If Perpetual Energy isn’t real, then how do Dams generate energy forever?
In: Engineering
Dams generate power by extracting it from falling water. Water on the high side of the dam moves down to the low side, picking up speed from gravity to turn a turbine to generate power. The water that was high is now low and the way it is “reset” is through the water cycle.
Water evaporates from the low area (rivers, lakes, oceans, etc.) and condenses to rain or snow back down at higher elevations. The evaporation is powered by the Sun adding heat to Earth, and the Sun is powered by fusion that consumes a finite fuel. It will last for a very long time but eventually the Sun will run out of fuel which means it is not perpetual energy.
Dams get their energy from the sun, albeit in a roundabout way.
Water evaporates from the oceans thanks to solar radiation. That water then rains down, forming rivers which flow to the dams and spin the turbines. It is not perpetual motion because it gets energy from an external source (the sun) and that energy source will eventually run out.
Perpetual energy means that your energy-making process requires no external input to sustain itself indefinitely, but DOES output energy.
A dam generates energy by taking advantage of the water cycle and gravity. These are external inputs. If they stopped, the dam stops making energy.
Closed system vs open system. The laws of thermodynamics apply to closed systems which are theoretical (can one really prove that any system is completely closed to outside influence?). An “open system” refers to a system (i.e. dam power generation plant) that receives stimulus external to itself (water at a certain height/potential energy) which has an effect on the system output. You could pose the same question about solar power or geothermal power or wind farms etc…
False premise—they don’t.
Dams convert kinetic energy of moving water into electricity. The water moves because it had gravitational potential energy: at some point work was done (energy was expended) to lift that water up in elevation, thereby imparting it with gravitational potential energy. Dams are just cashing in on that previously done work that has caused the elevated water to now store potential energy. Once that water moves through the dams’ generators, it will be at a lower energy state, and won’t be usable again for extracting energy, unless something does work to move it up again.
That something is the meteorological processes on earth, the weather, which is itself powered by the sun.
If no new water gets added to the dam, it’ll obvious run out of water. That’s why its not perpetual energy. Perpetual energy requires that no new stuff be added to the system.
The water cycle is explained in the other posts.
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