What is hydropower?


Hydropower, also known as hydroelectric energy or hydroelectric power, is a renewable energy technology that harnesses the power of water in motion to generate electricity. Due to its ability to provide flexibility on a large scale, it plays an essential role in the integration of its variable sisters wind and PV and thus in the fight against climate change. To grasp a fuller picture of this source of clean electricity, it's crucial we learn more about the technologies behind it, the different hydropower plant types and their history.

What’s the history of hydropower?

The desire to harness the power of water dates back thousands of years. The story begins with the simple water wheel, whose rotation, driven by the incessant flow of water, was used to grind grain or saw wood. Over time, this innovation evolved, mechanizing various processes and shaping the course of industrial history. Remarkably, this ancient energy source is among the earliest forms of renewable energy.

Yet, it was the industrial revolution in the 19th century that led to the development of water power. This era saw the birth of the first water turbines, replacing the old, inefficient water wheels. Paired with generators, these turbines ushered in a new wave, converting kinetic energy into electricity. Consequently, hydropower plants of all sizes proliferated along streams and rivers, meeting the growing demand for electricity. 

However, these so-called run-of-river power plants had an obvious disadvantage: their output was subject to the natural flow, resulting in considerable seasonal fluctuations in energy production. High runoff periods, like spring and fall, yielded surplus power, while low runoff periods, such as summer or winter, led to decreased output. To alleviate this issue, so-called reservoir hydropower plants emerged. Nestled in mountain valleys or using existing natural lakes, these plants stored water during high precipitation or snowmelt, ensuring more consistent power generation. This reliability not only bolstered rural prosperity and social welfare but also played a pivotal role in enabling urban electrification.

With the rise of alternative power technologies like coal and nuclear, coupled with fluctuating energy demands, a new challenge emerged for hydropower: storing electricity. Enter pumped storage hydropower plants, where water shuttles between upper and lower reservoirs. During surplus power periods, pumps hoist water to the upper reservoir, acting as flexible absorbers. Conversely, during electricity demand peaks, water is released from the upper reservoir, facilitating flexible electricity generation. Today, many hydropower projects blend different power plant types to maximise energy output from available water sources like a river or lake.

In the continuous battle against climate change and its effects, hydroelectric power is viewed by experts, scientists and governments alike as a great method of creating green energy without having to emit carbon dioxide. It is therefore considered a crucial piece of the puzzle for our energy transition with an important role to play in meeting the EU's 2030 and 2040 climate targets as discussed in the repower EU for 2030 report and the EU’s 2040 communication.

How does hydropower work – What are the physics behind it?

The fundamental principle of hydropower revolves around harnessing the gravitational potential energy inherent in water's height, converting it successively into motion which is kinetic energy, then into mechanical energy, and ultimately into electrical energy. This retrieved energy is the final product, used to power our devices and technologies. Here's how the process works:

  1. Basically, water flowing downhill possesses large gravitational potential energy. This is due to its position above the Earth's surface. This potential energy is converted into kinetic energy as the water gains velocity during its descent.
  2. To effectively harness this energy, dams or diversion structures are built to manage the flow of water. By restricting the flow, the stored potential energy in the water can be released in a controlled manner, akin to releasing pressure from confined sructures.
  3. The technologies through which this energy transformation occurs in is known as the penstock. Penstocks are purpose-built channels that direct the water flow through a turbine, where this kinetic energy is directly translated into rotational motion, causing the turbine blades to spin. This motion is then transferred to a generator, where the principle of electromagnetic induction allows for the conversion of mechanical energy into electrical energy.

This generation of electricity is then ready to be transmitted to end consumers via power lines. Notably, this entire process operates with an efficiency of 85-90%, indicating that only a small amount of energy is lost during this process.

But what are the downsides?

The simultaneous trends of population growth and urbanisation, coupled with escalating demand for residential, agricultural, industrial and power generation zones, has led to significant strain on water bodies like rivers and lakes and their ecosystem. This mounting pressure highlights the urgent need for sustainable and renewable water management services. Although the specific effects of a hydropower plant vary based on local conditions, it is generally understood that run-of-river plant projects notably affect river continuity, while reservoir plants influence the discharge patterns through artificial water storage and release. Pumped storage power plants can have a particularly low impact, especially when their two artificial basins are isolated from natural water bodies.

During the environmental movements of the 1970s, a strong opposition to hydroelectric power plants arose, particularly spurred on by large-scale power plant projects outside of Europe, where social and environmental concerns were often overlooked. in response to the concerns raised by opponents, the hydropower sector embarked on intensive research and development efforts aimed at mitigating, minimising and offsetting adverse effects. By implementing both constructive and operational measures, substantial strides have been made in promoting biodiversity. The ongoing commitment to holistic, nature positive approaches reflect the journey towards sustainability and responsible resource management. In this regard, it's worth noting that hydropower plants account for less than 10% of barriers in European rivers.

Hydropower operators are actively engaged in implementing comprehensive mitigation measures to preserve river continuity. Improving European water bodies in accordance with EU Water and Nature legislation implies collaboration across all sectors involved, striking a balance of interest and sharing efforts. In this context, the hydropower sector demonstrates a keen eagerness to exchange valuable experience as well as actively pursuing collaborative opportunities.

Showcasing best practices, Germany’s hydropower plant in Töging-Jettenbach stands out from the crowd. Through refurbishment, the plant grew its renewable energy capacity by 40% and boosted power generation by a quarter. Notably, the refurbishment included the construction of a two-way fish, re-establishing river continuity and facilitating the migration of aquatic species upstream and downstream.

