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Previously on the same setting (:

  1. How close is too close for a human habitation to be near an erupting volcano?
  2. What factors could delay the rescue of a small group of survivors on a Pacific volcanic eruption?

TL;DR synopsis: early XXI century, south pacific island, VEI 4~5 volcanic eruption, survivors find shelter in a mansion atop a high cliff by the seaside. Rescue seems to be taking forever.
Hard survival psychological thriller mood.

The survivors find out that the Ash Manor (the stonemasonry mansion by the seaside cliff, singed by but still defying the erupting volcano) has elecricity. Rather strange, since everything else in the island melted in the lava flow, including one cell phone tower nearby.

The island's power plant is offline, and they discover that the power source of the manor is:

  • No visible features, at least from the mansion grounds.
  • Somewhat limited in output.
  • Not magical.
  • Not alien.
  • Not from the future.
  • Not geothermal.
  • Not nuclear.

How does the Ash Manor get its electrical power?

Looking for to answers.

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  • $\begingroup$ Not nuclear, or completely not radioactive? $\endgroup$
    – user8827
    Apr 14, 2015 at 6:10
  • $\begingroup$ @SeanBoddy lets rule radioactive out for the sake of simplicity. $\endgroup$
    – Mindwin Remember Monica
    Apr 14, 2015 at 6:19
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    $\begingroup$ Do you have any specific metrics for 'limited in output?' The options are pretty narrow at this point and it would help to know what we're up against. $\endgroup$
    – user8827
    Apr 14, 2015 at 6:22
  • $\begingroup$ What do you try to tell with CEI? $\endgroup$
    – Zaibis
    Apr 14, 2015 at 11:20
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    $\begingroup$ What's the problem with a geothermal generator? A volcanic island would in fact seem to be the ideal place to build one. $\endgroup$
    – Mike L.
    Apr 14, 2015 at 13:11

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The simple, obvious answers are either a gas-powered generator (like @DanSmolinske suggested) or just having a bunch of batteries in the basement (charged from the island's grid before it went offline).

For a more exotic and location-specific power source, consider some form of tidal power. For your scenario, a tidal lagoon / tidal barrage may be the best option. If the manor is on a cliff, there could be a cave at the shoreline with a small dam inside. As the tide rises, it goes through sluice gates into a reservoir. At high tide, the gates are closed and the water goes out through a generator, creating power.

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  • $\begingroup$ I was going to say, "subsurface tidal or wave generator." $\endgroup$
    – Zither13
    Apr 14, 2015 at 13:49
  • $\begingroup$ @Zither13 yes, this is how the story went. the cliff could be hollowed out with underwater channels. The vents could be used to several purposes inside the manor. $\endgroup$
    – Mindwin Remember Monica
    Oct 28, 2015 at 16:15
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You say "not nuclear" presumably because you want your power source to be hidden and credulous, and the idea of a secret, private, autonomous nuclear power plant stretches credibility.

I'm going to propose a sub-type of nuke power called Radioisotope Thermoelectric Generator. I think it actually works rather well here. It is small, requires no maintenance, and has existed for decades. RTGs are used to power the Voyager Space probes, which were launched in 1977.

Additionally, RTGs provide very low levels of power (on the order of hundreds of watts), and over the years their power output drops. This fits well with your desire that the source be limited.

They are generally used in remote locations, where tampering is not a concern and sending someone to perform maintenance is hard - space probes, Arctic lighthouses, etc. An isolated geological monitoring station could fit the bill.

Wikipedia article: http://en.wikipedia.org/wiki/Radioisotope_thermoelectric_generator

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  • $\begingroup$ Who in their right mind would use this to power a mansion? This seems WAY too limited $\endgroup$
    – gillonba
    Apr 14, 2015 at 20:35
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    $\begingroup$ @rotard -- the RTG systems in space service (Voyagers, Cassini-Huygens, etal) aren't even 10% efficient at converting heat to energy as they rely on thermocouples for this task. State-of-the-art designs using alternative conversion technologies could achieve efficiencies of 20 to 30%, which would make kilowatt scale RTGs feasible; in addition, waste RTG heat could be picked up by a heat exchanger and used for space heat in a terrestrial application such as the one proposed here. $\endgroup$
    – Shalvenay
    Apr 14, 2015 at 23:29
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    $\begingroup$ @rotard -- furthermore, many of the heavy loads in a house are heat loads (space heat, cooking, clothes drying), and the major motor loads are compressor motors for central A/C or a heat pump and refrigeration. However, when you have a big fat waste heat source (RTG) in your basement, absorption cycles become practical, and you can use them to either refrigerate/cool or concentrate heat -- imagine cooking on a stove that used hot water and oh, <1A of current as its only inputs! $\endgroup$
    – Shalvenay
    Apr 15, 2015 at 0:04
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    $\begingroup$ @rotard And who in their right mind would build a mansion on top of a volcano on an uninhabited island in the middle of no-where? We are clearly dealing with a Bond villain. :-) $\endgroup$
    – codeMonkey
    Apr 15, 2015 at 11:15
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    $\begingroup$ More seriously, I would envision the island as having been inhabited, and then a catastrophe (previous eruption?) led to its abandonment. A university Earth Sciences department then installed a geological survey mission to learn from the volcano. Eruptions would coat solar panels with ash, wind requires maintenance, geothermal requires a constant temperature, which the shifting lava dome impedes, no one is going to resupply the station with fossil fuels... so the only option left is an RTG. If desired, the team installing the monitoring equipment can become your castaways. $\endgroup$
    – codeMonkey
    Apr 15, 2015 at 11:22
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Photovoltaic panels on the roof.

