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What would be the best way to send energy that is generated outside the Earth's atmosphere, possibly in the asteroid belt (nevermind the means), so that it can be used on the surface of the planet?

Let's say solar power generation. With enough mirrors you can get really high output. The energy thus "gathered" can be "transmitted" down to Earth's surface, but it will be, in essence, a laser beam (i know, it will be concentrated sunlight, but I mean effect, not the naming details), that will be dangerous to anything in it's path, including the atmosphere.

Assuming level tech of today but include current experiments in all stages of advance, what would be the best - that means safest, cheapest and most efficient - way to supply energy to the grid on the Earth's surface? Additionally: what would be the upper limit of the power levels to be transmitted?

To clarify after some very good comments:

  1. for starters let's look at powering Earth from orbit in 100%. So 200 TWh
  2. Current level tech +20 years caveat means no space industry in place. So let's say I want to start working on it next year (2018).
  3. Any way of sending and/or form of energy goes.
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  • $\begingroup$ en.wikipedia.org/wiki/Energy_storage#Methods - pick one and say they have perfected it. If you do not like these, you should maybe tell us 1) How much energy 2) If it has to be transmitted from orbit or if the good old battery is good enough for you 3) If it has to be send from the asteroid belt directly 4) If so how you plan on dealing with a rotating earth? I could go on and on and on. This will be a popular question since it is so easily answerable (see my link), but I do not think you thought this one through $\endgroup$
    – Raditz_35
    Jul 13, 2017 at 12:05
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    $\begingroup$ One of the big problems of sending large amounts of energy from orbit to Earth is that you're basically building a death ray (or several ones). Anything that works for transfering that much energy is also instantly a WMD which can strike at large portions of the globe, if not anywhere. So political, legal and military (war, terrorism, sabotage, etc) questions have to be answered before deplaying this (in reality, of course in fiction you can always handwave them away). $\endgroup$
    – Autar
    Jul 13, 2017 at 14:37
  • $\begingroup$ Not worth adding another answer, but one more vote for "use it in space". Lots that could be done there more efficiently/easily than under gravity. If getting NRG to terra firma is a MUST then use whatever you are collecting solar wise in space to power dive ships that can hit a gaseous atmosphere and collect hydrogen, methane, etc. compress it and deliver that back to dirt side to be burned to generate power. Not very efficient. And any method you come up with will probably be expensive and net negative due to having to get it down here... $\endgroup$
    – ivanivan
    Jul 13, 2017 at 20:46
  • $\begingroup$ In that short a timeline, there is little need for or benefit from space-based power generation. Until you have orbital manufacturing going already, which would make use of the power in situ, the energy costs of getting generation facilities up would be too great for the return - easier to build more solar panels in the desert and transmit it a couple thousand kilometers than try to send facilities up out of our gravity well and around the solar system and then send the power back to Earth. $\endgroup$
    – pluckedkiwi
    Jul 19, 2017 at 19:06

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Personally, I would go a different route here.

Sending energy down to the planet, through all that atmosphere, will cause huge losses - the "cable down the space elevator" idea would probably be the most feasable, if you want to give your civilization the technology to build one.

But: why do that at all? The energy required for ground-bound use will be utterly dwarved by what your civilization uses in space if they set up operations in the asteroid belt (and I assume on other planets too). Mining and refining ores, manufacturing spacecraft, sattelites and whatnot from them, refining the fuel for said spacecraft... Heck, if you have lots of cheap(er than elsewhere) energy in space, data processing centres and server farms would probably be placed there too (assuming there's an efficient way to get rid of the excess heat without an atmosphere).

Also, note a big problem with using energy gathered in space down on earth: energy is not lost, only transformed. Which means, any "losses" while beaming down microwave or laser energy, AND the NOT lost energy "used" later, will in the end be converted into heat. Currently, the planet is at a certain temperature level where its temperature causes it to radiate off roughly as much energy as the sun's rays add to it - if there's an imbalance there, the temperature rises until a new equilibrium is reached (the higher the temperature, the more energy will be radiated off - there's much more complicated stuff in there too, like greenhouse effects and the exact formulas, but for a basic understanding saying it like this should work). So if you constantly bring in X amount of energy from the asteroid belt, the global temperature will rise by Y degrees because of that. Unless you want to compensate for the - more or less - directly usable energy you bring in by reducing the unfocused energy the sun adds with huge sunshade sattelites or seeding clouds to reflect more sunlight or whatnot, you will run into big problems.

