Example data
These samples show typical inputs and expected outputs.
| Mode | Gross head | Loss | Efficiency | Volume / Flow | Duration | Approx usable result |
|---|---|---|---|---|---|---|
| Stored | 40 m | 2 m | 90% | 3.0 m³ | — | ~0.310 kWh usable |
| Flow | 60 m | 5 m | 85% | 0.20 m³/s | 1 h | ~9.16 MWh usable |
| Flow | 20 m | 1 m | 75% | 500 L/s | 30 min | ~0.97 MWh usable |
| Stored | 10 m | 0.5 m | 80% | 5000 L | — | ~0.104 kWh usable |
| Flow | 12 m | 2 m | 70% | 50 L/s | 2 h | ~6.9 kWh usable |
Formula used
How to use this calculator
- Select Stored for a tank/reservoir, or Flow for a turbine system.
- Enter gross head and an estimated head loss.
- Set efficiency to match your system (turbine, generator, piping).
- Provide volume (stored) or flow rate + duration (flow).
- Click Calculate, then export using the download buttons.
Hydro potential energy in practice
1) Hydro potential energy basics
Hydro potential energy comes from water mass held above an elevation. The theoretical energy is E = m·g·H, measured in joules (J), where g ≈ 9.80665 m/s². Doubling head or mass doubles energy, so surveys and volume estimates matter.
2) Net head and why losses matter
Head in the field is rarely just “dam height.” Net head is gross head minus losses from friction, bends, screens, valves, and turbulence. Small systems often see 1–15% loss; long penstocks or rough pipes can be higher. If you only have a rough estimate, test a few loss values to see sensitivity.
3) Stored reservoirs: volume to mass
Stored mode converts volume to mass using density (ρ). Fresh water is close to 1000 kg/m³, but colder water can be slightly denser and warm water slightly lighter. Example: 1.0 m³ at 50 m net head stores about 1000×9.80665×50 ≈ 490,332 J, which is roughly 0.136 kWh before efficiency. A 10 m³ tank at 50 m holds about 1.36 kWh.
4) Flowing systems: power and time
Flow mode uses power first: P = ρ·g·Q·H. With Q = 0.20 m³/s and H = 55 m, theoretical power is about 108 kW. At 85% efficiency, usable power is ~92 kW. Over 1 hour, that becomes roughly 92 kWh of usable energy.
5) Efficiency assumptions you control
Efficiency (η) bundles turbine, generator, mechanical coupling, and electrical losses. Micro-hydro setups may run 70–85%, while well-optimized installations can reach 90–95% at design flow. If your flow varies a lot, calculate at minimum, average, and peak Q to bracket expected output.
6) Unit checks and planning with results
This calculator accepts common units so you can match site data. Remember: 1 cfs ≈ 0.0283 m³/s, and 1 US gpm ≈ 6.31×10⁻⁵ m³/s. For energy comparison, 1 kWh = 3.6 MJ. Use kW to size wiring and equipment, and kWh to estimate daily output; 1 kW continuous produces 24 kWh per day. Combine results with seasonal flow and downtime to judge yearly energy, realistic payback, and feasibility. Many homes use 200–500 kWh monthly, so kWh/day compares easily. For sites, consider capacity factor and spill flow.
FAQs
1) What is “net head” in this calculator?
Net head is the effective height that produces energy after losses. It equals gross head minus head loss. Use net head because friction, fittings, and intake screens reduce the usable pressure available to the turbine or outlet.
2) Why does changing water density affect results?
Energy and power scale with density because mass flow or stored mass increases with ρ. Fresh water near room temperature is about 1000 kg/m³. If you model warmer water, seawater, or muddy flow, adjust density accordingly.
3) Can I enter values in feet, gallons, or gpm?
Yes. Head can be entered in feet, and volume/flow can be entered in gallons, liters, cfs, or US gpm. The calculator converts everything internally to SI units before computing joules, watts, and kWh.
4) Why is usable energy lower than theoretical energy?
Theoretical values assume perfect conversion with no mechanical or electrical loss. Usable values multiply by efficiency (η), which accounts for turbine, generator, gearbox, and wiring losses. Head loss also reduces net head, lowering both power and energy.
5) What efficiency should I use for quick estimates?
For preliminary checks, 75–85% is a reasonable range for many small systems. If you have a turbine datasheet, use its efficiency at your expected flow and head. For well-tuned installations at design flow, 90–95% is possible.
6) Does this replace a full hydro engineering design?
No. It is a planning and education tool for first-pass estimates. Real projects require site surveys, seasonal flow studies, cavitation checks, pipe sizing, electrical protection, and local permitting. Use safety factors and consult a qualified engineer for final designs.