Based on that Fermi estimate, the plan actually sounds surprisingly viable. It’s already on the same order of magnitude as traditional farmland even without optimizing very hard, which means just a bit of added cleverness should put it in the realm of tractability.
That’s a fair point. Let’s look at some other sources and include fixed costs, and do some sanity checks on water requirements.
An inch of rainfall is about 27,000 gallons per acre, so to supply a 5 square mile farm with an inch of rainfall equivalent is about 87 million gallons of water. High yield corn needs 22-30 inches of rainfall per year. Peak season for corn is about May-September, so let’s assume we therefore need about 22 inches of rainfall equivalent (1.9 billion gallons) spread out over 5 months or about 150 days. That averages to about 13 million gallons of water per day. That tracks very well with the original estimate of 5,000 gallons/acre/day, which would come out to 16 million gallons per day for this farm.
This company says a 27 MGD plant cost $87 million. If cost scales ~linearly with capacity, that suggests a $50 million price tag for the desalination capacity—now perhaps 4 times the normal cost of a farm of equivalent size. That puts the cost of desal much higher than the lower bound I used from the OP.
They also claim a unit cost (including capital cost, debt service, and operating cost) of at least $1.25 per 1,000 gallons of desalinated brackish water, which would therefore cost about $20,000 per day for this farm and create an added $3 million cost per year.
I don’t have a great source here, but it looks like groundwater use for farm irrigation is typically free. Corn and soy yield optimistic profits of $100-$200/acre, or perhaps $320,000 for a 5 square mile farm. A $3 million cost per year is again an order of magnitude higher than those expected profits.
Based on that Fermi estimate, the plan actually sounds surprisingly viable. It’s already on the same order of magnitude as traditional farmland even without optimizing very hard, which means just a bit of added cleverness should put it in the realm of tractability.
That’s a fair point. Let’s look at some other sources and include fixed costs, and do some sanity checks on water requirements.
An inch of rainfall is about 27,000 gallons per acre, so to supply a 5 square mile farm with an inch of rainfall equivalent is about 87 million gallons of water. High yield corn needs 22-30 inches of rainfall per year. Peak season for corn is about May-September, so let’s assume we therefore need about 22 inches of rainfall equivalent (1.9 billion gallons) spread out over 5 months or about 150 days. That averages to about 13 million gallons of water per day. That tracks very well with the original estimate of 5,000 gallons/acre/day, which would come out to 16 million gallons per day for this farm.
This company says a 27 MGD plant cost $87 million. If cost scales ~linearly with capacity, that suggests a $50 million price tag for the desalination capacity—now perhaps 4 times the normal cost of a farm of equivalent size. That puts the cost of desal much higher than the lower bound I used from the OP.
They also claim a unit cost (including capital cost, debt service, and operating cost) of at least $1.25 per 1,000 gallons of desalinated brackish water, which would therefore cost about $20,000 per day for this farm and create an added $3 million cost per year.
I don’t have a great source here, but it looks like groundwater use for farm irrigation is typically free. Corn and soy yield optimistic profits of $100-$200/acre, or perhaps $320,000 for a 5 square mile farm. A $3 million cost per year is again an order of magnitude higher than those expected profits.
That’s more like the sort of picture I was expecting.