Of course, that might just be where your story is going - in which case I recommend combinations of the other answers. Particularly the space elevator - not neccesarily as a huge cable, but because it makes delivering your space-batteries to the ground that much more efficient too.

If you don't have the material science for a full-blown space elevator, look into space fountains instead - basically, a magnetically-controlled round-trip system slinging containers up into space and catching them again when they come back down.

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    $\begingroup$ +1 if only for the consequence of adding energy to Earth, we're in enough trouble because of Global Warming without adding to our own woes. $\endgroup$
    – Matthieu M.
    Jul 13, 2017 at 19:19
  • $\begingroup$ No matter how much use for the energy you find in space itself, earth will always need some energy, too. And it may be cooler to beam it down than to burn fossil fuels. $\endgroup$
    – ths
    Jul 13, 2017 at 21:29
  • $\begingroup$ Currently we are several orders of magnitude from worrying about direct heating. And if we could make some kind of rocket fuel efficiently enough and ship it to space cheaply enough we could even net export energy. $\endgroup$
    – user25818
    Jul 13, 2017 at 22:44
  • $\begingroup$ The primary reason to send down is to have enough to get up cheaply. $\endgroup$
    – Joshua
    Jul 14, 2017 at 3:47
  • $\begingroup$ Well, pointers are good, but the issue really is that you can build energy generation industry in space WITHOUT EXPANDING into it. Our energy buget (by which I mean available production level) is so low that sending anything up OR down between ground and orbit is hideously expensive and will stay that way for a while now. Thank you, well thought answer, even if not exactly for my question. $\endgroup$
    – AcePL
    Jul 14, 2017 at 8:23
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Well a few ideas come to mind:

Focused electromagnetic radiation

Something along the lines of the microwave power station mentioned in other answers. Have a large maser (microwave laser) on your generation point and aim it at a secluded area of Earth for collection via a large collecting array. The collection site will have to be large due to beam scattering issues, which is actually a good thing, by spreading the power out it makes for less issues with atmospheric absorption or death ray style damages. This is currently thought to be the best and most feasible method, and has been studied fairly well with lots of information available about the particulars of how it would work.

Portable power storage

For this type of energy transfer you want things with very high energy density, which you then transport to Earth, this is not going to be very effective in general due to the high transport costs involved, especially if you need a soft controlled landing to transport it to Earth's surface, but with very high energy dense materials it might make sense.

The top of the potentials here, based on energy density, would be anti-matter, you would need a much more energy efficient method of producing it than is currently possible using particle colliders as well as other technologies for storage, transport and energy generation that do not currently exist, but if you had those a shipment of ~3 tons of antimatter could power Human society for a year (5.6x10^20 J / 9x10^16 J/kg = 6200 kg divide by two for the normal matter in the reaction = 3100kg).

More realistic options for energy carriers would be artificial hydrocarbons produced from asteroid and comet materials, or refined metals such as aluminum which can be unrefined to produced electricity. These would have fairly low energy density meaning that you would need some very efficient methods of shipping it to Earth to make it at all viable.

A possibly useful method, depending on it's availability in asteroid or other space mining, would be nuclear fission or fusion fuels. He3 has been theorized to be present in space locations produced by the solar wind, if we developed fusion power that could use this or other exotic isotopes available more readily in space I could definitely see mining for nuclear fuel as viable.

In terms of currently usable energy storage you really can't beat Uranium. If you do all of the dangerous refining and fuel processing in space transporting refined Uranium fuel to Earth would offer a very high energy transport capability.

Direct Connection

Far down the list of theoretical methods is one of my favorites, the space elevator. The whole problem seems really easy when you can just run a long distance high voltage power line from Space to Earth!

