The details don't matter, just that a large fraction of people have died (let's say 90%) and society has completely collapsed. It's only a year or two later, and people have started to gather together again and attempt to build communities. The leader of a large-ish (~200) band of people has a plan to rebuild as best as possible, and so plans to have everyone take up residence in a nearby city that is built near one of the US' hydroelectric power plants. This city has specifically been chosen so that the nearby hydroelectric plant can be restored and power can be available to the city.

Obviously there is a lot that can go wrong with this plan, but I'm only interested in one aspect of it. I'm handwaving away some details:

  1. Assume that the survivors manage to restore the plant
  2. Assume that the survivors are able to keep it functional for some extended period of time

Given those things, my question is:

Can a standalone hydroelectric plant actually be useful and provide power to a nearby city in otherwise modern USA? If not, are there any steps that could be taken to make it work?

The reason I'm uncertain is things like:

  1. Our power grid is quite complicated, and it isn't obvious to me if modern day power plants can even really operate on their own
  2. I'm not quite sure if power plants are actually designed in such a way that they provide their own power - I wouldn't be surprised if an external power source (even if just generators) is required at various parts
  3. Presuming that the plant can operate on its own, I'm not sure if that means it can power a city that is likely connected to many other places in the grid. You might end up effectively attempting to power half the nation, which obviously isn't possible.
  4. It also seems likely that the plant wouldn't be tied directly or even closely into a city anyway, and so getting power to the city would require a major overhaul of infrastructure.

In terms of power usage, the plant itself should be more than sufficient. Looking at the list of US hydroelectric plants, even the smallest generates roughly 1.3GW of electricity. We're talking roughly a couple hundred survivors, and even if they each have their own house and use electricity at standard US rates (peak at roughly 20kW) that still leaves room for tens of thousands of houses. Presumably only logistics will be an issue for our survivors for quite a while.

  • 3
    $\begingroup$ You don't need a city - 200 people is a small village. There are many hundreds of small dams (in rural North America alone) easily capable of such tiny amounts of power. $\endgroup$
    – user535733
    Commented Jun 27, 2019 at 17:12
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    $\begingroup$ If they are capable of restoring and maintaining a hydroelectric power plant then they are most certainly able to restore and maintain some cables and transformers. Restoring and maintaining the power plant is much more difficult than maintaining a small grid. $\endgroup$
    – AlexP
    Commented Jun 27, 2019 at 17:23
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    $\begingroup$ That's not a list of all the hydroelectric plants that is a list of the largest, of course the output looks huge. there are plenty of small hydroelectric plants in the US. Literally hundreds many of them are quite small. esajournals.onlinelibrary.wiley.com/doi/full/10.1002/fee.1746 $\endgroup$
    – John
    Commented Jun 27, 2019 at 17:49
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    $\begingroup$ Hardware's not a problem. The problem is finding enough wetware with the knowledge -- or finding enough smart wetware plus a full seat of comprehendable user manuals. $\endgroup$ Commented Jun 27, 2019 at 18:18
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    $\begingroup$ According to the documentary "Fallout New Vegas" a big hydroelectric power plant is very useful indeed :) $\endgroup$
    – Fels
    Commented Jun 28, 2019 at 7:23

9 Answers 9


On September 28 2003, Italy experienced a nation wide black out.

After three hours, energy was restored in northern regions. Electricity was restored gradually in most places, and in most cities electricity was powered on again during the morning.

Energy was restored first in the northern region because there is where hydroelectric plants are located, and they could be used to power back the other plants, needing electricity to start up and operate. Ref.1 Ref.2

As long as you isolate the network that you want to supply from the network that you don't want to supply, you can use the hydroelectric plant as standalone for quite some time. (this addresses your points 2, 3 and 4). You "just" need to know the schematics of the network.

Moreover, one of the advantages of hydroelectric plants it their flexibility

Hydropower is a flexible source of electricity since stations can be ramped up and down very quickly to adapt to changing energy demands. Hydro turbines have a start-up time of the order of a few minutes. It takes around 60 to 90 seconds to bring a unit from cold start-up to full load; this is much shorter than for gas turbines or steam plants. Power generation can also be decreased quickly when there is a surplus power generation.

This is particularly important if you are supplying a relatively small city with not too much load, where load fluctuations might be relatively large.

