Niall McMahon

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Dispatch Down is a Problem for Ireland


A note about dispatch down in Ireland. Dispatch down means removing a power generator from the grid for good reasons.


Disconnecting a power generator from the grid, or reducing its output, is done to maintain the electrical stability of the grid, i.e. to ensure that demand equals supply as well as other more technical concerns, and to prevent the overload of lines that may be underrated for the amount of power generated, i.e. in rural areas, especially south and west of Ireland, where the grid is relatively underdeveloped.

Disconnecting a generator to maintain electrical stability is often called curtailing, while disconnecting because of underrated power lines to the wind farm is often called constraining, as in there are capacity constraints on the power line from the generator. The terms are not strictly defined.

Constraints are a problem for wind energy in Ireland, mostly in the west, from north to south. In 2019, about 386,000 MWh of energy was dispatched down due to line constraints out of the region. A typical home uses something close to 3 MWh in a year, so this equates to enough energy to power many more than 100,000 homes for a year, or about 5% of the total number of homes in the country.

There are many solutions to this problem. The most obvious are to build or upgrade transmission lines, to build energy storage or use close to the generators, to leverage new technologies to maximise line capacity and to create entirely new uses for energy. The industry body Wind Energy Ireland has recommended better reporting about constraints from Eirgrid, the grid operator, and ESB Networks, the company that builds and repairs electricity lines and equipment.

Of the principal ways that dispatch down can be avoided, using the energy close to the generator is the best solution. If the data around wind farm production and constraints were easily shared, they could be better understood and the schedules of large energy users adjusted to use energy when a dispatch down event is likely. This might be when wind speeds are forecast high. The aim would be to shift the curve of local usage to coincide better with local production.

Additionally, home users with smart equipment might make use of excess local energy.

Clearly, this work is not brand new exactly but there seems to be a lack of clarity about dispatch down and constraints. There is room for a well designed interface and an API that allows the sharing of energy data from generators and users. In parallel, there is an opportunity to do something with the "wasted" energy.


Wind farms being ‘instructed to reduce amount of power they generate’, AgriLand. Aug 26, 2020.

Blog: ‘Dispatch Down’ and the fight against climate change, Wind Energy Ireland. 03 Sep 2019.

IWEA Response to the CRU’s Discussion Paper on the Approach for Transmission & Distribution Price Review Five, IWEA (Wind Energy Ireland). January 2020.
Good summary and proposals to minimise dispatch down. None directly involving data.

IWEA’s recommendations for Dispatch Down:
  • EirGrid should review its policy on counter trading and also prioritise I-SEM improvements that could facilitate the increased use of interconnectors during wind curtailment periods.
  • We request that the resourcing and tools in the NCC are increased to ensure that dispatch down of renewable generation can be minimised.
  • We request that in PR5 there is substantial focus on the reduction of outage periods which can be managed via increased reporting, appropriate resourcing, process improvements and incentives.
  • IWEA would also request that EirGrid and ESBN complete greater levels of ongoing analysis and reporting to minimise dispatch down. It is important that PR5 provides sufficient resources for ongoing monitoring and analysis to minimise dispatch down levels of renewable generation.
  • We recommend the use of key performance indicators that monitor ongoing improvements on the drivers of dispatch down, for example, total dispatch down MWh and CO2 equivalent levels, interconnector exports, minimum conventional generation levels and SNSP limits.

Saving Power, IWEA (Wind Energy Ireland). August 2020. This is a good summary with useful ideas. Some of these are:

  • Battery storage, demand side response and synchronous condensers will be needed to provide future system stability with variable resources.
  • In 2019, according to Eirgrid, dispatch down in Ireland represented 6.9% of all produced renewable energy, or 710,591 MWh. This was 3.1% as a result of curtailment and 3.8% as a result of constraints.
  • Line constraints can make a project commercially unfeasible; in some instances, projects may not be able to connect to the transmission system for years.
  • Dynamic line ratings, smart wires, energy storage and demand side response can all be used to mitigate the impact of constraints.
  • An electricity market based on the marginal cost of generating one unit of electricity is not suitable for a future where most electricity will come from zero-marginal cost generation, i.e. the wind and sun are essentially free resources once the equipment is in place.
  • In the future, on wind and sunny days, there may be more energy produced than can be used in the country. This is a third reason for dispatch down, energy balancing. Again, solutions include creating more elexible demand, storage and additional interconnection with other countries.
  • Electrifying heat and transport will create extra demand and, also, storage.


Other Work

DSSED: Decision Support System for Energy use in Dairy Production, CIT/Teagasc.

Identifying the relative and combined impact and importance of a range of curtailment mitigation options on high RES-E systems in 2030 & 2040, Mullan Grid, (Carton) DCU etc.

Impact of wind curtailment and storage on the Irish power system 2020 renewable electricity targets: a free open-source electricity system balancing and market (ESBM) model, E J McKenna*, M Thomson. Centre for Renewable Energy Systems Technology (CREST), Loughborough University.

Studies concerned with accommodating large penetrations of renewables and decarbonising power systems show the need to avoid curtailment, by making use of excess wind power, for example by charging electrical energy storage systems [2-5].

Increasing Time Granularity in Electricity Markets. Innovation Landscape Brief.
From the document, trends include:

RENews. Ireland Special Report 2020, July 2020.

The Irish industry has warned that creaking grid infrastructure and proposed new noise restrictions could stop the surging development pipeline in its tracks.Multiple developers have pointed to the need for significant new transmission lines and network reinforcement nationwide as the biggest challenge facing the sector this decade.The grid is already under pressure after years of strong wind capacity growth. Irish transmission system operator Eirgrid constrained or curtailed wind farm output a record near-11% of the time in the Republic in the first quarter of this year, up on the previous high of 8% in the third quarter of last year.

Overcoming grid constraints for renewable energy provision, European Commission, Research and Innovation information Centre. 2018.

More electricity is generated from renewable sources in Orkney than the population can use and the surplus is usually transferred to the UK’s national grid network. However, it often happens that surplus energy is available but the cables transferring it are at full capacity. On such occasions, wind turbines are switched off or ‘curtailed’ and the energy is lost, with the turbines on the islands of Shapinsay and Eday losing over 30 % of annual output.

Harvard Electricity Policy Group Eighty-Ninth Plenary Session, Harvard Kennedy School. January 2018.

Respondent 1: I'm not sure we will necessarily de-average prices. There's a social context here. Clearly there was with the extension of the grid, it turned out Sam Insull discovered that running electric lines out to rural Chicago was cost effective, not because it was cheap to run the lines, but because the load imposed by the dairy farmers was off-peak from the residential, and he could run his power plants 24/7, because the dairy farmers came in at 3:00, 4:00 in the morning from milking, and he could get additional revenue, so it was load-building and filling in the peaks and valleys. And so, on that basis, line extensions were made, when otherwise, without that cost benefit, you wouldn't have done it.