Hydropower Output Calculator
Falling Water Has Been Turning Turbines Longer Than Any Other Renewable
Hydropower's output depends on just two physical quantities working together: how much water is flowing and how far it falls before reaching the turbine. A large volume of water falling only a short distance can produce as much power as a small volume falling a long way — flow rate and head height trade off against each other directly in the underlying physics.
The Formula
ρ is water density, g is gravitational acceleration (9.81 m/s²), Q is flow rate, H is head height (the vertical drop of the water), and η is turbine efficiency — the fraction of the water's potential energy actually converted to electricity.
Where This Is Useful
- Micro-hydro site assessment — estimate the power a small stream or existing water infrastructure could generate before investing in a feasibility study.
- Comparing generation technologies — benchmark expected hydropower output against solar or wind for the same site.
- Sizing storage or grid connection — annual output feeds directly into decisions about battery storage or grid interconnection capacity.
Worked Example
A flow rate of 2 m³/s with a 15 m head, at 85% turbine efficiency, operating 24 hours a day:
| Flow rate | Head height | Efficiency | Power output | Annual output |
|---|---|---|---|---|
| 2 m³/s | 15 m | 85% | 250.16 kW | 2,191,358 kWh/year |
Unlike solar and wind, a run-of-river hydro source with steady flow can operate near-continuously, which is why 24-hour operation is used as the default in this example.
How to Use This Calculator
- Enter the Flow Rate in cubic meters per second.
- Enter the Head Height in meters.
- Optionally enter Turbine Efficiency % — defaults to 85% if left blank.
- Optionally enter Operating Hours per Day — defaults to 24 if left blank.
- Select Calculate to get power output in kilowatts and projected annual energy output.
Related Calculations
Compare with wind generation using the Wind Turbine Output Calculator, or work out storage costs for the resulting output with the Energy Storage Cost Calculator.