Hydropower is the largest single renewable electricity source today, providing 16% of world electricity at competitive prices. It dominates the electricity mix in several countries, developed, emerging or developing. 

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About hydropower


Hydropower derives energy from turbines being spun by fresh flowing water. This can be from rivers or from man-made installations, where water flows from a high-level reservoir down through a tunnel and away from a dam.


Hydropower is a mature and cost-competitive renewable energy source. It plays an important role in today’s electricity mix, contributing to more than 16% of electricity generation worldwide and about 85% of global renewable electricity.

Furthermore, hydropower helps stabilise fluctuations between demand and supply. This role will become even more important in the coming decades, as the shares of variable renewable electricity sources – primarily wind power and solar photovoltaic (PV) – will increase considerably.

The contribution of hydropower to decarbonising the energy mix is thus twofold: the primary benefit is its clean, renewable electricity. The secondary benefit is as an enabler to greater contribution of other renewables on the grid.

Hydropower development often contributes other benefits. The most important are water supply, flood and drought control, and irrigation; but navigation and recreational activities also have their place. These objectives can conflict at times, but are more often complementary. 


Hydropower generation and and forecast by region:

IEA, (2015), Medium-Term Renewable Energy Market Report 2015, OECD/IEA, Paris.

Hydropower technologies

Run-of-river hydropower plant harness energy for electricity production mainly from the available flow of the river. These plants may include short-term storage or “pondage”, allowing for some hourly or daily flexibility in adapting to the load demand profile, but the generation profile is mostly driven by natural river flow conditions or releases from any upstream reservoir hydropower plant (HPP). In the absence of such upstream reservoir HPP, generation depends on precipitation and runoff, and normally has substantial daily, monthly, seasonal and yearly variations.

Reservoir hydropower plant relies on stored water in a reservoir. This provides the flexibility to generate electricity on demand, and reduces dependence on the variability of inflows. Very large reservoirs can retain months or even years of average inflows and can also provide flood protection and irrigation services. The design of the hydro plant is very much dependant on the environment and social needs of the region and local project conditions. Most reservoirs are artificially created by building a dam to control the natural river flow. When local conditions allow, natural lakes can also function as reservoirs.

Pumped storage plants (PSPs) use water that is pumped from a lower reservoir into an upper reservoir when electricity supply exceeds demand or can be generated at low cost. When demand exceeds instantaneous electricity generation and electricity has a high value, water is released to flow back from the upper reservoir through turbines to generate electricity. Pumped storage plants take energy from the grid to lift the water up, then return most of it later (round-trip efficiency being 70% to 85%). Hence, PSP is a net consumer of electricity but provides for effective electricity storage. Pumped storage currently represents 99% of on-grid electricity storage.


For more information on hydropower please refer to the IEA Technology Roadmap: Hydropower.

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Fast facts

  • 159Number of countries where hydropower is a fully mature technology.