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There is a very very large dam in the middle of a desert; it operates similarly to the Qattara Depression Project, and was constructed both to power the areas south of it, but primarily for political reasons.

The dam has recently finished construction & operation has been handed off to a private company to operate.

However it is generating an incredibly immense amount of excess energy, even after so many things that need a lot of energy were built. This private company now wants to find a way to sell this excess energy. Unfortunately, there's nothing more to power further nearby, and environmental conditions prevent power-lines from being built to further away areas.

So, this newly formed company is faced with a problem, how does move this energy to where it can be sold & used without too much cost getting there?

Density & weight are not problems due to broad gauge & very high loading gauge railway line access to major ways being built to move materials for the construction of the dam. Salt water is abundant & can be assumed to be effectively free.

Technologies that would be available up until our own roughly early 1970s are available. The goal is to move large volumes of electricity without power lines at the lowest cost possible. What is the best way to achieve this?

EDIT: I probably should have described the geography better initially, to the south is the area where things are being powered, there isn't much of anything to the east further inland, west to the coast can be done easily but there isn't much of anything there, while to there north there's a lot but there's a large impassable area between the dam & the things that can be powered that can't be easily crossed by anything. The rail lines go to the south & to the coast.

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    $\begingroup$ If you can build heavy-guage rail lines, what exactly is preventing you from building power lines? $\endgroup$ Apr 14, 2023 at 2:47
  • $\begingroup$ @LoganR.Kearsley i probably should have described the geography better, to the south is the area where things are being powered, there isn't much of anything inland, to the coast can be done easily but there isn't much of anything there, while to there north there's a lot but there's a large impassable area that can't be easily crossed by anything. $\endgroup$
    – OT-64 SKOT
    Apr 14, 2023 at 2:58
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    $\begingroup$ Realistically they would just reduce the number of generators running in the dam and produce less electricity. They would save money by reducing wear and tear costs and also decreasing the number of people needed to operate and maintain the facility and also have redundancy in the event of a break down. If there is not enough demand, there is no need to produce excess supply. Dams don't have a fixed output, they can control the output by controlling how many turbines are active, and by controlling the water flow. The supply is produced to meet demand, not the other way around. $\endgroup$ Apr 14, 2023 at 3:14
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    $\begingroup$ @Corey, I think the problem the post is resolving is the company/governemtn wants to recoup the cost of constrction. If a dam can produce 100MW, you want to sell 100MW, not 5MW and never make up for maintenance costs. This happens a lot when a project is built to provide a supply with no demand. They either need to reach where there is demand or artifically create a demand. $\endgroup$
    – Sonvar
    Apr 14, 2023 at 16:46
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    $\begingroup$ (1) The "private company" would have noticed this problem beforehand, and not bought the company. (2) Energy intensive heavy industry does not build up as fast as you think it does around "recently finished" electric generating stations. $\endgroup$
    – RonJohn
    Apr 16, 2023 at 0:51

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One of the most energy-hungry processes in the world overall is the Haber-Bosch process, it accounts for more than 1% of our total electricity use globally.

So wherever you've got water, atmospheric nitrogen, and plenty of excess electricity, you bet somebody's going to use it to make ammonia.

(This is kind of a frame challenge though because while ammonia can be used as fuel for certain processes, it's much more valuable as a precursor for many other nitrogen compounds, like fertilisers or indeed explosives.)

P.s.: you could of course transport the green hydrogen itself that you make from the water but hydrogen transportation requires cryogenic or high-pressure equipment, and even then it leaks like crazy. Ammonia is nasty but can be handled with much more standard equipment.

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    $\begingroup$ Coincidentally scientists in Tokyo have apparently developed new iron based catalysts that will produce ammonia at temperatures a low as 100c but optimally at about 300c and at a pressure of .9 MPa phys.org/news/… $\endgroup$
    – Mon
    Apr 16, 2023 at 0:46
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    $\begingroup$ Alternatively if it is near a desert, desalinate water, if you don't want to sell it water crops. $\endgroup$
    – John
    Apr 16, 2023 at 3:08
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    $\begingroup$ And you can decompose the ammonia back to hydrogen, nitrogen and heat, it is a far better way to move hydrogen then directly moving hydrogen! $\endgroup$
    – Dan Mills
    Apr 16, 2023 at 14:07
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    $\begingroup$ There's ongoing research to making fuels beyond H2, called electrofuels. For example, you can imagine taking your hydrogen and combining it with carbon from atmospheric CO2, to make a hydrocarbon fuel, which could drop into existing engines. $\endgroup$
    – user71659
    Apr 17, 2023 at 5:06
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If you can't lay powerlines, but you can lay rails... electrify the rails, and use them as powerlines. Bonus: electric trains!

