# Solar panels around the sun - how would the energy get back home? **URL:** \ **Category:** Factual Questions\ **Created:** [August 23, 2013, 3:51pm UTC](https://boards.straightdope.com/t/solar-panels-around-the-sun-how-would-the-energy-get-back-home/666976 "2013-08-23T15:51:40Z")\ **Posts on this page:** 15\ **Page:** 2
**Author:** ![zwede](https://avatars.discourse-cdn.com/v4/letter/z/ac91a4/32.png) [@zwede](https://boards.straightdope.com/u/zwede)\ **Post date:** [August 25, 2013, 12:52am UTC](https://boards.straightdope.com/t/solar-panels-around-the-sun-how-would-the-energy-get-back-home/666976/21 "2013-08-25T00:52:12Z")
The purpose of a Dyson sphere is not to collect solar power. They are intended to maximize livable space. Think of populations numbered in the thousands of trillions. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [August 25, 2013, 4:18am UTC](https://boards.straightdope.com/t/solar-panels-around-the-sun-how-would-the-energy-get-back-home/666976/22 "2013-08-25T04:18:51Z")
> [@](#): > > The purpose of a Dyson sphere is not to collect solar power. Actually, that’s exactly the purpose, in Dyson’s original concept. Since then, of course, science fiction writers have taken the concept and run with it, in many different directions. And **Wesley** , while it’s true that battery tech would have to advance enormously to make that practical, there are so many other techs that would also have to advance enormously that it’s not inconceivable that by the time we have Dyson spheres, we just might do something like that. Ultracapacitors would be a lot more likely than chemical batteries, though, or possibly some sort of “nuclear battery”. ---
**Author:** ![Der\_Trihs](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/der_trihs/32/233_2.png) [@Der\_Trihs](https://boards.straightdope.com/u/Der_Trihs)\ **Post date:** [August 25, 2013, 5:15am UTC](https://boards.straightdope.com/t/solar-panels-around-the-sun-how-would-the-energy-get-back-home/666976/23 "2013-08-25T05:15:26Z")
> [@crucible](#): > > all well and good and theoretical is important to consider, but, folks, we have plenty of unused southwestern desert perfect for setting up solar farms that will take care of our needs for as long as we can speculate we will be around. Not really. Solar isn’t a very dense energy source, and it’s unreliable. I doubt there’s enough desert on the planet. And “as long as we can speculate we will be around” is more than long enough for us to expand into the solar system, which would make trying to support ourselves with a patch of land on Earth even more impractical. ---
**Author:** ![Habeed](https://avatars.discourse-cdn.com/v4/letter/h/a587f6/32.png) [@Habeed](https://boards.straightdope.com/u/Habeed)\ **Post date:** [August 25, 2013, 5:21am UTC](https://boards.straightdope.com/t/solar-panels-around-the-sun-how-would-the-energy-get-back-home/666976/24 "2013-08-25T05:21:07Z")
By the time you get to the Dyson swarm stage, you have disassembled the earth for raw materials. ---
**Author:** ![Habeed](https://avatars.discourse-cdn.com/v4/letter/h/a587f6/32.png) [@Habeed](https://boards.straightdope.com/u/Habeed)\ **Post date:** [August 25, 2013, 5:22am UTC](https://boards.straightdope.com/t/solar-panels-around-the-sun-how-would-the-energy-get-back-home/666976/25 "2013-08-25T05:22:43Z")
> [@Der\_Trihs](#): > > Not really. Solar isn’t a very dense energy source, and it’s unreliable. I doubt there’s enough desert on the planet. > > And “as long as we can speculate we will be around” is more than long enough for us to expand into the solar system, which would make trying to support ourselves with a patch of land on Earth even more impractical. This is completely wrong. To power the entire United States, including the energy used by planes and cars, we would need about 100 x 100 miles of desert. Give or take a bit, it depends upon the efficiency of the panels and the efficiency of the other conversion steps. (for instance, to power airplanes with solar, you would have to convert that electricity to liquid hydrogen or some other appropriate fuel) ---
