The global transition to renewable energy sources is radically changing the nature of energy systems. Although sources such as solar and wind are environmentally friendly and sustainable, they increase the risk of imbalance in electricity networks due to their intermittent production characteristics. This makes energy storage systems an integral part of the energy transition.
Pumped Hydroelectric Storage (PHS), the most popular system among energy storage systems in recent times, is a method that converts excess electrical energy into potential energy by pumping water into a high reservoir during times of low demand and allows this water to be passed through turbines to generate electricity again when energy is needed.
Pumped Hydroelectric Storage Systems (PHES) use excess electricity to pump water into a high reservoir and release this water into the reservoir below when energy is needed to generate electricity. This technology stands out with its high efficiency (70-80%), long life and ability to respond quickly to sudden demand changes.
Pumped hydroelectric systems basically consist of two water reservoirs: one is located at a high altitude and the other at a low altitude. When the demand for electricity is low and the supply is high, water is pumped from the lower reservoir to the upper reservoir and stored as potential energy. As the demand increases, this water is released from the top to the bottom, turning the turbines and electricity production is provided. This mechanism allows the system to act like a battery, but the energy is stored mechanically, not chemically.
One of the important advantages of PHES is that it has extremely long operating times compared to its capacity. These systems, which have the capacity to provide electricity for hours or days, also contribute to frequency control by providing inertia to the network. Moreover, since energy production can start instantly, it also provides a solution to sudden demand increases.
However, the installation of PHES facilities usually requires very high capital and depends on suitable geographical conditions. In mountainous regions and areas with abundant water resources, these systems are easier and more efficient to install.
England can be considered the best example from the world for this system, the success rate of which also increases depending on geographical conditions. The United Kingdom has natural advantages for PHES, especially thanks to its mountainous geography in Wales and Scotland. Dinorwig (1.728 MW) and Ffestiniog (360 MW) power plants are strategic assets that provide rapid response to the country’s grid balance and are currently operating integrated.
The United Kingdom is making significant investments in PHES to ensure flexibility while increasing the share of renewable resources in its energy system. Dinorwig (1.728 MW) and Ffestiniog (360 MW) power plants located in the north of Wales constitute 74% of the country’s total PHES capacity. Dinorwig and Ffestiniog Power Plants located in the United Kingdom are two pioneering and strategic facilities in this field.
Dinorwig Power Plant is the fastest-responding pumped storage power plant in Europe, reaching full capacity in 75 seconds. Ffestiniog is the first PHES facility to be commissioned in the UK. A £1 billion modernisation project, launched in 2025, will extend the life of both facilities by 25 years, increase grid stability and adapt to increasing renewable energy supply.
The UK is targeting 18 GW of energy storage capacity by 2035. 10 GW of this capacity will come from pumped hydro. PHES plays a central role in this goal, including grid balancing, security of supply and independence from fossil fuels.
Ffestiniog Power Station, which was commissioned in 1963, is the first pumped hydroelectric energy storage facility to be commissioned in the UK. Although it is a medium-sized facility with a capacity of 360 MW, it is of great importance due to its pioneering role in the system and its technological continuity.
The £1 billion comprehensive modernisation project, launched in 2025, aims to update the infrastructure of both facilities and ensure they can operate for another 25 years. With this investment:
- The efficiency of the power plants will be increased,
- Control systems will be digitalized,
- Grid stability will be ensured more effectively,
- Variable renewable energy sources such as solar and wind will be better integrated.
Dinorwig and Ffestiniog are not only engineering achievements of the past, but also strategic assets that shape the energy system of the future. With their high responsiveness, energy security and the role they play in the transition to a carbon-neutral grid, they concretely demonstrate the power of pumped hydroelectric energy storage.
This will enable:
- Renewable excess production to be stored more efficiently,
- The grid to respond more quickly and decisively,
- The need for fossil fuel backup generation facilities to be reduced.
As a result, reliable and responsive energy storage solutions have become critical as energy systems move towards carbon neutrality. In this context, PHES plants such as Dinorwig and Ffestiniog are not only engineering marvels of the past, but also the pillars of the clean energy infrastructure of the future.
The transition from fossil fuels to renewable energy is reshaping not only energy production sources, but also energy storage and grid management strategies. Pumped hydroelectric energy storage (PHES) systems play an indispensable role in this transformation with their high capacity, fast response time and long life.
Pioneer plants such as Dinorwig and Ffestiniog not only contribute to today’s grid stability, but also act as a bridge in the transition to low-carbon energy systems of the future. These facilities, whose lifespans have been extended with modernization investments, will continue to be strategic infrastructure elements in the integration of increasing renewable production into the system.
The success of the global energy transition depends not only on the transformation of production resources, but also on the safe, flexible and sustainable management of these resources. PHES systems are at the key point in this equation with their reliability and balancing capacity, forming the backbone of the future energy system.
Sources
Department for Business, Energy & Industrial Strategy (BEIS). (2021). Energy storage and flexibility. UK Government. https://www.gov.uk/government/publications/energy-storage-and-flexibility
Electricity Storage Network. (2020). The role of long-duration energy storage in a net zero grid. Renewable Energy Association. https://www.r-e-a.net/resources/the-role-of-long-duration-energy-storage-in-a-net-zero-grid/
First Hydro Company. (n.d.). Dinorwig and Ffestiniog power stations. https://www.firsthydro.com/
International Energy Agency (IEA). (2023). Pumped storage hydropower. https://www.iea.org/reports/pumped-storage-hydropower
National Grid ESO. (2022). Future Energy Scenarios 2022. https://www.nationalgrideso.com/future-energy/future-energy-scenarios
RenewableUK. (2023). Pumped hydro: Enabling a flexible, low-carbon electricity system. https://www.renewableuk.com/
Strbac, G., et al. (2020). Role and value of flexibility in facilitating cost-effective decarbonisation of the UK electricity system. Energy Policy, 137, 111099. https://doi.org/10.1016/j.enpol.2019.111099
Welsh Government. (2025). Investment in North Wales energy infrastructure. [Basın duyurusu]
She graduated from Çankaya University Faculty of Law in 2005. In the same year, she completed her master’s degree in Constitutional Law at Çankaya University, Department of Public Law. Until 2011, she worked as an ODY-ÜDY Instructor at Vocational Training Centers affiliated with the Ministry of Transport. For approximately 15 years, she has been working as a legal expert at the Union of Chambers and Commodity Exchanges of Turkey (TOBB). Initially, she was involved in Foreign Trade and International Logistics at TOBB and represented the United Nations for nearly seven years. She is currently serving as a legal expert in the SME Policies Directorate within the TOBB Department of Real Sector R&D and Implementation.
Meanwhile, she is working on completing her doctoral dissertation in Administrative Law at Gazi University, Department of Public Law-Administrative Law. After completing her thesis on TOBB, which is recognized by the Council of Higher Education (YÖK) in Turkey, she plans to publish it as a book.
Additionally, since 2023, she has been writing columns in the London section of “DÜNDAR HUKUK” and “DÜNDAR LEGAL SERVICE CONSULTANCY,” which have established themselves internationally, particularly in the field of energy and renewable energy.