Or, use microwave links. Microwave rectennas can be up to 90% efficient; you'll need repeater stations to get around the curve of the Earth (or over mountains and down the other side), but as long as you aren't going too far with it, most of the energy will get where it's going.

But really... frame challenge: in the real world, people don't try to move electricity when it's inconvenient. Instead, they move energy-hungry industries to where the electricity already is. So, set up an aluminum smelter next to your hydroelectric dam, and sell the aluminum. That's easy to transport!

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  • $\begingroup$ t he rails just go to an o cean port & an area where the powerlines can reach, there are already plenty of energy hungry industries but there's m ore power than even they can use & there aren't that many more things where there isn't a closer source of cheap electricity, they've already tried that & there's still a lot more left to go. microwave links seem intresting tho. $\endgroup$
    – OT-64 SKOT
    Apr 14, 2023 at 3:33
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    $\begingroup$ I would agree with the frame challenge. I your world the designers royally screwed the pooch in building such a high capacity facility without appropriate demand. however, this has been done in real life, most notably in places such as Egypt, Sudan and Ethiopia. they built the structure in hopes to attract future development. Have the government of your world provide subsitites to allow companies come in to use your excess power generation capacity $\endgroup$
    – Sonvar
    Apr 14, 2023 at 16:52
  • $\begingroup$ If you don't mind some slightly larger energy losses, you only need one microwave relay - in orbit. $\endgroup$ Apr 14, 2023 at 23:55
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    $\begingroup$ @Clockwork-Muse If you can put a relay in orbit, you can just slap some solar panels on that and skip the hydropower.... $\endgroup$ Apr 15, 2023 at 0:40
  • $\begingroup$ @LoganR.Kearsley the dam would make a lot more electricity than a satellite $\endgroup$
    – Seggan
    Apr 16, 2023 at 1:11
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Frame Challenge

So, you have Railway access and a large amount of cheap Electricity.

Rather than transporting the Electricity, here is my suggestion: Encourage a power-heavy industry to setup near the Dam.

For example: Tiwai Point Aluminium smelter in New Zealand. It's in the middle of Nowhere, with no natural Bauxite around, instead it is supplied bauxite from Australia.

Tiwai Point from Wikipedia

Bonus points - you called for 1970s tech, that was opened in 1971.

Other factors as to why you might do this - there are other heavy industries that produce unpleasant by-products, which makes homing them near to major cities or population centers undesirable - especially if using 1970s tech (AKA Environmental Regs weren't a thing)

So, that is what I would do - partner with a heavy, power hungry industry to provide power in the middle of nowhere and use the rail network to ship out the manufactured products.

Guaranteed revenue stream for the Power Company, Economy grows etc.

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    $\begingroup$ well, in real life, all of the energy intensive industry moves to where power is cheap, so you would have none anywhere else. Partly because power simply can't be transported as such. $\endgroup$
    – camelccc
    Apr 14, 2023 at 10:45
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    $\begingroup$ @OT-64SKOT, you seem to have suck yourself in an unwinable perdiciment. large infrastucture projects have failed spectacularly because they could not resolve the supply/demand imbalance the project created. Seems like your project is doomed to be caught in the same imbalance. $\endgroup$
    – Sonvar
    Apr 14, 2023 at 16:55
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    $\begingroup$ well in real life, energy projects go get abandoned if power lines are a pain, unless there are political reasons to pay them to do nothing, which also happens. There are also very real limits on how long power lines can be. Also bear in mind the Three Gorges Dam 22GW peak is large enough to measurably affect the speed of the earths rotation. I don't know what size you are planning, but from your description its going to be so much water moving around it will affect the orbit of your planet $\endgroup$
    – camelccc
    Apr 14, 2023 at 19:48
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    $\begingroup$ any sufficiently energy intensive industry would relocate nearer to the source of energy rather than incur the cost of transporting it, if, for some reason, power lines are not a thing (which is a big question mark to begin with) $\endgroup$
    – njzk2
    Apr 15, 2023 at 21:20
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    $\begingroup$ Hydroelectric generation requires water to flow through the dam. If there's too much electricity, then irrigate the surrounding lands to grow crops. instead of sending it through the generators. $\endgroup$
    – RonJohn
    Apr 16, 2023 at 7:33
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Hydrogen

Split water into oxygen and hydrogen and ship the hydrogen back in tanks via rail.

