Grid Supply Point Technical Limits for accelerated non-firm connections

Currently there is over 625GW of generation in the pipeline to connect nationally, which is driving an increasing number of required network reinforcements, in accordance with industry technical standards.

Under the current connection assessment approach, the impacts of new customers (at transmission or distribution) are appraised on a ‘first come, first served’ basis. This approach then leads to the formation of a ‘queue’ for capacity irrespective of the actual status of individual projects. The huge increase in the volume of connection applications across GB is now causing many customers to receive long lead time connection dates, with some of these spanning out to the mid-2030s.

As a result of these long lead times, and to ensure that the UK is able to meet its net zero ambitions, a revised approach to the allocation of capacity and the management of how and when parties can access this available capacity is required. 

Customers with more agile ‘shovel ready’ projects are currently being held off behind long, slow-moving distribution and transmission connection queues, as transmission capacity already committed cannot be easily transferred to parties outside of the normal queue ‘structure’, and for the most part it cannot be temporarily made available and managed for faster-moving projects.

In response to this, network companies and the Electricity System Operator (ESO) are working together to develop and adopt urgent changes to existing processes to ensure potential blockers to decarbonisation are removed. These changes concentrate on what can be achieved in the short term (considering current industry code and licence obligations), whilst focusing efforts on speeding up existing processes and developing improvements based on enhanced whole system coordination.

The ENA is pushing forward with actions in three key challenge areas, of which the use of Technical Limits at Grid Supply Points (GSPs) forms a key part of this approach. The three areas of focus to help deliver short-term improvements for customers are:

• Reforming the distribution network connection queue – adoption of milestones for projects with offers made prior to 2017 (but are still in the connection queue) with potential to remove them from the queue. Adopting a ‘first ready, first connected’ approach.
• Changing how transmission and distribution networks coordinate connections – development of Technical Limits at GSPs.
• Greater flexibility for storage customers – the use of flexible capacity (e.g., non-firm offers) to enable faster connection.

Building on the existing processes and principles that have been developed through Regional Development Programmes (RDPs), the ENA is focused on making further improvements to help cater for increases in the volume of connection applications (particularly at distribution level), whilst also considering how the use of queue management milestones can be deployed to better allocate capacity as it becomes available.

The roll-out of Appendix G trails (now known as Transmission Impact Assessments) across many sites in England and Wales over the last few years, has already provided Distribution Network Operators (DNOs) with additional degrees of flexibility in terms of how distribution customers are assessed from a transmission perspective.

These initiatives were further refined and improved through the RDP work across the South West and South Coast, which brought further flexibility regarding the management of capacity across multiple, smaller Distributed Energy Resources (DER). The RDPs also introduced the concept of ‘Connect and Manage’ to DNOs, which only previously applied to transmission connections. These, together with the development of new principles for managing embedded generators, such as the implementation of visibility and control requirements through MW Dispatch projects, have further enabled more DER to connect, using an alternative approach whilst maintaining compliance with the Security and Quality of Supply Standard (SQSS), and ensuring the safe operation of the networks.

RDPs are whole electricity system initiatives to unlock more network capacity, reduce constraints and open new revenue streams for market participants. Find out more here.

The Security and Quality of Supply Standard sets out the criteria and methodology for planning and operating the National Electricity Transmission System (NETS). Find out more here. 

 

What are GSP Technical Limits?

GSP Technical Limits are thermal (MW) limits for specific GSPs, agreed between the ESO, Transmission Owner (TO), and DNOs. The DNO is granted the capability to connect customers ahead of the completion of transmission reinforcement works on the basis that the combined capacity contributions from connected customers does not exceed either the import or export GSP Technical Limits established. To maintain the power flows across the GSPs within their Technical Limits, the DNO will deploy automated control schemes, such as Active Network Management (ANM) or Distributed Energy Resource Management Systems (DERMS), to control generation customers’ power imports and exports, on the basis that relevant commercial and technical requirements have been agreed.

Calculated on an individual GSP basis, GSP Technical Limits are captured in the technical appendices of the DNO’s relevant Bilateral Connection Agreement (BCA) with the ESO. It is important to note that commercial and technical requirements may vary between GSPs, and across different DER. However, there is a clear methodology associated with these requirements, detailed again in the technical appendices of the BCA, to ensure the DNOs take a transparent and fair approach to applications, especially when considering changes that may affect queue positions, or queue management milestones.

The DNOs will utilise GSP Technical Limits to actively manage the queue of unconnected non-firm generators that have chosen to connect under the relevant terms. These generators will be referred to as 'Restricted Customers’ throughout the rest of this document. Under GSP Technical Limits terms, Restricted Customers’ DER schemes will connect on a non-firm basis, subject to receiving sufficient notices/evidence to progress from developers, and will be subject to unpaid curtailment by the DNO. The DNO will be responsible for reporting to the ESO any changes to the DER as part of the existing processes.

