A Quick Family Tree Of Hydro Power Systems
The same trick runs a turbine the size of a bucket and a dam the size of a mountain. Water falls, spins a wheel, and a generator turns that spin into electricity. Same idea, wildly different scale.
So engineers sort hydropower by its capacity, which is just how much power it can produce, a bit like sorting bikes, family cars and school buses by size.
Pico is anything up to 5 kW. Think cabins, sheds and workshops.
The next class up runs from 5 to 100 kW. That covers whole homes, farms and tiny villages.
Above 100 kW you hear names like mini and small hydro, and every country draws those lines a little differently. The British Hydropower Association calls anything over 1 megawatt large.
For off-grid living, you'll be choosing between the first two. So let's look at them one at a time.
Pico Water Turbines (Up To 5 kW)
The whole water turbine and generator might fit in a wheelbarrow, and some kits come with the two built as one piece of equipment. The penstock, which is just the pipe that carries water down the hill, might be a 50-meter run of 75-millimeter pipe. The intake can be a simple concrete box with a screen.
What does a pico setup actually run?
A 100-watt unit: LED lights and phone charging in a remote hut.
A 500-watt unit: lights, a fridge, a radio and a laptop for one or two people.
A 1000-watt unit: the basics of a little house, including some power tools.
A 3000-watt unit: a full off-grid home with a washing machine, well pump and internet.
Here's a trick that makes pico punch above its weight. Water keeps flowing at night, so the generator charges batteries around the clock. That stored energy, sent through an inverter, can provide 2 to 5 kW for short peaks, like a kettle, even when the water only gives a few hundred watts.
Most pico setups are run-of-river. That means no dam and no reservoir: a pipe borrows some water, and it goes straight back into the stream below the turbine. That's why a run-of-river system has very little impact on the plants and fish around it.
→ Can your stream qualify for pico?
Micro Hydro Power (5 to 100 kW)
Micro is what most off-grid families with a strong river end up building.
This is a real project. The turbine and generator are installed on a concrete pad, the penstock is buried plastic pipe, and the intake has a screen, a valve and sometimes a settling pond to catch silt.
What can a system this size do?
A 5 kW system: a family home with all the appliances, electric cooking, maybe a heat pump for warmth.
A 10 kW system: a large home with room for an electric car and a workshop.
A 25 kW system: a farm with several buildings.
A 100 kW system: a hamlet or a remote lodge.
At this size the design matters more. Which type of turbine works best depends on whether you have lots of drop and little water, or the other way around.
Bigger systems require bigger civil work, which is a fancy name for the digging and concrete. That's where most of the money goes. The Centre for Alternative Technology says the turbine itself is often only about 20% of the total cost.
They almost always require permits too, often with an environmental check, because you are moving enough water from the river that the people who look after it will care.
→ Why you probably need a permit
→ What a home hydro system really costs
How Much Energy Do You Need?
Three things decide which class you fall into: your water, your energy use and your budget.
Start with the water. How much head and flow do you have? Head is how far the water drops, and flow is how much water passes each second. If your stream can only produce 2 kW at most, no amount of money turns that location into a micro site.
Then your energy use. The average US home uses about 899 kWh (kilowatt-hours) a month, which is roughly 30 a day.
Water has one big advantage here: it keeps flowing. A 1 kW turbine running nonstop makes 24 kWh every day, close to what that average home uses.
A 5 kW turbine makes 120 kWh a day. That's about four average homes' worth.
→ Calculate your actual energy needs
When Pico Beats Micro
Sometimes the smaller option is just smarter.
If your stream is borderline, a pico setup is the only thing that fits. A micro turbine would sit there starving for water.
If you only need power for a workshop or weekend cabin, pico is plenty.
If you want to learn before you commit, a pico turbine is a cheap way in. If it works well, you can scale up later.
But don't count on pico skipping the paperwork. In England, Wales and Scotland you need an abstraction licence once you divert more than 20,000 liters a day, even though the water goes straight back. That's only about a quarter of a liter per second, so many pico setups cross the line.
The Benefits Of Going Bigger
Other times, going bigger pays off.
If a strong river makes the water available (for example 20 meters of head and 50 liters per second, about 5 kW), pico leaves a lot of power on the table.
