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The Understand Energy Learning Hub is a cross-campus effort of the Precourt Institute for Energy.


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Fast Facts About

Principal Energy Use: Electricity
Forms of Energy: Kinetic, Potential

Hydropower, also known as hydroelectricity, is a semi-renewable resource that uses the flow of water to generate electricity. We categorize this resource as semi-renewable, because it has to be carefully managed to ensure we are not using it faster than it can be replenished. There are two major approaches to generating electricity from hydropower:

  1. Storage hydroelectric systems store water for later use, which makes them a versatile resource for the grid. For example, large hydroelectric dams can be sited on rivers with valleys, creating an artificial lake or reservoir. Turbines and generators in the powerhouse generate electricity when water flows from higher-to-lower elevation. The six largest electricity generation facilities in the world are all conventional storage hydropower facilities.
  2. Run-of-river systems are generally smaller and use the river’s natural flow to generate electricity, so there is no water being stored and less disruption to the natural river system.

Hydro can also be used to store electricity in systems called pumped storage hydropower. These systems pump water to higher elevation when electricity demand is low so they can use the water to generate electricity during periods of high demand. Pumped storage hydropower represents the largest share (> 90%) of global energy storage capacity today.

Note: The small amount of marine/ocean-based hydropower is not included in this data and is covered on our Ocean Energy page.


Energy Mix

6% of world 🌎
2% of US 🇺🇸

Electricity Generation

15% of world 🌎
6% of US 🇺🇸

Hydroelectric Capacity by Type

Conventional Storage and Run-of-River Systems
(Electricity Generation)

Pumped Storage Systems
(Energy Storage)

Global Electricity Generation from Hydropower



Most Installed Capacity

China 30% 🇨🇳
of global hydroelectric generation installed capacity (excluding pumped storage)

Most Generation

China 32% 🇨🇳
of global hydroelectricity generation

Highest Penetration

Paraguay >99% 🇵🇾
of country’s electricity generation comes from hydroelectricity


Most Installed Capacity

Washington 27%
of US hydroelectric generation installed capacity

Most Generation

Washington 27%
of US hydroelectricity generation

Highest Penetration

Washington 55%
of state’s electricity generation comes from hydroelectricity

Note: These figures do not account for non-utility scale or off-grid hydropower generation.

Pumped Storage Hydropower

Most Installed Capacity

China 22% 🇨🇳
of global pumped storage installed capacity

Share of Global Energy Storage Capacity

Pumped Storage Hydropower: 92%
Lithium-Ion Batteries: 5%
Other: 3%

Pumped Storage “Roundtrip” Efficiency

of the energy used to pump water uphill can be converted back into electricity

Global Pumped Storage Capacity



  • Abundant
  • Co-benefits: flood control, water storage for agricultural, residential, commercial, recreational purposes
  • Can be used to “black start” the electricity grid after major outages*
  • The lowest-cost source of electricity globally based on LCOE**
  • Qualifies under some nations’ renewable energy targets (although large hydro may not count in some jurisdictions due to environmental impacts)
  • Financial incentives such as production tax credits (PTC) and feed-in tariffs
  • Pumped Storage alleviates intermittency when integrating other renewables


  • Site-specific resource, only available in some geographies
  • Droughts and climate change can impact water cycle, changing long-term resource availability
  • Competing downstream uses for water can limit its use for electricity generation
  • Destruction of cultural heritage sites and human settlements, forcing mass relocation and compensation
  • Flooding of terrestrial habitat, disrupting ecosystems that rely on lakes and rivers
  • Impacts on aquatic species (e.g., fish mortality and barriers to migration); may also be culturally and economically important to Indigenous communities
  • Seasonal changes in reservoir levels can affect soil quality and crop yields
  • Seismic impacts from large reservoirs
  • Expensive initial capital costs to build dams
  • Lengthy planning, permitting, and construction process
  • Local opposition to dam construction (NIMBY/BANANA***)
  • Inconsistent policy support
  • Movement to remove dams due to environmental harms

*Black start - recovering from a blackout by individually restarting power systems and gradually reconnecting them to form an interconnected grid
**LCOE (levelized cost of electricity) - price for which a unit of electricity must be sold for system to break even
***NIMBY - not in my backyard; BANANA - build absolutely nothing anywhere near anything

Climate Impact: Low to Medium

Gradient from green to yellow to orange to red, with rectangle around the green and yellow portion.
  • Near-zero carbon emissions during operation
  • However, reservoirs created by dams can flood ecosystems upstream in some climates, releasing significant amounts of methane (a potent GHG) as vegetation decomposes, which potentially negates climate benefits

Environmental Impact: Medium to High

medium to high gradient
  • No local air pollution
  • Dams can submerge natural habitat, cultural heritage sites, and human settlements, potentially displacing tens of thousands
  • Impacts to aquatic ecosystems can disrupt life cycles by blocking or injuring migratory species
  • Some run-of-river systems can avoid major environmental impacts

Updated October 2023

Before You Watch Our Lecture on
Hydroelectric Power

We assign videos and readings to our Stanford students as pre-work for each lecture to help contextualize the lecture content. We strongly encourage you to review the Essential videos and readings below before watching our lecture on Hydroelectric Power. Include selections from the Optional and Useful list based on your interests and available time.


Optional and Useful

Our Lecture on
Hydroelectric Power

This is our Stanford University Understand Energy course lecture on hydropower. We strongly encourage you to watch the full lecture to understand hydroelectric power as an energy system and to be able to put this complex topic into context. For a complete learning experience, we also encourage you to watch / read the Essential videos and readings we assign to our students before watching the lecture.

David Freyberg

Presented by: David Freyberg, PhD; Associate Professor, Civil and Environmental Engineering, Stanford University; Senior Fellow, Woods Institute for the Environment
Recorded on: May 24, 2023  Duration: 78 minutes

Table of Contents

(Clicking on a timestamp will take you to YouTube.)
0:00 Introduction to Hydroelectric Power
6:27 Power of Flowing Water and Energy Transformation
8:09 History and Context of Hydroelectric Power
19:16 Energy Systems and Hydroelectric Facilities
44:12 Hydropower Operations
58:25 Summary of Hydropower Features and Limitations
1:00:24 Impacts and Issues of Hydroelectric Power

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Additional Resources About

Government and International Organizations

Fast Facts Sources
World Energy Mix, 2022. (Our World in Data, 2023)
U.S. Energy Mix, 2022. (EIA 2023)
World Electricity Mix 2021. (Ember 2022)
U.S. Electricity Mix 2022. (EIA 2023)
Installed Capacity, 2022. (International Hydropower Association IHA 2022)
Global Demand 2021. (Ember 2022) and (IRENA 2022)
Most Generation 2022. (IHA 2022)
Highest Penetration 2022. (IRENA 2022, Paraguay - Energy Profile)
US State-Level Capacity, Generation, Penetration. (DOE 2018)
Most Generation 2022. (EIA 2023: Where Hydropower is Generated)
Highest Penetration. (Washington State, Department of Commerce 2022)
More details available on request.
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