Capacity workbooks

This workbook provides indicative "headroom" capacity available for new demand connections at existing 110 kV and 38 kV substations. Forecasts are produced for every year up to 2030, and then for every five years after that out to 2050. The workbook indicates the spare or “headroom” capacity available at a station under four different growth rate scenarios. Note that the information provided is indicative. There can be upstream network limitations on High Voltage (HV) feeders and transmission system feeders that will limit capacity at local substations.  In order to secure capacity for a new connection, customers are advised to follow the new connection application process available on the ESB Networks website www.esbnetworks.ie.

Version 1.0 of the Demand Capacity Workbooks include projects that are planned for the Price Review 5 (PR5) period. Version 2.0 of the Capacity workbooks will be released in 2025 and will include reinforcement projects planned for the PR6 period to 2030. These projects will address many of the emerging capacity constraints.

Every 5 years ESB Networks make a submission to the Commission for the Regulation of Utilities (CRU) to outline the expenditure needs on the distribution network. The PR5 period runs from 2021 to 2025. The PR6 period runs from 2026 to 2030. The CRU will issue the determination for the PR6 period in 2025.

This workbook provides indicative "headroom" capacity for new generator connections available at existing 110 kV and 38 kV substations. Forecasts are produced for every year up to 2030, and then for every five years after that out to 2050. The workbook indicates the spare or “headroom” capacity available at a station under four different growth rate scenarios. Note that the information provided is indicative .There can be upstream network limitations on High Voltage (HV) feeders and transmission system feeders that will limit capacity at local substations. In order to secure capacity for a new connection customers are advised to follow the new applications process available on the ESB Networks website www.esbnetworks.ie.

Firm capacity is the capacity that a HV station can sustain over a prolonged period under both normal feeding operation and during an outage due to a fault or maintenance of a transformer at a station. Non-firm capacity is additional capacity in excess of the firm capacity that could also be provided at a station. During an outage of a transformer, non-firm capacity is available if there are adequate load transfer arrangements in place to transfer demand to adjacent stations or there is flexible load at the station that can be used to reduce demand within the required timeframe.

Four growth rate scenarios are presented in the workbooks, conservative, base, aggressive and best view. These scenarios are based on different assumptions for growth of the existing and future load, economic and commercial growth, electrification of transport and heat and new housing developments. There is a degree of uncertainty around predicted growth rates as they are dependent on a number of factors such as the rate of economic growth, rate of new housing construction and the rate of adaption of electrification of heat and transport targets under the Climate Action Plan (CAP). These growth scenarios will be updated and developed further for the capacity workbooks v2.0 to be released in  Q4 2025.

The capacity workbooks will be updated on an annual basis.

The DNDP is due to be published in 2025 and will be updated every two years thereafter. The DNDP consists of the network scenario headroom report (capacity workbooks) in conjunction with a Distribution Network Development Report (DNDR). The aim of the DNDP is to provide transparency to customers on the medium-term and long-term development plans for the network. The Distribution Network Development Report (DNDR) will outline the infrastructure CAPEX reinforcement plans and also indicate areas of the network where flexibility services will be required.

Customers are encouraged to engage early with ESB Networks if they are planning a new development that will require a connection to the electricity network. 

To secure capacity for a new connection customer are advised to follow the new applications process available on the ESB Networks website: Types of new connections

ESB Networks' network planners must carry out a detailed network study for each application before a connection is issued.

For more information please refer to this page flexible demand.

• An example is provided for a typical 38 kV/MV substation.
• A typical configuration of a 38 kV station in an urban setting is that two 10 MVA transformers are installed. 
• For this 2x10 MVA station, the total installed capacity is 20 MVA, the firm capacity is 15 MVA and the non-firm capacity is 18 MVA. 
• When a fault on a transformer occurs, there is a single transformer remaining operational in the station. This is referred to as an N-1 scenario. 
• Subsequent to an N-1 fault on a 10 MVA transformer, the remaining transformer can be loaded up to 180% (18 MVA) of its capacity for a short period. Load must be transferred by operational switching on the MV system to adjacent stations to reduce the load to 15 MVA (150%). The transformer can carry this 15 MVA on a cyclic basis for a number of days until the second transformer is repaired or replaced. This is the firm capacity of the station.
• If the peak demand on the 38 kV station is 10 MVA, the capacity workbooks will indicate that there is 5 MVA of firm capacity or 8 MVA of non-firm capacity available at the station.

• The firm and non-firm capacity results are based on a scenario where one transformer in a standard two-transformer station arrangement has a fault outage at the peak system demand.  
• The peak system demand generally occurs around the 5pm to 7pm period on a winter evening in December or January and is the most onerous or “worst-case” scenario.  
• Maintenance outages are generally planned to occur when loads on the system are lower.  
• In general, transformers are operating normally and faults at the system peak are a rare occurrence.  
• In the event of a fault occurring, load can generally be transferred away to adjacent stations in order to reduce the loading on a transformer. 
• If workbook indicates that a 38 kV/MV (2x10 MVA) station has a negative firm capacity (-3 MVA), this means there is 18 MVA on the station at peak time.
• This means that at peak time December/ January there is usually 9 MVA peak demand on each 10 MVA transformer.
• This is not a problem generally. 
• The issue only arises if you get a fault at 6pm, within 30 minutes you must reduce load to 15 MVA (firm capacity 150%) and then this can be carried for a number of days  
• However, a negative result for headroom capacity is a good indicator that there is a requirement for a new network reinforcement project to add capacity to the network and facilitate further customers connections.

The capacity heatmap provides an indication of the capacity available on the network at the current point in time. The capacity workbooks provide a projection into the future of the headroom capacity at stations based on different growth rate scenarios. The capacity heatmaps can be found here availability capacity heatmap.