  • 1
    $\begingroup$ I've already given you thumbs up. I was going to say the same thing. Other events show the same general thing. en.wikipedia.org/wiki/Northeast_blackout_of_2003 The generating station on Niagara Falls never went off line, and the city of Niagara Falls never went dark. The station was one of the "anchors" when the grid was being restored, and allowed the communication grid to be powered to help stations coordinate as they came back on line. $\endgroup$
    – puppetsock
    Commented Jun 27, 2019 at 17:31
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    $\begingroup$ Gnitpique: simply because the OP placed a "hard science" tag on their query, you might consider placing links to newpaper or journal articles for the event & history in question -- a source other than Wikipedia -- in order to satisfy the "other citations" and "empirical evidence" requirements. WP itself claims that it is is not a reliable source for academic writing or research which means it really can't be used to defend a hard science response. $\endgroup$
    – elemtilas
    Commented Jun 27, 2019 at 17:32
  • $\begingroup$ @elemtilas, added reference to italian newspaper of the period $\endgroup$
    – L.Dutch
    Commented Jun 27, 2019 at 17:37
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    $\begingroup$ Although we shouldn’t trust a source that anyone can edit anonymously, Wikipedia articles do usually have links to more reliable sources. This makes them more useful than a typical web search. $\endgroup$
    – WGroleau
    Commented Jun 28, 2019 at 14:07
  • $\begingroup$ @WGroleau, related $\endgroup$
    – L.Dutch
    Commented Jun 28, 2019 at 14:12

Hydroelectric dams are definitely not maintenance-free, nor are power grids. You have three life-threatening problems for your small band of experimenters.

1) Grid power is really dangerous and complex for the inexperienced. It's quite possibly fatal for the new, inadequately equipped, untrained lineman or electrician who it trying to puzzle out the city's electrical network.

Expect several quite nasty casualties before your new settlers figure out how to isolate their neighborhood from the larger (uncontrolled) grid and energized. Expect a lot of destroyed hardware and perhaps a few more casualties before they learn how to control phase, voltage, and amperage reliably.

2) On the dam itself, your new crewfolk are also trying to handle high volumes of high pressure water through the turbines and the spillways. Again, without proper equipment or training, expect some on-the-job casualties as they learn the hard way.

3) Finally, the dam itself requires maintenance and observation lest the structure fail catastrophically. One hopes that among the new settlers are a skilled hydrologist and a good structural engineer, because repairing a breached dam is definitely another skill you don't want to learn on-the-job...and one hopes the settlers' neighborhood isn't downstream of the breach.

  • $\begingroup$ Keep in mind: this query has a "hard science" tag attached: you need to provide external links to reliable academic, scientific or engineering related resources. Wikipedia does not count. $\endgroup$
    – elemtilas
    Commented Jun 27, 2019 at 17:35
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    $\begingroup$ Wikipedia does count. "arXiv can be quite good for citations, though Wikipedia is usually OK too." From the hard-science tag description. $\endgroup$ Commented Jun 27, 2019 at 19:30
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    $\begingroup$ And worse, the casualties will be from the smartest electrical types which you do have; which means each replacement is even dumber... this was a constant problem on Japanese ships and Forrestal when the damage control teams were fighting the damage and got killed by it... $\endgroup$ Commented Jun 28, 2019 at 14:20
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    $\begingroup$ On the subject of maintenance, you want a gravity dam like Grand Coulee rather than an arch dam like Hoover: there's far less to go wrong. $\endgroup$
    – Mark
    Commented Jun 29, 2019 at 1:07


With a little work it is completely possibly, you just need to cut off unused parts of the grid. This can be done by flipping switches on lines individually or going to transmission stations a shutting down different parts. You are either using an existing microgrid or creating one by cutting apart a larger grid. Grids have to be built to be sectioned off, otherwise every downed powerline would shutdown an entire city. Many places even have existing microgrids for military bases, college campuses, and hospitals. Small power plants often have small local grids as well.

Not only can most hydroplants supply their own power most are designed to run that way, separate generators may be used for start up but the powerplant runs off its own power, it does not make a lot of sense to build parts of a power plant that need anything but the plants electricity for normal running, it just adds unneeded complexity and points of failure. There is not actually much to smaller hydro electric plants.

This does not mean it is easy, you need skilled technicians to close off the grid and to keep it running, but an existing microgrid will make it easier. You also need maintenance, which dam will determine how hard this is. Some dams need little upkeep in an off themselves at least compared to others, this is determined by size and design. There is a big difference between the hoover dam and the Rutherford Creek dam. There are actually a lot of small hydroelectric dams which are fairly low maintenance. The advantage of a small dam is you literally can get away with one person running it.