enter image description here

Maybe the owner was an environmentalist, or off-gridder, or just wanted to pay less for electricity. As the panels are high up they can easily survive the eruption and any lava. Put them on the side facing away from the volcano to avoid debris and they should be fine.

Now for the conditions:

  • No visible features, at least from the mansion grounds.

If the panels all faced an inner courtyard they might be completely unobservable from the ground. Or if the protagonists can't get far enough away from the mansion to see the roof you could place them anywhere, or just have them facing the sea.

  • Somewhat limited in output.

Even without ash clouds solar cells aren't the most reliable source of power. With volcanic dust in the air the power output can be limited to whatever best suits the story, it doesn't even have to be constant as the wind blows the ash around.

  • Not magical.

  • Not alien.

  • Not from the future.

  • Not geothermal.

  • Not nuclear.

All good, though to keep within the "Not from the future" and Hard-Science goals you'll probably want to look at this guide to estimate how large the panels need to be to get enough power for your story.

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    $\begingroup$ If downwind from the volcanoe I would expect the occupants to need to go out regularly to wash the panels. Most of the ash settle to the ground(or rooftop) $\endgroup$
    – Taemyr
    Apr 14, 2015 at 11:02
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    $\begingroup$ If there is a nearby erupting volcano you can expect a ton of ash. During the Mount St. Helens eruption (the one that blew its cap off) a thick ash cloud at Denver caused cars and other surfaces to be coated in inches of ash. Unless our heroes can go on the mansion roof and clear the ash off (which defies the invisibility condition set by OP) it would be covered in ash after day 1. $\endgroup$
    – Jax
    Apr 14, 2015 at 13:00
  • $\begingroup$ Ash build-up would be reliant on the wind direction staying constant. If the wind moved every few hours, or just gusted a bit, there could be just enough ash to be atmospheric without necessarily enough to cover the panels. $\endgroup$
    – ForgeMonkey
    Apr 14, 2015 at 13:05
  • $\begingroup$ If you want it to be truly not noticeable, you could adopt the new clear solar panels that they are working on as the windows of the manor. $\endgroup$
    – Jake
    Apr 14, 2015 at 13:05
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    $\begingroup$ OP asked for a CEI 4 to CEI 5 event. There will be significant amounts of Ash. I am not sure if this violates the condition that the panels should have no visible features from the manor grounds - it would violate the condition that the power generators be unknown to the survivors. $\endgroup$
    – Taemyr
    Apr 14, 2015 at 14:09
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The mansion is equipped with solar power, and battery backup. Not just any solar power, either, but solar roofing shingles or tiles and solar windows which, to anyone but an expert, appear to be regular roofing and windows.

These solar electric panels are typically less efficient than obnoxiously obvious solar panels, but the mansion is large, and on installation they were only meant to offset the power supply, not replace it. The size of the roof and window area provide perhaps 10-20% of the usual consumption of the mansion, but if it were a regular sized home it would be 100%. As such they have enough power for lighting, plumbing (pumps, filtration), refrigeration, and to run the furnace if needed, but probably not enough to run the whole house air conditioner for cooling, or the indoor pool system (sorry, but it probably reeks of algae by now).

They did install batteries as a part of the solar system for backup purposes, so there's power at night. They have to be somewhat frugal, but it works well enough.

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The Manor has a backup gasoline-powered Electric Generator.

Since it's a rather nice manor, the gasoline is stored and supplied from an underground fuel tank. A very small tank has a capacity of perhaps 600 gallons, and a generator can provide a limited electrical output for something on the order of 3 hours/gallon. So that's 1800 hours (75 days) at basically the very low end of the scale. It could easily have more capacity and last for longer, or you could scrounge for gasoline to keep it running.

Note: My hours/gallon estimate is based on a quick perusal of commercial generators for sale, going by fuel capacity/hours of operation. I then divided the number in half to get a better estimate for supplying a larger building. Depending on the exact size of the manor and the power needs you want supplied, you might need to adjust those numbers further.

