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Shipping costs time as well as money. Cheap shipping also requires trade-offs that are not always advantageous with foods.

For instance, it may be cheaper to grow tomatoes in Florida rather than in Manhattan, but in order to get a Florida tomato to Manhattan, the tomato itself has to be a bruise-resistant variety with predictable shape and size, harvested while green, and artificially ripened with ethylene gas. The tomato grown in Manhattan and eaten in Manhattan can be one of those bulbous, deeply-pigmented heirloom varieties, harvested while ripe, and eaten within hours, bursting with actual tomato flavor.

The tomato grown in Florida must be grown during the tomato-growing season for Florida. The vertical farm tomato can be grown as easily in the local regular season or for harvest in mid-February.

Rather than solar panels and LEDs, the rooftop could support advanced deck prisms that pipe natural sunlight through optical fibers. That alone is likely insufficient to meet the lighting needs of the plants, but it would be more efficient, and a watt of natural sunlight is a watt that you don't have to pump through the LEDs. The true advantage of LEDs is not in energy efficiency, but in wavelength tuning. The farming LEDs don't even produce the green light that is usually reflected by plants. Also, the red-blue balance can be altered to produce different effects on the plants. Blue light produces growth, and red light influences the plant hormones for germination, rooting, etiolation, and flowering. Tinkering with the red-blue schedule could allow the farmer to grow larger heads of lettuce or cabbage without bolting.

And, as you mentioned, hydroponics and aeroponics are more water-efficient.

Vertical farming will never entirely replace land-surface farming, but it will complement it. And it will allow farming underground, and in non-terrestrial habitats.

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