Australia is right in the middle of basically doing this. We have vast deserts so we are building like half the world's supply of green hydrogen plants in central Australia which will be shipped overseas by ships

New hydrogen pumps hundreds of billions into economy

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  • $\begingroup$ I feel this answer can be massively expanded. Hydrogen is also much more like oil and gas, being able to charge a 'battery' very quickly by just pumping it in. It also requires energy, but the biggest concern is storing energy. If you store it and ship it like this worldwide it would be a huge boon to the energy economy. $\endgroup$
    – Trioxidane
    Apr 14, 2023 at 18:09
  • $\begingroup$ @Trioxidane but it's uneconomical for the same reason it's already uneconomical - hard to store, for example $\endgroup$
    – user253751
    Apr 17, 2023 at 14:52
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I see a lot of good answers so far, I don't want to steal from them too much but it is difficult since this is a problem already seen in the real world and the solutions provided have been proven viable in the real world. What it comes down to is finding an energy dense product that is both valued and easy to transport.

Ammonia is a good idea because the raw materials will be air and water, and with a hydroelectric dam there's going to be plenty or both. Shipping out liquefied oxygen and hydrogen are good ideas, that's valuable as fuel and raw material for other commodities produced at an industrial scale.

What I haven't seen suggested yet is synthesized hydrocarbons.

We have known how to synthesize hydrocarbons from electricity for a long time but it is rarely a viable commodity because we can get hydrocarbons easily from petroleum. If this is an environment where petroleum is scarce then producing hydrocarbons as an energy dense fuel could be viable. Consider the energy density of various materials that could be synthesized. Look at the chart on Wikipedia to see how well each stacks up: https://en.wikipedia.org/wiki/Energy_density

There will be a limit on how many rail cars that can pass by this dam so choosing products that can be shipped out by energy density, by mass or volume, would be important to get the most out for the least in. Getting the hydrogen for synthesizing hydrocarbons would be easy enough by electrolysis of water or a number of chemical processes that could be driven by electricity. The carbon for the process can be extracted from CO2 in the air, CO2 dissolved in the water (a process the US Navy is developing now for synthesizing fuel), or from carbon rich materials brought in on rail (such as sawdust, sewage/manure, plastic and paper trash, or many other things that would be cheap and abundant).

If there's an option to run pipes out then hydrocarbon fuels can be pumped through those pipes. Ammonia could be piped out too. Running cryogenic fuels through a pipe is likely impractical since it would be difficult to keep cold, and liquid hydrogen is cold enough to freeze oxygen solid which can create other problems.

Also, hydrocarbons are certainly useful for more than fuel. We use hydrocarbons for lubricants, hydraulic fluid, and even building material. Asphalt and tarmac are mixtures of heavy hydrocarbons and aggregate to make pavement.

One last thing I can think of right now is ice. People like ice. Use the extra electricity to clean up some water and then freeze it. I've heard of a power plant get in the ice business as a means to turn extra electric output into a valuable commodity. The ice would be bagged and sold to restaurants and such.

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The easiest way, in my opinion, is to simply compress regular air to a liquid, in pressurized (reusable) tanks that can be transported by rail, and when they arrive at their destination, the pressurized air can be used to drive electric turbines. There is some "round-trip loss" in this, but I have read that 75% of the energy used to compress the air can later be recovered.

It takes strong tanks, but you said that would not be an issue. Perhaps 1000 gallon re-usable tanks of liquefied air, and it is a train, so as many as you can pull at once.

This eliminates any need to purify water or separate or purify materials (air or sea water). Compressing air is relatively low-tech, it requires only electricity produced by the dam, and the air is free. Also, compression can be made more efficient as your technology develops.

Because it is low tech, the cost is relatively low also; the engines are "off the shelf", and if you want, I am sure your dam can hire (or already employs) many mechanical engineers capable of designing a giant air compressor.

You can also automate most of this production so it is all a quite robotic assembly line of filling tanks already on rail cars. Even with 1970's level computers, like the IBM 360.

Another advantage here is environmental; if the train derails, there will be no toxic clouds of anything threatening lives. There will be damage, perhaps tanks will rupture and explode, but the contents are as non-toxic as it gets.

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    $\begingroup$ minus transportation costs. what's the energy density? $\endgroup$
    – njzk2
    Apr 15, 2023 at 21:22
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Creating Portland cement requires a lot of energy and accounts for 8% of the world CO2 emissions. If you have limestone in the area, that could be a good way to use the energy.

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Desalinate Water, grow crops to make biodiesel

Desalinate water, which you can use to grow crops. You already have lots of empty land. Trees, grain, ethanol, or even cattle all have high energy densities. Use whichever works best on the available land.