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    $\begingroup$ I'm not sure a tank of gasoline, even if buried underground, would handle lava flowing over the ground very well. If we're allowed to posit that the tank, pipes, pump(s) etc. are in good working order during and after that ordeal, then however this might work. It would probably require at least some small amount of handwavium, though. At least the generator could be placed somewhere off the ground. (That didn't help in Fukushima-Daiichi, but that was for a different reason.) $\endgroup$
    – user
    Apr 14, 2015 at 9:27
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    $\begingroup$ @MichaelKjörling The tank is going to be somewhere on the property of the house. If the survivability of the tank was an issue, the survivability of the house that's being powered would be equally suspect. It's already clearly stated the house is fine (plus, if it weren't, the whole question would be moot). $\endgroup$
    – T.J.L.
    Apr 14, 2015 at 12:48
  • $\begingroup$ @T.J.L. Actually, the question states that the masonry is "singed by but still defying the erupting volcano". Whatever exactly that means. That said, I agree with the point of your comment; it's just another factor to keep in mind if the OP were to go with this answer. $\endgroup$
    – user
    Apr 14, 2015 at 16:17
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The island's power grid includes a pumped-storage hydroelectric system, located near the mansion. Although the rest of the grid is offline, the connection from the hydraulic generator to the mansion is still in place, and the pumped-storage management system kicked in when the connection to the rest of the grid was lost.

A pumped-storage system moves water between a low area and a high area to store or generate electricity. When electricity from other sources is available, you use some of it to pump water uphill. When you need to generate more power, you let the water run back downhill through a hydroelectric generator. Depending on the local geography, you could pump the water uphill into a storage basin (ie, a lake). Or you could pump it out of a deep storage area like a mine shaft or cavern.

The island has a pumped-storage system because the island's main source of power is variable (wind or solar) or unreliable (connection to another island?). The ocean would serve as one of the storage basins. The other end could be a lake located near the mansion (uphill from the ocean). In this case, they'd run out of generating capability when the lake emptied.

Alternately, the other end could be a cavern, lava tube or similar underground structure which has been put to use as the downhill basin. In this case, they'd lose generating capability once the cavern filled up. However, maybe the eruption has opened up a leak in the cavern, and water is disappearing into the bowels of the earth. In that case, they could generate power for a long time, as long as the inflow from the generator matched the outflow from the leak.

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Ash Manor could be powered by an Ocean thermal energy conversion generator, which is similar to a geothermal generator but makes use of the temperature difference between the surface and deep ocean. Since the installation might (for aesthetic or other reasons) be entirely underwater, it wouldn't be obvious at first sight.

There would be the problem of taking the power up the cliff but perhaps there are sea caves under the manor carrying the conduits.

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mansion by the seaside cliff

Others suggested

  • "hydroelectric" but for any considerable amount of energy, the stream would need to be rather large and creating high pressure. Large rivers on small islands are hard to come by.

  • "pumped storage" - this requires power input to keep running.

  • Oceanic/Wave Generator - okay, but it's fairly low efficiency.

Let's take something "hybrid": Tidal hydroelectric power plant

There is a huge network of caverns in the cliff. They fill with water during high tide and drain during the low tide. Somebody's been smart enough to install generators on the mouth of these caves.

The ocean takes care of pumping the water in or out, and the the turbines are far more efficient than wave generators.

There's the problem of the moments of equlibrium, when the engines stop, twice a day, as the water reverses direction. You could supply a shed of batteries to carry you through these periods, or use them as quirks of the system for dramatic tension.

One more interesting quirk would be that unless the "backend systems" take care of it, all three-phase motors would switch direction depending on which tide it is. Normal single-phase devices would work normally.

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A turbine in a blowhole.

"Blowholes are likely to occur in areas where there are crevices, such as lava tubes" https://en.wikipedia.org/wiki/Blowhole_(geology)

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There are a multitude of possible ideas for this, though as I assume you want something that's a little more interesting, take a look at these:

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Oceanic/Wave Generator:

This one is very simple, wondrously ingenious, and would not be seen on the mansion grounds.

To take a quote from my cited source, "The idea is remarkably simple: Anchor a copper wire. Put a magnet around it. Move the magnet up and down (in this case, that’s the job left to the waves). This induces an electric current in the wire"

Further information at the cited source.

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Hydroelectric:

Also a simple and interesting solution. By funneling water from a nearby stream into a reservoir, and then through a hydro-generator that converts the kinetic force into electrical energy. This can be done without visible sight from the mansion grounds, and presents the extra concern of the remaining water level in the reservoir.

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Sources:

http://matadornetwork.com/change/8-ingenious-ways-of-generating-electricity/ http://www.greenoptimistic.com/hydroelectric-generator/

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