This project will evaluate the environmental, economic and energy-security impacts of underground long-duration energy storage (UG-LDES). Aspects studied will include the technical performance, system value (investigated by way of an open-source system wide modelling tool), bankability, lifecycle environmental impacts, contributions to energy system flexibility, resilience and security, and how UG-LDES should be addressed in energy policy.
The UK’s transition to net zero requires unprecedented expansion of variable renewable energy sources (VRE) such as wind and solar. This creates a pressing need for LDES to provide system balancing, seasonal adequacy, and resilience against prolonged periods of low VRE output and high demand. LDES also contributes substantially to the UK’s energy security, reducing the impact of price-shocks in the oil and gas sectors, as highlighted by the recent geopolitical events in the middle east. While short-duration flexibility options such as batteries or demand-side response (DSR) can contribute, they are insufficient to manage multi-day or seasonal energy imbalances or mitigate the impact of price shocks. UG-LDES technologies – such as compressed air energy storage, underground hydrogen storage and high temperature water storage – are some of the most promising due to their potential for large energy storage capacities which scale much more favourably than overground options.
It is thought that the UK has several petawatt hours of underground storage available that could be operated over interseasonal timescales. This includes established technologies for compressed gas storage, like salt caverns, alongside lower technology-readiness options, such as aquifers and decommissioned oil and gas assets. Salt caverns are already recognised as a key strategic asset for interseasonal LDES in the UK, and they can be used for hydrogen storage, biogas or for compressed air energy storage (CAES). The recent Royal Society report on LDES advocates for 60-100TWh of primarily salt-cavern-based storage of H2 or CAES. However, for all the underground LDES options, the economic viability, investment case, the embodied energy/environmental costs and the weather dependent integration pathways have not been adequately studied. As a result, LDES technologies cannot be properly compared and this is a key barrier in deciding the best course of action regarding LDES deployment.
Our overarching objective is therefore to evaluate the following six research questions:
- How do different UG-LDES technologies (CAES, underground H2, underground high temperature water) compare in terms of cost and technical performance?
- From a system perspective, how do the different UG-LDES technologies complement, compete with, or displace other flexibility providers (batteries, interconnectors, DSR, generators)?
- What are the lifetime costs and emissions associated with different UG-LDES options under different future energy scenarios and how do they compare with (bio)methane?
- How much can UGLDES technologies contribute towards system resilience in the event of extreme weather events and fossil-fuel price shocks?
- What revenue streams, financing mechanisms, and regulatory enablers are needed to make UG-LDES assets investable?
- How should LDES be incorporated into forthcoming planning and regulatory frameworks, e.g., Strategic Spatial Energy Planning (SSEP), Centralised Strategic Network Plan (CSNP), RIIO, and LDES strategy, to ensure timely, bankable deployment?
To tackle these six important research questions, the programme of work is split into five work packages (WP). WP1 leads the development of an open-source energy model (WeSIM-OS), which is used to model system interactions of LDES within different future-looking integration scenarios. WP2 undertakes a high-level characterisation of the UG-LDES options in terms of their technical and economic performance. WP3 examines salt caverns in detail, since these represent the most technologically mature UG-LDES technology, comparing their use for H2 and for CAES. WP4 undertakes the lifecycle and environmental analysis of UG-LDES technology options and benchmarks these against methane and biomethane storage. Finally, WP5 leads the policy and stakeholder engagement.
Meet the Principal Investigator(s) for the project
Marko Aunedi - Marko Aunedi is a Senior Lecturer at the Department of Electronic and Electrical Engineering at Brunel University London with 25 years of research experience in energy system modelling and optimisation. He obtained his MEng and MSc degrees from the University of Zagreb, Croatia, and his PhD from Imperial College London. Between 2007 and 2023 he held several positions at Imperial College London, most recently the role of Advanced Research Fellow.
Marko's research interests cover system integration of renewables and low-carbon technologies in future energy systems, impact assessment of heat and transport electrification, integrated whole-energy system modelling, impact of flexible demand and benefits of energy storage. His expertise lies in building optimisation and simulation models for low-carbon energy systems.
Marko contributed to many European and UK-based research projects focused on energy system flexibility and grid impact of transport and heat decarbonisation. He has led several strategically important studies on the value of flexibility for energy system decarbonisation carried out for organisations such as the Climate Change Committee (CCC), BEIS, Ofgem and Carbon Trust, as well as for many industrial partners.
Marko has published over 40 papers and delivered invited lectures on smart grids and energy storage in various events around the world. He regularly reviews manuscripts for leading energy journals and research project proposals for EPSRC, Innovate UK and Latvian Council of Science. As an external expert, he has worked with major international organisations such as IRENA, IEA, IAEA and the UNFCCC Secretariat.
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Project last modified 10/09/2026