Reply from reddit/u/ignorantwanderer 

This is very cool.

Early on, almost all food will be brought from Earth, with fresh veggies grown in hydroponic setups just like this. I can easily imagine a whole set of social interactions growing up around swapping plants and serving exotic salads to guests.

I think these personal hydroponic gardens will be a very big deal for moral.

But as soon as the base starts getting large, you need to start growing a significant amount of the colony's calories on Mars. That will be a very big production.

It is estimated that Starship will be able to transport 100,000 kg to Mars. If a Starship full of food is launched every synod, that is every 780 days. So that comes out to 128 kg of food for each day. A single person eats about 1.5 kg of food a day, so one Starship of food each synod is enough to support a base of 85 people.

So when the Mars base is less than 85 people, I doubt they will put too much effort into growing calories on Mars. They will have these hydroponic setups for moral reasons, but that's it.

Once the Mars base gets above 85 people, there is more incentive to start growing food on Mars. It just makes sense logistically.

Lets give some thought to what it will look like.

Dr. Gene Giacomelli at the University of Arizona has done a great deal of research on growing hydroponic food in space, both for oxygen creation and calorie creation. He designed a 5.5 meter long, 2 meter diameter greenhouse that would provide half the food requirement for a single astronaut. So let's say we want to provide half the food for 190 people (so the other half can be brought by a single Starship flight, once a synod.

That would require greenhouses 2 meters in diameter with a total length of 1 km. Giacomelli's greenhouses generally run on artificial light, which means you could potentially pack that 1 km by 2 meter tube into a single sphere that is 18 meters across. That would be really stupid because if something goes wrong you lose half of your food supply. So instead we could have 4 greenhouse spheres that are each about 12 meters across if we want. That way if we lose one of them we only lose 1/8th of our food supply.

We have an idea of how much space it will take, now lets figure out how much power it will take assuming we use LEDs.

A person burns on average about 100 watts of power. So if you have to grow the food to power half of that for 190 people, you have to grow 90,000 watts worth of food. This is a weird way of expressing it, but what it means is that every second you have to grow enough food to provide 90,000 joules of energy.

So 90 kW of food needs to be grown. There are many plants where we can not eat the whole plant. Something like wheat, we only eat the seeds, and the rest of the plant we can't eat. But then with things like lettuce we can eat the whole thing except the roots. So lets assume that on average we can eat 2/3 of the plant. So if we need 90 kW of food, we need 135 kW of plant growth.

Plants are incredibly inefficient at turning light into plant matter. They have an efficiency generally between 0.1% and 2%. Let's assume on average we grow plants that are 1% efficient. That means to get 135 kW of plant growth, we need 13.5 MW of photons. LED lights can be about 90% efficient, so to get 13.5 MW of photons, you need 15 MW of electricity.

So to grow half the necessary food for 190 people using LED lights is going to require 15 MW of electricity. Just to have something to compare this to, that is 125 time more power than the International Space Station produces. That is the amount of power used by the average American town with a population of 11,000.

As you can imagine, the energy requirements of growing a large fraction of calories from LEDs will quickly become very large. Really the only practical way to grow the food is with natural sunlight greenhouses. This will require a larger growing area. With LED growing, you don't have to worry as much about plants shading each other, with natural light growing you do. But the plants can probably still be more crowded than typical because you will use reflectors to increase the light intensity to levels optimal for the plants.

To get 13.5 MW of photons your farm will have to cover an square 300 meters on a side. This is if you make the assumption that 50% of sunlight hits your plants, and 50% hits something else. The greenhouses will be cylinders laying on their sides with the smallest feasible diameter. Crops will be mostly tended by robots that run along rails the length of the greenhouse. When human interaction is needed they can be sitting on chairs that run on the same rails. So the diameter of the greenhouse can be less than the height of a human.