**Author:** ![eburacum45](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/eburacum45/32/8690_2.png) [@eburacum45](https://boards.straightdope.com/u/eburacum45)\ **Post date:** [August 25, 2013, 6:33am UTC](https://boards.straightdope.com/t/solar-panels-around-the-sun-how-would-the-energy-get-back-home/666976/26 "2013-08-25T06:33:32Z")
> [@zwede](#): > > Spin the sphere and you’ll have gravity and atmosphere on a sizable portion of it. The land mass would be incredible. This doesn’t work, unfortunately. A spinning Dyson sphere would fall apart because of hoop stress. The largest hoop you could make which rotates to give one gravity of centrifugal force would be made from carbon nanotube, and have a radius of around one thousand kilometres. You could make a swarm of smaller habitats in a range of different orbits that would, in total, have a fantastically vast surface area; but they would each have a maximum diameter of two thousand kilometres (smaller still if you allow for safety factors). ---
**Author:** ![Valgard](https://avatars.discourse-cdn.com/v4/letter/v/7feea3/32.png) [@Valgard](https://boards.straightdope.com/u/Valgard)\ **Post date:** [August 26, 2013, 2:39pm UTC](https://boards.straightdope.com/t/solar-panels-around-the-sun-how-would-the-energy-get-back-home/666976/27 "2013-08-26T14:39:13Z")
> [@eburacum45](#): > > This doesn’t work, unfortunately. A spinning Dyson sphere would fall apart because of hoop stress. The largest hoop you could make which rotates to give one gravity of centrifugal force would be made from carbon nanotube, and have a radius of around one thousand kilometres. > > You could make a swarm of smaller habitats in a range of different orbits that would, in total, have a fantastically vast surface area; but they would each have a maximum diameter of two thousand kilometres (smaller still if you allow for safety factors). Oh nonsense. Scrith and gravity generators, exact design will be left as an exercise for the curious reader. What _are_ they teaching kids in school these days? Sheesh. 😃 ---
**Author:** ![Finagle](https://avatars.discourse-cdn.com/v4/letter/f/b19c9b/32.png) [@Finagle](https://boards.straightdope.com/u/Finagle)\ **Post date:** [August 26, 2013, 3:06pm UTC](https://boards.straightdope.com/t/solar-panels-around-the-sun-how-would-the-energy-get-back-home/666976/28 "2013-08-26T15:06:43Z")
> [@Shodan](#): > > And would they sell Slurpies? > > Regards, > Shodan Until they used up Halley’s Comet. Because, according to Futurama, that’s the only source of ice in the solar system without giant bugs. ---
**Author:** ![pravnik](https://avatars.discourse-cdn.com/v4/letter/p/8edcca/32.png) [@pravnik](https://boards.straightdope.com/u/pravnik)\ **Post date:** [August 26, 2013, 3:58pm UTC](https://boards.straightdope.com/t/solar-panels-around-the-sun-how-would-the-energy-get-back-home/666976/29 "2013-08-26T15:58:49Z")
> [@si\_blakely](#): > > No - the microwaves are beamed into a rectenna (rectifying antenna) for direct conversion to DC current. This can be up to 90% efficient. I’m glad you clarified what a “rectenna” is. I was really, really afraid it was going to be something very different. ---
**Author:** ![dracoi](https://avatars.discourse-cdn.com/v4/letter/d/90db22/32.png) [@dracoi](https://boards.straightdope.com/u/dracoi)\ **Post date:** [August 26, 2013, 4:24pm UTC](https://boards.straightdope.com/t/solar-panels-around-the-sun-how-would-the-energy-get-back-home/666976/30 "2013-08-26T16:24:22Z")
> [@Randy\_Seltzer](#): > > Instead of using the energy to power devices, why don’t we just use it to create matter (m = E/c[sup]2[/sup] … I’m sure we’ll have something worked out by the time we’re worrying about Dyson swarms) for more Dyson swarm space stations? No waste heat that way. The laws of thermodynamics are pretty clear on the issue of waste heat. No matter what useful energy you get out of a process, nothing is 100% efficient. Many processes have a calculated maximum efficiency and this can be pretty low. For example, metabolizing carbohydrates can’t be more than about 50% efficient, no matter how fine-tuned the system is. ---