If you want to run your whole house including electric heat, you need micro. A pico turbine cannot keep up with a heat pump and an electric stove running for hours.
If you might add things later (a workshop, an electric car, more buildings), micro gives you headroom. Swapping a turbine for a bigger one means new pipe, new wiring and often a new permit.
Most turbines last at least 25 years, so this is a long-term choice either way.
The Sweet Spot For Most Families
For many families, the sweet spot is around 3 kW, right near the line where pico ends and the bigger class begins. But first check that your water can make that much.
The sum is: power in watts = 9.81 × flow in liters per second × net head in meters × efficiency.
Net head is the drop minus the friction losses in the pipe. Home systems usually reach 50 to 70% efficiency overall, because the turbine, generator and wiring each lose a bit. And use the water flow from the driest month, not spring, because that's when your power is lowest.
Two examples, using 50%:
- 4 meters of head and 20 liters per second: 9.81 × 20 × 4 × 0.5 = about 400 watts. That's a pico system.
- 20 meters of head and 30 liters per second: 9.81 × 30 × 20 × 0.5 = about 2.9 kW. That's the sweet spot.
The Centre for Alternative Technology in Wales runs a turbine on almost exactly that recipe: up to 20 liters per second dropping about 30 meters, for about 3 kW.
→ Do the 30-second check on your own stream
If your water can carry it, a 3 kW system runs everything in a normal off-grid home. It's a reliable, renewable source that keeps going after dark.
If your stream is too weak, drop to a 1 to 2 kW pico setup and add solar to fill the gap. If it's stronger, scale up. There is no wrong answer if the math works.
→ How hydro stacks up against solar and wind
→ Back to the full hydro overview
Sources
- energypedia, Micro Hydro Power (MHP) Plants
- British Hydropower Association, Types of hydropower
- NCAT, Micro-Hydro Power: A Beginners Guide to Design and Installation
- Centre for Alternative Technology, Micro-Hydro Power
- US EIA, How much electricity does an American home use?
- Government of Ontario, Micro-hydro systems
- Wikipedia, Pico hydro
Hard Words
| Term | What it means |
|---|---|
| Pico-hydro | A system up to 5 kW. Right size for a cabin, shed, or single off-grid room. |
| Micro-hydro | A system from 5 to 100 kW. Right size for a whole home, farm, or hamlet. |
| Mini-hydro | The class above micro, from 100 kW up. Where it ends depends on who you ask. |
| Small-hydro | Bigger again. Some groups use it for 100 kW to 1 megawatt, others for up to 10 or 15 megawatts. |
| Kilowatt (kW) | 1000 watts of power output. 1 kW running for an hour makes 1 kWh of energy. |
| Kilowatt-hour (kWh) | How much energy a turbine makes over time. 1 kW for 24 hours is 24 kWh. |
| Civil work | The digging and concrete. Grows fast as the turbine gets bigger. |
| HDPE pipe | The flexible black plastic pipe used for most home penstocks. |
| Settling pond | A pond before the intake where silt sinks before it reaches the turbine. |
| Abstraction licence | The permit you need in England, Wales and Scotland to divert more than 20,000 liters of water a day, even if it goes back. |
Common Questions
What's the difference between pico hydro and micro hydro?
Pico is up to 5 kW, the right size for a cabin or shed. Micro is 5 to 100 kW, big enough for a whole home or a farm.
How much can a pico setup actually run?
A 100-watt unit runs LEDs and phone charging, and a 500-watt unit adds a fridge and laptop. A 3000-watt unit can run a full off-grid home, especially with a battery bank for peaks.
How much can a micro setup do?
A 5 kW system covers a family home with electric cooking, 10 kW adds an electric car, and 100 kW runs a hamlet.
Which one should I build?
Match the turbine to the smallest of three things: what your water can make, how much energy you use, and your budget.
Do I need a permit for a pico turbine?
Often, yes. In England, Wales and Scotland, diverting more than 20,000 liters a day needs an abstraction licence, which is only about a quarter of a liter per second. Check your local rules before you buy anything.
What's the sweet spot for most families?
Around 3 kW, if your water can deliver it. That takes about 20 meters of head and 30 liters per second in the dry season, while 4 meters and 20 liters per second only gives about 400 watts.