Written by Beth Howell Published on 31 August 2022 ✔ Hydropower has been around for over 2,000 years✔ Hydropower only accounts for 2.1% of UK renewable energy sources✔ Hydropower plants aren't always green As countries continue to work towards their net-zero-emission goals, governments are pushing for more renewable capacity, which includes creating a wider range of green energy sources to rely on.The primary sources of renewable energy in the UK are offshore wind, onshore wind, and solar power – but what about hydropower?Although hydropower is the fourth-largest renewable energy source in the UK, it only accounts for 2.1% of the country’s overall renewable energy mix (National Grid, 2022).There’s a lot to know about hydropower. We’ll take you through everything in this article, from what it actually is and how it works, to whether it has a place in the UK’s future energy scene. What’s on this page? 01 What is hydropower? 02 Is hydropower expensive to produce? 03 How much hydropower is there in the UK? 04 The pros and cons of hydropower 05 Does hydropower have a future in the UK? What is hydropower?Hydropower – also known as hydroelectric power or hydroelectricity – harnesses energy from the natural flow of moving water, which can then be used to generate electricity.This is 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 two thousand years ago, which was used to ground wheat into flour.How does hydropower 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 hydropower varies depending on the type of system used – we’ve listed the three most common below:Impoundment facilities – This is the most common type of hydropower facility. 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 spinDiversion facilities – Unlike impoundment 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 generatorPumped-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 around the world, hydropower is a cheap way of generating electricity. The International Renewable Energy Agency (IRENA) states that hydropower “has historically provided the backbone of low-cost electricity in a significant number of countries”. But the cost of hydropower projects can vary, mainly depending on the scale of the undertaking.Check out the table below to get a better idea of how much the average hydropower project costs per kilowatt (kW) installed.Maximum power outputEstimated project cost10 MW£18,350,00050 MW£91,750,000100 MW£183,500,000250 MW£458,750,000Based on Statista’s estimate that hydropower installation cost £1,835 per kW in 2021 These figures might not seem very “cheap”, but are reasonable compared to oil and gas refinery projects. The UK government spent £1.4 billion on gas and oil projects in the tax year 2021/2022 alone – and this level of investment will continue each year that we use fossil fuels. We also need to take hydropower operating costs into account, which also 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 outputEstimated annual operational costs5 kW£2,20025 kW£4,00050 kW£6,300100 kW£11,000250 kW£25,000500 kW£48,300 How much hydropower is there in the UK?Hydropower only 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 much more 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 £30 billion ($36.3 billion).However, Hydropower.org suggests that expansion in the UK will probably be limited to small-scale projects, with the exception of pumped-storage systems.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:TypePower outputApplicabilityPico<5 kW1–2 housesMicro5 – 100 kWSmall isolated communitiesMini100 kW – 1 MWSmall factory or isolated communitiesSmall1 – 10 MWSmall communities with the possibility to supply electricity to the regional gridMedium10 – 100 MWMedium urban population centresLarge>100 MWLarge urban population centres The pros and cons of hydropowerProsConsClean energyNegative environmental impactCheaper than fossil fuelsUpfront costGood for going off-gridIt isn’t 100% greenCan be produced domesticallyTemperamental with weatherAdvantages of hydropowerClean 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 pollutionCheaper 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 OECDGood 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 returnCan 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 homesDisadvantages of hydropowerEnvironmental impact – Despite providing a cleaner energy source, some hydropower 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 upUp-front cost – Although hydropower plants provide cheap electricity, the initial cost of setting up the facility can cost billions of pounds, depending on the size of the projectIt 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 biomassTemperamental 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 Does hydropower have a future 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 ten-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. Hydropower, 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.SummaryDespite being the earliest example of renewable energy generation in human history, hydropower isn’t as popular as some other clean energy sources in the UK.But maybe that’s not a bad thing. Despite being able to produce clean energy, some hydropower facilities do more harm than good – especially when it comes to impacting the local wildlife. If the UK does eventually ramp up its hydropower capacity, it’s worth considering how we can do it in the most environmentally friendly way possible. Written by: Beth Howell Content Manager Beth has been writing about green tech, the environment, and climate change for over three years now – with her work being featured in publications such as The BBC, Forbes, The Express, Greenpeace, and in multiple academic journals. Whether you're after a new set of solar panels, energy-saving tips, or advice on how to reduce your carbon footprint, she's got you covered.