Meaning and mechanism
The water moving from higher elevations to lower elevations loses gravitational potential energy. Turbines and generators then transmit a portion of this as electrical energy.
When a greater volume of water flows with the same drop in elevation, the energy transferred per unit of time is larger. With the same flow rate, a larger drop in elevation results in a greater loss of potential energy for the water.
Relationships and conditions
The density ρ, flow rate Q, and effective head P=ρgQhη are what determine the ideal hydraulic power that water can provide.
Pipe friction and changes in water level affect the effective head and flow rate. A simplified efficiency model does not fully reproduce all operating conditions of a real turbine.
What to observe in the simulation
At fixed efficiency, doubling flow or head doubles power.
Steady flow and constant efficiency are assumed. Pipe friction, changing water levels, floods and ecological impacts are omitted.
Key relationships and symbols
P = ρgQhη · ρ = 1000 kg/m³ · g = 9.80665 m/s²
| Symbol | Meaning | Unit |
|---|---|---|
| Q | Volumetric flow rate | m³/s |
| h | Effective hydraulic head | m |
| η | Generation efficiency | 0~1 |
Worked example
At fixed flow and head, what happens when efficiency drops from 80% to 40%?
It's half · At fixed efficiency, doubling flow or head doubles power.
Common misconceptions
- A flow rate in m³/s and a total water volume in m³ cannot be substituted as the same quantity in the power equation.