The increase in renewable capacity and the electrification of energy demand to phase out fossil fuels, result in grid congestion and intermittency challenges to manage the balance of supply and demand. Therefore, energy storage is required to prevent the energy transition from slowing down. Various storage technologies exist, differing in applicability, capacity, scalability, size, cost, and environmental impact. An understanding of the behaviour and impact of those technologies on the power system is necessary to make a proper trade-off regarding system benefits. That is why Mandy Bouwhuis developed a regional power-flow model for Zeeland's high-voltage network to assess through in-depth modelling research the impact of Underground Pumped Hydro Storage (UPHS) on the power system. Mandy started working at Pondera Consult as an energy system engineer after successfully defending her thesis. 

What is Underground Pumped Hydro Storage?

Underground Pumped Hydro Storage (UPHS) is an energy storage technology that utilizes the principle of traditional Pumped Hydro Storage (PHS) for subterranean applications. It is designed to store excess electrical energy by pumping water from a 1500m-deep lower reservoir to an upper one located at ground level. During peak demand periods, the stored water is released to flow back down through turbines, generating electricity as it descends. Currently, no UPHS systems are in place but potential suitable locations for implementation might be Zeeland and Limburg due to suitable hard rock formations in those areas. An example of how such a system looks like is visualised in the images below.  

Reseach findings

The research findings emphasize that a UPHS system with a capacity of 8.4 GW can play a crucial role in the energy landscape, balancing renewable energy integration with grid stability and economic and social considerations. However, due to the high investment costs in combination with the uncertainty in the energy market, implementation faces challenges to find investors, although a viable business case can be expected, for instance because of the long lifetime (50 years+) We have listed the key findings:

• UPHS can significantly reduce curtailment of renewable energy, potentially storing up to 2.7 TWh annually.  
• Charging behaviour of UPHS aligns with the dominant renewable sources, solar in summer and wind in winter. Carbon emission reduction is most pronounced in the winter months.
• UPHS is less effective in addressing local power shortages, suggesting that smaller storage assets on lower voltage grids may be more suitable for this purpose.  
• The optimization  of the grid would benefit establishing parameters for using the UPHS because just trading on the ‘market could increase both power import and export quantities while reducing export hours, which implies that the power grid is not being relieved in this approach.  
• In a purely market-based use case, UPHS requires a price difference of about 70 EUR per MWh between buying and selling power for a 20-year return on investment. However, when considering system-wide benefits such as curtailment savings and reduced carbon emissions, the return on investment period is reduced to 10 years.   

Data-driven services and advanced modelling solutions

Pondera offers comprehensive expertise in renewable energy and system integration, encompassing energy engineering, economics, policy-, permitting- and contracting consultancy for complex renewable energy challenges. The advanced modelling approach, as demonstrated by Mandy’s research, enables us to optimise complete energy systems, including power, heat, hydrogen, and ammonia flows, analyse market mechanisms and environmental impacts, and evaluate technologies from a holistic perspective. We develop customised models tailored to your specific requirements, adjusting the level of detail and scale. Our services include energy system optimisation, technological and economic feasibility studies, strategic advisory services, decision-making support, and analysis of the effectiveness of policy interventions. The scenario analysis part of our method covers a wide spectrum of potential outcomes, providing a comprehensive view of future possibilities. This approach ensures that our clients are well-equipped to navigate the complexities of the renewable energy landscape.  

Contact us to discuss how our expertise can drive your renewable energy initiatives forward.  

The thesis project was supervised from Delft University by Aad Correljé and Pieter Bots, and by Martijn ten Klooster and Nienke Firet within Pondera Consult.