Curtailment is what happens when a wind farm or solar farm is told to reduce its output even though it could be generating more electricity. Imagine filling a bath with the tap running at full blast – if the drain cannot empty fast enough, you have to turn the tap down. On Ireland’s electricity grid, curtailment is the equivalent of turning down the renewable energy tap because the system cannot safely absorb all the clean power that is available. The energy that could have been generated but was not is effectively wasted – the wind still blows, but the turbines are instructed to feather their blades and produce less.
In Ireland, curtailment is one of the biggest practical challenges in the transition to 80% renewable electricity by 2030. In 2025, the wind dispatch-down rate in the Republic of Ireland was 11.3%, meaning more than one in ten megawatt-hours of available wind energy was not used. Understanding why this happens – and what can be done about it – matters for anyone tracking Ireland’s progress on climate targets or investing in renewable energy.
🌿 Curtailment vs Constraints: Two Types of Dispatch-Down
EirGrid, Ireland’s transmission system operator, uses the umbrella term “dispatch-down” to cover all situations where renewable output is reduced below what is available. This splits into two distinct categories:
Curtailment happens for system-wide stability reasons. The main cause is the requirement to keep a minimum number of conventional fossil fuel generators online at all times to maintain frequency, voltage and reserve capacity. Currently, eight large synchronous units must run across the island (five in Ireland, three in Northern Ireland). Even if wind could power the entire country, those eight gas or oil plants cannot be switched off without risking a system collapse. In 2024, EirGrid reported that 96% of curtailment in the Republic was caused by this minimum conventional generation requirement.
Constraints happen for local network reasons – essentially, traffic jams on the transmission grid. If a wind farm in Kerry is producing at full output but the power lines connecting it to Dublin are at capacity, the farm must reduce output regardless of what the rest of the system looks like. In 2025, constraints accounted for 6.6% of the total 11.3% wind dispatch-down rate in the Republic, with curtailment making up the remaining 4.7%.
🌿 The SNSP Limit
The System Non-Synchronous Penetration (SNSP) limit is another system-wide factor that can trigger curtailment. SNSP measures the proportion of total generation coming from non-synchronous sources – primarily wind, solar and electricity imported via HVDC interconnectors. Ireland’s SNSP limit is currently 75%, one of the highest in the world, meaning up to three-quarters of the electricity on the grid can come from inverter-based (non-fossil-fuel) sources at any moment.
When renewable output would push SNSP above 75%, wind and solar farms are curtailed to stay within the limit. However, EirGrid data shows that the SNSP limit itself was responsible for only about 1% of all dispatch-down across the island in 2024 – far less than the minimum generation requirement. That share rose to 17% in 2025, suggesting the SNSP ceiling is becoming a more significant constraint as renewable capacity grows. EirGrid is working toward raising the limit to 80%, and the Operational Policy Roadmap sets out further relaxations planned through to 2030 as grid-forming battery storage and synchronous condensers reduce the system’s dependence on fossil fuel generators for stability services.
🌿 Why Curtailment Matters for Ireland
Every megawatt-hour of curtailed renewable energy is a megawatt-hour that must be replaced by burning gas, pushing up both emissions and wholesale electricity prices. On the windiest days in December 2024, the average wholesale price of electricity dropped to EUR 78.86 per MWh, but on calm days relying almost entirely on gas it more than trebled to EUR 294.37 per MWh. Curtailment directly undermines both the environmental and economic case for renewable investment.
As Ireland installs more wind and solar capacity to meet its 2030 targets – 9 GW onshore wind, 5 GW offshore wind and 8 GW solar PV – the curtailment problem will intensify unless the grid expands in parallel. The solutions include building new transmission lines to relieve local constraints, commissioning more battery storage to absorb surplus renewable energy, completing the Celtic Interconnector to France (700 MW, operational by 2027) and reducing the minimum number of conventional generators required online. EirGrid began trialling a reduction from eight to seven minimum units in 2023, but further reductions depend on new technology proving it can deliver the stability services that conventional generators currently provide.
🌿 Frequently Asked Questions
🌿 Do wind farm owners get compensated for curtailment?
Under the Single Electricity Market (SEM) rules, generators that are dispatched down may be eligible for compensation depending on the circumstances and their contract type. Renewable Electricity Support Scheme (RESS) auction prices factor in expected curtailment levels when developers submit their bids. Higher curtailment therefore feeds back into higher support costs, which are ultimately passed through to electricity consumers via the Public Service Obligation levy.
🌿 Is curtailment getting better or worse?
It depends on how you measure it. EirGrid has made world-leading progress in raising the SNSP limit from 50% to 75% over the past decade, which has reduced one source of curtailment. However, the rapid growth in installed renewable capacity means the total volume of energy being dispatched down continues to rise. In the Republic of Ireland, wind dispatch-down was 11.3% in 2025, with constraints (6.6%) now outweighing curtailment (4.7%) as the dominant issue – signalling that the physical grid infrastructure needs to expand.
🌿 Can batteries solve curtailment?
Batteries can help by absorbing surplus renewable electricity during periods of high generation and releasing it when demand picks up. Ireland had 756 MW of battery storage operational across 21 systems by early 2025. But batteries alone cannot solve all curtailment – they typically provide 1-2 hours of storage, while windy periods can last for days. Longer-duration solutions like green hydrogen production, pumped hydro and expanded interconnection are needed alongside batteries for a comprehensive approach.
🌿 What is the difference between curtailment and dispatch-down?
Dispatch-down is the umbrella term for any reduction in renewable output below what is available. Curtailment specifically refers to reductions for system-wide reasons (stability limits, minimum generation requirements, SNSP). Constraints refer to reductions for local network reasons (transmission bottlenecks). Together, curtailment and constraints make up total dispatch-down.