I understand heat (or more specifically the transfer of heat) can produce electricity through something called a thermocouple by running a wire through something hot to the side of something cold. What equation determines the amount of joules produced based on the temperature difference and the size of the wire?
Can thermocouples be used to cool and power a spacecraft, station, or satellite? I hear it gets really hot in space when exposed directly to the sun but really cold on the other side not exposed to the sun. The movie Armageddon” had a line about the temperature of space in the sun verses in the shade being very different and I would think a metal wire would radiate heat very easily in a near vacuum.
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Depends on the size of the thermocouple and the metals involved in the bimetallic junction. Not a lot though, far less than 1.
It doesn’t produce energy. It’s a change in resistance over a temperature range.
The magic word you’re looking to research is the seebeck effect.
Look into radio-thermal generators. They use a radioactive material and peltier generator for power. They’re extremely inefficient and low power, but very reliable
Arguably, if the solar heat flux is significant, it is likely still far more efficient to collect that energy in PV cells than through thermoelectric effects. This is why most satellites that orbit our earth, where sun is plentiful, use solar panels, while deep space and extraplanetary probes were more often powered by RTG’s
basically thermocouples produce tiny tiny tiny amounts of energy, it’s enough to be useful when coupled with sensitive measuring equipment to measure a difference in temperature, however it’s pretty much useless to be used for powering anything.
What you are talking about is the Seebeck effect. Yes, you can generate electricity using it. In fact deep space spacecraft that travel too far away from the sun are powered by RTGs, or Radioisotope Thermoelectric Generators are based on this fact.
I’m an electrical engineer who has done systems engineering for satellites, so I can help.
> Can thermocouples be used to cool and power a spacecraft, station, or satellite?
Power, yes. This is what a radioisotope thermal generator does. These are commonly used for deep space probes, or any other spacecraft that can’t reliably use solar panels.
Peltier devices can be and are used in spacecraft, but they don’t actually cool the spacecraft as a whole down. They actually add heat to the spacecraft, because they’re not perfectly efficient (quite inefficient, actually).
They do move heat around, though, which can be helpful for keeping specific components (usually processors) from overheating. But ideally you want to limit the need for active heat management, using passive thermal management instead. Especially since it takes more power to move more heat, so you’d use a peltier for a hot chip or two, and a heat pipe from the full electronics to the radiator (which works on radiative cooling, basically the energy of the blackbody radiation). But even here, you’d rather design the satellite to be able to keep within its operating range solely with passive heat management.
> I hear it gets really hot in space when exposed directly to the sun but really cold on the other side not exposed to the sun.
This is true, but it’s primarily an issue for the sunny/dark parts of the orbit, rather than the two sides of the spacecraft. The average temperature at the hottest and coldest parts of an orbit are typically many times larger than the difference in the sunny and dark sides of the satellite while in the sun. Mostly because the metal the satellite is made from conducts heat so well from the hot side to the cold side.
In short, there’s not enough of a temperature difference to make a big peltier device practical. And even if you did, the power output would vary as the satellite entered the sunlight, warmed up, and evened out. Add on the efficiency difference, and it’s just so much more convenient and consistent to use solar panels instead.
I can try and answer any follow-up questions you have.
You are wanting the field of thermoelectrics those devices do as you are describing.
I work with satellites in college and I can tell you that this wouldn’t really work! Depending on your satellite and your ADCS, your ability to keep a temperature differential is pretty hard without serious effort (ie James Webb). It’s just not reasonable to get enough power from thermocouples and solar radiation without serious commitment that can be achieved with solar panels. In general, your satellite is going to normalize in temperature fairly fast and even at the hottest your normal LEO orbit gets… it’s not hot enough for thermocouples to viable. But… some satellites do use thermocouples to generate electricity! RTG’s use nuclear fuel to generate the temperature gradient and thermocouples to generate power.
You’re looking for seebeck coefficient but it’s important to note that the voltage is tiny for thermocouples. The 500+ thermocouples in an RTG with a huge temperature gradient produce maximum a few hundred watts (I think the most powerful RTG flown only ever produced 300 watts and it was huge ( .5m diameter and 1m long).