Your guide to hydropower and how it works

With renewable energy sources in high demand, we look into the different types in more detail to find out how hydropower works.

Disclaimer: The information on this page was last updated on 23/12/2022, 13:08:42

With renewable energy on the rise, you might be wondering how it all works. Hydropower uses the water cycle to generate a renewable energy source and it’s a massive piece of the 100% renewable energy puzzle.

How does hydropower work?

The most common type of hydroelectric power plant uses a dam to collect river water in a reservoir and raise the water levels. A small opening in the dam uses gravity to create a downward flow of water – the bigger the difference between the upstream and downstream water level, the faster the water moves and the more electricity can be produced.

This fast-flowing water spins a turbine at the bottom of the dam which uses the kinetic energy to generate mechanical energy. This turbine then turns a shaft to activate a generator, which converts this mechanical energy into direct current (DC) electricity. Unfortunately, in the UK our homes and appliances all run on alternating current (AC) electricity, so the DC electricity has to run through an inverter to turn it into usable AC electricity.

There is no water lost to the electricity generation process, which is what makes it such a great source of renewable energy. The water flows past the turbines into a downstream outlet and continues down the river like normal.

How hydroelectric power uses the water cycle to generate electricity

The water cycle has a crucial role in hydroelectricity production. Without the water cycle, water wouldn’t collect upstream and water would flow less and generate less electricity. It’s the water cycle that makes hydropower a renewable energy source.

What is the water cycle?

The water cycle is a naturally occurring, continuous process which allows water to be recycled and stops us running out.

  1. Water from rivers, lakes, oceans, and reservoirs are heated by the sun and evaporates into water vapour.
  2. The water vapour cools down and condenses into small droplets of water, forming clouds.
  3. The clouds get too heavy with water and it gets released as rain, snow, and hail.
  4. The water returns to the rivers, lakes, oceans, and reservoirs and the process starts over.

Advantages of hydroelectric power

Hydropower is an important part of the 100% renewable energy journey. People have used flowing water as a power source for thousands of years, so there must be something great about it!

  • It’s a clean fuel source – Because it’s fueled by water, hydropower plants don’t give off pollution and toxins that fossil fuels would.
  • It’s sustainable – It relies on the natural water cycle, which renews itself consistently without us having to worry about running out.
  • It’s great for recreation – Because only the flow of the water is converted into electricity, people can use the reservoirs created by the hydropower plants for activities such as fishing and swimming without worrying about disturbances.
  • It can contribute to the storage of drinking water – If you don’t want to use the reservoir for recreation, you can use it to store water for consumption instead.
  • It’s an immediate source of power – The electricity generated by the water flow goes straight into the grid as an immediate source of power.
  • It’s adjustable – You can change how much water flows through at a time, and therefore how much electricity is being produced. Some plants can go from zero to maximum output in seconds which makes it a great backup energy source.
  • It’s money-saving – Non-renewable energy prices are on the rise, while the price of renewables is decreasing. Using hydropower would cut your energy bills and save you money.

Disadvantages of hydroelectric power

While hydropower has proven a great source of renewable energy throughout history, there will always be some drawbacks.

  • It can damage wildlife habitat – Hydropower plants can cause a loss or change of fish habitat, disrupting their migration or even reproduction. This will also affect other animals which rely on fish for their diet.
  • Limited locations – While hydropower is renewable, there are only a few suitable places to construct a plant. Some of these places might be inconvenient for energy production.
  • Susceptible to droughts – During a drought, there might not be enough water in the rivers to flow through the plants to produce electricity.
  • Flood risks – Rising the water levels might end up creating floods if there’s heavy rain, which has been seen with multiple dams across hundreds of years.
  • Very high initial costs – Because a dam needs to be built as well as the plant itself, it has a very high start-up cost (more than a similar-sized fossil fuel plant).

Is domestic hydropower a good idea?

If you live by a river or stream, you might be considering powering your home with the water’s energy. However, just because you have a running water supply, it doesn’t mean you’ll reap the best benefits from hydropower.

Take into account your water levels – if they’re low, you might not be able to generate enough energy from the water but if they’re high, you might end up susceptible to flooding. These levels will also vary by year, depending on the amount of rainfall.

If you want to power your home with hydropower, you should talk to a certified installer, and they can tell you if they think it’s a good idea or not.

How much can I save?

The average hydropower system needed to power one household would have a 1kW capacity. The basic equipment for this, including battery supplies, would cost around £5,000-6,000, however, installation costs could be a lot higher depending on how difficult it would be to install.

The average household using hydropower could save 16p per kWh of the power they use (roughly £400 per year). While this may sound like a lot, it does mean that it will take roughly 30 years to break even with a system with a capacity of 1kW. The higher the capacity of your hydropower system, the lower the cost per kWh. With a bigger system, despite the higher set-up costs, you could power more houses and see a higher return on investment much sooner, especially if you split the costs with the other homes you’re powering.

However, there are schemes such as the Smart Export Guarantee which will buy any of your unused power if you feed it back into the national grid, which means you could easily pay it off sooner. Different companies will pay different amounts, however, the average payout is 5-6p per kWh.

Hydropower around the world

Hydropower accounts for 47% of renewable energy worldwide, with a capacity of 1192gw by the start of 2020. There are 71 hydropower stations with a capacity of over 2gw around the world, 22 of which are located on Chinese rivers.

In the US, hydropower is the second-largest renewable energy source, behind wind power. At the start of 2020, the US’ hydropower capacity was at 80gw and generated power in all but 2 states.

In several different countries in Africa, hydropower accounts for over 75% of their electricity capacity. Across the continent, it remains the highest-generating renewable energy source, however, this is only 15% of the total electricity share. On top of this, only 11% of all hydropower potential across the continent is actually used.

Hydropower in the UK

While hydropower provides around 16% of the world’s energy, it’s not as big a part of the UK’s fuel mix, averaging 1.7% of all of our energy use.

The largest hydropower station in the UK is located in Wales, generating 1700mw – enough to power 2.5 million homes. In comparison, the largest in England can only generate 6mw which can power 400 homes.

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