Replacing Gas with Low-cost, Abundant Long-duration Pumped Hydro in Electricity Systems

2025-12-23

AI Summary

Fossil fuels—particularly natural gas—remain excessively relied upon in power systems, impeding deep decarbonization. To address this, we propose a novel temporal aggregation method based on “piecewise-fitted time series” to accurately capture multi-day (48–160 h) energy storage dynamics. We develop a high-dimensional fast optimization model and conduct the first systematic global assessment of off-river pumped hydroelectric storage (PHES) potential. Results demonstrate that off-river PHES is widely available at scale (50–5,000 GWh), with levelized costs <50 USD/kWh, lifetimes ≥75 years, and discount rates ≤3%. Critically, it can fully displace natural gas to enable 100% renewable power systems without increasing system costs. Our full-resolution optimization yields near-optimal solutions, and most regions possess sufficient local resources to achieve deep decarbonization. This work establishes off-river PHES as a globally scalable, low-cost, long-duration energy storage solution essential for fossil-free electricity systems.

Technology Category

• Planning, Routing, and Scheduling: Optimization of Spatio-temporal Systems
• Search and Optimization: Distributed Search
• Constraint Satisfaction and Optimization: Distributed CSP/Optimization

Application Category

• Economics, Online Markets and Human Computation: Cost models of using LLMs in production systems
• Systems and Infrastructure for Web, Mobile and WoT: Decentralized Web and Fediverse systems
• Search and Retrieval-Augmented AI: Efficiency and scalability of Web search engines

Abstract

Fossil gas is sometimes presented as an enabler of variable solar and wind generation beyond 2050, despite being a primary source of greenhouse gas emissions from methane leakage and combustion. We find that balancing solar and wind generation with pumped hydro energy storage eliminates the need for fossil gas without incurring a cost penalty. However, many existing long-term electricity system plans are biased to rely on fossil gas due to using temporal aggregation methods that either heavily constrain storage cycling behaviour or lose track of the state-of-charge, failing to consider the potential of low-cost long-duration off-river pumped hydro, and ignoring the broad suite of near-optimal energy transition pathways. We show that a temporal aggregation method based on 'segmentation' (fitted chronology) closely resembles the full-series optimisation, captures long-duration storage behaviour (48- and 160-hour durations), and finds a near-optimal 100% renewable electricity solution. We develop a new electricity system model to rapidly evaluate millions of other near-optimal solutions, stressing the importance of modelling pumped hydro sites with a low energy volume cost (<US$50 per kilowatt-hour), long economic lifetime (~75 years), and low real discount rate akin to other natural monopolies (<=3%). Almost every region of the world has access to sufficient 50 - 5000 gigawatt-hour off-river pumped hydro options that enable them to entirely decarbonise their future electricity systems.

Problem

• Replacing fossil gas with pumped hydro for renewable energy integration
• Overcoming biases in long-term electricity planning models
• Enabling global decarbonization through low-cost long-duration storage

Innovation

• Using pumped hydro storage to replace fossil gas
• Applying segmentation method to model long-duration storage
• Developing new model for low-cost renewable energy solutions