Look, I don't want to start a big argument about the merits of tank-less water heaters versus the ones with a tank. I only brought up the idea in order to offer the opening poster another possible option he could consider. He could consider the option, or he could reject the idea, it is entirely up to him. I wish now I had kept my mouth shut and said nothing. Whether anybody likes it or not, no matter how anybody feels about a tank-less water heater, they are out there and they are available to anybody who wants to buy one.
With all due respect, if it is of major importance to you to have hot water during or after a major storm knocks out power in your area, then by all means, buy whatever you feel you need to buy in order to have all the hot water you want. Around here if power goes out during the Winter, our furnaces won't work and we will be without heat. Some people buy generators to alleviate that problem, others buy wood burning stoves or some other type of heater that will work without electrical power. If power goes out during the Summer and it is as hot as it was this past year, then we would have no air-conditioning. Again, some people have a generator to use for those times so they can at least try to keep half-way cool. But as I said, I can't remember the last time power went out around here.
All I am getting at is, if the power around here should happen to go out and stay out for an extended period of time, having hot water would not be very high on my list of priorities for things to get working. So again, not trying to be a jerk or anything, but we all have our priorities and it would seem my priorities and yours are completely different for those times when there is a power outage. But that's OK, this is America, a country where we can disagree and still be friends.