British utility SSE has secured planning permission for an 80-MW/160-MWh battery energy storage system (BESS) in County Mayo—signaling a cautious but necessary step toward bolstering grid flexibility.
Approved by Mayo County Council, the project is located adjacent to SSE’s legacy Tawnaghmore gas and oil power station. Although originally consented in 2018, the permit had lapsed, prompting a revised application earlier this year. The new approval incorporates an updated system design, including 26 to 38 modular battery units.
Ireland’s grid has one of the highest proportions of wind energy in Europe—wind accounted for 34% of electricity generation in 2023, according to EirGrid. While this supports decarbonization goals, it introduces acute challenges for system balancing, especially during periods of excess supply or sudden drops in wind output.
The planned 160-MWh capacity of the Mullafarry battery will be able to supply more than 75,000 homes for up to two hours—equivalent to a short-duration but fast-responding buffer during peak load or renewable troughs. However, as Ireland pushes toward 80% renewable electricity by 2030 under its Climate Action Plan, this scale of storage remains incremental rather than transformative.
By comparison, the national grid operator has warned of needing at least 2 GW of new grid-scale storage by the decade’s end. Ireland currently operates less than 700 MW of installed battery storage, indicating the gap still to be closed.
Despite receiving planning approval, SSE has not yet committed to construction. The company stated that a final investment decision (FID) is pending, with a tentative start date in 2026 and commissioning by 2028. These long lead times point to ongoing economic and regulatory uncertainties surrounding storage monetisation in Ireland.
Revenue stacking—relying on multiple value streams like frequency response, arbitrage, and capacity payments—is essential for battery project viability, yet remains volatile. The absence of a firm government-backed long-duration storage policy or dedicated revenue guarantee mechanisms adds to the risk profile.
Moreover, while co-location with a gas plant offers grid interconnection advantages, the regulatory framework for hybrid assets in Ireland is still evolving. The economics of battery deployment will likely remain dependent on reforms to capacity market rules and deeper integration of storage in system services procurement.
That SSE opted to reapply for a previously approved site rather than seek a new location suggests an opportunistic but targeted approach: leveraging existing assets to minimize permitting risk and infrastructure costs. It reflects a broader trend across European utilities—reactivating dormant or shelved energy storage projects as the cost of inaction grows more visible.
Ireland’s grid has experienced several system alerts in recent years, including near-miss events triggered by tight reserve margins. While the Mullafarry battery’s contribution is modest in the national context, it fits into a growing portfolio of decentralized assets needed to stabilize the grid during high renewable penetration.
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