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  • $\begingroup$ #4, based on #2, would be "use the energy to complete energy-intensive manufacturing/refining processes off-planet, and deliver the goods planetside". If fuel refining is one of those processes, then the fuel for the delivery craft could be produced off-planet as well. This frees up the planet's existing energy resources that would otherwise be used to refine or manufacture products to be used elsewhere. $\endgroup$
    – Doktor J
    Jul 13, 2017 at 15:04
  • $\begingroup$ ^ This also has the benefit of not only NOT introducing extra heat into the planet's atmosphere when the energy is consumed, but also may REDUCE the existing on-planet heat load, as less total power needs to be generated on-planet since there is no need to power the refining and manufacturing processes that have been "outsourced". $\endgroup$
    – Doktor J
    Jul 13, 2017 at 15:08
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    $\begingroup$ I feel like running an extension cable from the asteroid belt to earth is a trivial problem. $\endgroup$
    – amflare
    Jul 13, 2017 at 16:16
  • $\begingroup$ +1 for producing hydrocarbons off-planet. Haven't thought of that. Rest is, as you say yourself, not very efficient. Except for space elevator, but wit that one, due to potential differences on the ends of the cable would not require, actually, an off-planet production of energy. Or, at least, not that much as is needed. And tech for that one is still far off. For so many reasons this one is a reject, too. $\endgroup$
    – AcePL
    Jul 14, 2017 at 8:25
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Find Wireless power transfer and use any exist technology, or invent one to suit your work.

Microwave power plant in SimCity use Microwave from satellite to earth (with picture below). In reality, Microwave power transmission (MPT) is used to power helicopter in 1964 (Experimental Airborne Microwave Supported Platform)
microwave power plant

Laser seem possible too. Nasa laser powered plane (2003)

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    $\begingroup$ SimCity also showed you the hazards, as I often had the Microwave power plant, and its surroundings, burst into flame. $\endgroup$
    – Michael Richardson
    Jul 13, 2017 at 17:33
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    $\begingroup$ @MichaelRichardson That's only if things go terribly wrong. If things are doing just what they're supposed to you're still pumping energy into the atmosphere (microwaves makes water molecules jiggle and last I checked there was a lot of water in the atmosphere) which would cause other problems. $\endgroup$
    – Draco18s no longer trusts SE
    Jul 13, 2017 at 17:58
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    $\begingroup$ @Draco18s Microwaves of particular frequencies make water molecules jiggle. There are other wavelengths of microwaves which are inactive against water; power transmission would likely use those. (That said, that doesn't mean they don't have other effects on the atmosphere.) $\endgroup$
    – R.M.
    Jul 13, 2017 at 18:42
  • $\begingroup$ Good one, but for levels required the stations would need to be fairly densely located, else we would have a Death Ray. And downsides are nasty when (and I point you to Murphy's Law here, so no if) things go sideways. But still a viable idea. Maybe stages of development and this one to be simply just first and temporary? Well thought out, thanks. $\endgroup$
    – AcePL
    Jul 14, 2017 at 8:32
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The obvious answer is to use as much in space as possible!

There are relatively easy ways of producing large quantities of metals and other materials from asteroids using space foundries; these are just large thermal focusing of the sun's energy using simple aluminum mirrors to melt the asteroids. Add a small centrifugal force and a melted ball can be separated by molecular weight for purification, then used for either further purification or recombination.

I think in space you could manufacture the same kind of heat-resistant ceramic tiles we used on the space shuttle to protect it from re-entry. You should be able to easily make very large (tanker sized) steel canisters to hold highly compressed, liquefied gases, hydrogen and oxygen, for example. Transport those to Earth, shielded by tiles and with a parachute splashdown, and use them as fuels to power electric generators. They burn clean, and the containers are non-toxic, and perhaps can be constructed in shapes that are even useful in their own right. To be clear, I am not talking about a few, but a production line of millions of them per year, or however many Earth (or a country) needs.

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  • $\begingroup$ Good idea except for the part that it requires extensive industry in space in the first place. But I will think on it, thanks. $\endgroup$
    – AcePL
    Jul 14, 2017 at 8:37
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Two space elevators.

Three if you want to send three-phase. (though given the distances, AC is probably a very terrible idea, speed-of-light and all.)

Imagine if you needed to get several gigawatts into Manhattan. You use the Queensboro Bridge as one conductor, and the Brooklyn Bridge as the other. No railroads, an insulation zone for a safe transition, the structure is the conductor. Get it?

