5 ms·

This is challenging because you probably don't want a phone that is hot all the time. There is however a very interesting technology which uses beta radiation a

This is challenging because you probably don't want a phone that is hot all the time. There is however a very interesting technology which uses beta radiation and what are essentially "solar cells" to generate electricity directly[1]. Basically you could paint some Cesium 137 on to a solar cell and it would generate power 24x7! [1] Beta Voltaics a new kind of nuclear battery -- https://en.wikipedia.org/wiki/Betavoltaic_device https://en.wikipedia.org/wiki/Betavoltaic_device

Dylan16807 3y ago
Currently single digit efficiency so it's still going to be unacceptably hot.
- ChuckMcM 3y ago
  I think you meant "big" rather than "hot"? It's decay rate is low enough that it doesn't even melt itself when not cooled (and it melts at room temperature). Adding precision here, a 'thin layer' would not melt itself, you could probably keep a 10+kg chunk liquid. But the low efficiency means you need a lot of surface area between the Cs137 and the silicon lattice, so it one could calculate the number of sq meters of "battery" surface you would need to power a device and then see if you could topologically fold that into a relatively small area. Cs137 also can produce a small amount of gamma radiation which you'd want to shield against so the whole thing might end up in a lead box. (not great for making it light :-)) It would be a fun engineering challenge and a good use of nuclear waste but difficult to sell politically because the association with "nuclear." And yes, it isn't actually practical at this level. Looking at where folks are looking at this seriously it seems to be more of a spacecraft thing (long duration probes far from the Sun kind of thing)
  - Dylan16807 3y ago
    Being big is also a problem, but I did in fact mean heat. "Not melting itself" is not the threshold we need to meet for a phone. We should probably consider 5 thermal watts the limit. If we have a 30% efficient betavoltaic panel, then we can produce 1.5-2 watts of device power within that limit. If we have a 5% efficient panel, then we're only getting a quarter of a watt. A quarter of a watt can stop an idle phone from draining, but you'd only recover about 1% of a normal phone battery per hour. By the time we're considering external devices, I think "battery bank with a solar panel" beats betavoltaic on the technical merits even when we're ignoring difficulty and radiation. Even a tiny panel built into the back of a phone generally wins.
    - Reason077 3y ago
      Higher levels of waste heat could be sold as a benefit, especially in cold climates. Nice little personal heating device to keep you warm on cold nights? Optional accessories could harvest the heat to heat water, make coffee, cook food, etc?
      - Dylan16807 3y ago
        Those people typically want to use their phone indoors too. There's really no good way to spin an uncomfortably hot phone. If it's separate from the phone then you don't have to worry about that, but again if it's separate from the phone the entire scenario that made you want this kind of device starts to collapse because the requirements are so different.

Dylan16807 3y ago

Currently single digit efficiency so it's still going to be unacceptably hot.

ChuckMcM 3y ago
I think you meant "big" rather than "hot"? It's decay rate is low enough that it doesn't even melt itself when not cooled (and it melts at room temperature). Adding precision here, a 'thin layer' would not melt itself, you could probably keep a 10+kg chunk liquid. But the low efficiency means you need a lot of surface area between the Cs137 and the silicon lattice, so it one could calculate the number of sq meters of "battery" surface you would need to power a device and then see if you could topologically fold that into a relatively small area. Cs137 also can produce a small amount of gamma radiation which you'd want to shield against so the whole thing might end up in a lead box. (not great for making it light :-)) It would be a fun engineering challenge and a good use of nuclear waste but difficult to sell politically because the association with "nuclear." And yes, it isn't actually practical at this level. Looking at where folks are looking at this seriously it seems to be more of a spacecraft thing (long duration probes far from the Sun kind of thing)
- Dylan16807 3y ago
  Being big is also a problem, but I did in fact mean heat. "Not melting itself" is not the threshold we need to meet for a phone. We should probably consider 5 thermal watts the limit. If we have a 30% efficient betavoltaic panel, then we can produce 1.5-2 watts of device power within that limit. If we have a 5% efficient panel, then we're only getting a quarter of a watt. A quarter of a watt can stop an idle phone from draining, but you'd only recover about 1% of a normal phone battery per hour. By the time we're considering external devices, I think "battery bank with a solar panel" beats betavoltaic on the technical merits even when we're ignoring difficulty and radiation. Even a tiny panel built into the back of a phone generally wins.
  - Reason077 3y ago
    Higher levels of waste heat could be sold as a benefit, especially in cold climates. Nice little personal heating device to keep you warm on cold nights? Optional accessories could harvest the heat to heat water, make coffee, cook food, etc?
    - Dylan16807 3y ago
      Those people typically want to use their phone indoors too. There's really no good way to spin an uncomfortably hot phone. If it's separate from the phone then you don't have to worry about that, but again if it's separate from the phone the entire scenario that made you want this kind of device starts to collapse because the requirements are so different.