- Hydropower has been around for over 2,000 years
- It only accounts for 2.2% of UK renewable energy sources
- Hydropower plants aren’t always green
Hydropower is the fourth-largest renewable energy source in the UK, accounting for 2.2%, as of December 2024.
It is often forgotten, though, and countries favour other renewable energy sources, such as offshore and onshore wind and solar power.
But this renewable energy source shouldn’t be written off just yet, and we’ll tell you why.
What is hydropower?
Hydropower is also known as hydroelectric power or hydroelectricity and it harnesses energy from the natural flow of moving water. This can then be used to generate electricity.
It is actually one of the oldest sources of renewable energy, dating back thousands of years. National Geographic even states that people in Greece used flowing water to turn the wheel of their mill over 2,000 years ago, which was used to ground wheat into flour.
How does it work?
Generally, a hydroelectric power plant has a reservoir of water, and a gate or valve that controls how much water flows out of the reservoir.
Water gains energy when it spills over the top of the dam, which is then converted into kinetic energy as it flows downhill. The water is then used to turn the blades of a turbine to generate electricity.
However, the process of creating energy from this varies depending on the type of system used – we’ve listed the three most common below:
- Impoundment facilities – A dam is used to control the flow of water, which is stored in a reservoir. When more energy is needed, water is released from the dam, flows through a turbine, and powers a generator as the blades of the turbine spin
- Diversion facilities – This type of plant doesn’t use a dam. Instead, it uses a series of canals, which channel river water toward the turbines to power the generator
- Pumped-storage facilities – This system has two water reservoirs, which are located at different inclines on a steep slope. First, water is pumped from the lower to the upper reservoir using reversible turbines when demand is low. When demand is high, the water is released downhill into the lower reservoir, driving the turbines in the other direction to generate electricity
Is hydropower expensive to produce?
For most countries, hydropower is a cheap way of generating electricity. The International Renewable Energy Agency (IRENA) states that hydro “has historically provided the backbone of low-cost electricity in a significant number of countries”.
Check out the table below to get a better idea of how much the average hydropower project costs per kilowatt (kW) installed.
| Maximum power output | Estimated project cost |
|---|---|
10 MW | £18,350,000 |
50 MW | £91,750,000 |
100 MW | £183,500,000 |
250 MW | £458,750,000 |
Based on Statista’s estimate that hydropower installation cost £1,835 per kW in 2021
Although these costs seem quite significant, they are reasonable compared to oil and gas refinery projects. The UK government spent £1.4bn on gas and oil projects in the tax year 2021/2022 alone, but has since increased by a further £7-£8bn from 2022-2023.
We also need to take hydropower operating costs into account, which vary depending on the size of the system and the type of turbine used in the process.
Generally, hydropower systems are reliable, with debris removal being the biggest maintenance task.
You can find the average operational costs for different hydropower systems in the table below.
Maximum power output | Estimated annual operational costs |
|---|---|
5 kW | £2,200 |
25 kW | £4,000 |
50 kW | £6,300 |
100 kW | £11,000 |
250 kW | £25,000 |
500 kW | £48,300 |
How much hydropower do we use in the UK?
Hydropower accounts for 2.1% of UK renewable energy sources, which has been the case since 2000. However, the UK is actually home to 1,561 hydropower plants – a fivefold increase since 2003.
Despite this development, other renewables, such as wind and solar power, have received higher amounts of funding from the UK government, which is why hydropower still only accounts for a fraction of the overall renewable mix.
Most of the UK’s installed hydropower capacity is located in Wales and northwest Scotland – this is because their wet and mountainous landscapes are ideal for hydropower production.
Moving forward, global hydropower capacity is predicted to grow. Rystad Energy, an independent energy research company, reported that hydropower capacity is set to exceed 1,200 gigawatts (GW) in 2022, whilst investments climb to £30bn ($36.3bn).
What is small-scale hydropower?
Small-scale hydropower systems generate between 1 MW–10 MW of electricity. Unlike large-scale hydropower systems, small-scale projects can be installed in small rivers, streams, or in drinking water or wastewater networks – with minimal environmental impact on wildlife or ecosystems.
