Long-Duration Storage In The Australian Nem: A Security- and Reliability-Constrained Evaluation

Lithium-ion batteries, typically deployed as shortduration storage, have been effective in addressing intraday volatility and evening peaks, particularly in solar-rich regions. Their cost structure and market rules have reinforced this role, favouring short-duration applications over extended storage. However, growing electrification of heating and increased weather variability are leading to extended winter peaks and multi-day renewable shortfalls, frequently observed in Australia’s southern regions. These challenges, also faced globally in isolated, weakly interconnected, or variable renewable energy source-reliant grids such as Ireland, highlight the limitations of short-duration storage. This paper develops a security-constrained integrated system planning (SC-ISP) framework that co-optimises generation and storage investment while explicitly enforcing RoCoF, frequency nadir, and quasi–steady-state constraints under an N−1 contingency criterion. Liquid air energy storage (LAES) is modelled with asymmetric charge–discharge blocks and inertia provision, and its system value is compared with battery energy storage systems (BESS) and pumped hydro energy storage (PHES) in a 2040–41 South Australian case study. Results show that short-duration BESS remains cost-effective under high intraday renewable volatility, whereas long-duration technologies are favoured under extended renewable drought conditions. LAES becomes competitive with PHES and BESS when capital costs decline by approximately 20–30%, particularly under stricter reliability thresholds and higher demand growth.