On average, it takes about 12 months after it's been processed.   Different brands have different amount of stabilizing agents in them, so different gases expire at different rates, but that's pretty much the mean average.<br/><br/>Saying that they've found more stable forms of fuels in the future would be a good idea to mitigate that little thing; I just can some times be a stickler for realism.  Sorry about that.<br/><br/>What if we go, as I mentioned earlier, with solar cells of some kind? They could be jury-rigged, thus adding some reliability issues and the matter of batteries; it's not likely that, out in the desert, they won't have an excessive amount of sunny days, but for how long could they operate, for instance, at night? Solar energy would probably be their best bet for any electrical needs in the desert.