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Idaho is not sending the water into Oregon at any lower elevation because they added a dam and a hydro-plant upstream! Hydro plants don’t harvest the ambient k

by zaroth 8y ago

Idaho is not sending the water into Oregon at any lower elevation because they added a dam and a hydro-plant upstream! Hydro plants don’t harvest the ambient kinetic energy because the terminal velocity of the water is quite low! You can’t build a hydro plant at 0ft elevation, even if that water just flowed down a 10,000ft mountain. A hydro plant takes a specific localized elevation drop and turns that drop into power by harvesting the gravitational mass of the water to rotate turbines installed along the way. The water at the top entrance to the hydro plant is sitting perfectly still in a reservoir built to feed the plant. If you tried to put a turbine at the bottom of a fast flowing river it wouldn’t work. You need the weight (mass) of millions of tons of water pushing directly down on your turbines to generate the necessary power. Now here’s a fun thought. All that potential energy in the water at the top of the mountain, that potential energy got into the water when it evaporated from the surface and raised up into the atmosphere. So really it’s all just another form of solar power.

thaumasiotes 8y ago
Which hypothetical river contains more energy when it reaches Oregon? - A river that came from 8,000 feet - A river that came from 3,000 feet Oregon potentially has access to energy that Idaho cannot extract from the river, by virtue of Idaho's higher elevation. But any and all energy that Idaho does extract from the river is energy that would otherwise have been available downstream. Again, all gains to Idaho are losses to Oregon. The reverse is not true: Oregon enjoys some minor gains which are not losses to Idaho.
- JshWright 8y ago
  That's not how physics works... Are you claiming that the dam somehow changes the elevation of the Idaho/Oregon border?
- adwn 8y ago
  In your world, a river would be flowing at a speed of 132 m/s (= 295 mph) after coming from 3000 ft [1]. Now compare this to rivers in the real world and you will see that you're overlooking a factor which reduces the speed of the flow by two orders of magnitude. [1] Potential energy of 1 kg water at 3000 ft: 1 kg * 900 m * 9.81 m/s² = 8829 J. Kinetic energy: 8829 J = 0.5 * 1 kg * v² ==> v = 132.88 m/s
- zaroth 8y ago
  I’m about ready to give up :-) The potential energy in the water at the top of the mountain gets eaten away as it flows downstream whether there is a hydro dam or not, due to the massive friction of the water flowing downstream. This is what I mean by terminal velocity of the river. The water does not just keep speeding up and speeding up as it flows downstream. At first the water starts to flow faster, and indeed it is converting potential energy into kinetic energy. But as the water starts to flow, the kinetic energy starts getting sucked out through massive amounts of friction in the flow. Ever hear a river roaring? That’s the audio track of massive amounts of kinetic energy draining out into the surrounding earth. (A frictionless river would flow silently) As the water keeps speeding up as it flows downstream it reaches a point where the friction is costing as much energy as the elevation drop is adding. Terminal velocity. At that point, every foot of elevation drop keeps the river flowing but does not increase net kinetic energy in the river. Take one kilogram of water and pour it down a chute at the top of a 100 foot high drop. Take another kilogram of water and pout it down a 200ft high chute. A 1,000ft high chute. At the bottom of the chutes we measure the speed of the water. You will find the water is flowing at exactly the same speed in all three cases. Why?
  - gnode 8y ago
    For a typical hydroelectric dam, kinetic energy is not particularly important (although smaller kinetic hydroelectric plants do exist). The relevant factors are pressure (determined by the hydraulic head) and volumetric flow. In ideal conditions, if you have two sections of identical pipe, and a turbine in the middle, water flowing through the pipe will not change velocity (incompressible fluid, and none is gained or lost), yet the turbine can harvest one Joule per cubic metre per Pascal of pressure. This is the predominant principle by which a dam works; it creates a large pressure differential, and then drives a turbine at a relatively much slower velocity than the maximum possible by converting all the GPE to KE. To adapt this to your chutes idea. Water will not pour down the longer chute significantly quicker than the shorter one, yet if you fill them, the longer chutes will have a proportionately larger pressure at the bottom. Thus a flow of 1m^3/s will deliver proportionately more energy across a turbine which reduces the pressure to ambient.
- cgriswald 8y ago
  > But any and all energy that Idaho does extract from the river is energy that would otherwise have been available downstream. This is false. Huge portions of that kinetic energy are going to be lost to transfer, heat, and sound if it is not captured by Idaho. > Which hypothetical river contains more energy when it reaches Oregon? Assume a spherical cow... In order for any of your claims to be true, your 'rivers' would have to be straight, frictionless channels. To know the actual impact on flow you would have to measure it. It is possible the flow will be reduced. But this is irrelevant for energy generation, since it is the gravitational potential that is being harvested[0]. Any kinetic energy coming into the system from upstream is dissipated when it reaches the reservoir. [0] - Yes, step 1 is to convert the gravitational potential energy into kinetic energy, so you can be pedantic and say you are actually harvesting kinetic energy. However, this is not the kinetic energy in the pre-existing flow.
achenatx 8y ago
most power is solar power (hydro, wind, solar, oil, natural gas, coal).

