A landmark study from Energy Storage Ireland (ESI) and TNEI has revealed that the large-scale deployment of long-duration energy storage could reduce fossil fuel generation on Ireland's electricity grid by more than 2 TWh annually.

This reduction represents nearly 30% of projected fossil fuel use, marking a significant step toward a decarbonised power system.

The "Energy Storage Grid Benefits Report" models a future all-island system featuring 9 GW of onshore wind, 8 GW of solar, and 5 GW of offshore wind, in line with Ireland's Climate Action Plan. The research demonstrates that even with high renewable capacity, fossil fuel generation—primarily gas-fired power—would remain at roughly 7.4 TWh annually by 2035 without adequate storage.

The report examines two primary scenarios: eight-hour storage portfolios and 100-hour duration storage. The eight-hour models were found to reduce fossil fuel use by up to 1 TWh per year, equivalent to the energy consumption of 238,000 Irish homes. Meanwhile, 100-hour storage, strategically placed across the grid, could displace over 2 TWh of fossil fuel generation by shifting surplus renewable energy into periods of peak evening demand.

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In addition to displacing carbon-intensive generation, the report identifies storage as a solution to "dispatch down"—the curtailment of renewable energy. While waste is projected to reach 11 TWh annually by 2035 due to network constraints, long-duration storage would significantly capture this surplus, reducing import costs and lowering consumer bills.

Bobby Smith, Director of ESI, said: "The report finds that even under a high-renewables scenario, fossil fuel generation remains at approximately 7.4 TWh annually in 2035. Based on Ireland's energy system, this would be primarily gas-fired power. However, when energy storage is introduced at scale, reliance on fossil fuels falls significantly. In fact, eight-hour storage portfolios reduce fossil fuel generation by up to 1 TWh annually, while 100-hour duration storage, deployed across strategic grid locations, reduces fossil fuel generation by more than 2 TWh per year.

"This represents a nearly 30% reduction in fossil fuel use within the power system and demonstrates the transformative role long-duration storage can play in a deeply decarbonised grid. Taken together, the findings show that while long-duration storage will be essential in a very high-renewables system, shorter-duration batteries already provide substantial carbon and system benefits, making storage deployment a critical near-term and long-term priority."

Bobby Smith added: "While the study does not assess market economics, it demonstrates the clear system-level value of energy storage in enabling a secure, low-carbon electricity system. The findings underline the importance of long-duration storage technologies in delivering Ireland's climate ambitions and maximising the value of renewable generation already connected to the grid. As Ireland accelerates toward a carbon-free electricity system, energy storage emerges not as an optional add-on, but as essential infrastructure for decarbonisation."