Hydro in brief
Hydropower generates electricity from water moving downhill. It is the world's largest source of renewable electricity and among the oldest.
Large reservoirs can store water and release it on demand, making hydro one of the most flexible sources on the grid. Pumped storage uses the same principle to store energy.
How it works
- Water is held or channelled. A dam creates a reservoir, or a weir diverts part of a river.
- It falls through a penstock. The height difference (head) gives the water pressure and speed.
- It spins a turbine. Francis, Kaplan or Pelton turbines suit different heads and flows.
- The generator feeds the grid. Output can be raised or lowered within minutes.
Main technologies
- Reservoir (dam): Large storage, highly flexible.
- Run-of-river: Little storage; output follows river flow.
- Pumped storage: Pumps water uphill when power is cheap, releases it when needed.
Strengths
- Dispatchable and fast to respond
- Very long asset lives
- Large-scale storage with pumped hydro
Challenges
- Limited new sites in many countries
- Ecological and social impact of dams
- Exposure to drought
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