You can energize each space elevator at several megavolts compared to each other, and half that compared to earth. Insulate the daylights out of the anchorage.

Do not run a railway up to the space elevator, require people come the last 10km in rubber-tired vehicles. As they cross the large insulating apron, they will bias up to the couple of megavolts, without realizing it. Just like a lineman can work on high tension lines with the power on, if he only contacts one of them at a time.

There is basically nothing special about the space elevators, except their structures are electrically bonded to assure they carry electricity well.

The reason not to do it with one space elevator is the voltage needed would be rather high, needing considerable insulation separating the two "wires". This would make it much more difficult to use the structure itself as both conductors, making it necessary to carry one conductor and insulation as useless deadweight. Any insulation failure could create an arc which could damage and sever the space elevator. Use two space elevators and you do an end-run around these problems.

This isn't a death ray

Almost any other form of energy transmission would be very damaging if it were abused. Not this. There isn't really a way to weaponize it. **

** as a power transmission method. This says nothing about any vulnerabilitie of space elevators in general.

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  • $\begingroup$ Upside: they are generating a nice heap of electricity on their own. Downside: length counted in thousands of kilometers means that if someone attempted to damage it in any point rest is a really big mass dropping down on earth. OTOH there's a lot of empty space at the equator, so it wouldn't be very bad, hopefully. But do we have tech for that? AFAIK max they did was 20 miles of cable from a space shuttle ways back ad they had to abort to prevent destruction of the shuttle. And it was rather thin cable... $\endgroup$
    – AcePL
    Jul 14, 2017 at 13:48
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Wireless power has problems - notable weather - and besides, it's covered on the Wiki

What you could try is a bit more direct: Refine metals, send them to the Earth's surface, and burn them. As you are in the Asteroid belt, there will be plenty of magnesium and aluminium silicates that can be refined to Aluminum and Magnesium respectively, with whatever energy is available - 24/7 solar power makes this easy. You can then launch large blocks of these metals into an orbit that intersects with that of Earth; arranging a landing mechanism might be hard, but not impossible - it's not like you need a gentle landing. Then, simply powder and burn the metal in power stations.

With an automated refinery in the asteroid belt and hence a steady stream of metal 'bricks', you have a continuous energy source.

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  • $\begingroup$ Good ideal. But convert energy to mass and convert back to energy is costly (low efficiency). Except they are any fictional material can store and release energy without so much overhead. $\endgroup$
    – Haha TTpro
    Jul 13, 2017 at 16:13
  • $\begingroup$ That is something to think on. Since we can generate much more power in space safely, "conversion" to mass is probably part of the answer - we can refine materials very sloppily, even, and it still will be a net gain. So @HahaTTpro points to downside, but it might be a much, much less steep slope to climb up to... Definitely a partial answer. Thanks. $\endgroup$
    – AcePL
    Jul 14, 2017 at 8:36
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Mirrors

The earth is already receiving power from space. The fusion furnace at the centre of the solar system provides Earth with 174 petawatts of power. It has the potential to provide much more, the total output is around 400 septawatts of power, far more that I would ever want to be beamed at the fragile surface of our tiny planet.

The obvious ways of directing more solar power to earth are lenses and mirrors; large lenses can be heavy, so mirrors are as sensible choice. There are a number of ways of receiving solar power. The most familiar are solar panels, but if you are directing a large amount of power to small location, you might want molten salt generators. Molten salt generators have two advantages. Firstly they are able to store power so you can handle demand fluctuations. Secondly molten salt is much better than molten solar panels.

The mirrors could have a control module in the centre. The module could have a vertical and horizontal set of solar powered wheels. Spinning the wheels in one direction will rotate the mirror in the other. This would allow us to direct the reflected energy.

Plausibility

Often the future doesn't involve new technologies, but rather existing technologies becoming cheaper. No known material is strong enough for a space elevator. Perhaps in the future new materials are discovered that could be used to build a space elevator. Then again, it was predicted that we would be able to live in all plastic houses... I guess we can now but why would we want to? Without a space elevator we are limited to various forms of beaming energy down to earth, and reflecting energy to existing solar power plant seems like an incremental step.

All of this technology could be made today. Putting mirrors in space would be prohibitively expensive today, but presumably prices will fall if industrial production is moved to space.

