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Yup, Voyager 1 and 2 are still running off RTGs right now since 1977. However the thermoelectric converter used in those RTGs exploit a different effect, and a
by tomxor 5y ago
Yup, Voyager 1 and 2 are still running off RTGs right now since 1977.
However the thermoelectric converter used in those RTGs exploit a different effect, and appear to have quite different properties as a result... What I can tell from a quick dig:
- Thermocouples ("Seebeck effect") operate on a temperature difference, and are more commonly used as temperature sensors. They have the advantage of working at a larger range of temperatures, but the disadvantage of needing to maintain a temperature gradient for power production... Any inherent efficiency is likely negated by the requirement for constant cooling. [0]
- Themal Diodes ("Thermophotovoltaic") is more like a solar panel for a different wavelength (infrared). The principle they operate on suggests no temperature gradient is required, not sure about cooling for other reasons though, but the clear disadvantage is the requirement for a high operating temperature for effective use in power production. [1]
Historically thermal diodes don't appear to have been particularly efficient compared to thermocouples either, obviously this particular one changes that.
[0] https://en.wikipedia.org/wiki/Thermocouple#Power_production https://en.wikipedia.org/wiki/Thermocouple#Power_production
[1] https://en.wikipedia.org/wiki/Thermophotovoltaic https://en.wikipedia.org/wiki/Thermophotovoltaic
- the8472 5y ago> The principle they operate on suggests no temperature gradient is required A temperature gradient is absolutely required. Ignoring materials problems (such as melting) a photovoltaic cell ultimately does work off a temperature differential because it has to absorb photons. It cannot do that if its temperature is the same as the black body temperature of the lightsource illuminating it, otherwise they would be at an emission/absorption equilibrium. This is also why PV cells could theoretically work in reverse mode at night, emitting IR into space. They'd just do that paltry power ratings because ΔT(earth, cosmic background) is much smaller than ΔT(photosphere, earth). And they'd have to be made of a material with a much smaller bandgap.
- tomxor 5y agoYou're right, I kinda knew it needed cooling, but I guess your point is even though the effect being exploited doesn't require a temperature gradient, in practice the heat dissipation requirements are the same if the TVP is to survive - or are they different... surely for the purposes of satisfying the first law the temperature dissipation requirements are dependent on the efficiency of conversion? Which would make the cooling requirements of this TVP lower (relative to input) due to it's higher efficiency? but still substantial.