If you want maximum energy density grow an oil crop like rapeseed or palm oil, biodiesel (plant oil) is actually more energy dense than crude oil, 42mJ/kg. If the local soil is not up to it, use some electricity and the Haber-Bosch process process to make your own fertilizer as Biziclop mentioned.

There are several way to desalinate so you can pick your method based on land availability and local water quality. Electrodialysis is likely your best bet if power is free, but Steam desalination works better with poorer technology but needs lots of empty land. As a bonus water production allow for more fluctuation in production than a normal power grid and you can sell salt for extra profit.

This is the only method that, hypothetically at least, can actually get you more energy at the end than you put into it.

https://www.researchgate.net/figure/Average-plant-oil-yield-showing-efficiency-comparison-among-different-major-oil-crops_fig2_325398464

enter image description here

https://www.sciencedirect.com/science/article/abs/pii/S030626191931339X

Desalination methods

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I will assume that the "the areas south of it" are completely isolated.


If it is similar to the Qattara Depression Project, you will have multiple canals leading from the depression to a much larger body of water, which is probably a sea or ocean.

While transporting goods upstream might not be particularly energy-efficient, your rails can be used to tow boats—similarly to the horse-drawn boat, but with mechanical horses (or, you know, simple carts with cables)—loaded with batteries containing excess energy.
If/whenever the wind is in your favour, wind-borne or wind-powered ships, featuring regular sails, rotor sails, or rigid sails, can be used.

Once these ships arrive, the batteries can be picked up by larger cargo ships and distributed to places further away.

Disclaimer: This is all slightly simplified (mostly because I barely know what I'm talking about), but it might offer a good starting point for a more advanced system. It could be that using solely the rails to transport the batteries is more efficient, but that requires some computations I am neither familiar nor at ease with. As for the batteries: I'm assuming the energy-efficiency and running costs of using Lithium-ion batteries is sufficient enough to offset the losses otherwise incurred.

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Bitcoins.

Probably your dam has some internet connection at least for the sake of receiving/transmitting some emergency signal. Also satellite Internet connection may be an option even in desert. The idea is that you install as much of mining equipment as possible and just generating crypto currencies, they need not very fast access to Internet but very large amount of energy. Then you convert the bitcoins to that kind of money which supports buying some other energy resources in a place where you need to spend the energy (you might need a good lawyer if you are going to spend crypto in too developed country which use to hate cash). That is not a real move of energy so it totally will not work if you need to move a significant percentage of energy produced on Earth, but if you are not going to spend more energy than money can buy - this trick is one of the easiest.

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    $\begingroup$ OP stated technology level of 1970s. $\endgroup$ Apr 16, 2023 at 17:09
  • $\begingroup$ Electronic computers existed in the 1970s so a computation center of some sort is not out of the question. Satellite communications was also 1970s technology. Large computation centers would be useful for things like weather prediction and breaking encrypted communications. Large data centers would need considerable cooling and with a large body of water nearby the cooling issues would be made much easier. Mining for bitcoin would be anachronistic but the general idea of a computation center is not. $\endgroup$
    – MacGuffin
    Apr 17, 2023 at 0:29
  • $\begingroup$ @CemKalyoncu Even better - you can be this universe's Satoshi Nakamoto :) $\endgroup$
    – user253751
    Apr 17, 2023 at 14:54
  • $\begingroup$ Most 1970's computers were slower than the dollar store digital clock on my desk. Fastest one seems to be around 10MFlops which 1/10 of 2$ STM32f4 series microcontroller. Sure a data center would make sense but digital currency requires at least 90's computing power to be meaningful. $\endgroup$ Apr 17, 2023 at 17:37
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From your description, it seems there are two regions of this country, if it's even a single country, and the dam is in the southern one. I don't see why else the coastal west would not have "much of anything there", while the presumably inland south and north are both teeming with people. It also seems that you've saturated the south's power market, to the point where it might as well be a hydropower utopia, and no amount of power hungry industry will put a dent in that. So you have to get the power to the north, but you can't go north. What to do?

Go west. Then go north. Submarine power cables are a thing, and have been since 1811, at least. And the north would not be settled if it were completely inaccessible.

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  • $\begingroup$ afaik submarine power cables of l engths comparable to the one required in this case weren't really a thing until the 1980s $\endgroup$
    – OT-64 SKOT
    Apr 16, 2023 at 21:54
  • $\begingroup$ Stuff built in the 80s was designed in the 70s. If this is one nation, a southern capital would want to work as fast as possible to appease a starving north, while a northern capital would want to work as fast as possible to connect with a suddenly powerful south. If it's two nations, it's just good business to get a connection going, so there will be a bit more patience. $\endgroup$
    – No Name
    Apr 16, 2023 at 22:39

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