Hydroelectric power converts the gravitational potential energy of water into electricity. It has been the largest single renewable source for over a century and still leads renewables by generation. This guide covers the technology, plant types, and role in the modern grid.
The basic principle
Water flows from higher to lower elevation. That flow drives a turbine. The turbine spins a generator. The generator produces electricity. Everything else is engineering detail on how to control the flow, extract maximum energy, and deliver electricity to the grid.
Hydro plant types
| Type | Description |
|---|---|
| Reservoir | Dam creates storage; controlled release drives turbine |
| Run of river | No significant storage; generation follows river flow |
| Pumped storage | Pumps water uphill during cheap electricity; generates during expensive |
| Small hydro | Under 10 MW; distributed generation |
| Micro hydro | Under 100 kW; off grid rural |
| In stream tidal | Emerging; use tidal or river currents |
Main components
| Component | Function |
|---|---|
| Dam or intake | Direct water into penstock |
| Penstock | Pipeline delivering water to turbine |
| Turbine | Convert water flow to rotation |
| Generator | Convert rotation to electricity |
| Transformer | Step up voltage for transmission |
| Spillway | Bypass flow around turbine when needed |
| Tailrace | Return water downstream |
| Fish passage | Enable fish migration around dam |
Turbine types
See our companion article on hydropower turbines explained.
Global scale
Leading hydro countries
| Country | Installed hydro (GW) |
|---|---|
| China | ~400 |
| Brazil | ~110 |
| US | ~102 |
| Canada | ~85 |
| Russia | ~55 |
| India | ~50 |
| Norway | ~34 |
Capacity factor
Reservoir hydro capacity factor 35 to 60 percent; run of river 25 to 45 percent. Higher than wind and solar, lower than nuclear or geothermal. Dispatchable in reservoir case.
Cost
Existing hydro is often the cheapest source available due to sunk capital. New hydro is expensive (USD 1500 to 4000 per kW) and constrained by suitable sites.
Pumped hydro storage
The largest energy storage technology globally at 175 GW. Pumps water uphill during low electricity price; generates during high price. Round trip efficiency 70 to 85 percent.
Environmental considerations
Growth prospects
Major new hydro concentrated in Asia (China, India, Southeast Asia) and Africa. New hydro in developed markets is limited by suitable sites, environmental concerns, and displacement issues. Modernisation and repowering of existing plants is significant.
Climate change effects
Drought reduces reservoir output. Melting glaciers may reduce long term water availability in some regions. Higher rainfall variability requires more sophisticated water management.
Future outlook
- Modest growth in installed capacity globally.
- Significant pumped hydro expansion.
- Existing plant modernisation.
- Small hydro deployment in Africa and rural areas.
- In stream and tidal technologies emerging.
Frequently asked questions
Is hydro renewable?
Yes. Water cycles indefinitely through evaporation and precipitation.
Which is the largest hydro plant?
Three Gorges Dam in China at 22.5 GW.
Do hydro reservoirs produce methane?
Some yes, from flooded biomass. Tropical reservoirs generally higher than temperate.
Can we build more hydro?
Yes in some regions. Limited by suitable sites in developed markets.
What is pumped hydro?
Energy storage using water pumped uphill for later generation.
How reliable is hydro?
Very. Drought is the main variability driver.
Does hydro affect fish?
Yes. Fish passage and ecosystem impacts require management.
Is hydro dispatchable?
Reservoir yes. Run of river no.
How long do hydro plants last?
Very long. Some over 100 years with maintenance.
Where can I see hydro plants?
The UtilityRadar directory lists hydro plants.
Summary
Hydroelectric power converts water flow into electricity through turbines. Reservoir hydro provides bulk dispatchable generation; run of river provides variable base; pumped storage provides energy storage. Global installed capacity 1,400 GW; generation 4,300 TWh. Environmental and social impacts require careful management. Modest growth expected globally with concentration in developing markets.
Next reading
- Hydropower turbines explained
- Renewable energy complete guide
- Energy storage ranked
- Browse the UtilityRadar directory
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