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Actually this is not an idea for a book, I thought about it after reading this article. The power grid they propose for the moon would require a lot of electric cables and robots that bring power where the cables do not arrive. But even if the moon is smaller than the Earth a not too small range of operations would require distances in the order of thousands of kilometres. It would take a long time and a lot of resources to set up such a network.

I have in mind a completely different type of grid. The Moon in any case is not going to be as crowded as the Earth, if there were microwave beams crossing around they would have little interference, this is one of the few cases where wireless energy transmission would make sense. For the first period there could be different photovoltaic plants placed in such a way that at least one of them is in full sun light. Then the plant that is working transmits a microwave beam to a satellite in orbit that relays it to second satellite and then to a base on the side where it is night time. Each base acts as a recharging station for all the robots that work in the area.

Wouldn't it make more sense than a cable carrier robot based version?

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    $\begingroup$ Wouldn't it be much easier to ship a nuclear reactor up there and just not bother with cables or power beaming equipment ? Or alternatively, if you cant go nuclear put a few Satellites into orbit that beam power down. Similar to what you said but moving the panels into space / orbit. $\endgroup$
    – ErikHall
    Jun 28, 2023 at 17:27
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    $\begingroup$ @ErikHall It is meant for operations spread over large areas. Exploring the land. Prospecting for minerals, etc. Operation around a single generator would have a small radius. $\endgroup$
    – FluidCode
    Jun 28, 2023 at 17:30
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    $\begingroup$ The natural problem with this setup is that you are converting light (solar) into electricity, then back into light (microwave) and then again into electricity. There's going to be a lot of conversion losses. $\endgroup$
    – M S
    Jun 28, 2023 at 18:25
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    $\begingroup$ From the very article you link "Such direct electrical connections are preferable to microwave- or laser-based power transmission, which involve inefficiencies and can potentially present dangers to astronauts working in the area." In other words people paid to consider this rejected the idea you propose, that it would not make sense. $\endgroup$ Jun 28, 2023 at 20:52
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    $\begingroup$ Whilst you're at it, you might want to solve the issue of differential static charges being transmitted around the grid due to photoelectric effects (no earthing/grounding on dry regolith).. $\endgroup$ Jun 29, 2023 at 12:45

4 Answers 4

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While taking an economics course in college, we were divided into groups and asked to write a decision paper explaining our choice for how to dry one's hands in a bathroom to executive management. That experiment was enlightening. Without taking serious time to think things through, you're almost guaranteed to come up with the wrong answer.

Where are you getting your resources?

In a comment you surmised that:

panels built on the Moon, even if with lower quality and lower efficiency would be way cheaper.

That's not true. That's not true at all. Consider this chart:

enter image description here
Source: NASA

What that chart tells you is that most of the minerals you need are "minor" or "trace" elements. If you open the linked document, you'll learn that "minor" minerals comprise less than 5% of available material and "trace" less than 0.1%. So...

  1. You'll need significant mining assets to acquire useful minerals on the Moon.

  2. You'll need smelting assets to process those minerals.

  3. You'll need manufacturing assets to produce your panels.

  4. And for all of that you'll need people, food, administration/medical/security/etc....

Manufacturing almost anything on the Moon will be considerably more expensive than manufacturing it on Earth and shipping it. Notably because shipping doesn't require crewed flight and could be reasonably based on the belief that if you have as much infrastructure on the Moon as you suggest, then the Earth already has a cost effective solution for bringing materials to orbit.

Further, efficiency in a harsh environment is a big deal. Even if it were cheaper to build a less-efficient lower-quality panel on the Moon, the increased cost of operations due to increased redundancy, maintenance, and replacement could (and likely would) entirely negate the value.

What costs more: inefficient power beaming or laying cables?

There's a reason why hundreds of millions of miles of Internet cable have been laid in the U.S. The cost of laying cable here is lower than the cost of setting everyone up on wireless. That's changing over time, but only after technology has improved the stability, throughput, security, and traffic-handling abilities of wireless solutions.

You're running into the same problem. Satellites? Never. Way too expensive to build, place, and maintain with much to low efficiency. Beamed power (e.g. lasers?) Possibly, but every time you convert from one form of energy to another (e.g., electrical to photonic), you lose something. Then there's no such thing as perfect optics, and the laser must hit dead on your target, so little to no mobile power solutions using focused beam technologies. Just to make a point: wireless charging is still a novelty here because it's too expensive with too little benefit.

Conclusion

Keep It Simple! Unless the industrialization of the Moon occurs at such a late date that Clarkean Magic can be invoked, the cheapest solution will...

  • be the most power efficient,
  • require the least maintenance,
  • enjoy the longest Mean Time Between Failures.

