Hydroelectric power turns the energy of falling or flowing water into electricity, and the amount you can generate comes down to just three numbers: how much water moves (flow rate), how far it falls (head), and how efficiently your equipment converts that energy. This calculator applies the standard physics formula used by engineers and hydrologists to estimate power output, annual energy generation, and which turbine type and project scale fit a given site.
How the Hydroelectric Power Calculator works
The calculator uses P = ρ·g·Q·H·η, the standard formula for hydroelectric power output. The theoretical hydraulic power available is the product of water density (ρ = 1,000 kg/m³), gravitational acceleration (g = 9.81 m/s²), flow rate (Q), and head (H) — this is the total potential energy per second flowing through the site. Multiplying by the turbine + generator efficiency (η) accounts for real-world mechanical friction and electrical losses, giving the actual usable electrical output in watts (converted to kW for display).
For the Annual Energy tab, the calculator multiplies rated power by 8,760 hours per year and a capacity factor — the percentage of the year the site effectively operates at that power level. This is necessary because stream flow varies seasonally; a site rated at 100 kW rarely produces 100 kW around the clock.
Inputs and what they mean
Flow rate (Q) is the volume of water moving through the turbine per second — get this from a stream gauge, a hydrology study, or a measured discharge at your site. It has the single largest effect on output alongside head, since power scales linearly with both.
Head (H) is the vertical drop from intake to turbine, measured along the penstock. A common newcomer mistake is measuring the horizontal distance across a property instead of the actual vertical fall — this can produce a wildly optimistic estimate.
Efficiency (η) defaults to 85%, a reasonable mid-range figure for modern small-hydro turbine + generator sets, but manufacturer-rated efficiency for your specific turbine model will be more accurate.
Capacity factor (Annual Energy tab) should reflect your site's actual seasonal flow pattern — a site with a strong dry season needs a lower capacity factor than one with steady year-round flow.
Limits and edge cases
This calculator estimates raw hydraulic-to-electrical conversion; it does not model penstock friction losses (which reduce effective head over long pipe runs), intake screening losses, transformer losses, or transmission losses to the point of use — all of which reduce real-world output somewhat below this estimate. It also does not account for minimum environmental flow requirements that regulators often require to be left in the stream, which reduces the flow rate actually available to the turbine.
For a real project, a hydrology study measuring flow duration across the full year, a site survey for accurate head measurement, and a quote from a turbine manufacturer are all necessary before committing capital. Use this calculator for early-stage feasibility screening, not final engineering design.