In his 1976 essay on (or against) genetic engineering [1] Erwin Chargaff wrote "But screams and empty promises fill the air: Don't you want cheap insulin? (...) And how about a green man synthesizing his nourishment: 10 minutes in the sun for breakfast, 30 minutes for lunch, and 1 hour for dinner?" Nice to see that scientists are actually trying.
It also comes up at least once in John Varley sci fi books. People can get themselves turned into space-floating plants and just sort of hang around saturn. I can't remember if they get genetically modified to photosynthesize or they wear a suit that does it.
I always imagined this as a future basic genetic modification with a gene trigger: before starvation sets in your cells would manufacture a bunch of chloroplasts and turn your skin green, to give you a chance with water and sunlight to get some more run way on survival. Then if your calorie levels rise the chloroplasts get re-absorbed.
unfortunately to meet animal energy requirements one would need a huge canopy; it'd probably only be feasible outside our gravity well.
The metabolic rate of an animal scales as 0.75 the mass, I guess surface area is about the 0.66 power of mass so I guess it gets more favorable when you get smaller but not by a lot. See https://book.bionumbers.org/how-does-metabolic-rate-scale-wi...
Note thermal efficiency is a problem too.
For instance you could imagine wearing an LED suit that exposes you to a lot of light. You need 100W for your basal metabolism, if photosynthesis were 10% efficient you'd be dealing with 900W of waste heat which is a lot, real-life efficiency would be worse than that.
You're thinking entirely replacing our energy source. What about just boosting it passively. Imagine if energy requirements for every human were decreased by 2%
Probably not dolable on planetary scale but ii imagine it'd help in space, esp if combined with some other mods like fiximg the vitamin c gene to remove scurvy. If we could use light to suppliment our metabolism it'd mean fewer physical resources to bring alon.
> Imagine if energy requirements for every human were decreased by 2%
Taking the spherical human to require 8400 kJ/day, we're talking ~170 kJ replacement, or:
~6g butter, or
~1/3 of a can of Coke, or
~1/3 of a single Bounty piece, or
~1 McNugget (without sauce)
Maybe this would be enough to get people onto more lean meats, and a reduction of cattle industry? (Is that worth biohacking for?)
per day though. I think others are right that it has applications in space. going with the butter example, 5 people on a year long mission is almost 11kg you don't have to bring up to space.
on an environmental perspective, if applied to everyone, its almost half a quadrillion kJ removed a year, plus supply chain logistics, waste, packaging,
I still think its probably a ridiculous pipedream, but even pipedreams are meant to be dreamt.
11kg is nothing...
Relevant what-if-xkcd https://what-if.xkcd.com/17/
How come chlorophyll photosynthesis isn't more efficient? 6% for plants, 20% for (ordinary) solar panels. Don't plants have to outcompete other plants? Then there's red algae, which inhabit dark places like caves and the ocean, and they're apparently way more efficient. Is it somehow not advantageous to a tree to photosynthesize efficiently?
plants only use part of the spectrum. Likely they have hit some local or maybe even global maximum that would be hard to evolve past. See https://en.wikipedia.org/wiki/Photosynthetic_efficiency