Because transport costs occur only once and, I sincerely believe, will always be cheaper than mining limited minerals on the moon, smelting them, manufacturing goods, and hoping you don't need a lot of people to do that. (I know what you're thinking... automated equipment. O'course, by the time you shipped all that automated equipment up there you could have shipped your entire power grid and been up and running.)

In an environment that doesn't have access to abundant atmospheric oxygen and industrially available hydrocarbons, it's going to be very hard to beat wires, transformers, and lithium batteries. (And lithium isn't found on the list of minerals available on the moon... Neither is copper and a large number of minerals we use today.)

Success is benefited by technology, but it wholly depends on economics.

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    $\begingroup$ @FluidCode Not necessarily. Alloys could be used. Insulation is better than you're surmising. The reality is simply this. You write your story the way you want to, but if you're asking us to comment on the idea, you need to embrace both the pros and cons we offer you. In the long run, it's rarely the single answer you like best that's most valuable, but the aggregate of information that you can use to enrich your world and your story. But in the end, the cost of a single trip must be truly breathtaking to be less valuable than establishing mining & manufacturing on the moon. Breathtaking. $\endgroup$
    – JBH
    Jun 28, 2023 at 19:20
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    $\begingroup$ @FluidCode what about burring the cables ? $\endgroup$
    – ErikHall
    Jun 28, 2023 at 19:39
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    $\begingroup$ @ErikHall Good point! Buyring the cables will help. $\endgroup$
    – JBH
    Jun 28, 2023 at 19:42
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    $\begingroup$ You can't just lead with a story like that and not tell us what your decision paper said! $\endgroup$
    – Cadence
    Jun 29, 2023 at 0:18
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    $\begingroup$ @Cadence My group got schooled! We did a three-page analysis of why paper dispensers would be the best choice. Another group did a far more in-depth analysis that included customer reviews, industry costs and statistics, costs of maintenance, operation and deployment, the value of recycling.... they blew us out of the water (and proved hot air blowers were best). They were the only group in the class to get an A on that project. But what they really proved is that people who don't take the time to work through all the numbers and see the bigger picture are unlikely to get the right answer. $\endgroup$
    – JBH
    Jun 29, 2023 at 6:13
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Just store the power.

No, you do not want to use a bunch of expensive batteries when storing 15 days worth of power at industrial scales. What you want to do is store your power at an very large scale. Here on Earth, the best storage technique for large volumes of energy is hydro-pumping. On the moon, using a hydro-pumping station (but with Regolith instead of water) would probably still be cheaper than the wire around the moon or the microwave transmission method, but the moon is a very different environment than the Earth. It has less gravity, and much more extreme day/night cycles than we have here on Earth which not only reduces the effectiveness of some options, but opens up some new ones as well. I've done the math on a few things under Moon Conditions, and the winner appears to actually be a method that is grossly impractical on Earth, but pretty reasonable on the Moon.

Let's start off by creating a more discrete scenario so that we can talk in real numbers. The OP can adjust as needed for his setting. Let's assume you have 2 bases that each have a power need similar to a small town: about 10 megawatts. Producing 10 megawatts of power on the moon (during the day) takes about 100 tons of solar panels, plus about another 100 tons of supplemental hardware. If we assume you are transporting these from earth using current technology, that is about a 2.4 billion dollar investment... however, once space flight becomes a mass produced service, this number could drop to as little as 40 million dollars per base. You should assume we are talking an ideally cheap space program is in place before largescale colonization happens; so, it is probably a safe bet that your total solar powerplant cost (before you solve the night time problem) will be closer to 80 million dollars than 2.4 billion, but anywhere in this range is plausible.

Now let's take a look at our contenders:

Microwave Transmission

Microwave transmitted power loses a lot of efficiency each time you relay it. Even in a perfect vacuum, at relatively short ranges, you would be lucky to achieve more than 45% efficiency per transaction. If we assume your transmitters can perfectly focus the microwaves over thousands of km, you are still looking at a 3 stage relay system resulting in only 9% efficiency. However, in practice, those long distances will matter a lot and actual efficiency will probably be less than 1%. This means that even in a highly idealized scenario, you'd need over 10x as many solar panels to power the dark side of the moon as the day side using microwave transmission. So before you even factor in the cost of the transmitters and satellites, you are looking at at a 900 million dollar price tag in solar power plants alone... again this is super idealized. Using current technology, it would be somewhere in the hundreds of billions of dollars, maybe even in the lower trillions.

