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Page last updated on 3rd July 2025

What is hydropower and how does it work?

This guide will break down the science behind hydroelectric power, the advantages of hydroelectric energy and the role it might play in generating more sustainable energy.

Learn more about hydropower

Learn more about Britain's energy system

Generating over 50% of the world’s renewable energy, hydropower is one of the oldest and most widely used renewable sources of energy. However, hydropower made up just 2% of electricity generation in Great Britain in 2024. But what is hydroelectricity exactly? And how does hydroelectricity work?

What's on this page?

What is hydropower energy?
How does hydropower work?
Hydropower benefits
How does hydroelectricity work with smart meters?
Hydropower and the future

What is hydropower energy?

What is hydro energy exactly? Similarly to tidal energy, hydroelectric energy is a type of renewable energy that generates electricity by harnessing the power of moving water (known as ‘hydropower’). Hydropower has been used for renewable electricity generation for hundreds of years with the first hydroelectric project being set up right here in Great Britain.

Large-scale hydropower plants use dams and reservoirs to generate electricity for the grid. Micro hydropower systems, which are typically used locally to power individual homes, are smaller, generating electricity using small streams and rivers.

So, what is hydropower? Hydropower is a form of renewable energy that can provide a consistent supply of energy. Hydropower is a low-carbon alternative to fossil fuels.

An aerial view of a hydropower dam, with hills in the background.

How does hydropower work: hydropower explained

If you’re wondering “How does hydroelectric power work”, the first thing to understand is how hydroelectric systems use water to generate electricity:

Hydroelectric systems are built in areas where water runs downhill, like lakes, rivers and reservoirs.
The running water passes through a tunnel, then a spinning turbine.
Like with wind turbines, the movement of the spinning turbine is converted into electrical energy.
This electrical energy is then sent out to the grid, or used locally, in the case of micro hydropower.
The water flows back to the sea, allowing the cycle to repeat and generate electricity continuously.
The electricity generated from hydropower can then be used to power homes and businesses.

The higher the water source, the more electricity the system can generate. This means that hydropower can be best used in hilly or mountainous regions with lots of water sources. It also explains why Scotland generates 85% of the UK’s hydroelectric power.

For more information, check out Energy Saving Trust’s guide to hydroelectricity generation.

Hydropower benefits

“What are the advantages of hydroelectric energy?” Like other renewable energy sources such as biomass and wind energy, hydropower has a wide range of benefits:

Clean energy

Hydropower uses the power of water to generate electricity, which can be reused again and again. This makes hydropower a renewable source of energy that does not emit greenhouse gases or other pollutants when producing electricity.

Cost-effective

Aside from its environmental benefits, the long-term operating costs of a hydroelectric system are low, making it a cheap source of renewable energy once the hydroelectric system has been installed. Micro hydropower for homes can be especially cost-effective for off-the-grid homes close to a water source.

Reliable

Unlike solar or wind power which rely on weather conditions to operate, hydropower systems are in operation 24/7, generating a constant supply of electricity, as long as water is always readily available.

Wider environmental benefits

Hydropower benefits the environment beyond being a clean source of energy, because, depending on the set up, it can:

Reduce the risk of flooding (especially hydropower systems with reservoirs), as the flow of water is regulated continuously.
Provide water for irrigation and clean drinking water for communities.
Preserve biodiversity by encouraging the growth of vegetation around hydropower plants.

Disadvantages of hydropower explained

“What is hydroelectricity not as good for?” While hydroelectricity is an efficient source of low-carbon energy, there are some potential drawbacks:

Geographic limitations

Hydropower systems are dependent on access to a suitable source of flowing water. This means that micro hydropower systems will only work in very specific locations. So, they aren’t a practical option for most homes, especially for people living in cities, or far away from suitable water sources.

Build or installation costs

Large hydropower facilities can have high upfront costs to build. Similarly, micro systems can also be expensive for people to install in their homes.

Environmental impact of hydropower systems

Some of the most essential components of large-scale hydropower systems are dams and reservoirs, which help generate hydroelectric power. Hydropower dams can disrupt river ecosystems by changing water temperatures, water flow, and water quality, affecting fish migrations and other aquatic life.

Micro hydropower is much less harmful to river ecosystems, although there will be some disruption to the natural water flow.

Water availability

While hydropower is more reliable than other renewable sources of energy, water is not always readily available. Droughts and regional changes in rainfall can make hydropower less reliable.

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How does hydroelectric power work with smart meters?

At a large scale, for hydropower and other renewables to be used efficiently within the grid, the energy system needs to balance electricity supply with usage. That's where smart meters come in. Smart meters send meter readings automatically, so you don’t have to. This means that suppliers will receive regular and consistent meter readings, helping them understand energy demand across the country, particularly during peak times when many of us are cooking or heating our homes.

Smart meters can also help reduce the strain on the energy system during peak demand by enabling energy suppliers to encourage you to shift your electricity use to off-peak periods by offering time-of-use tariffs. This could allow our energy system to rely more on renewables like hydropower instead of using fossil-fuelled power stations to meet demand.

Get a smart meter and help Britain use more renewable energy. Simply enter the name of your supplier in the box below to get started.

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Hydropower and the future

Even though hydropower only makes up a small proportion of energy generated in Great Britain, as the country works towards its target of net zero by 2050, hydropower will support the transition to low-carbon energy, alongside other renewables.

Smart meters can support this transition by helping households across the nation understand and manage their energy use in a more energy-efficient way.

Get a smart meter

Find out more:

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Understanding the energy system in Great Britain

Benefits of smart meters for Great Britain and the environment

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