Say you have a large group of people living underground. The only light available is artifical and while it is possible to use to to grow some crops, due to the high energy requirements it is not possible to do so on a large enough scale to feed everyone that way. What food sources could be cultivated/raised with little to no light? I’ve already come up with mushrooms but man cannot live by mushrooms alone.
Meat animals could eat the mushrooms…
Since you mention things like high energy requirements of lights and not being able to use lights to make food on a large enough scale, but you want to be able to grow food with the lights for a large group I think you’ll have to define a few things…
How large is the group and how much energy/electricity is available?
There are indoor greenhouses that rely totally on lights that make a wide variety of different vegetables as well as run pumps to keep a fish farm operational.
But you’ll have to give us the specs so we have something to work with.
ETA here’s short article on a place I took a tour of a few years ago. Vegetables (mainly leafy stuff) and fish, all indoors.
Well, there are chemosynthetic organisms in the deep ocean that draw their power by breaking down chemicals in their environment, not from photosynthesis. Such organisms might form the basis of a food chain in an ecosystem if your hypothetical cave people had access to hydrothermal vents and the water from those vents were high enough in the necessary chemicals. Such a system would not be truly self-sustaining, as it depends on outside input in the form of chemicals.
The population is between two hundred and four hundred. To be honest, I don’t have any idea as to what sort of energy requirements an artifically lit greenhouse would have beyond ‘a lot’, so I’m going to be having a close look as the site that was linked. As for the rest of the specs, I’m still trying to figure them out (this is for a story idea I’ve had). Sorry for the vagueness.
Tech level and general resources are roughly level with what’s available today and no, they don’t have access to hydrothermal vents.
Can you run fiber optics to the surface?
Not sure. Probably not though. adds to list of things to figure out
Could you have cracks in the rock that lets in daylight? How far underground are these people? Are they living in the subway under a city or in a cave system?
The group that my story focuses on are living in a old mine (said mine is rather large and free from flooding). There are others referred to who are living in everything from old bomb shelters (there’s some impressive ones here in the UK) to subway systems to old RAF ammunition depots though.
Yeast would be a good source of food. It’s a fungus, so that’s covered in the mushroom category. But yeast grows fast, and has the side benefit of producing alcohol. Yeast and mushrooms need food themselves, and they seem to grow well on manure, something that ought to be available. Yeast can be grown in a liquid making effective use of limited underground space. Yeast can also be used to make something called Marmite, but that has only been found digestable by Australians. It is toxic to most other people. I think the drawback may be that yeast and other fungi don’t get their carbon from the air like photosynthetic plants. Since the humans will be converting a lot of what they eat into CO2, you’ll be losing a lot of carbon out of the system. Maybe there’s fungus that feed directly off of coal?
I can’t remember the book but there is an old sci fi series that talks about using oil as a food source for yeast which they use to feed an over populated earth. In it the main character lamented that 20th century man wasted so much oil dragging themselves and a few thousand extra pounds of metal over the surface of the earth instead of feeding the hungry.
There have to be ventilation shafts in an old mine, possibly there could be a system of mirrors to reflect sunlight underground. Otherwise, yeast and other fungi would probably be your best bet.
Have you seen this?
Marmite is British and no self-respecting Aussie would be caught dead eating it.
Yeasts and fungi need feeding - and the things they feed on are part of a food chain that includes the conversion of sunlight to food energy - so those are only going to be sustainable as long as there is a stockpile of something to feed them on.
And you can’t feed them on the wastes of the organisms consuming them - that’s a closed system, which will run out of energy.
Out of curiousity, how long would it take for the energy to run out? Also, would a relatively small quantity of plants grown under artifical light combined with occasional runs to the surface to grab plant matter (the question is story research and the setting does allow brief trips to the surface but it’s very risky) be enough to keep things going?
It would run out pretty much straight away. Even if it was possible to live on yeast alone, there’s nothing much in human excreta that is of interest to yeast as their food. The same goes for amy closed cycle - you can’t just keep extracting energy out of a substance and expect it to remain valuable as food - for anything.
And a small amount of artificially-grown plant would contribute a small amount - no more than their intrinsic value as food themselves.
Fungi can’t extract carbon dioxide from the air. And a lot of the carbon we consume ends up getting exhaled as carbon dioxide. It’s a closed cycle with an enormous hole in it leaking carbon. Now if fungi can extract carbon directly from coal or oil, or it can be fixed through some other method, there’s a means of keeping things going.
What do blind cave fish eat? Perhaps those could be cultivated; the lack of light wouldn’t bother them.
Small invertebrates, which will probably be variously grazing on bacterial films, and/or feeding on other invertebrates or single celled organisms - anything that’s edible and has food value, really - it’s the food chain below the fish that’s going to limit the scalability of that.
There are plants which don’t need as much light to grow, but then the question is how quickly do they grow? If they need half as much light but take twice as long to double their mass, you haven’t gained anything. If energy is the limiting factor than the question is what plant does the most efficient job of converting light into humanly edible biomass? My guess would be probably some form of algae.