  • 1
    $\begingroup$ No need to cut; the grid is full of throwable switches that let you cut off sections of line. There are 3 within a block of my house. $\endgroup$ Commented Jun 28, 2019 at 15:41
  • $\begingroup$ @Harper very true I will change that. $\endgroup$
    – John
    Commented Jun 28, 2019 at 19:19

How large is the plant?

Here in Austria there are lots of small hydroelectric power plants. Often they are old saw (or grain) water mills which have been converted to electric power generation. They produce around 100kW or even less.

Unfortunately I can’t find good sources but I think they are quite simple and maintenance free, like a small rooftop photovoltaic system or small wind turbine. Just a generator and an inverter, no complicated high-voltage lines, controlling etc.


There are already some excellent answers to this question, particularly L.Dutch explaining that hydro is suitable because it is often contracted by network operators to provide 'black start' capability to provide power to a failed network and user535733 explaining that it may be unsuitable as dealing with mains power is dangerous and the maintenance of a hydro plant is complex work.

To build on the existing answers, I would suggest that for your small group what you need is a small local hydro scheme. This will be one that is already designed to supply a community, so the required cabling will already be there, and it will be less complex to maintain than a large national scheme. See for example the projects highlighted here: https://www.hydro.org/policy/technology/small-hydro/. The Bowersock Mills project on the linked page, before extension, claims to be capable of providing power for 1,800 homes. This will be 1,800 homes at the current rate of consumption in the US and it would be fair to assume that in a post-apocalyptic world that people would use less electricity overall. This means that your group would be able to expand considerably using a system of this size alone,.

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    $\begingroup$ "it would be fair to assume that in a post-apocalyptic world that people would use less electricity overall" - I don't think that is true at all. If a small (<10,000) group of people have access to a medium sized hydro plant they will have lots and lots of cheap energy. They might well decide to use it for heating (getting access to gas or oil for space heating will be hard; getting access to wood is a lot of effort they can better spend on other things). There are probably lots of other reasons to be profligate with electricity when it is essentially free ... $\endgroup$ Commented Jun 28, 2019 at 12:42
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    $\begingroup$ You just described Ontario @MartinBonner ... $\endgroup$ Commented Jun 28, 2019 at 14:21

You're too late

The ability of hydroelectric plants to run independently has been lost.

In an apocalypse, without competent people to keep it up, the power grid is going to fall apart. Getting it back online will depend on Black Start, the ability of certain plants to self-bootstrap, get to full power and feed the grid to feed other plants so they can power up. Most plants cannot do this; they require power from the grid to spin up.

A thermal (coal/gas/oil) plant takes up to 10% of its generating capacity just to get on its feet - for fuel preparation (powderizing coal), feedwater pumps and blowers. (all these, plus RBMK and CANDU reactors, are water-tube boiler designs, which absolutely require continuous feedwater). So for thermal plants, blackstart is out of the question because the diesel generators would be positively enormous.

Nukes have local diesel generators for in-plant needs (mainly, core cooling after shutdown), but they don't blackstart for policy reasons, and because of that, they're not physically equipped to blackstart. It might be possible to hack one to blackstart, but it would take months.

Wind and solar can't blackstart for policy reasons. They use inverters whose software is specifically written to follow the grid and shut off if unable (see UL 1741). Some windmills physically lock-sync with the grid, spinning at a constant rate. They were never conceived to be blackstart and wouldn't be trusted, because a thermal plant could take damage (water-tube boilers) if clouds or calm suddenly shut off its startup power. Although software can be rewritten if key people survive.

So now we're down to hydro. As it happens, almost every hydro plant was built with a small "donkey" turbine whose solitary purpose is to power the station during station blackouts. Electrical needs of hydro plants are small - just control circuits, lighting and main-generator excitation - which means the donkey turbine can blackstart the plant. Just one problem. The bright bulbs in the power industry have

  • been replacing cheap-but-weird donkey turbines with common-but-expensive diesel generators, to provide their blackstart capability, and
  • expecting grid operators to pay them to maintain the blackstart infrastructure. To which grid operators have been saying NO, because they contract out blackstart capability to the lowest bidder.

