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You can have the plants indoors and protected from temperature extremes in a single story greenhouse with natural illumination. Theoretically, an infinite-junc
by philipkglass 10y ago
You can have the plants indoors and protected from temperature extremes in a single story greenhouse with natural illumination.
Theoretically, an infinite-junction solar cell can achieve up to 68.7% efficiency under non-concentrated sunlight. The best demonstrated so far is about half of that: https://www.sciencedaily.com/releases/2016/05/160517121811.htm https://www.sciencedaily.com/releases/2016/05/160517121811.h...
Efficiency under concentrated illumination is higher but concentrating designs require direct illumination and have their performance fall off a cliff under even partially cloudy conditions.
Spectral tuning of the light sources can make illumination more photosynthetically efficient, and so can evening out the illumination intensity. If you could get lights and multi-junction solar cells that operated at the theoretical limit it might be more efficient than natural sunlight growing, but that's a tall order to achieve in practice. To achieve a net environmental benefit not only does it have to be more efficient than single-story natural illuminated structures, it has to be enough more efficient to pay back the environmental costs of manufacturing the extra equipment required up-front in the vertical case.
- the8472 10y agoI was particularly thinking about applications in arid climates. Where just spraying water on plants or cooling large greenhouses has inefficiencies on its own. Or is cooling horizontal greenhouses easy enough, even in deserts?
- philipkglass 10y agoThe Sundrop Farms approach pumps seawater through an evaporative structure to control the temperature inside a greenhouse in a desert climate. That way the salt doesn't get on the plants but you only need a little electricity to run the cooling system. In a desert far inland you need extra piping/pumping or a more expensive cooling system, but I still can't see a terrestrial scenario where artificial-illumination greenhouses provides calories at a lower environmental or financial cost than natural sunlight greenhouses or fields. Artificial illumination farming of course does make sense for crewed deep space missions because there's not any other option. That's actually how I first started thinking about this problem -- "what if you wanted to feed a crewed nuclear powered outpost in orbit around Neptune?" It turns out that it takes a lot of electricity to feed people that way because our food crops suck at turning light-energy into human-edible energy. Having a rough idea of the enormous electricity expenditures, I started doing double-takes when vertical farm enthusiasm started spreading a few years ago.
- nl 10y agoI'm lucky enough to be able to purchase Sundrop-grown tomatoes[1] (or at least I'm pretty sure they are Sundrop) and can confirm they are both price competitive (as in they are always the cheapest option) and taste great. [1] http://www.abc.net.au/news/2016-10-01/sundrop-farms-opens-solar-greenhouse-using-no-fresh-water/7892866 http://www.abc.net.au/news/2016-10-01/sundrop-farms-opens-so...