This question already has an answer here:

Its a very common answer to this:

After Machines took over, sunshine never reached earth surface.

Isn't it shown like Sun was destroyed?
In Revolutions (III), sunshine was displayed when our heroes flied to higher altitude. Why didn't Machines choose solar energy of higher altitude and outer space?

marked as duplicate by Valorum, Blackwood, KutuluMike, Skooba, Chenmunka Dec 10 '16 at 13:48

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    Just an observation, but if the sun were destroyed then I'd imagine the machines would be among humanity's smaller problems. – Chad Levy Mar 2 '12 at 0:44
  • @Pearsonartphoto Its not a duplicate. In that question, focus is on: "Why Humans".. and why not nuclear energy etc. But, my question is: Why those questions? Solar energy was still an option... – Lobo Mar 2 '12 at 9:12
  • @SachinShekhar: I'll re-open it, upon further thought I will agree that this is legitimately different. – PearsonArtPhoto Mar 2 '12 at 14:20

The machines were using solar power initially, but Morpheus points out that humans, knowing that the machines needed solar energy, "scorched the sky" presumably with nuclear weapons and thrusting the Earth into a nuclear winter-type scenario (this is what I assume. The exact line in the movie is:

We don't know who struck first, us or them. But we know it was us who scorched the sky. At the time they were dependent on solar power and it was believed they would not be able to survive without an energy source as abundant as the sun.

Of course, as we know, the machines figured out that humans were a better source or energy.

  • "it was believed they would not be able to survive without an energy source as abundant as the sun." It was said by Morpheus. Isn't it something like Sun was destroyed? Solar energy was still an option as mentioned in question.. – Lobo Mar 1 '12 at 16:04
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    According to dictionary.com, the definition of nuclear winter is: "The general devastation of life, along with worldwide darkness and extreme cold, that some scientists believe would result from a global dust cloud screening out sunlight following large-scale nuclear detonations." No sun destruction necessary. It is interesting to note that some scientists also believe a similar effect occurred to the remaining dinosaur species who survived the initial asteroid impact during the K-T extinction. – Meg Coates Mar 1 '12 at 16:26
  • (cont).The machines are smart, and, if they were capable of fighting humans initially, then it might stand to reason that they were also capable of a sense of revenge. Besides, why go through all the work to harvest the sun's energy at high altitude when a defeated, plentiful energy source is right there in front of you? – Meg Coates Mar 1 '12 at 16:30
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    @Meg Your answer is canonical and therefore correct. However, I disagree with the Wachowskis: humans are not a better source than the Sun, since everything on Earth ultimately needs the Sun as an energy source. Their reasoning is as flawed as claiming you don't need a power plant, since you can buy batteries at the store (oh yeah? and who built the batteries?) – Andres F. Mar 1 '12 at 17:08
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    @Andres F Absolutely. And I also agree with Xantec that there has to be a good reason why the machines chose humans over sunlight. I don't think (nor recall a mention of) the sun was ever destroyed, merely blotted out. Perhaps it was a multitude of reasons: revenge, the inefficiency of capturing and transporting solar energy to the surface (even the photosystems of plants are not 100% efficient at this). Perhaps it was a choice of what was the more efficient energy source, realizing that neither option was ideal. – Meg Coates Mar 1 '12 at 17:17

In the Animatrix, it shows that the people of the Earth, as a last resort, scorched the sky with some bomb that would continuously cause no light to enter the atmosphere. It mentions that they would figure out how to reverse it after the threat of the machines was over.

It proved futile as the machines then invaded the rest of the Earth from their central city of Zero One, and created the living batteries that the Matrix ran off of in the movies.


I am not sure there is any canon answer to this (hopefully someone finds one), but I would bet that the machines found the act of getting the captured solar energy to the surface was impractically inefficient, compared to simply using humans as batteries.
Short of leaving Earth altogether (which would be a separate question) the least resource-intensive method of getting energy back to Earth would to "beam" it, but this is problematic due to the "scorched" sky. Any low frequency beam that would penetrate the clouds with little interference would be too low power, it wouldn't be able to power very much of anything. On the other hand a high frequency beam would lose a lot of power due to cloud interference.
In the end it just came down to how much work was required to produce the amount of energy necessary to power all the machines. Apparently bio-batteries won the consensus in that town hall and the machines never looked back.

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    Let's say fetching solar energy through the clouds is unreasonable (because of inefficiency and/or energy expenditure). Then there must be another power source, and humans aren't it (because living beings don't generate energy, they merely transform it). So it must be the case that humans have found an alternative power source, likely the planet's core. If so... why don't the machines skip the middle men and use that power source directly? It would be way more effective than raising human-cattle! – Andres F. Mar 1 '12 at 18:35

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