As a result, black-start capability has been stripped out of almost all hydro plants. Getting the general grid back up requires a Rubik's Cube of sequencing plants, and that requires high trade expertise to make that work, in 4-5 "knowledge pinch points". It might survive a Thanos snap, but a 90% culling? You're bound to lose a key element.

Heck, it would be enough to lose a key power line or substation, and that could be due to enemy action.

Solar/battery tech to the rescue

Superstorm Sandy. Some of the most powerful people on earth are riding out the storm at home, smug with their new solar panels. Power goes out and remember UL 1741? Their solar system dutifully shuts off, while they shiver in the dark going "WTH my $40,000 solar system?"

Anyway, this woke people up, making it now possible to market technology like Tesla PowerWalls etc. that allow houses to use their solar panels (and batteries) to stay up during blackouts.

So, in your apocalypse scenario, your people won't even bother relighting the grid. They will either live in those homes, or go strip those systems out of homes that are in the wrong location, or combine tech like that to supply industry as needed. Maybe they could even put some on a hydro plant and get it black-startable LOL...

Hydro still needs power

One problem with all hydro dams is they are bombs. The dam holds back a tremendous amount of potential energy. If unleashed, it will blow the dam and wipe out communities and crops downstream. If unmanaged, it may be unleashed.

For instance if you followed the Oroville crisis, that dam would've been in a world of hurt if your apocalypse hit February 1 2017. At the very least you need to open enormous spillway gates from time to time. These are normal dam problems. You need the guy there who knows when to do what, and there needs to be electrical power for him to do that. In your scenario, the dam is a consumer of power, not a provider.

So you could actually have a problem with hydro dams starting to fail, and this will be similar to the problem of nuclear plants cooking off if their core cooling isn't attended to. It will be a serious demand on the finite skill of your survivors.

  • $\begingroup$ Could a 750KW diesel electric barge tug provide the power to permit starting a large hydro facility? $\endgroup$
    – K7AAY
    Commented Jun 28, 2019 at 20:37
  • 1
    $\begingroup$ Or cut the lock at the local CAT distributor, sure. Large diesels are readily available @K7AAY (in fact that wasn't the problem at Fukushima), but that only works if all the connecting apparatus hasn't been torn out too. $\endgroup$ Commented Jun 28, 2019 at 21:11
  • $\begingroup$ I was visualizing Grand Coulee en.wikipedia.org/wiki/Grand_Coulee_Dam and checked on the barge tugs which run up and down the Columbia. But, then, BPA.gov owns the dam AND the grid hereabouts, so surely they wouldn't... $\endgroup$
    – K7AAY
    Commented Jun 28, 2019 at 21:21
  • $\begingroup$ FWIW: Given time and some labor force and ideally someone else to swap ideas with - and better still a small team of somewhat similar people - I'd expect to be able to handle the electrical aspects of Blackstarting any Hydro, wind or solar system - even if there was/ had been software designed to thwart me. Mechanical & operational aspects that need advanced knowledge may foil me in some situations - eg stopping a hydro turbine over running destructivel - or a wind turbine in some cases. Nuclear I'd steer clear of as I know just enough to know that I don't know nearly enough to do it safely. $\endgroup$ Commented Jun 29, 2019 at 2:33
  • $\begingroup$ Exactly. Avoid nuke, focus on hydro... what could go wrong? or or Seriously, blackstart is a challenge to retrofit even when suppliers are available. It's not as simple as giving a UL 1741 generator a sinewave heartbeat. $\endgroup$ Commented Jun 29, 2019 at 18:11

Yes. Complexity is scalable. Both of my grandfathers were electrical engineers and one of them was the resident electrical expert at a hydroelectric dam in Arizona. Complexities can be managed to meet lower power requirements. A single person can operate a fairly large dam, so there is not good reason why he could not operate a much smaller one or a subset of its functions. As with automobiles, older hardware is in some cases easier to use as a fallback because the complexities of the larger grid or more computer-driven setup are emergent rather than baked-in. Either way, a turbine is a turbine and it would not be infeasible to draw power directly from them, circumventing any needlessly complex control or routing mechanisms. To prevent overload issues related to using a large-scale network to supply energy to a relatively small community, a single turbine can be used and the others left idle. As with all generators, turbines are responsive to load in the amount of electricity they will produce. Reduce the load, and the blades will rotate more freely, simply letting water pass through. Increase the load, and more of the kinetic energy from the water will be absorbed. Floodways and spillways also act as overload circumvention, by regulating the amount of water let into the turbine pathway versus the amount diverted, so even with a very crude mechanical control system the power supply could be kept nearly constant, or within a threshold. The low-maintenance argument used elsewhere in this thread applies, but any major repairs would take an experienced crew and heavy equipment, and be very risky if the dammed area is not drained in case of structural integrity issues.


