To get electrictiy from water you have to (1) heat it to boiling; (2) dry the steam; (3) use the steam to drive an engine (turbine has the best energy conversion) connected to some sort of alternator; (4) condense the steam; and (5) pump it back to your steam generator. Call it $3 million for code equipment and installtaion. You can do it in a pretty small space, call it 3,000 sq ft with 30 ft ceilings. Don't forget to budget a licensed stationary engineer to run it ('round the clock, 'round the caledar) and lawyers to get the zoning variances.
My experience with turbo-alternators has been that even very small ones outrun the energy collection capacity of solar panels very quickly. It takes a lot of panels to make a small amount of steam, and what is your energy source at night?
If you
must do this, then you could use a gas-fired boiler and go to the panels for superheat (steam will only become superheated if a coherent gas-water interface is absent).
I'm really confused about why you are looking at "energy per pound" and then comparing the infrastructure of a lead acid battery to the working fluid of water. When you add the infrastructure of vessels, piping, generators, valves, and insulation, the battery is probably at least 10-20 times the energy density of a steam plant. If you look just at working fluids of the two, you get even more impressive results. The "working fluid" of the battery with PV panels is electrons and not enough of them to weigh very much - I would expect energy per pound of electrons to be pretty high.
David Simpson, PE
MuleShoe Engineering
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The Plural of "anecdote" is not "data"