by zaroth 8y ago

thaumasiotes 8y ago

Which hypothetical river contains more energy when it reaches Oregon? - A river that came from 8,000 feet - A river that came from 3,000 feet Oregon potentially has access to energy that Idaho cannot extract from the river, by virtue of Idaho's higher elevation. But any and all energy that Idaho does extract from the river is energy that would otherwise have been available downstream. Again, all gains to Idaho are losses to Oregon. The reverse is not true: Oregon enjoys some minor gains which are not losses to Idaho.

JshWright 8y ago
That's not how physics works... Are you claiming that the dam somehow changes the elevation of the Idaho/Oregon border?
adwn 8y ago
In your world, a river would be flowing at a speed of 132 m/s (= 295 mph) after coming from 3000 ft [1]. Now compare this to rivers in the real world and you will see that you're overlooking a factor which reduces the speed of the flow by two orders of magnitude. [1] Potential energy of 1 kg water at 3000 ft: 1 kg * 900 m * 9.81 m/s² = 8829 J. Kinetic energy: 8829 J = 0.5 * 1 kg * v² ==> v = 132.88 m/s
zaroth 8y ago
I’m about ready to give up :-) The potential energy in the water at the top of the mountain gets eaten away as it flows downstream whether there is a hydro dam or not, due to the massive friction of the water flowing downstream. This is what I mean by terminal velocity of the river. The water does not just keep speeding up and speeding up as it flows downstream. At first the water starts to flow faster, and indeed it is converting potential energy into kinetic energy. But as the water starts to flow, the kinetic energy starts getting sucked out through massive amounts of friction in the flow. Ever hear a river roaring? That’s the audio track of massive amounts of kinetic energy draining out into the surrounding earth. (A frictionless river would flow silently) As the water keeps speeding up as it flows downstream it reaches a point where the friction is costing as much energy as the elevation drop is adding. Terminal velocity. At that point, every foot of elevation drop keeps the river flowing but does not increase net kinetic energy in the river. Take one kilogram of water and pour it down a chute at the top of a 100 foot high drop. Take another kilogram of water and pout it down a 200ft high chute. A 1,000ft high chute. At the bottom of the chutes we measure the speed of the water. You will find the water is flowing at exactly the same speed in all three cases. Why?
- gnode 8y ago
  For a typical hydroelectric dam, kinetic energy is not particularly important (although smaller kinetic hydroelectric plants do exist). The relevant factors are pressure (determined by the hydraulic head) and volumetric flow. In ideal conditions, if you have two sections of identical pipe, and a turbine in the middle, water flowing through the pipe will not change velocity (incompressible fluid, and none is gained or lost), yet the turbine can harvest one Joule per cubic metre per Pascal of pressure. This is the predominant principle by which a dam works; it creates a large pressure differential, and then drives a turbine at a relatively much slower velocity than the maximum possible by converting all the GPE to KE. To adapt this to your chutes idea. Water will not pour down the longer chute significantly quicker than the shorter one, yet if you fill them, the longer chutes will have a proportionately larger pressure at the bottom. Thus a flow of 1m^3/s will deliver proportionately more energy across a turbine which reduces the pressure to ambient.
cgriswald 8y ago
> But any and all energy that Idaho does extract from the river is energy that would otherwise have been available downstream. This is false. Huge portions of that kinetic energy are going to be lost to transfer, heat, and sound if it is not captured by Idaho. > Which hypothetical river contains more energy when it reaches Oregon? Assume a spherical cow... In order for any of your claims to be true, your 'rivers' would have to be straight, frictionless channels. To know the actual impact on flow you would have to measure it. It is possible the flow will be reduced. But this is irrelevant for energy generation, since it is the gravitational potential that is being harvested[0]. Any kinetic energy coming into the system from upstream is dissipated when it reaches the reservoir. [0] - Yes, step 1 is to convert the gravitational potential energy into kinetic energy, so you can be pedantic and say you are actually harvesting kinetic energy. However, this is not the kinetic energy in the pre-existing flow.

achenatx 8y ago

most power is solar power (hydro, wind, solar, oil, natural gas, coal).