Using long-range wires

As for wires: Transmitting power through a wire loses voltage over distance, and the longer you want to go, the thicker you need to make it to reduce resistance. Running 64 amps of DC at 155,000 volts means that running a 1000kcmil wire would result in a 28% power lose, plus you'd have additional 10% loses at the destination when you try to invert that power down to a usable amperage resulting in a 72% efficient system... pretty standard for long-distance high voltage wires... but this is a very thick and expensive wire for so little power. A wire this size costs about ~530 million dollars and weighs about 26 tons. This adds ~310 million dollars under current lunar shipping costs, and only a few million under idealized future costs; so, if your future world has really cheap shipping, the cost of this much copper wire actually becomes a much bigger concern than the cost of sending it to space. That puts this solution somewhere between ~640 million and 4.3 billion dollars depending on tech level making it clearly cheaper than microwaves... but it comes with a huge problem. 1/2 of your wire will always be on the hot side of the moon where temperatures reach a boiling 120°C. As a wire heats up, its electrical resistance increases meaning that all of those thousands of kilometers of wire need to be buried pretty deep in order to keep them thermally stable. Here on Earth, it would cost about 3.4 billion dollars in equipment and labor to bury that much wire just 50-70cm under ground. On the moon, you'd have to go much deeper to reach thermal stability... so this method may in fact get to be more expensive than the OP's satellite idea if future tech is good enough at shipping and microwave transmission, but does not make any significant strides in trenching and burial techniques.

Using "Hydro" Pumped storage

A 10MW turbine costs about \$50,000-100,000 and weights in at 35 tons. If you decide to save on weight and spend more on materials, you could probably get a \$1,000,000 turbine down to about 20 tons. Pumped hydro has up to 87% efficiency which should be similar to conveyored sand. Your station needs to store 3600MWH of potential energy which at lunar gravity requires a pair of reservoirs equal to about 8.4 million cubic meters located at different elevations... but due to overlapping craters, such features are naturally common on the moon. This places your total power solution at somewhere between 95 million and 3.3 billion dollars... but like the wire issue, this becomes a gargantuan construction project with a difficult to assess cost to gather all those millions of cubic meters of regolith and terraform the craters into the actual forms you need. It's still probably the best solution that uses science that is well understood today, though.

enter image description here

A better near future tech solution: super conductor storage

The night time temperature on the moon is about -130°C which is very close to the operating temperature of a few kinds of super-conductors. Super-conductors can hold a massive charge and only suffer about a 5% loss on discharge (the storage itself is lossless). Now how MUCH power a super conductor can store before it hits its critical magnetic field capacity is... complicated to say the least having all sorts of things to do with the size of your wire, temperatures, exact materials, etc. Here it is really difficult to account for future technologies, but using some of the best super conductors currently be experimented with, a bit of refrigeration and daytime sun shielding techniques your results are... still wildly inconclusive. But future tech is your friend here because better super conductors are being invented all the time. If you were to invent a material that is superconductive at room temperature, you could make a passively cooled system that could store 15 days worth of power in ~24 cubic meters. Depending on the density of this super conductor, it could mean a "battery" that only weighs 30-100 tons, and requires practically no additional infrastructure. Depending on how expensive this material is to manufacture, you could be looking at powering each base for under \$100 million... assuming a lot of ideal future tech stuff.

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    $\begingroup$ Here on earth we do this only with water and only where nature already mostly prepared a reservoire for us. In the other cases its not economic viable. On the moon with much less gravity and much more difficult to build things, it would be even much less viable. $\endgroup$
    – LazyLizard
    Jun 29, 2023 at 10:46
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    $\begingroup$ @LazyLizard I would object, here is a fully artificial reservoire for a hydro power station. There are several of such stations around the world that have their reservoires built from scratch. Normal hydro power plants that use energy of falling water and not employ power storage are definitely build where there's enough natural flow, these only require enough flow to fill the delta between filling up daily and emptying on demand, which is about 100 times less than that's needed for a regular plant of the same power. $\endgroup$
    – Vesper
    Jun 29, 2023 at 12:52
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    $\begingroup$ @Vesper well yes but no, nature provided the mountain on which that reservoir is build. Of course the moon also has montains, but that does not help much if you use dust instead of water, wich will not flow freely down that montain through pipes etc. Also potential energy is proportional to the mass of the object and the strenght of the gravitational field. On the moon this is about 1/6 of earths, so for equal energy storage 6 times the mass has to be moved. $\endgroup$
    – LazyLizard
    Jun 29, 2023 at 13:43
  • $\begingroup$ @LazyLizard if this is what you meant under "mostly", I have to agree, the humanity is not yet able to erect mountains of this size. PS/OT I miss the formers in SMAC/X. $\endgroup$
    – Vesper
    Jun 29, 2023 at 14:59
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    $\begingroup$ There's just one problem with your proposal: lunar regolith doesn't flow. It's got a sharp, jagged shape that tends to interlock. It also tends to abrade whatever it's in contact with -- trying to run it through a turbine would be considerably more destructive than trying to run the turbine with the output of a sandblaster. $\endgroup$
    – Mark
    Jun 30, 2023 at 3:17
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The Moon is small. With the Apollo missions, the horizon is often only a few hundred yards away. A line of sight energy beam is not going to go far on the Moon before it leaves the surface entirely.

