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

TL;DR

This paper demonstrates that low-cost, long-duration pumped hydro can replace fossil gas in electricity systems, enabling full decarbonization without additional costs, by improving system modeling and exploring numerous near-optimal solutions.

Contribution

It introduces a segmentation-based temporal aggregation method that accurately captures long-duration storage behavior and evaluates the potential of off-river pumped hydro for global decarbonization.

Findings

Pumped hydro can fully replace fossil gas in electricity systems.

Segmentation method closely matches full-series optimization results.

Most regions have access to sufficient pumped hydro options.

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.