New grasslands and wetlands were created, and floodplains were reconnected to provide essential habitats for endangered species. The renovation also improved the freshwater river ecosystem’s biodiversity through the implementation of comprehensive structural and hydromorphological measures. These included creating areas with higher and lower flow velocity to support fish migration and constructing pools to rejuvenate natural ecosystems found in a river or lake.

Another success story to take into account is the refurbishment of the Romanche-Gavet hydropower plant in France. Five consecutive barriers were removed and replaced by a single upgraded facility, resulting in a 20% increase in energy capacity and a 40% boost in generation of electricity. This decision facilitated the creation of a free-flowing river stretch and the restoration of over 10 hectares of terrestrial and fluvial habitats.

Why is hydropower important for Europe?

Today, hydropower stands as the EU's second-largest renewable energy source, generating 355 TWh of electricity annually. This source of clean energy plays a major role in ensuring the secure and stable operation of the electricity grid. Through reservoirs and related run-of river plants, hydropower provides flexible renewable electricity generation solutions for both short-term and long-term needs.

Despite the significant advancements in other climate friendly electricity storage technologies, pumped storage hydropower currently accounts for over 90% of the  available storage capacity in the EU. This source stands as a mature technology, capable of meeting electricity storage demands across a wide range of timescales from minute to seasonal. The Renewable Energy Directive's binding target of 42.5% renewables requires the addition of over 1000 GW of new variable renewable electricity capacity from wind and solar photovoltaics (PV) in the EU. This target is equivalent to the total current capacity installed, including fossil, nuclear and renewable energy sources (RES), and must be achieved in less than six years. As the power sector strive to meet this renewable energy target, the importance of flexible generation and storage capacities will become even more central. Hydropower holds immense potential in effectively integrating variable generation, preventing curtailment during periods of excess power output and guaranteeing security of supply in periods of shortages.

Europe has firmly established itself as a global leader in hydropower technology. By leveraging a transparent and sustainable European value chain, hydropower provides significant autonomy and independence from critical raw materials imports, fossil fuels, skilled labour or technological deficits. On this basis, European project developers, operators, and equipment manufacturers are strategically poised to capitalise on the vast opportunities emerging from substantial investments in the modernisation of existing and the development of new hydropower plants, both within Europe and globally. As the EU and Europe's national governing bodies endeavour to establish robust supply chains for technologies vulnerable on third countries are prominent, hydropower emerges as an immediate solution.

What makes it special compared to other power technologies?

Hydropower plants boast an outstanding lifespan, providing sustainable electricity for generations, often exceeding 100 years. When measured in terms of the energy payback ratio – which compares energy generated to the energy expended in the construction, operation, maintenance, and decommissioning of the power plant – hydropower outperforms all other renewable electricity generation technologies. Despite its already remarkable efficiency and large lifespan, both science and industries consistently allocate substantial resources into research and development, aimed at further enhancing this source of power's capabilities.

Hydropower stands out not only from a technical perspective but also in terms of its cost-effectiveness. This assertion has been validated by both the World Bank and the International Renewable Energy Agency, recognising this source of sustainable power as one of the most competitive generation technologies in terms of levelised costs of electricity.

However, it is important to acknowledge that, similar to solar PV and wind power plant projects, the implementation of hydropower projects entails rather large upfront costs. Making these investment decisions is no small feat and will require a stable legal framework and long-term revenue visibility.

What are additional benefits of hydropower? 

Recent years have highlighted the importance of implementing a comprehensive water management strategy, particularly in light of the increasing frequency of extreme weather events leading to either excessive or insufficient water flows. Hydropower plants offer numerous advantages for climate change adaptation. These projects not only regulate flood events and strategically release water during drought periods to protect ecosystems and agriculture, as well as facilitate navigation. They also play a crucial role in ensuring a reliable water supply for a large spectrum of applications, including drinking, irrigation, industrial processes, and firefighting.                                                                                  

What are the challenges and how to overcome them?

Hydropower projects operate within a complex regulatory landscape, which encompasses environmental, social and safety considerations. It is imperative to adhere meticulously to these regulations in order to avoid potential legal hurdles for hydroelectricity. This involves securing permits, conducting regular inspections and upholding safety standards to the letter.

While EU legislation recognises the essential role of hydropower across various dossiers, including the Water Framework Directive, Renewable Energy Directive, Taxonomy Regulation, Nature Restoration Regulation, and Electricity Market Design, there is a pressing need for a technology-neutral, stable regulatory environment. Such an environment is vital to strengthen the long-term visibility and confidence of hydroelectric power plant owners, operators and investors.

Furthermore, it is critical to refrain from market interventions as well as maintain market principles in order to enable the efficient dispatch and storage of electricity (i.e., activating flexible sources  when they provide the greatest value to the electricity system). While public support mechanisms can offer short-term signals and catalyse essential long-term investments in hydroelectric power, it's essential they they align with existing regulations to allow flexible plants to maximise their incomes across various markets. These mechanisms and technologies should not solely prioritise new constructions but rather concentrate on optimising and expanding the utilisation of existing hydropower assets.

It is clear that successfully navigating the challenges inherently found in hydropower projects requires a delicate balance of foresight, community engagement and unwavering regulatory compliance. By addressing these issues through  transparent approaches, the true potential of hydropower can be unlocked.

These mechanisms should not exclusively prioritise new constructions but instead focus on optimizing and expanding the utilization of existing hydropower assets.

It is clear that successfully navigating the challenges inherent in hydropower projects demands a delicate balance of foresight, community engagement and unwavering regulatory compliance. By addressing these issues through embracing transparent approaches, the potential of hydropower can be truly harnessed.