# Are heat powered solar cells possible? **URL:** \ **Category:** Factual Questions\ **Created:** [October 27, 2011, 5:10am UTC](https://boards.straightdope.com/t/are-heat-powered-solar-cells-possible/600945 "2011-10-27T05:10:24Z")\ **Posts on this page:** 9\ **Page:** 1
**Author:** ![AaronX](https://avatars.discourse-cdn.com/v4/letter/a/7bcc69/32.png) [@AaronX](https://boards.straightdope.com/u/AaronX)\ **Post date:** [October 27, 2011, 5:10am UTC](https://boards.straightdope.com/t/are-heat-powered-solar-cells-possible/600945/1 "2011-10-27T05:10:24Z")
Background: solar cells work by a photon creating an electron-hole pair, which are then shuttled apart by the built-in electric field before they can recombine. Would this be possible using thermal energy? Doing some rough calculations kT at T=300K is 0.026eV, which is ridiculously small, but how about high temperature semiconductors with a low band gap? ---
**Author:** ![Absolute](https://avatars.discourse-cdn.com/v4/letter/a/b2d939/32.png) [@Absolute](https://boards.straightdope.com/u/Absolute)\ **Post date:** [October 27, 2011, 5:33am UTC](https://boards.straightdope.com/t/are-heat-powered-solar-cells-possible/600945/2 "2011-10-27T05:33:00Z")
Yup. [http://www.jxcrystals.com/ThermoPV.htm](http://www.jxcrystals.com/ThermoPV.htm) ---
**Author:** ![AaronX](https://avatars.discourse-cdn.com/v4/letter/a/7bcc69/32.png) [@AaronX](https://boards.straightdope.com/u/AaronX)\ **Post date:** [October 27, 2011, 5:37am UTC](https://boards.straightdope.com/t/are-heat-powered-solar-cells-possible/600945/3 "2011-10-27T05:37:29Z")
Wow, but those seem to use IR instead of heat? I wonder if heat \> electricity violates the second law of thermodynamics. ---
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [October 27, 2011, 5:59am UTC](https://boards.straightdope.com/t/are-heat-powered-solar-cells-possible/600945/4 "2011-10-27T05:59:39Z")
> [@AaronX](#): > > Wow, but those seem to use IR instead of heat? I wonder if heat \> electricity violates the second law of thermodynamics. Only if you’re trying to reduce entropy. If you have a concentrated heat source and a cold place to spread the heat into, then the 2LoT is on your side. Fossil fuel and nuclear power generation plants mostly convert heat into electricity. You just can’t ever get 100% efficiency, is all. ---
**Author:** ![engineer\_comp\_geek](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/engineer_comp_geek/32/504_2.png) [@engineer\_comp\_geek](https://boards.straightdope.com/u/engineer_comp_geek)\ **Post date:** [October 27, 2011, 6:55am UTC](https://boards.straightdope.com/t/are-heat-powered-solar-cells-possible/600945/5 "2011-10-27T06:55:50Z")
It is possible to convert heat directly into electricity. That’s how thermocouples work. Google “Seeback effect” if you want the gory technical details. Peltier devices, aka thermoelectric coolers, are found in CPU coolers, portable drink coolers, and all sorts of things. If you run electricity through one, one side gets hot and the other side gets cold. Reverse the current and the hot side gets cold and the cold side gets hot. They work in reverse though, too. If you apply heat to one side and cold to the other, they will generate electricity. A more mechanical way to convert heat into electricity is to use a Sterling engine to drive a generator. The second law of thermodynamics is just fine and happy with all of these. ---
**Author:** ![Absolute](https://avatars.discourse-cdn.com/v4/letter/a/b2d939/32.png) [@Absolute](https://boards.straightdope.com/u/Absolute)\ **Post date:** [October 27, 2011, 7:06am UTC](https://boards.straightdope.com/t/are-heat-powered-solar-cells-possible/600945/6 "2011-10-27T07:06:48Z")
> [@AaronX](#): > > Wow, but those seem to use IR instead of heat? I wonder if heat \> electricity violates the second law of thermodynamics. Doh, I read your OP too quickly and thought that was what you meant. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [October 27, 2011, 8:02pm UTC](https://boards.straightdope.com/t/are-heat-powered-solar-cells-possible/600945/7 "2011-10-27T20:02:40Z")
Yeah, the key is that you always need a temperature _difference_ between two things. ---
**Author:** ![AaronX](https://avatars.discourse-cdn.com/v4/letter/a/7bcc69/32.png) [@AaronX](https://boards.straightdope.com/u/AaronX)\ **Post date:** [October 28, 2011, 3:28pm UTC](https://boards.straightdope.com/t/are-heat-powered-solar-cells-possible/600945/8 "2011-10-28T15:28:34Z")
Hmm I think if charge carrier creation occurs by temperature, that’s a conductor. ---
**Author:** ![Kevbo](https://avatars.discourse-cdn.com/v4/letter/k/e47774/32.png) [@Kevbo](https://boards.straightdope.com/u/Kevbo)\ **Post date:** [October 28, 2011, 4:54pm UTC](https://boards.straightdope.com/t/are-heat-powered-solar-cells-possible/600945/9 "2011-10-28T16:54:33Z")
There are also thermoelectric generators, which are based on vacuum tube principals. This is what is running some of our deep space probes, the ones that venture so far from the sun that solar cells are not feasible. > **[Radioisotope thermoelectric generator](https://en.wikipedia.org/wiki/Radioisotope_thermoelectric_generator)** > > A radioisotope thermoelectric generator (RTG, RITEG), sometimes referred to as a radioisotope power system (RPS), is a type of nuclear battery that uses an array of thermocouples to convert the heat released by the decay of a suitable radioactive material into electricity by the Seebeck effect. This type of generator has no moving parts. Because they don't need solar energy, RTGs are ideal for remote and harsh environments for extended periods of time, and because they have no moving parts, there...