If a group of people live in a closed loop environment, with all energy coming from a reactor. What crops would you grow if you only care about keeping people fed for the absolute minimum amount of power consumed?

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    $\begingroup$ Power consumption is only a single facet. What about soil quality? What about water quantity? $\endgroup$
    – Ian Kemp
    Feb 12 at 11:03
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    $\begingroup$ @IanKemp in closed loop, water should not be a factor. You've got a good point RE: soil $\endgroup$ Feb 12 at 11:18
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    $\begingroup$ Humans need a wide variety of amino acids to grow and thrive. Are you looking for a crop that will provide ALL of the amino acids, or will you allow something else as well that will provide the necessary amino acids? And do you consider insects a 'crop'? $\endgroup$ Feb 12 at 13:41
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    $\begingroup$ Please clarify in the question if you need UV light in particular. You might have gotten the impression that UV light is what plants need to grow, however that is a misconception - UV lights are used for inside growing mostly to force plants to produce resin that protects them from UV. Most notably when growing mariuhana. However for something like peas or potatoes or some algae, you essentially need 5000K white light. $\endgroup$ Feb 13 at 8:36
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    $\begingroup$ Why did you choose UV instead of something less destructive to life? $\endgroup$
    – RonJohn
    Feb 14 at 3:15

5 Answers 5


UV is a poor energy source for agriculture, with enough energy per photon to easily damage living organisms. If you have a source of kilowatts of UV and want to grow crops, you need to convert it to kilowatts of longer-wave light, which can be done quite efficiently with a variety of phosphors. This is in fact how fluorescent lights and most white LEDs work.

Then, once you have light tailored to the plants needs (likely pink or purple in appearance): plants using the C4 pathway are somewhat more efficient at photosynthesis. These include maize, sugar cane, and sorghum, among numerous others: https://en.wikipedia.org/wiki/List_of_C4_plants

You will of course produce large amounts of cellulose as well. With the help of the right microorganisms, you should be able to convert that into carbohydrates with more food value for humans or substances of use in your chemical industry, use it to produce plastics and fibrous materials, or just compost it to produce more growth medium for plants. Likely a combination of these.

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    $\begingroup$ Phosphors typically convert one photon of short wavelength into one longer wavelength photon plus heat. As such, the further the shift along the spectrum, the worse the energy efficiency. At some point it's better to first convert the radiation into electricity, and then power some LEDs. That said, with the energy coming from a reactor, why turn it into UV in the first place? $\endgroup$ Feb 12 at 9:55
  • $\begingroup$ You can just feed insects with the cellulose and eat the insects rather than composting it. $\endgroup$
    – Michael
    Feb 12 at 14:21
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    $\begingroup$ @cmaster-reinstatemonica if you can't produce high efficiency, high intensity red and blue LEDs in the needed quantities, fluorescent lamps are one of your more efficient options for grow lights, and most LEDs used for general illumination use the same approach. If you have an especially efficient way of producing UV, this may be the best available way to get light for plant growth. That said, it's not clear why they want to grow plants with UV in the first place... $\endgroup$ Feb 12 at 14:23
  • $\begingroup$ True. Yet, afaik, those plant growth LEDs, as well as quite a number of white LEDs, are actually a blue LED behind a phosphor that turns part of the blue light into green/yellow/red light. In a white LED, this produces a spectrum with a sharp blue spike and a flat yellow hill. This is quite efficient, because blue and yellow are relatively close together. If you used an actual UV source instead (like in fluorescent lights), the efficiency goes down the harder the original UV light. The most efficient version remains putting several LEDs of different wavelength together without a phosphor. $\endgroup$ Feb 12 at 14:47

It's going to be hard to get more efficient than algae. We're happy (some of us, at least) to put spirulina powder in smoothies, and so forth, so we already eat it.

Algae will be probably the simplest source of nutrients, taking the least energy per gram to grow up.

Unfortunately, I've no idea if it's nutritionally balanced, but I suspect it could be engineered to be. It'll also be able to use any waste heat to speed production, and be possible to grow in a sphere around the light source, maximizing growing surface area.

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    $\begingroup$ Actually, mushrooms would be better, but yes. Take my +1 $\endgroup$ Feb 12 at 0:55
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    $\begingroup$ @SamKitsune Do mushrooms photosynthesize? $\endgroup$
    – user253751
    Feb 12 at 15:01
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    $\begingroup$ @SamKitsune So they use energy that is not light. What do they use and how does the reactor make it so everyone can feed the mushrooms? $\endgroup$
    – user253751
    Feb 12 at 15:09
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    $\begingroup$ What @user253751 is getting at is that mushrooms don't produce. They don't magically grow without any source of energy. They aren't a "better" solution, they aren't even a working solution. You might use them to get a little more out of photosynthesizing plants, but algae don't make a particularly good pairing with them, you'd be better off with something like corn that produces lots of inedible waste. And even then, if you really want to maximize results, feeding such materials into reactors full of yeast and bacteria probably wins over growing mushrooms. $\endgroup$ Feb 12 at 18:41
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    $\begingroup$ @BobaFit, while still maybe true, the page you linked just tries to sell us overpriced food supplements... $\endgroup$
    – fgysin
    Feb 13 at 9:49

Microbial electrosynthesis is more energy-efficient than photosynthesis. Engineer microbes to produce nutrients and use electricity from your reactor to power the process.

