This could never make a dent in New York City's needs.
Let's suppose that one acre of hydroponic "land" can sustain 10 people per year. (A real stretch.) And let's suppose we want to meet just 1% of NYC's needs this way.
That would require 8,000 acres for NYC's 8 million people. That works out to 344 million square feet of floor space. That is roughly the total amount of office space in all of Manhattan (and probably only one order of magnitude less than the total amount of residential space in all of NYC).
The opportunity cost of that space in Manhattan would be well north of $1 trillion. But even in the cheaper outer boroughs, the opportunity cost would be more than $100/sq. ft. In short, you'd have to pay at least $34 billion dollars for this urban farmland. By contrast, 8,000 acres in Indiana might cost $16 million. To three significant digits, that is a premium of $34 billion for the "urban farmland" in New York City. Just to meet 1% of the city's food needs.
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This could never make a dent in New York City's needs. Let's suppose that one acre of hydroponic "land" can sustain 10 people per year. (A real stretch.) And let's suppose we want to meet just 1% of NYC's needs this way. That would require 8,000 acres for NYC's 8 million people. That works out to 344 million square feet of floor space. That is roughly the total amount of office space in all of Manhattan (and probably only one order of magnitude less than the total amount of residential space in all of NYC). The opportunity cost of that space in Manhattan would be well north of $1 trillion. But even in the cheaper outer boroughs, the opportunity cost would be more than $100/sq. ft. In short, you'd have to pay at least $34 billion dollars for this urban farmland. By contrast, 8,000 acres in Indiana might cost $16 million. To three significant digits, that is a premium of $34 billion for the "urban farmland" in New York City. Just to meet 1% of the city's food needs.