Hydro Energy from Flow Duration

Converts a simple flow‑duration breakdown (discharge classes and share of the year) into annual energy for a run‑of‑river or storage plant, given net head, efficiency and turbine discharge limit.

Inputs (SI units)

Net head Hm

Overall efficiency η0–1 (turbine × generator)

Turbine discharge limit Q_t,maxm³/s

Flow classes (Q, % of year) sum of % can be ≤/≈/≥ 100, we use given values directly

#	Q (m³/s)	% of year
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Summary

Enter net head, efficiency, turbine discharge limit and a few flow classes (Q and share of the year). Click Compute energy to see the annual energy per class, total annual energy, installed capacity and capacity factor.

Profile, table & exports

Energy contribution by flow class

Bars show how much each flow class contributes to annual energy (MWh/year). Turbine discharge limit caps the used flow; any excess is treated as spill.

Flow Q	% of year	Hours/yr	Turbine Q_used	Spill Q	Power used	Energy used
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Theory (brief)

Instantaneous power for one unit (SI units):

P = ρ g Q H η, internally converted to kW using ρ g ≈ 9.81 kN/m³ so P [kW] = 9.81 · Q · H · η.

For each flow class i with discharge Q_i and share of the year f_i (%):

Hours per year: t_i = (f_i / 100) · 8760 (h/yr)
Effective turbine flow (capped by turbine limit Q_t,max):
Q_i,used = min(Q_i, Q_t,max)
Spill flow: Q_i,spill = max(0, Q_i − Q_i,used)
Power used at that class: P_i = 9.81 · Q_i,used · H · η (kW)
Energy from that class: E_i = P_i · t_i / 1000 (MWh/yr)

Total annual energy:

E_year = Σ E_i (reported in MWh and GWh).

Installed capacity (if turbine fully loaded at Q_t,max):

P_inst = 9.81 · Q_t,max · H · η (kW)

Capacity factor:

CF = E_year / (P_inst · 8760 / 1000), expressed as a fraction or percent.