  • $\begingroup$ Seems useful i synthesizing other chemicals, but the article is not clear on it making edible, nutritious foods. $\endgroup$ Feb 13 at 17:31
  • $\begingroup$ @JustinThymetheSecond That's because industrial chemicals are the market. The same metabolic pathways that energize the creation of nutrients like sugars are involved, but the developers of this tech don't want to try competing with farming in the beginning. $\endgroup$
    – John Doty
    Feb 13 at 18:11
  • $\begingroup$ THIS this is the way to go Edit: bacteria can be Crispr'd to produce just about anything as well, with their easy editability and whatnot. What might be an issue is to keep the microbe genes from drifting too much, the worst case scenario, you could create a deadly superbug after incompletely sterilizing a batch of "food" and botching the antibiotic course. $\endgroup$
    – Harry Mu
    Feb 17 at 21:54

Most important question to properly answer it is: for how long?

For whatever reason you chose to concentrate on power consumption. This is fine and I can see at least several reasons for doing so, all perfectly legitimate, but I believe you failed to consider several factors, most important of which is that proper diet is needed to keep humans in more or less healthy condition. And it's not constrained to just physical health. For example, if you'd limit your people to corn you'd eventually end up with serotonin deficiency and pellagra, which some studies link to Aztec cannibalism, for example.

So, depending on the time you plan your group to spend in the closed environment, you have some options, but since vegan diet is very hard to get right without really wide food variety available, you may have to revise your assumptions.

If we're talking about 6 months tops then soybeans or mentioned corn. Soybeans are really good in photosynthesis department, but need to be properly fermented (which takes energy). Corn is also a good choice. But you have to add supplements to it, or introduce more plants, especially vegetables and nuts or oily seeds; though not necessarily a lot.

If you are talking long-term, then without either supplements (vitamins, fats and minerals) or really varied foodstuffs (grains, beans, vegetables, fruits and/or - unfortunately - animals), your group will not survive long.

This means you have to either invest seriously in the area for food production or, which is a better way, introduce plants with much better photosynthesis efficiency (be it breakthrough in cross-pollination or selective breeding or genetic engineering), because then you can get 10 times or 100 times higher yields from area, which you can use for diversified heavily crops or still have room for animals (should you choose so).

Obviously upside of any farming area in closed loop environment is a good way to boost air scrubbing of CO2 and water vapour, so this is a good way to offset energy expenditure there. Also, this whole area may be an excellent place to have for improving all-round wellbeing of the crew. Humans do not do well long-term in enclosed spaces, so having an area that can double as recreational is a benefit.

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    $\begingroup$ Heavy metals in plants are sourced from the soil they grow in and bio-accumulate. I'm sure they will be using carefully designed soil. $\endgroup$
    – user253751
    Feb 13 at 13:08
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    $\begingroup$ @user253751 - true, but it's not only from soil. Environment, more like, so if anything, carefully designed environment. Well made point, though, thanks. $\endgroup$
    – AcePL
    Feb 13 at 14:37
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    $\begingroup$ also I'll point out heavy metals are not less of a problem when eating meat. Animals eat those plants and the heavy metals bio-accumulate in animals, too. The animal poops out some of the part that is not bio-accumulating, so its meat has a higher concentration of bio-accumulating heavy metals than the plants did. In this manner, organisms further up the food chain have more poison in them. en.wikipedia.org/wiki/Bioaccumulation $\endgroup$
    – user253751
    Feb 13 at 14:39

Ideally Mushrooms

That or a genetically modified analog, as you need to give better details on the level of technology you have available and the amount of space you can afford. If this is a colony ship for example, space, weight and power are your currencies, while for a space station, the space is most valuable.

But I will assume a closes cycle explorer starship, in which case mushrooms would be your primary choice. They grow with little sunlight, can be modified to decompose crew waste and can be grown in artificial mediums. Only problem is that they kind of suck at making oxygen, if you care about that.

Otherwise, Soylent Green

If you do care about oxygen, then algae, reprocessed into edible bars are most efficient. They'd taste pretty alright and you are making oxygen while you do it, so you'd fit food and life support into a single system.

Do remember that I assume you have relatively advanced genetic modification, or otherwise find the perfect kind of edible mushrooms and seaweeds to feed your crew, which might be hard.

Growing It

For mushrooms, a hydroponic artificial medium combination, possibly along walls of a farming level of the ship, would use reprocessed waste as fertilizer. Otherwise, algae would be grown in well-lit vats of water, with carbon dioxide being bubbled through. If you want to maximize the shielding efficiency, then you'd make the walls of your space ship serve as the water tanks, filled with algae or otherwise, but do note that it would make cleaning them a pain in the rear end.

  • $\begingroup$ Comments have been moved to chat; please do not continue the discussion here. Before posting a comment below this one, please review the purposes of comments. Comments that do not request clarification or suggest improvements usually belong as an answer, on Worldbuilding Meta, or in Worldbuilding Chat. Comments continuing discussion may be removed. $\endgroup$
    – L.Dutch
    Feb 15 at 17:50

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