**Author:** ![Wesley\_Clark](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/wesley_clark/32/20581_2.png) [@Wesley\_Clark](https://boards.straightdope.com/u/Wesley_Clark)\ **Post date:** [August 27, 2013, 12:18am UTC](https://boards.straightdope.com/t/solar-panels-around-the-sun-how-would-the-energy-get-back-home/666976/31 "2013-08-27T00:18:22Z")
> [@Chronos](#): > > And **Wesley** , while it’s true that battery tech would have to advance enormously to make that practical, there are so many other techs that would also have to advance enormously that it’s not inconceivable that by the time we have Dyson spheres, we just might do something like that. Ultracapacitors would be a lot more likely than chemical batteries, though, or possibly some sort of “nuclear battery”. If we had massive ships that were like barges, except they carried extremely low cost, high density batteries and they were somehow solar powered I could see it being feasible. The ships would have to carry thousands of tons of batteries I’m sure, if not more. But the cost of a ship going to/from the earth would have to carry a lot of electricity to be cost competitive with technologies on the earth which are also going down in price. ---
**Author:** ![eltro102](https://avatars.discourse-cdn.com/v4/letter/e/7cd45c/32.png) [@eltro102](https://boards.straightdope.com/u/eltro102)\ **Post date:** [August 27, 2013, 10:04pm UTC](https://boards.straightdope.com/t/solar-panels-around-the-sun-how-would-the-energy-get-back-home/666976/32 "2013-08-27T22:04:46Z")
have the dyson sphere constantly reform (eg made up of loads of orbiting space stations or whatever which can rotate so the whole thing is roughly shaped like something) into a zone plate which focuses the suns rays onto the earth ---
**Author:** ![Steve\_MB](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/steve_mb/32/5339_2.png) [@Steve\_MB](https://boards.straightdope.com/u/Steve_MB)\ **Post date:** [August 27, 2013, 11:02pm UTC](https://boards.straightdope.com/t/solar-panels-around-the-sun-how-would-the-energy-get-back-home/666976/33 "2013-08-27T23:02:48Z")
> [@si\_blakely](#): > > No - the microwaves are beamed into a rectenna (rectifying antenna) for direct conversion to DC current. This can be up to 90% efficient. That’s because the Dyson equipment produces smooth energy conversion, without the buffeting and choppiness of conventional blades. ---
**Author:** ![si\_blakely](https://avatars.discourse-cdn.com/v4/letter/s/d9b06d/32.png) [@si\_blakely](https://boards.straightdope.com/u/si_blakely)\ **Post date:** [August 27, 2013, 11:14pm UTC](https://boards.straightdope.com/t/solar-panels-around-the-sun-how-would-the-energy-get-back-home/666976/34 "2013-08-27T23:14:37Z")
The point of space-based energy collection is not to get energy to earth (beyond a certain point) - you cannot divert that much more energy on to the planet before heat buildup becomes a problem. The point of a Dyson sphere was to collect the entire output of the sun for space-based projects - planet disassembly to make the components of the sphere (assuming you have any planets left by this stage), manufacture of goods, living habitats, laser-powered interstellar craft, things like that. A chunk goes into maintaining the sphere itself - a rigid sphere is impossible (as noted above due to material strength limits), and a full cloud is not stable and requires energy to keep all the components in orbit. Most of that energy will eventually be re-radiated as IR radiation having done some work on the way through the sphere. ---
**Author:** ![si\_blakely](https://avatars.discourse-cdn.com/v4/letter/s/d9b06d/32.png) [@si\_blakely](https://boards.straightdope.com/u/si_blakely)\ **Post date:** [August 28, 2013, 5:27am UTC](https://boards.straightdope.com/t/solar-panels-around-the-sun-how-would-the-energy-get-back-home/666976/35 "2013-08-28T05:27:49Z")
> [@Steve\_MB](#): > > That’s because the Dyson equipment produces smooth energy conversion, without the buffeting and choppiness of conventional blades. Ah yes - Dyson Engineering, you can be full of it and still suck 😉 [Previous page](https://boards.straightdope.com/t/solar-panels-around-the-sun-how-would-the-energy-get-back-home/666976.md?page=1)