Getting an AC generator online is possible. It may follow the structure of a 1960's generator I have at my house, and the problems bringing it back online.

My generator is a two-stage generator.

The high power side is an AC alternator. The rotor is driven with a DC field and spun inside the fixed stator, which connects with the AC load. The frequency of the AC is controlled by the shaft rotary velocity. The voltage is determined by the DC field strength and the rotary velocity. For a hydroelectric dam, both of these control functions could be implemented by a person riding the controls. With some cleverness, the existing controls could be re-applied.

Notice that this AC alternator requires DC power, delivered through slip-rings, to generate AC power. "Blackstart" is a bootstrap problem.

This power generation system has a lower-power stage that is a DC generator on the same shaft as the AC alternator. It uses a commutator through brushes on the rotor to provide DC. Its exciter stator field is a coil powered by a stream of DC current. Increasing the exciter current increases the DC voltage out, which increases the high-power field strength, which increases the AC output voltage. The DC generator exciter winding is driven from its own DC output through a control system (in the simplest case, an adjustable series resistor).

There is no external source for the initial current needed to run the exciter. How is a "blackstart" bootstrap performed?

It turns out that the system is initially driven by residual magnetism in the exciter iron poles. They are energized by DC, and are of a type of iron that retains a small field. In effect, having once run the generator makes the exciter field core into a low-strength permanent magnet. Spinning the rotor makes some power, which adds to the exciter field, which increases the output of the DC generator, which increases the exciter field... and bootstrap happens.

What if the residual field is completely gone? There are several approaches. First, the ambient Earth magnetic field may be sufficient to bootstrap. Second, a pulse of electric current delivered to the field core will induce a residual field. Third, a permanent magnet could be used to apply some initial magnet field to the exciter core.

If I were faced with a small hydroelectric dam, I would expect to find something like this. After two years, there would still be sufficient residual magnetism to bootstrap the process. Because I would start with a single generator, there would no issues of synching to the other generating equipment.

This question calls for "hard science". I haven't included any numbers or formula, but I have referenced how small-to-medium AC generators work. The voltages and currents involved will scale with the installation. I would feel confident that given a small hydroelectric plant that has only been down for two years, I could handle the electronics and control system part to bring it back online.

  • $\begingroup$ We can do it! :-). If your residual exciter magnetisation is truly zero we can use a BLDC type washing machine motor (say 400 Watts), or an e-bike or e-scooter - up to some kW depending on model or just about anything with a permanent magnet motor or alternator to act as an alternator. Certainly enough to excite an exciter. We could lash up a basic wind turbine, or given the available water flow, a pelton wheel or under/over shot type water wheel or ... . If there are any PV panels on nearby roofs they would be eminently usable. ... $\endgroup$ Commented Jun 29, 2019 at 8:01

Given time and some labor force and ideally someone else to swap ideas with - and better still a small team of somewhat similar people - I'd expect to be able to handle the electrical aspects of Blackstarting any Hydro, wind or solar photovoltaic system - even if there was/ had been software designed to thwart me.

Mechanical & operational aspects that need advanced knowledge may foil me in some situations - eg stopping a hydro turbine over running destructively - or a wind turbine in some cases.

Nuclear I'd steer clear of as I know just enough to know that I don't know nearly enough to do it safely.

Gas turbines are a maybe perhaps.

References: Some more later maybe but

Sort of anyway. ME electrical,
50+ years "playing" in many areas.
Bring it on :-).

ie I'm saying that, based on what I think I know I believe that there are numerous people "around" who could restart many power plants. Even power stations such as the ones mentioned where diesel engines have been used to provide excitation current for large alternators. There will usually be a way given enough time and will, and as long as the zonbies really aren't coming back.

Questions welcome.

  • $\begingroup$ I expected maybe a few downvotes and dnsarky comments, or just maybe some positive response, but not utterly zero reaction :-). Must be night time in the Northern hemisphere population concentration centres. $\endgroup$ Commented Jun 29, 2019 at 7:56

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