Practice

Micro-hydro

Also known as: Micro-hydroelectric, Small-scale hydropower

Small-scale hydroelectric power generation — typically under 100 kW, often under 10 kW for residential. Where a year-round flowing stream with sufficient head (vertical drop) is available, micro-hydro is among the most reliable, lowest-cost renewable energy sources — typically generating 24/7 unlike solar's daily and seasonal cycles. Practiced for centuries (water mills); modernized for electricity production in the late 19th century. Today hundreds of thousands of micro-hydro systems supply rural electricity worldwide, particularly in Nepal, Indonesia, the Andes, and remote Western United States.

Components

A typical micro-hydro system:

Intake — diverts water from the stream into a pipe (penstock); usually with a screen to keep debris out
Penstock — pipe conveying water from intake to turbine; the longer and steeper, the more head
Turbine — converts water flow + pressure to rotational mechanical energy. Pelton (high head, low flow), turgo, crossflow, propeller turbines depending on conditions
Generator — converts rotation to electricity
Charge controller and battery ([[off-grid-living|off-grid]]) — for regulation and storage
Tailrace — water returns to the stream

Power output

Micro-hydro power = head × flow × efficiency. Rough approximation:

1 GPM at 100 ft head ≈ 100 watts
10 GPM at 100 ft head ≈ 1 kW (continuous = 24 kWh/day = ~720 kWh/month)
A typical U.S. home uses ~900 kWh/month — so a small but adequate stream can fully power a home

Where it works

Site requirements:

Year-round flowing water — even minimal flow with significant head
Vertical drop (head) — even 10-20 feet of drop is workable; more is better
Distance from house — economical up to ~1,000 ft, sometimes more
Minimal seasonal variation — drought-prone streams need backup or sizing for low-flow

Sites that work well:

Mountain creeks and streams with reliable flow
Old mill races (often pre-1900s; rights and infrastructure may persist)
Springs with significant flow
Small creeks dropping through hilly terrain

Considerations

Permitting — varies by jurisdiction; smaller systems often exempt or simpler; larger systems require water rights, environmental review
Fish and ecology — well-designed systems include fish screens and minimal ecological disturbance
Cost — high upfront ($5,000-$30,000 typical residential); minimal ongoing; lifetime 30-50 years
Reliability — often the most-reliable home power source where conditions allow

Adoption

Nepal — micro-hydro has electrified thousands of villages outside the grid
Indonesia — substantial micro-hydro program in remote islands
Andes (Peru, Ecuador, Bolivia) — Indigenous-community micro-hydro
Pacific Northwest U.S., British Columbia — homestead and rural-residential common
Vermont, New Hampshire — old mill-race revivals

Sources

Micro-Hydro Design Manual, Adam Harvey (Practical Action, 1993)
Serious Microhydro, Scott Davis (New Society, 2010)
Home Power magazine archive

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