Micro-Hydro Power Calculator
Micro-hydro kW from stream flow and head.
What it does
Streams make watts from falling water. Flow times head times efficiency sets output: 0.1 cubic meters per second over 10 meters at 60 % makes 5,886 watts, near 141 kWh a day for almost five American homes. Every site multiplies the same three numbers.
The tool above runs both unit systems. Metric takes m3/s with meters; imperial converts gpm with feet inside. Defaults give 5.89 kW; the handbook check at 0.3 m3/s gives 14.71 kW while a trickle site gives 0.59.
Energy agencies confirm the physics. DOE hydropower guides state output follows flow with elevation, while Canadian and Colorado handbooks print P equals rho-g-H-Q with 0.5-0.7 efficiencies and worked checks. EIA household use near 10,500 kWh a year sets the 1.2 kW home divisor.
Net head decides honesty. Pipe friction steals 5-10 % of gross head, seasonal flows swing output across months, and permits with fish screens gate projects before math. Measure low-water flow, then size to the lean season.
How to use
- Pick metric or imperial.
- Enter usable flow.
- Enter net head.
- Enter efficiency (0.6 plans well).
- Read kW first, then kWh/day.
- Read homes powered.
Formula
- Q
- Usable flow: m3/s or gpm by system.
- H
- Net head: m or ft by system.
- eff
- Water-to-wire efficiency, 0.2-0.9.
DOE confirms flow-times-head physics; NRCAN/CU handbooks give P=QHg(eff) with 0.5-0.7 and EIA the 1.2 kW home divisor.
Worked example
Example: 0.1 m3/s, 10 m head
Metric defaults: 0.1 m3/s, 10 m, 0.6. Imperial mirrors in gpm/ft.
- Inputs: 0.1 m3/s flow, 10 m head, 0.6 efficiency.
- Watts: 1000 x 9.81 x 0.1 x 10 x 0.6 = 5,886.
- kW: 5.89. kWh/day: 5.886 x 24 = 141.3.
- Homes: 5.886 / 1.2 = 4.9 at US average.
- Tool shows 5.89 kW, 141.3 kWh/day, 4.9 homes.
Reference table
| Flow x Head | kW | Homes |
|---|---|---|
| 0.1 m3/s x 10 m | 5.89 | 4.9 |
| 0.3 m3/s x 10 m | 14.71 | 12.3 |
| 0.02 m3/s x 5 m | 0.59 | 0.5 |
Limits
- Planning math only. Surveys needed.
- Efficiency guessed; turbines vary.
- Seasonal flows swing output.
- Permits and rights excluded.
Common mistakes
- Gross head instead of net.
- Ignoring pipe friction losses.
- Sizing to flood-season flow.
- Skipping efficiency derates.
- Forgetting permits and screens.
Try it yourself
Quick checks. Answers sit tucked under each question.
0.3 m3/s, 10 m, 0.5 efficiency?
W = 1000x9.81x0.3x10x0.5 = 14,715. kW 14.71. kWh 353.2. Homes 12.3.
0.02 m3/s, 5 m, 0.6 efficiency?
W = 1000x9.81x0.02x5x0.6 = 588.6. kW 0.59. kWh 14.1. Homes 0.5.
Questions
How are hydro watts figured?
1000 x 9.81 x flow x head x efficiency. Here 5,886 W.
What efficiency?
0.5 to 0.7 typical for micro water-to-wire per DOE/NRCAN handbooks.
How many homes per kW?
About 1.2 kW from ~10,500 kWh a year per EIA. Here 4.9 homes.
Gross or net head?
Yes. Net head after 5-10% pipe friction; measure flowing, not static.
Does flow vary by season?
Yes. Seasonal flows swing output; size for low-water months.
Do I need permits?
Yes. Permits, fish screens, and water rights gate projects before math.