The main solution would be to use most of the power close to where it is generated. If you have plants extracting materials from the moon, those would use a lot of power. You can then ship the materials. The Nordic countries use their surplus hydroelectric power to smelt aluminium.

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  • $\begingroup$ Line of sight can be extended by using towers. On a level plain on the Moon, you'll have line-of-sight between the tops of two 30m tall towers that are separated by as much as 20km. In rugged terrain, you put the stations on mountain peaks, and they potentially will be able to see much farther than that. [P.S., I am not endorsing free-space power transmission. Wires are totally the way to go.] $\endgroup$ Jun 30, 2023 at 4:18
  • $\begingroup$ Yes. There are plans to beam solar power to a tower at the edge of the Shackleton crater. While this may not happen, it does make sense for this unique location. I wondered whether to mention it in my post, and left it out because the is hardly a 'power grid'. $\endgroup$ Jun 30, 2023 at 6:43
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Why do you want to make a grid?

The reason we make a power grid on Earth is because the place where we produce power, and the place we use it, are in separate locations.

The factors that affect where we produce power and where we use it are...

  • Location of natural resources for power generation

  • Location of natural obstacles for settlement

  • Location of natural values for settlement

  • Settlement spread, we want to live in many different places

As far as we can tell, there are two ways to create usable energy on Luna:

  • Solar panels

  • Nuclear fission / nuclear fusion

There is no need to place solar panels far away from a settlement. Why would we want to? There are no special places on Luna that are better than any other to place solar panels. There is no local weather to consider, since lunar weather always comes in "sunny" or "night" everywhere; there are no natural features that make solar panels unsuitable but settlement desirable; there are no natural resources that we risk covering or make less beautiful.

And there is no need to place a nuclear reactor far away from a settlement. Because there are no rivers/oceans that we need for cooling.

"But what about nuclear accidents?!" you say. This is much less of a problem on Luna because unlike on Earth you do not have fallout — i.e. materials lofting (no air to be lofted into) and falling out of the sky (no rain or wind to make it fall out) — in the same way.

Also, as Three Mile Island showed, you can reduce the radionuclide problem of an accident to a minimum with scrubbers. And whatever is left you simply vent in a direction away from the settlement, and let it Newton itself in a nice ballistic trajectory to a designated area.

So, to sum things up...

  • Every place is as good as any other to generate power

  • Every place is as good as any other to settle

  • If you can make one settlement self-sufficient, you can make all of them self-sufficient.

As far as we can tell, none of factors first mentioned for separating power production and power consumption by large distances exist on the Moon.

So why would you want to build a power grid on the Moon?

Hence...

There is no need for a power grid on Luna.

It makes no sense with centralised power production and subsequent redistribution on the Moon. There is no need to shunt power "thousands of kilometers" on the Moon.

So...

You are trying to solve a problem that does not exist.

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    $\begingroup$ The solar panels next to a settlement will be in the dark for two weeks out of every month, and at a very bad angle to the sun for much of the sunlit period. Storing enough energy to supply a major settlement across that gap would be enormously resource-intensive. The object of the grid is to enable continuous solar power from multiple solar installations at geographically separate locations. And nuclear power plants are too expensive and complex to just plop down wherever you need power, so they're no argument against grids. $\endgroup$ Jun 29, 2023 at 14:48
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    $\begingroup$ @Nosajimiki, There is no reason, in principle, why a nuclear power station must "churn through millions of gallons of water per day." What's important is, it must somehow be able to get rid of heat. If you can't "cool" it, then you can't generate any useable power from it. Power stations don't turn heat into electricity. They use the flow of heat from a source (the reactor) to a sink (millions of gallons of water) to generate electricity. There's no water on the Moon, but maybe they can find some other way... Then again, maybe not. Cooling anything in vacuum is a hard problem. $\endgroup$ Jun 30, 2023 at 4:30
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    $\begingroup$ @MichaelK, Re, "Reactors have already flown in space." Yes, but how many of those produced enough power to meet the needs of a self-sustaining colony? My point was that it can be done without having a natural source of water near by, but that doing it at city/industrial scale could be a significant engineering challenge. $\endgroup$ Jun 30, 2023 at 11:50
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    $\begingroup$ @MichaelK I agree Christopher James Huff. There may be many ways to store energy, but to store enough energy for the two weeks of the cold night on the Moon there is not a simple solution. A grid is better. $\endgroup$
    – FluidCode
    Jun 30, 2023 at 14:27
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    $\begingroup$ @MichaelK I am not the only one saying that such energy storage in not feasible. This is also written at the beginning of the article I linked and it is for a project that is being considered for a real implementation, not just sci-fi (maybe). $\endgroup$
    – FluidCode
    Jun 30, 2023 at 14:36

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