Thermoelectric generation in a RTG (radioisotope thermoelectric generator) on space probes like Voyager or Cassini are another. https://solarsystem.nasa.gov/mi

Thermoelectric generation in a RTG (radioisotope thermoelectric generator) on space probes like Voyager or Cassini are another. https://solarsystem.nasa.gov/missions/cassini/radioisotope-thermoelectric-generator/ https://solarsystem.nasa.gov/missions/cassini/radioisotope-t... You can also do hobby-level usage like charging a cell phone with a candle. https://www.instructables.com/Thermoelectric-USB-charger/ https://www.instructables.com/Thermoelectric-USB-charger/