Heat energy to Electric energy?

  1. ranger

    ranger 1,663
    Gold Member

    Is it possbile to covert heat energy (like that from the surface of a hot radiator) to electric energy? Whats the theory behind this?

    --thank you.
  2. jcsd
  3. chroot

    chroot 10,351
    Staff Emeritus
    Science Advisor
    Gold Member

    Of course. You can use heat to turn water into steam, and then use that steam to drive turbines which are connected to electric generators. This is what power plants do -- the fundamental energy released from fuel, be it coal or gas or nuclear, is heat.

    Or, you can use a Peltier device in reverse.

    There are many such possibilities.

    - Warren
  4. ranger

    ranger 1,663
    Gold Member

    Turbines are a little far off for me. I was hoping to build a circuit to do this.
    Can this only be accomplished with rotational motion(turbines)?

    Are there any smaller scale things that I can possibly experiment with?
    Last edited: Jan 13, 2006
  5. chroot

    chroot 10,351
    Staff Emeritus
    Science Advisor
    Gold Member

  6. If you have a source of cooling, and some time to build a relatively simple device you may be able to use a small sterling engine hooked up to a simple generator. Haven't built either, but I know you can get the instructions to the sterling, and I would assume the generator, on the internet
  7. You can also build a photoelectric cell to convert heat energy to electric energy.
  8. back to basics....

    how about a non-Ph.D level answer?

    if you have a gas hot water heater in your home and it's an "older" model that uses a pilot light, you've got an element inside it that converts heat to electricity, and you can buy one down at the neighborhood hardware store.

    it's called a "thermocouple."

    made of two dissimilar metals, when the metals' junction is exposed to heat, a voltage differential develops. in your hot water heater, the resulting current is brought to a small solenoid which holds the gas valve to the burner under the water tank in an "open" position.

    if the pilot light goes out, as in a failure of the gas supply or a water leak extinguishes the flame, the thermocouple goes cold, stops producing the EMF differential, and the solenoid "drops out", cutting the flow of gas. this safety device has been in use for MANY decades, and a stop at your local Home Depot or ACE hardware store should be a quick place to buy one in the water heater repair parts department.

    measure its output versus temperature. if you can afford to buy multiples of 'em, try them in series and parallel. determine their Norton and Thevenin (sp?) equivalent circuits. see if they can deliver enough power to run a tiny motor or light an LED.

    have a hot time!
  9. true!

    Stirling Engines, steam engines, tied to a generator. yep, they all convert heat energy to electrical energy.

    guess i got caught in the "direct conversion" trap....


  10. rcgldr

    rcgldr 7,696
    Homework Helper

    Some sattelites use radioactive material to heat up thermalcouples for a long lasting electrical energy supply.
  11. absolutely right!

    especially the deep-space ones, where solar cells and gasoline engines won't work...
  12. rcgldr

    rcgldr 7,696
    Homework Helper

    People are worried what would happend if a nuclear powered sattelite crashed during launch. Do a web search for "satellite plutonium power" and you find a lot of hits, like this one:


    Note that the plutonium is encased into little buttons, which keep the actual plutonium centers spaced so that the actual heat generated falls into a pre-determined range. The cases are ceramic and some hard metal that is supposed to prevent leakage into the atmoshpere in case of a bad launch.

    Even the Apollo missions used these mini nuclear reactors on the lunar module. Alll but one of these never came back. Apollo 13's lunar module's nuclear reactor is sitting at the bottom of the ocean somewhere.

    Anyway, it may not be efficient, but thermalcouples inserted into a "bottle" of plutonium buttons makes for a very long lasting and reliable power supply.
    Last edited: Jan 20, 2006
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