Comments on Could grow lights on a massive scale replace 100% of sunlight for 100% of the growing season?
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Could grow lights on a massive scale replace 100% of sunlight for 100% of the growing season?
In a world where pollution and population have drastically reduced the effectiveness of sunlight to grow food, would light-panels be capable of completely replacing the sun?
The problem I'm trying to solve is rationalizing indoor farming for 100% of the Earth's agriculture. Piping in water is a big deal, but believable. Fertilizing is believable. Temperature control might be believable.
But is it believable that light panels could replace 100% of the sun for 100% of the growing season?
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For the purpose of the question, the building in question is 14,500 square kilometers (a bit bigger than the U.S. State of Connecticut) It has ten stories (allowing for agriculture roughly the size of the U.S. State of New York). Don't worry about how the building can be that large and carry that much weight. This question is only focusing on the lights.
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The lights are timed to fade-to-starlight-black and fade-to-full-sun with appropriate changes in timing to emulate natural growing seasons. For the purpose of this question, let's assume we're dealing with wheat, which allows for a winter wheat during the cold months and a spring wheat during the summer months.
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You can hand-wave the right types of lights that produce the right mix of wavelengths, but you can't hand-wave away the power requirements.
Sunlight reaching the earth's surface is about 1.2 kW/m2 on a clear day with the sun high in the sky. You probably don't need all that if you focus on particular wavelengths that plants use. Let's say you still need 500 W/m2 just to pick something. Even if your lights and power delivery system are 100% efficient, you still need 500 W for every square meter of growing area when you want to simulate sunshine.
You say you have 10 floors of 14,500 square km each, so 145,000 square km to illuminate. That's 145 Gm2. Times 500 W, the power is 73 TW. You are simulating day/night cycles, so let's say you only need ⅓ of that on average. Since this is all indoors removed from the actual day/night cycles, you can have different parts of your farm on different schedules so that you need the average power all the time instead of the full power part of the time. That gets you to 24 TW. To put this in perspective, the total electric generating capacity of the United States is a bit over 1 TW.
Sunlight is a huge source of energy to earth, with the energy generated by humans a tiny fraction of that. Any system that tries to replace sunlight with something artificial will require huge amounts of power.
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