In PSH stations, when the turbines change spin direction, how is it possible for them to pump the water back up into the upper reservoir while the water is still flowing downhill from there? Are they just that powerful?
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Pretty much. For the water to get back up into the reservoir, the pumps have to be able to create as much pressure in the pipes as there is when the water is coming down by gravity to run the turbines. In the PSH I visited they had 1 pump per turbine, and those pumps were run by massive electric motors, maybe 3m tall.
They could have intermediate pumping stations along the pipe which would reduce the size of each individual pump, but since they’re pumping uphill, there would be no easy place to put the buildings that would house those new pumps. The easiest solution is really to just build massive pumps at the bottom that do the whole job.
PSH uses two water reservoirs at different elevations.
When there is excess electricity, water is pumped from the lower reservoir to the upper one, storing energy as gravitational potential energy.
When there is high demand for electricity, water is released from the upper reservoir to the lower one, passing through a turbine that generates power.
The turbines in PSH stations can work in two modes: **generation** and **pumping**.
In generation mode, they act like normal hydroelectric turbines, converting the kinetic energy of water into mechanical energy that spins the rotor and drives the generator.
In pumping mode, they act like pumps, using electricity to spin the rotor in the opposite direction and push water from the lower reservoir to the upper one.
To change from generation mode to pumping mode, or vice versa, the turbines need to change their spin direction. This can be done by using a reversible turbine, which has blades that can adjust their angle to suit the direction of water flow.
Alternatively, some PSH stations use separate turbines and pumps for each mode, which can be switched on and off as needed.
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