Sometimes you don't need power to be in the form of electricity. If a smelting plant needs something to be melted, concentrated solar energy could do the trick. Some malcontent complaining about energy prices? Be generous for a change and beam a free terawatt directly to their roof. In principle you could have an elaborate system of charging fancy lazcannons, and lend them to your goons. Sure you may be the power hungry leader of a futuristic mega-corporation bend on world domination. That doesn't mean that your CFO will let you hand out priceless prototypes to your incompetent minions... not when there are more cost-effective ways of vaporising your opposition.

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  • $\begingroup$ Good idea, but even small mirrors would act like a sail, and there still will be some gravitational force working it's magic on them. Whey would need some sort of a thruster pack to maintain them in place. Double that for collector mirrors (that would combine output of first stage mirrors). They would have to be resupplied regularly, unless some reactionless drive is available? $\endgroup$
    – AcePL
    Apr 8, 2021 at 7:54
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Someone thought of a skyscraper hanging from a geostationary asteroid. It is not possible with the current technology. I'll link the SE question about it. You could use this kind of space object to transport back to Earth in controlled conditions whatever you like.

If it is solar energy, you could use optic fiber to transport it from the asteroid to the surface, or you could even send a high energy laser beam through some vacuum tube until it reaches the ground.

Other materials like Uranium that you mine from the asteroids could be sent down by an elevator.

The building could be made using some high tensile materials and you could argue that graphene or carbon nanotube advances have made possible producing meter-long defect free structures of these materials.

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Slightly safer than directing a stream of radiation directly at a spot on the planet.

Scale up existing wireless power transfer mechanisms. You may need some handwavium to keep the magnetic field sufficiently concentrated for such long range power transport.

Generate power in space. Send electricity through a cylindrical coil of wire to generate a magnetic field.

Set up a coil of wire on earth. Point the cylinders at each other. The magnetic field from the space coil will induct an electric current in the Earth based coil.

So somebody could stand over the receiver and be absolutely fine**

Planes could fly overhead and be fine***

A Meteor hitting the space based coil and re aiming it slightly would be absolutely fine****

** As long as they don't have a steel belt buckle. if they do, they will get a very deadly wedgie.

*** As long as nothing made of iron is on board. Not sure if the electronics would be fried.

**** Best not to have any iron anywhere near the receiver.

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From Wikipedia: agriculture, mining, manufacturing, and construction consume about 37% of the total 15 TW (total Earth energy consumption).

Now, agricultural products are mass intensive so I don't think there will ever be a cost effective way to move them back to Earth (save maybe for an already built space elevator). Also, agriculture uses CO2 to produce food, so there must be a source of CO2 nearby. Down-porting meat or alcohol would be more favourable (as they are less mass intensive than grains), but even so the value is low. Now, mining and refining... dirty and energy intensive work. One could mine the asteroids - but to bring them back to Earth (or in Earth orbit) one must overcome large energy penalties. Also, zero g offer some unique opportunities (like alloys of components of different densities). Again, nuclear power won't need nuclear shielding in all directions (only impact shielding), considering that the Earth orbit is pretty bare.

So, I don't see much of a need to beam energy down to Earth - just to move energy intensive operations in orbit (like, for example, building solar panels). This assumes first, that we have resources already in orbit, and secondly that a reliable, inexpensive "downporting" technology exists.

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    $\begingroup$ Welcome to WorldBuilding Calin! If you have a moment please take the tour and visit the help center to learn more about the site. Have fun! $\endgroup$
    – Secespitus
    Jul 14, 2017 at 10:54
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    $\begingroup$ I don't think you have your numbers and units right... 15TW? If you mean 15 TWh, then this will be just electricity, not ALL energy. if you mean 15TW then do you think Earth consumes 53 PWh of energy a year? $\endgroup$
    – AcePL
    Apr 8, 2021 at 8:05
  • $\begingroup$ I just took some numbers from somewhere on the Internet... and probably didn't copied them right. $\endgroup$
    – Calin Ceteras
    Apr 9, 2021 at 9:12
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Atmospheres of the gas giants. Make a methane powered ship with a Jupiter scoop, enough energy to power man or space exploration for the next billion years or more.

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