Context: Managing power grid loads requires storing excess energy for peak demand times.

Application: Pumped-storage plants use reversible pump-turbines. During low-demand periods (nighttime), excess electrical energy from the grid is used to pump water from a lower reservoir to an upper reservoir. The machine operates as a centrifugal pump. During peak demand (daytime), the water is released back down to the lower reservoir, and the same machine operates as a reaction turbine (like a Francis turbine) to generate electricity. This dual capability is vital for grid stability, especially with the integration of variable renewable energy sources.

Context: Different turbine designs are optimized for specific site conditions.

Application: The choice of hydraulic turbine is dictated by the available head and flow. For very high heads and low flow rates (e.g., steep mountain streams), an impulse turbine like a Pelton wheel is used. For medium heads and flows, a Francis reaction turbine is standard. For very low heads (like run-of-the-river dams or tidal barrages) with massive flow rates, an axial-flow Kaplan turbine is required because its adjustable propeller blades maintain high efficiency even as the low head fluctuates.