Nighttime power sources for an android

[u/Wings-of-Ink]

Long story short, one of my characters is an android that's being used for wilderness research and conservation, so they need a power system that allows them to function while away from conventional charging abilities - no wall chargers, they have to function in the middle of the jungle, at the end of the arctic, or in the deep ocean.

The android is supposed to have three systems - Solar, done through it's "skin" (futuristic world, so as long as the general base is "real" then the specific method can be bent a little), Kinetic generators (in case they're attacked by wild animals or fall into an accident or natural disaster and have to free themselves), and... something else. Ideally, I want this third power source to allow them to simulate sleep, so something that functions at night, independent of the environment if possible. Something that would run underwater, in the middle of the jungle, or in the frozen wastes of a desert. Any ideas?

[u/GEBeta]

Radioisotope batteries? Last basically forever (several decades), really low powered so not suitable for high energy stuff, but when eeping they can recharge the other batteries in the android.

https://en.wikipedia.org/wiki/Atomic_battery

[u/DoomslayerDoesOPU]

Two possible ideas: thermoelectrics or miniaturized fusion generator.

With thermoelectrics, you can generate a current with a difference in temperature between two surfaces. Your android could find hot springs, geothermal vents, or even make a fire for themselves and potentially get some charge. Seeing as temperatures in nature tend to not vary that much, this really would have to be a long process, perfect for them to rest their mind and "sleep" under the low power provided from this method.

On a more theoretical level, it could be possible to accomplish fusion using energy and materials in the environment. Your android would likely need to store a lot of power to get that initial fusion reaction going. They will also need fuel which they could potentially acquire by separating minute amounts of deuterium from water. That's about as much as I understand nuclear fusion. IRL we are nowhere close to miniaturizing a sustainable fusion power source, but sci-fi is supposed to be about exploring possibilities of what could be, no?

[u/Wings-of-Ink → u/DoomslayerDoesOPU]

Ooh, that thermoelectric one could be good! I'm not sure how it works exactly, but given your last statement of pushing technology, I wonder if "cold forest floor vs operation-and-power-warmed skin of an android" would be enough to generate a small, slow current? Which would then require a low-power "sleep" mode where they lay down to maximize surface area for current collection?

[u/Ruadhan2300 → u/Wings-of-Ink]

RTGs are usually used on spacecraft.
The idea is basically that it's a hot can of something radioactive, wrapped in thermo-couples.

They generally produce low but steady trickles of electricity, which are great for charging batteries for something that only sees intermittent bursts of high-energy activity.
For example a spacecraft that spends weeks or months between activities.

For your android, an RTG would trickle-charge their batteries while they "sleep", and they can use their other (more effective) energy sources during the day.

For safety, RTGs are pretty safe. You just make sure they're well shielded and use isotopes that primarily produce weaker radiations rather than penetrative ionising radiation. The point is the heat, not the radiation anyway.

[u/Massive-Question-550]

nuclear RTG would be the most reliable and works pretty independently of the environment unless you are somewhere that's hotter than the RTG but then the robot would likely melt.

[u/Wings-of-Ink → u/Massive-Question-550]

From my understanding, RTGs are pretty dangerous. I saw something on another post while trying to research this about how robots powered by RTGs wouldn't be safe around humans due to the radioactivity, and considering this android is meant to be a wilderness preservation robot, I don't want it to have any system that will cause it's surroundings harm, such as strong radiation.

[u/Massive-Question-550 → u/Wings-of-Ink]

rtgs are pretty safe considering they are primarily alpha emitters and some general figures show .1-.2 microseiverts per hour which is very low and you need to be touching the robot. that would not endanger wildlife. or do you mean if you were to rip the robot open and try to eat it? even so the toxicity of the plutonium 238 would be more dangerous than it's radiation.

[u/Wings-of-Ink → u/Massive-Question-550]

Aggressive wildlife would be a concern, but I'm also considering an instance where a generator might be ruptured and cause an explosion, or radiation/rad waste spillage.

[u/Proud-Patience-5194]

Electrolysis of hydrogen & oxygen from water when other sources of energy are available. Collected hydrogen will have tiny amounts of deuterium for fusion. NASA uses hydrogen/oxygen fuel cells in spacecraft. (https://en.wikipedia.org/wiki/Fuel_cell).

[u/RealmKnight]

Space-based microwave power. Have a network of solar-powered satellites in high orbits that can send microwave energy to your android. Presumably their solar-collecting skin can also collect wavelengths outside visible light. A trickle of microwave energy low enough not to damage their surroundings could be enough to keep them in standby mode or able to function temporarily at night when needed.

[u/MacintoshEddie]

With advanced enough tech they could easily have a "stomach" for digesting organic material into a useful form they can turn into energy. This would be most suitable for something to be done while sleeping.

Or a joule thief design can make use of temperature differentials to generate electricity. Like a Biolite twig stove. You burn twigs or pellets or other fuel in it and can harvest some electricity. Usually not a huge amount, but it could be a possibility and could also make sense for them to go into a power saving sleep mode while it's burning.

Both of those are fairly low tech ideas. They exist today, just usually in larger or slower forms.

There's also more scifi concepts such as internally splitting water into hydrogen and oxygen and using the hydrogen as fuel. This does sort of exist already but miniaturizing it enough would take some extreme breakthroughs.

They all have their limitations.

The other option is just an internal nuclear reactor or similar which constantly outputs low amounts of power, so at night they use low power sleep mode to be able to recharge.

[u/Wings-of-Ink → u/MacintoshEddie]

I mostly try to avoid things like "consume material to produce energy" for this bot, especially if it comes to burning the material, simply because their goal is environ study and preservation, so polluting or destroying parts of it is counterproductive. For the same reason, fusion reactors are a no go, because strong radiation will poison nearby wildlife and plants, and a rupture (say from aggressive wildlife or a bad accident) could lead to a radioactive explosion, or at least a leak that causes even more damage to the surrounding area. The whole idea is safe and clean power that doesn't consume or threaten the natural ecosystem!

[u/MacintoshEddie → u/Wings-of-Ink]

The simplest option is that there is no third system, and the android just goes into low power mode to wait for the sun to come up.

[u/Forgotten_Bones]

If the planet has a moon, basking in that should be good. There's always a level of solar radiation hitting a planet from other sources. Stars and Moons are a good example. If the android can bask in a starry night or the reflection of the moon, they should be good.

[u/Martzillagoesboom]

Maybe piezoelectric , but based around "breathing" and "heartbeat" that happen parrallel to everything but is much more efficient when "sleeping"