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A "large" RTG puts out a few hundred watts of electrical. A very efficient electric car might consume 25 kWh/100 miles, so about 250 watt-hours per mile. If you

A "large" RTG puts out a few hundred watts of electrical. A very efficient electric car might consume 25 kWh/100 miles, so about 250 watt-hours per mile. If your car sits parked 6 days per week, it might work. Also: RTGs are typically 3-7% efficient, so your trunk will put out thousands of watts of waste heat continuously. Hope you live in a cold climate.

jandrese 5y ago
So if you're charging at a rate of 2 miles per hour you can drive 48 miles a day on average, which is a fair bit more than most cars do. Even a 1 mile per hour charge rate would be enough for some people, although at that point you'll probably supplement with solar panels or something. One advantage over solar charging is that this won't be affected by the weather and works all night long. The excess waste heat is a problem, but it is way down the list of problems with running a RTG.
- stickfigure 5y ago
  That still sounds incredibly optimistic. The most modern RTG: https://en.wikipedia.org/wiki/Multi-mission_radioisotope_thermoelectric_generator https://en.wikipedia.org/wiki/Multi-mission_radioisotope_the... Puts out 125W electrical, 2KW thermal, and costs $109M each (!) Most cars could support 600w of solar panels. Even in bad weather you'd still come out ahead.
  - duskwuff 5y ago
    The price is almost meaningless. We don't have enough refined plutonium available to build more than three MMRTGs right now.
    - eloff 5y ago
      You wouldn't use a plutonium based RTG in civilian use for obvious reasons.
eloff 5y ago
> Also: RTGs are typically 3-7% efficient, so your trunk will put out thousands of watts of waste heat continuously. Hope you live in a cold climate. Ouch. It might be possible to harness some of that with e.g. Thermal to electric circuits to improve the efficiency.
- duskwuff 5y ago
  The RTG is a thermoelectric generator -- it's already doing all it can with that thermal energy.
  - jandrese 5y ago
    RTGs also avoid having moving parts or working fluids. More efficient energy recovery systems are available if you're willing to accept some maintenance items.
  - eloff 5y ago
    I don't see how you can have it both ways. Either there isn't much waste heat, or there is lots of it and you can potentially harness that still.
    - stickfigure 5y ago
      Let me make an analogy: Your petrol car has a heat engine. It converts about 20% of the heat energy released by combustion into mechanical energy. The rest goes out the tailpipe. Yet harnessing that remaining energy is not so simple because the temperature gradient is (relatively) small. The thermoelectric effect also requires large temperature gradients, and efficiency is proportional to the gradient.
      - eloff 5y ago
        I think the car is a bad example because the temperature gradient is high and it should be possible to harness some of that waste heat. We just don't try. With hybrids we could definitely put that electricity to use, so I'm surprised no attempt is made to harness it. Especially for long haul trucking it could be worth it, but they're aren't diesel electric hybrid trucks that I'm aware of. Or at least they're not common. I do understand your point though.

jandrese 5y ago

So if you're charging at a rate of 2 miles per hour you can drive 48 miles a day on average, which is a fair bit more than most cars do. Even a 1 mile per hour charge rate would be enough for some people, although at that point you'll probably supplement with solar panels or something. One advantage over solar charging is that this won't be affected by the weather and works all night long. The excess waste heat is a problem, but it is way down the list of problems with running a RTG.

stickfigure 5y ago
That still sounds incredibly optimistic. The most modern RTG: https://en.wikipedia.org/wiki/Multi-mission_radioisotope_thermoelectric_generator https://en.wikipedia.org/wiki/Multi-mission_radioisotope_the... Puts out 125W electrical, 2KW thermal, and costs $109M each (!) Most cars could support 600w of solar panels. Even in bad weather you'd still come out ahead.
- duskwuff 5y ago
  The price is almost meaningless. We don't have enough refined plutonium available to build more than three MMRTGs right now.
  - eloff 5y ago
    You wouldn't use a plutonium based RTG in civilian use for obvious reasons.

eloff 5y ago

> Also: RTGs are typically 3-7% efficient, so your trunk will put out thousands of watts of waste heat continuously. Hope you live in a cold climate. Ouch. It might be possible to harness some of that with e.g. Thermal to electric circuits to improve the efficiency.

duskwuff 5y ago
The RTG is a thermoelectric generator -- it's already doing all it can with that thermal energy.
- jandrese 5y ago
  RTGs also avoid having moving parts or working fluids. More efficient energy recovery systems are available if you're willing to accept some maintenance items.
- eloff 5y ago
  I don't see how you can have it both ways. Either there isn't much waste heat, or there is lots of it and you can potentially harness that still.
  - stickfigure 5y ago
    Let me make an analogy: Your petrol car has a heat engine. It converts about 20% of the heat energy released by combustion into mechanical energy. The rest goes out the tailpipe. Yet harnessing that remaining energy is not so simple because the temperature gradient is (relatively) small. The thermoelectric effect also requires large temperature gradients, and efficiency is proportional to the gradient.
    - eloff 5y ago
      I think the car is a bad example because the temperature gradient is high and it should be possible to harness some of that waste heat. We just don't try. With hybrids we could definitely put that electricity to use, so I'm surprised no attempt is made to harness it. Especially for long haul trucking it could be worth it, but they're aren't diesel electric hybrid trucks that I'm aware of. Or at least they're not common. I do understand your point though.