.