What it runs
A creek doesn't stop at sunset. That's the whole case for micro-hydro: a small, steady output, 24 hours a day, adds up to more than it sounds.
| Drop | Flow | Power, all the time | A day | Runs about |
|---|---|---|---|---|
| 100 ft | 10 gal/min | 83 W | 2.0 kWh | A fridge and lights |
| 10 ft | 100 gal/min | 83 W | 2.0 kWh | A fridge and lights |
| 50 ft | 30 gal/min | 125 W | 3.0 kWh | A small cabin: fridge, lights, phones, a laptop |
| 100 ft | 30 gal/min | 250 W | 6.0 kWh | A small off-grid home's everyday use |
The rule from NCAT: watts ≈ drop (feet) × flow (gallons a minute) ÷ 12. Multiply by 24 for a day. Their example: 10 gallons a minute falling 100 feet "is enough to light an 80-watt bulb pretty much continuously."
Does your site have it?
- Year-round flow. At least about 10 gallons a minute, in the driest month. Measure it in late summer, not spring.
- Drop. The vertical fall from where you take water in to where the turbine sits. A few feet works with a lot of water; a lot of drop works with a little water.
- Water rights. Owning the land doesn't always mean owning the right to use the water, especially in the West. Permits can take a while. Ask your state water agency first.
NCAT's summary: a year-round flow and a few feet of drop can give you years of continuous power. Without them, it isn't an option at all.
Hydro plus a battery
The turbine charges a battery bank like solar panels do, so the rest of the system is the same: a server-rack battery and an inverter. Because the creek refills it all night, the battery can be smaller than a solar-only system needs.
No creek?
Most people don't have one, and that's fine. Solar sized for your darkest month does the same job: see what yours needs.
Questions people ask
How much power can a small stream make?
Multiply the drop in feet by the flow in gallons a minute and divide by 12 for usable watts. 10 gallons a minute falling 100 feet, or 100 gallons a minute falling 10 feet, both make about 83 watts, all day and all night.
What's the least water micro-hydro needs?
About 10 gallons a minute is the practical lower limit, and it has to flow all year. A creek that dries up in August gives you nothing in August.
Do I need a permit for micro-hydro?
Often, yes. Water rights don't always come with the land, especially in the West, and permits can be slow. Check with your state water agency before buying anything.
Is micro-hydro better than solar?
Where the water is there, it has one big edge: it runs 24 hours a day and doesn't care about winter or clouds. Most places don't have the water for it, which is why solar is the default.
Sources
Every number on this page comes from these sources. Spotted something out of date? Tell me.
Get the exact setup
A few taps and you'll know exactly what to buy for your situation.