Ireland has taken a major step toward deploying long-duration energy storage (LDES) with EirGrid, the national transmission system operator, launching a public consultation on how the country will contract, dispatch, and connect its first multi-hour storage assets. The consultation paper—published last week—marks a significant milestone in establishing a dedicated market structure for storage with durations beyond short-term battery systems.

Defining Long-Duration Storage and Technical Requirements

EirGrid has formally set the definition of long-duration energy storage at a minimum of four hours, with no upper limit. The operator outlines the rationale behind the threshold, noting that this duration is essential for supporting Ireland’s decarbonized power system as renewable penetration continues to rise.

The consultation proposes a minimum round-trip efficiency (RTE) of 75%, a requirement that may limit participation from certain technologies. Some thermal energy storage (TES) solutions—such as molten salt or phase-change materials—would struggle to meet that standard when converting stored heat back into electricity. Mechanical options like compressed-air energy storage (CAES) also typically fall below that efficiency benchmark.
(For example, Rondo Energy reports RTE above 97% for its thermal battery, but only in heat-supply applications rather than electrical output.)

Operational Control and Dispatch Rules

EirGrid is seeking storage assets that can provide instantaneous responsiveness and be fully dispatchable by the TSO. The service is defined as the capability to “import, store, and export electricity at times deemed suitable by the TSO to minimize re-dispatch.”

Under the proposed model:

• EirGrid will determine when participating assets charge and discharge.
• Each day at 10:00, operators will receive an “operational envelope” indicating their permissible charging/discharging windows.
• This envelope may be updated if grid conditions shift, particularly to prevent congestion or further curtailment of renewables.

Projects that demonstrate hybrid configurations or show efficient use of existing grid connection points will receive enhanced weighting during the tender evaluation, as EirGrid aims to speed deployment and reduce curtailment risks.

Procurement Structure and Capacity Targets

The consultation outlines a multi-stage procurement approach, beginning with an initial tender to secure at least:

• 201 MW of LDES capacity
• Equivalent to at least 804 MWh of storage

This first tender will be conducted through an EU-compliant competitive process. EirGrid will implement an ongoing qualification system, allowing future tenders without redoing the full pre-qualification phase.

Capacity thresholds for participation include:

• 20 MW minimum for hybrid (co-located) projects
• 75 MW minimum for standalone storage sites
• 100 MW maximum per site

Across all tender phases, the TSO aims to procure up to 500 MW of cumulative long-duration storage capacity.

Revenue Model: Floor Payments and Profit-Sharing

EirGrid proposes a dual-component revenue structure:

1. A guaranteed revenue floor—developers will bid their floor price.
2. A profit-sharing mechanism if actual market revenues exceed that floor.

The floor price will be capped based on Levelised Cost of Storage (LCOS) assessments. EirGrid intends to publish the underlying LCOS assumptions during the next consultation phase for market review.

For revenue sharing, the TSO suggests a 70/30 split in favor of the storage operator. Full open-book accounting will apply throughout the contract term.

Timeline and Next Steps

EirGrid’s consultation paper was published alongside notice of:

• An industry webinar on 5 November, and
• A consultation deadline of 24 November.

Further details—including cost caps, LCOS methodology, and how LDES will interact with Ireland’s capacity and flexibility markets—will be released in later stages.

According to the current timeline, the first operational LDES assets are expected by 2030, supporting Ireland’s renewable energy and grid decarbonization strategies.

Technology Eligibility and Tender Scoring

Though the scheme is described as technology-neutral, several criteria will shape which technologies qualify:

• Minimum 4-hour duration
• At least 75% RTE
• Use of commercially proven technologies
• Adherence to capacity rules (20 MW/75 MW minimum, 100 MW maximum per site)

Scoring Breakdown

Tender evaluation will be weighted across three primary factors:

• Cost (50%) – the biggest determinant of ranking
• Connection method (30%) – highest scores go to projects using existing grid connections, either through hybridization with renewables or established standalone points
• Location (20%) – favoring deployment in grid-constrained areas to maximize system value and reduce dispatch-down of renewables

Projects located in areas with historically high curtailment will receive better scores, aligning with Ireland’s strategy to leverage storage to ease grid congestion.