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Hydroelectricity - everything you need to know

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In our complete guide to hydroelectric power, we’ll explore how the power of water can be harnessed to generate electricity for our homes. We’ll take a closer look at the basics of hydroelectric energy, how it works and its key advantages. You’ll also see how households can benefit from hydroelectric power in Northern Ireland and the UK.

Article Contents

  • Hydroelectric power explained 

  • How does hydroelectric power work?

    • Understanding hydropower plants

  • What are the different types of hydroelectric power plants?

    • Advantages of hydroelectric power 

  • Getting started with hydroelectric power

  • Power NI - Go Green 

  • FAQs 

  • Further reading 

Hydroelectricity explained

Hydroelectric power or hydroelectric energy is a renewable energy source that utilises the power of water to generate electricity. This is achieved by using the powerful flow of water to turn turbines. The movement of the turbines generates hydroelectricity.

In Ancient Greece, hydropower was used to grind wheat into flour. There’s also a strong history of hydroelectricity in Northern Ireland. In the late 1800s, there were around 1,200 water-powered mills here. Hydroelectric power was the main source of electricity for many rural communities in Northern Ireland until the 1960s. 

How does hydroelectric power work? 

Hydroelectric power works by harnessing the power of fast-flowing water as it travels from a height to a lower point. Usually, this is done by controlling the flow of water out of a reservoir. When water is released from behind a dam, its powerful kinetic energy turns the turbines of a hydroelectric power plant positioned on the other side of the dam. This generates electricity.

Let’s take a more detailed look at a step-by-step process of how a hydroelectric power plant works. To operate effectively, a power plant first needs to be situated somewhere where there is a source of fast-flowing water or water that has the potential to be fast-flowing.

  • Water Intake - Water from the reservoir or other water source flows into the system.
  • Penstock - A gate or valve controls the flow of water into a pipe called a penstock and channels it downhill towards turbines. 
  • Turbines - The kinetic energy the water has created by flowing down drives the turbines.
  • Generator - The movement of the turbines activates a generator, which converts the energy into electricity.

The electricity generated goes through a transformer and is then moved to the electricity transmission network, where it is distributed around the network as electricity we can use in our homes.

Understanding hydropower plants

A hydroelectric power plant or hydroelectric system is the infrastructure that is put in place to generate hydroelectric power. This usually takes the form of the main components we mentioned above, but hydroelectric power plants can vary dramatically in their size, the scale of power production and the components used.

What are the different types of hydroelectric power plants?

There are various different ways of building hydroelectric power plants. The type of hydropower plant chosen will usually depend on the geography of the location.

  • Storage Systems - Also known as impoundment facilities, these are the most common type of hydroelectric power stations. They work in the way described above, with water from a reservoir being released through a dam to power turbines. The majority of hydroelectric power plants in the UK are storage systems.
  • Pumped Storage Systems - Also known as reversible or PSH facilities, these work in a similar way to conventional storage systems. The key difference is that they use cheap, off-peak electricity to pump water from a lower reservoir to an upper reservoir. The water from the upper reservoir is then released to generate electricity during peak periods. There are four pumped storage systems in the UK.
  • Run-of-River Systems - Also known as diversion facilities, these are hydroelectric power plants that rely on the power of a fast-flowing river to generate electricity. Some of the water from the river is diverted away from the main channel and through a penstock to turbines that create energy. There are four run-of-river systems in the UK but they have a much lower capacity than other types of hydroelectric plants.
  • Tidal Systems - Also known as off-shore systems, these are hydroelectric plants that harness the power of the tide to turn turbines and create electricity. A barrage is placed on a tidal bay or estuary to capture the kinetic power of the tide flowing in and out. Tidal energy only contributes around 1% of the UK’s electricity.

Advantages of hydroelectric power 

Hydroelectric power has many benefits for our electricity networks and each of us as individuals. Let’s explore these advantages in more detail.

Sustainable power - Hydroelectricity is a clean, renewable and local source of energy. Northern Ireland’s wet climate provides a regular supply of rainwater that’s useful for hydropower. Additionally, hydroelectric power plants themselves typically have a long lifespan.

Energy grid stabilisation - Since large amounts of potential energy can be stored in reservoirs, hydroelectricity is a reliable and flexible energy source. Water can be released at any time to meet peak energy demands and avoid power outages.

Flood prevention - In areas that are prone to flooding, a hydroelectric power system can be used to control waterways. The flow of water into and out of the system can be controlled to minimise the risk of flooding downstream.

Irrigation support - The large bodies of water in hydroelectric systems can be used for irrigation. This can support plant growth, agriculture and biodiversity. It also provides a valuable resource in times of drought.

Tourism opportunities - Reservoirs, dams and even hydroelectric plants themselves support a wide range of recreational activities. This includes cycle paths, hiking routes, fishing, watersports and visitor centres.

Lower operating costs - Although the initial investment to create a hydroelectric plant is high, they have a long lifespan and lower maintenance costs in comparison to other types of power plants.

Getting started with hydroelectric power

Hydroelectric power doesn’t always have to be generated on an industrial scale. You may be able to invest in domestic hydropower and create your very own micro-hydro system, similar to those that once powered many homes in Northern Ireland. The main considerations before getting started with a micro-hydro system area:

Site Specific Considerations - You will need a river or other body of water on your property. The water will need to be sufficiently fast-flowing and flow from a suitable height. You’ll also need to apply for a licence and, depending on the size of the installation, may need to make planning and grid applications. 

Cost Considerations - You'll have to weigh up whether the cost of installing a hydro system — which varies a lot depending on the situation — will deliver suitable returns. Your returns will depend on how much electricity you can generate. That in turn will depend on how often the water levels are high enough to supply the system and drive the turbine.

Maintenance Considerations - Although maintenance costs are lower than other technologies and hydro systems can last for up to 50 years, you do have to consider the potential cost of any damage caused by debris entering the system.

If your property and its water source are suitable, micro-hydro can provide a reliable, sustainable and cost-effective electricity supply for remote and off-the-grid properties in Northern Ireland. If your hydro system is particularly effective, you could even sell energy to us through microgeneration or Power Purchase Agreements (PPAs).

Power NI Go Green 

If your property isn’t suitable for a micro-hydro system, you can still power your home with 100% green energy. When you’re on our Eco Energy tariff, we’ll source the equivalent of all the electricity you use from renewable sources.


How much electricity can hydroelectric power generate?

The amount of electricity hydroelectric power generates varies dramatically depending on the size and type of hydroelectric system. Micro-hydro power typically generates between 5kW and 100 kW. Some small commercial hydroelectric systems in the UK have a capacity of 1,000kW. 

The Dinorwig Power Station — a pumped storage system in Wales — has a capacity of 1,728MW, making it the biggest hydroelectric power station in the UK. The world’s biggest hydroelectric power station, Three Gorges Dam in China, has a capacity of 22,500MW.

Are there any disadvantages to hydroelectric power?

The main disadvantage of hydroelectric power is the impact it can have on the local ecosystem. Building a dam and reservoir usually involves flooding what would have been the habitat of many plants, birds and animals. Damming a river also has an impact on fish and alters the natural flow of the river.

The other key disadvantage of hydropower is the high startup costs needed to build a hydroelectric power plant. In many cases, this can make a hydroelectric project unviable.

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