Let's Terraform West Texas

This idea will not work, but it is delightful to imagine and I had fun thinking about it.

• Farming is only really profitable in the USA when done on good farmland at large scale, on the order of several square miles. A square mile is 640 acres. The average price of an acre of good farmland is about $4,200, so buying a 5 square mile farm might cost about $13 million.
• Irrigating an acre requires 5,000-8,000 gallons of water per day, so one desalination plant could handle at most 10 acres. To irrigate a farm of 5 square miles would require at least 320 of these desalination plants. Assuming each costs $13,000 to build, that's a cost of about $4 million for the desalination plants alone. The land would cost another $2 million or so. My guess is that the total costs of terraforming 5 square miles of land add up to around $10-$20 million and probably require extensive permitting, since you're extracting water from the common aquifer. I'm uncertain if your listed price for the desalination plant includes the cost of labor to build/install it. Either way, though, my guess is that your costs in terraforming this farmland will exceed your revenues, and that the buyer will perceive the land as inferior to better farmland with more established farming infrastructure that they could buy elsewhere.
• Selling the minerals extracted from desalinated water might make some money, but in addition to evaporating off the water, you'd also need to separate the minerals and transport them to a buyer. The more minerals per gallon, the less viable the irrigation, and vice versa.

I would distinguish terraforming from irrigation. It sounds like you are talking about setting up a self-contained system to irrigate the land every year, whereas I would restrict terraforming to a permanent climate change, so that it rains and desalination is no longer necessary. This is what people mean when they talk about terraforming the Sahara. The desert was green five thousand years ago when the pyramids were built, so it probably has multiple equilibrium climates and a sufficient intervention could get it to jump to the other. I don't know how plausible this is for other deserts. The idea is to irrigate a bounded number of times to grow appropriate trees to trap water.

A permanent change could be much cheaper per acre because the solar panels and desalination plant can be reused for new parcels. The downside is that this probably has large gains from scale: air flows freely between neighboring parcels and thus humidity is an externality. Whereas the whole point of a self-contained system is that you can start small.

We should go all the way and do NAWPA.  NAWPA was a 1950s proposal to send massive amounts of fresh water from rivers in Alaska and Canada south, some of it going all the way to Mexico.  The water normally goes mostly unused into the ocean.  Yes, there would be massive environmental disruptions in part because the project uses atomic weapons to do some of the engineering, but the project might reduce the expected number of future people who will starve by millions. 

Aren't there limits to how much water you can pump out of an aquafer before destroying it?

How brackish is the brackish water there? because there are plenty of species of plants that tolerate brackish water, including some species of letuce, beets, barley etc.

You can also breed algae and fish in brackish water, like maybe crucian carp, silver carp or amur carp? Then use their crap to fertilise land?

Afaik, the practicability of pump storage is extremely location dependent. Building it on plain land would require moving enormous amounts of soil to create the artificial mountain for it. Also, there is the issue of evaporation.

Another alternative storage method for your scenario to consider would be molten salt storage. Heat up salt with excess energy, and use the hot salt to power a steam turbine when you need the energy back. https://en.wikipedia.org/wiki/Thermal_energy_storage

Many parts of west Texas are also suitable for wind power which could potentially be interspersed within a large solar array. Increasing the power density of the land might make it cost effective to develop high energy industries in the area or justify the cost of additional infrastructure.

This sounds to me a lot like a solution in need of a problem. Does the USA lack arable land? How much does arable land cost per acre in the USA?

I need a lot more convincing that this is worth doing...

I would imagine that indoor farming would be far more desirable for the region - much better water efficiency, for one.

What would be more advantageous about the region, I imagine, is the regulatory environment, being in the middle of nowhere, Texas.  With an abundance of power and minerals, who knows what you could think up?

What is the goal? Is it to consume a particular resource? Is it to produce a particular product?

Yes, West Texas has abundant light and should have solar panels. Then you can ask what to do with the energy. You could just sell it to the grid. The advent of solar power will mean large daily swings in the price of energy. If you have a use of energy that can run in the mornings, that will benefit from this. Desalination is one such application. Colocating it with the solar plant has some advantage of reducing the negotiation with the grid, but that isn't theoretically necessary. This doesn't seem to me like a good enough reason to do things in West Texas. 

It hadn't occurred to me that brackish water is a resource. If brackish water has 1/10 as much salt as seawater, then it takes 1/10 as much energy (I think that is true both in theory and in practice, where practice is 10% efficient for both). So if you must desalinate water, it is a resource. I'm skeptical of desalination for agriculture. It's quite expensive, even at 1/10 the price. Whereas humans consume very little water and desalination for residential use is cheap, comparable to the cost of distributing the water. Let people in Los Angeles water their yards as much as they like. If people want to live in West Texas, they can water their yards, too. But this isn't a reason to live there.

If the goal is to produce food, is this the optimal use of energy? Maybe better to make fertilizer and export it to places that have their own water.

If the goal is to promote decentralization, then maybe you don't want to export fertilizer. But you probably want to think more about what you mean by decentralization (eg, self-sufficiency to survive trade decline vs escape from political oppression).

The actual showstopper is way simpler than you considered.

Solar panels and desalination equipment costs money and human labor to deploy and maintain.

If the cost is greater than the economic value of the gain, where gain = (cheapest already arable land) - (price of a West Texas acre), it isn't worth doing.

If I had some numbers on the cost we could check this numerically.  

How could you make this plan work?  Cheaper equipment that mostly deploys and maintains itself.

How could you get equipment that is cheap enough?  Make SoTa in AI just a little bit better, and deploy it to robotics that autonomously do industrial tasks with minimal human supervision.  Tasks like manufacturing and mining.  Including the manufacturing of themselves.

Perhaps I'm missing something here. Doesn't distilling the water (given the local solar power that should be near 0 cost) kill two birds with one stone? Producing good water for farming, and other human uses, and leaving all the minerals behind for use? 

I would think one might even be able to do some type of multi-stage type desalination with the available power that includes centrifuges that would at least produce some level of mineral separation that would be a value added step.

Last, seems that vertical farming tech has come a good ways and would also be a great fit into the effort. Moreover, that would also produce additional expertise/experience that may well prove helpful for exporting farming to both space and other planets/the moon.

Its a nice idea, and I suspect that in the far future more sophisticated versions of roughly this kind of thing will happen.

But it won't happen soon. This is the high fruit on the geography tree. It might be possible to develop a desert, but it would be much more cost effective to develop places that already have fresh water/soil etc. There are still lots of forests, jungles and grassy plains out there to be developed first. 

For energy storage, you might consider the Ambri liquid metal batteries. They're being designed for this exact purpose: coupling intermittent renewable generating capacity to steady loads.

Also, they're cheap, rugged, and don't seem to lose capacity over multiple charge/discharge cycles.

I don't want to live in West Texas, I want to live in Kauai but have it be located in the Bay area. If I had post-scarcity powers, I'd build an enormous floating greenhouse with a lush tropical island and coral reef inside. I'd park it off the peninsula, or in the Bay if I was allowed, and commute via drone-copter. Many delightful things are possible once we get this alignment thing sorted out.

So you're suggesting we destroy some land and ecosystems in the desert in order to allow us to keep destroying the planet elsewhere?