Is Vertical Farming Really the Future of Agriculture?

Well that all depends on the exact numbers, doesn't it? But someone going to the farmers market twice as often as they'd need to go to the supermarket (because that produce doesn't last as long, although that mostly because of less efficient processing methods in small farms) is already almost surely polluting more than the person going to the supermarket.

That's not even mentioning the savings that can be had from home delivery. Although I had a local organic pig farmer deliver meat at home just yesterday, so that's not an advantage exclusive to large players (provided he has enough customers to do multiple drops on one tour - I should've asked him, come to think of it).

This may be a stupid idea, but is there any reason that this kind of heavy machinery needs a battery and couldn't just be connected to a power source via a (admittedly, very long) cable?

Sure, because those are the crops with the highest profit margin and that are hard to store and transport. You can pump grain through tubes into silos and store it for months while transporting and processing.

1) Depends where you live. In a lot of the world's biggest cities in terms of population you've got to travel really far to find land. Probably still cheaper to transport the goods into town than grow it locally, but that comes at the expense of freshness, time, and taxing a freight network that could be used to transport other things. Not to mention places like the Vatican, Singapore, Hong Kong, etc, which don't really have land to use.

2) Sure, it's ironic to harness solar energy to give light to plants, but it might well be more effective. Plants can in a theoretic perfect world collect 11% of the sun's energy for use in photosynthesis according to Wikipedia. In effect the figure is more like 3% to 6%. A majority of solar panels have an efficiency of between 15-17%. The building's owner might actually be able to sell surplus energy to the market after lighting and warming/cooling their plants. That's not mentioning wind power which is readily available at the top of tall structures. As for the lighting, I'm not sure where your claim that you're losing 90% of energy comes from... LEDs are quite effective.

3) As I've pointed out above, your dismissal of this idea rests on quite a few incorrect assumptions. Shipping is cheap..ish.. but there's an opportunity cost associated with it. Hong Kong, for example, is extremely reliant on imports of food. 47% of the city's fruit go through one market, 317,000 tonnes of it in 2014. If just a portion of that, by weight, was taken off the streets by urban farming on brownfield plots, rooftops, or property that for regulatory reasons can be neither residential or industrial (noise/safety) the cost of shipping other goods would drop.

I'm glad you mention the water. By 2050 the World Bank estimates the number of urban dwellers with seasonal water shortages will reach 1.9bn people. If urban farming can help this issue, even if all the other benefits weren't present, it would be worth it.

For high-value produce it probably is. More and more people are becoming aware of the dangers of all the chemicals (and often GMOs that are required to even endure all those chemicals) and the organic food movement is accelerating more or less exponentially. The only way to really grow a lot of food organically is indoors where you can carefully control the environment, and sterilize the whole system periodically as necessary.

I cannot imagine staples like wheat or rice would ever make sense to grow this way, but I could certainly see smaller beer and (say) sake breweries grow their own, as well as small-scale bakeries and even Italian restaurants and the like.

Long ago I had the idea of using cheap plastic or glass fiber optic cables to simply bring sunlight inside buildings, for plants as well as indoor tanning and to reduce depression for people living underground or whatever. I think a system could be easily designed to bring sunlight in directly instead of first making electricity and then powering batteries. Of course some electricity for pumps and fans will be needed but much less overall would be required this way.

By adding edible, herbivorous water animals to the system somehow, such as carp, snails, loaches, etc. you could reduce fertilizer needs while also utilizing leaves, roots, and so forth more effectively. The fecal matter from these animals would of course help fertilize, and also create CO2.

Speaking of CO2, well, the world seems to have a lot of that these days, so naturally that can be piped in from a nearby factory or power plant or whathaveyou to massively increase the speed of plant growth (also would possibly help with heating in the winter...)

As far as protein goes, Spirulina is super efficient to grow, as is hempseed. Perhaps friendly insects or earthworms could also be involved, to add to the freshwater animals already mentioned.

A really well-thought-out system could really supply a lot of nutritious fresh food for a lot of people. And I think a lot of people would buy beer from a company that grew organic wheat and hops right in their brewery too..people will pay a lot for the peace of mind and better taste coming from organic ingredients.