One of the advantages of small-scale hydropower systems is that most of them are run-of-river schemes, or are implemented in existing water infrastructure, which means there isn’t as much construction work needed. Not only does this keep the cost down, but it also means there’s less of an impact on the local environment.
But it doesn’t just come down to small and large hydropower plants – there are other sizes too:
| Type | Power output | Applicability |
|---|---|---|
Pico | <5 kW | 1–2 houses |
Micro | 5 – 100 kW | Small isolated communities |
Mini | 100 kW – 1 MW | Small factory or isolated communities |
Small | 1 – 10 MW | Small communities with the possibility to supply electricity to the regional grid |
Medium | 10 – 100 MW | Medium urban population centres |
Large | >100 MW | Large urban population centres |
What are the advantages?
Like most forms of renewable energy sources, there are both advantages and disadvantages to hydropower.
The advantages are:
- Clean energy – Unlike fossil fuels, hydropower is generated through a renewable source: water. Harnessing energy through this natural source avoids releasing more emissions into the atmosphere, and reduces air pollution
- Cheaper than fossil fuels – Analysis conducted by the Australian Energy Council found that countries like Canada and Norway, who rely heavily on hydropower, have the lowest household electricity prices in the OECD
- Good for going off-grid – Utilising hydropower is one of the most reliable alternatives to mains supply for isolated properties. Although installing a hydro system can be expensive, it’ll reward you with years of free energy in return
- Can be produced domestically – As Russia continues to threaten Europe by withholding gas supplies, countries are finding alternative energy sources to reduce their reliance on other nations. By increasing the amount of hydropower the UK generates, we’ll rely less on imports to power homes
What are the disadvantages?
Some of the disadvantages of hydropower include its upfront cost and its environmental impact. We’ve gone in more detail below:
- Environmental impact – Despite providing a cleaner energy source, some sites can do more harm than good. Hydropower can cause environmental and social problems, as it drastically changes the local landscape and rivers it’s built on. Dams and reservoirs can reduce river flow, raise water temperature, degrade water quality, and cause sediment to build up
- Up-front cost – Although hydro plants provide cheap electricity, the initial cost of setting up the facility can cost billions of pounds, depending on the size of the project
- It isn’t 100% green – Whilst some hydropower projects can produce a clean source of renewable energy, others can produce harmful emissions. In fact, roughly 10% of the world’s hydropower facilities emit as many greenhouse gases, per unit of energy, as conventional fossil-fuelled power plants. These emissions mainly stem from the decomposition of organic matter, which is either transferred to the reservoir via runoff, or is produced within the reservoir as aquatic plant and algal biomass
- Temperamental with weather – Like any type of renewable energy, hydropower is very dependent on climatic patterns. During droughts, hydropower is less successful because there’s simply less water to generate energy. For example, Norway is currently (summer 2022) having to fall back on its natural gas supplies, as the summer droughts are impacting its hydropower output
- Clean energy
- Cheaper than fossil fuels
- Good for going off-grid
- Can be produced domestically
- Negative environmental impact
- Upfront cost
- It isn't 100% green
- Temperamental with weather
What’s the future of hydropower in the UK?
Hydropower certainly has a place in the UK energy scene – but it won’t be as substantial as solar and wind power.
The government’s 10-point plan, which outlines how it will be investing in renewable energy over the course of the next decade, has a heavy focus on wind and solar energy. This particular renewable energy source, on the other hand, doesn’t even get a mention.
So it’s likely that hydropower will continue supplying energy in the UK, but only a fraction of the amount that wind and solar power produce.
Summary
- Hydropower is the fourth-largest renewable energy source in the UK, accounting for 2.2%, as of December 2024
- It is also known as hydroelectric power or hydroelectricity and it harnesses energy from the natural flow of moving water
- A hydroelectric power plant has a reservoir of water, and a gate or valve that controls how much water flows out of the reservoir
- Small-scale hydro systems generate between 1 MW–10 MW of electricity. Unlike large-scale systems, small-scale projects can be installed in small rivers, streams, or in drinking water or wastewater networks
- One of the advantages of small-scale systems is that most of them are run-of-river schemes, or are implemented in existing water infrastructure, which means there isn’t as much construction work needed
- Hydropower certainly has a place in the UK energy scene – but it won’t be as substantial as solar and wind power
