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Q&A Could grow lights on a massive scale replace 100% of sunlight for 100% of the growing season?

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...

posted 3y ago by Olin Lathrop‭ · edited 3y ago by Olin Lathrop‭

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#3: Post edited by

Olin Lathrop‭ · 2021-08-13T16:23:41Z (over 3 years ago)

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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 miles each, so 145,000 square miles to illuminate. That's 376 Gm2. Times 500 W, the power is 188 TW. You are simulating day/night cycles, so let's say you only need &frac13; 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 us to 63 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.

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 &frac13; 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.

#2: Post edited by

Olin Lathrop‭ · 2021-08-13T16:08:01Z (over 3 years ago)

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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 need. 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 miles each, so 145,000 square miles to illuminate. That's 376 Gm2. Times 500 W, the power is 188 TW. You are simulating day/night cycles, so let's say you only need &frac13; 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 us to 63 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.

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 miles each, so 145,000 square miles to illuminate. That's 376 Gm2. Times 500 W, the power is 188 TW. You are simulating day/night cycles, so let's say you only need &frac13; 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 us to 63 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.

#1: Initial revision by

Olin Lathrop‭ · 2021-08-13T16:07:09Z (over 3 years ago)

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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/m<sup>2</sup> 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 need.  Let's say you still need 500 W/m<sup>2</sup> 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 miles each, so 145,000 square miles to illuminate.  That's 376 Gm<sup>2</sup>.  Times 500 W, the power is 188 TW.  You are simulating day/night cycles, so let's say you only need &frac13; 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 us to 63 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 <i>huge</i> amounts of power.

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