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Is Hydroelectric power plant a perpetual motion machine of second kind from this classification https://en.wikipedia.org/wiki/Perpetual_motion#Classification ???

or not? If not which kind of perpetual motion machine is it? :)

Zlelik
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    It's not a perpetual motion machine, at all. It simply converts (some of the) potential energy of water into electrical energy. – CuriousOne Feb 22 '16 at 10:05
  • Well, it is not so simple. If it would be so simple all potential energy already would be finished. It is renewable energy, because water goes back to the top of the river due to solar thermal energy. It looks for me that Hydropower plant produce energy only from Sun heat. If we consider it from outside the Earth. – Zlelik Feb 22 '16 at 10:07
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    And if you want to go back all the way to the big bang, then you are converting the energy that got released in that event. In neither case are you going to end up with perpetual motion. – CuriousOne Feb 22 '16 at 10:11
  • I do not want to create perpetual motion of first kind. But about second kind I have some doubts, for example, I have solar panel which works on infrared waves (thermal energy). In this case I will produce electricity from the heat and later I can use it to heat another things. Actually I transfer thermal energy from colder body to warmer body with infrared solar panel and electricity.

    Is it violation of second law of thermodynamics or not?

     – Zlelik Feb 22 '16 at 10:22
  • It's not a violation. The second law says that heat can't flow from cold to hot UNLESS something else happens. That something else is happening (it's other heat flowing from hot to cold) because your solar panels are not 100% efficient. The hot source (sun) in this case has a temperature of about 5800K, your panels have a temperature of approx. 300K, the max. Carnot efficiency of that would be over 94%, which real panels can't do, of course. They are only about 15-20% efficient. – CuriousOne Feb 22 '16 at 10:36
  • With solar panel I do not mean the Sun at all. Let's consider experiment like this: I have a closed system where 3 bodies in total. 1 body has temperature 300K, it produces some infrared thermal radiation. 2nd boys is a solar panel with temperature 300K which works with infrared waves. 3rd body has initially the same temperature 300K but I use electricity from solar panel to heat it. After some time 1st body will has lower temperature like 280K, 3rd body will have higher temperature like 320K. I am not sure about solar panel but it can be warmer as well. – Zlelik Feb 22 '16 at 10:48
  • Or even with Sun, what if I use Sun 5800K, convert it to electricity with solar panel and then heat something with that electricity to 6000K? – Zlelik Feb 22 '16 at 10:49
  • Let us continue this discussion in chat. – CuriousOne Feb 22 '16 at 10:49
  • There is no violation because you have already paid your dues to thermodynamics with the limited solar panel efficiency. Whatever energy you get out at the end is for you to use on whatever you like without additional penalty. If you want you can run LHC on it and heat quark gluon plasmas to many billions of K. – CuriousOne Feb 22 '16 at 10:51

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It's not a perpetual motion machine at all: it's a machine which converts energy from the Sun to electrical energy, indirectly:

  1. the sun heats water in the sea and elsewhere, which evaporates;
  2. this condenses out as rain and falls on high up bits of land;
  3. and flows down hill to the sea again;
  4. the hydroelectric plant gets in the way of this flow and captures some of the energy from the water.

Almost all means we have of generating power look similar to this: energy from the Sun is captured somehow and we then extract it (nuclear power is a notable exception).