Whilst the initiative allows connection ahead of the completion of transmission reinforcement works, it is important to note that some customers may also be subject to local GSP ‘attributable works’, such as the need for a new bay, fault level/safety mitigation works which are crucial for a safe and efficient connection. In these instances, an earlier connection date utilising GSP Technical Limits will not be possible until those works have been completed.

This initiative enables accelerated connections for some Restricted Customers on a non-firm basis, however, it will not affect the access rights or curtailment of 'Unrestricted Customers’, i.e. those downstream of the GSP that are already connected or contracted to connect and not subject to transmission reinforcement works.

 

How is it calculated?

The calculation process provides GSP Technical Limits for both power export and import across a defined transmission and distribution boundary and are calculated using the formulae presented below.

 

Export GSP Technical Limits

The calculation for the export GSP Technical Limits uses the sum of the Unrestricted Registered Capacities of the DER connected or due to connect without the need for transmission works, a pre-defined list of scaling factors, and gross demand data for four periods of the year, known as cardinal points. For GSP Technical Limits applied in Scotland, scaling factors have not been used, and just one demand point from the year will be used.

Since there are four cardinal points, defined below, four export GSP Technical Limits will be calculated, and following agreement between parties, the largest figure given will be extrapolated across the entire year.

Export GSP Technical Limit =(Unrestricted Registered Capacity*Scaling Factors)-Demand at Defined Cardinal Points 

Definitions for formula:

Unrestricted Registered Capacity = all generation downstream of the GSP that is already connected or contracted to connect and not subject to transmission reinforcement works.

Scaling factors = specific to technology type, a value between zero and one that is multiplied by generator capacity to create assumed power output for scenario-based backgrounds. See Table 1 for Scaling Factors.

Demand at defined cardinal points = gross minimum GSP demand (i.e., absent of contributions from small, medium, or large embedded power stations), for each cardinal point, observed on dates below:

Winter cardinal point – 01 Dec to 28 Feb

Access Period (maintenance period) cardinal point – 01 Mar to 31 May, or 01 Sep to 30 Nov

Summer Solar Max cardinal point – 01 Jun to 31 Aug (between 10:00-16:00)

Summer Solar Min cardinal point – 01 Jun to 31 Aug (between 04:00-06:00)

Table 1: Scaling Factors proposed for creating assumed export/ import

Fuel Type	Winter	Access Period	Summer (Solar Max)	Summer (Solar Min)
Solar PV	0	0.051	0.84	0.051
Waste/ CHP	0.88	0.88	0.85	0.85
Hydro	0.84	0.84	0	0
Wind	0.7	0.7	0.5	0.1
Other	0.65	0.65	0.3	0.3
BESS/ Energy Storage	-1	-1	1	1

Note: For GSP Technical Limits applied in Scotland, scaling factors have not been used.

 

Import GSP Technical Limits

The calculation for the import GSP Technical Limits uses the maximum observed demand at the GSP for the four defined cardinal points, the import capacities of unrestricted Battery Energy Storage System (BESS) projects not yet connected, and 1 Year of Distribution Future Energy Scenarios (DFES) demand growth. A scaling factor for BESS was not used in this equation as import demand is assumed as maximum/full capacity.

Since there are four cardinal points, four import GSP Technical Limits will be calculated, and will be used accordingly throughout the year. During the summer period, the largest of the two GSP Technical Limits given, Summer Solar Max, will be used by the automated control schemes to operate to.

Import GSP Technical Limit= Maximum Observed Demand at Defined Cardinal Points+BESS Import+1 Year DFES Growth 

Definitions for formula:

Maximum Observed Demand at Defined Cardinal Points = maximum observed/net demand at the GSP (i.e., includes contributions from small, medium, or large embedded power stations generating), for each cardinal point, observed on dates below:

Winter Cardinal Point – 01 Dec to 28 Feb

Access Period (maintenance period) Cardinal Point – 01 Mar to 31 May, or 01 Sep to 30 Nov

Summer Solar Max Cardinal Point – 01 Jun to 31 Aug (between 10:00-16:00)

Summer Solar Min Cardinal Point – 01 Jun to 31 Aug (between 04:00-06:00)

BESS import = those BESS Unrestricted Customers not yet connected.

DFES growth = 1 Year of Distribution Future Energy Scenarios (DFES) demand growth is used to calculate GSP Technical Limits.

 

Alternative GSP Technical Limits

Under some scenarios, it is possible that the export GSP Technical Limit calculated could be less than the current observed power flow across the Transmission and Distribution Boundary at a certain GSP. In such a case, the DNO should share evidence of this with the ESO and the relevant TO. The export GSP Technical Limit should be the maximum observed export at each cardinal point added to, where applicable, the scaled generation of any unconnected Unrestricted Registered Capacity.

Each DNO’s DFES can be found on their respective websites, detailing the growth of the distribution network’s demand in the coming years.

Since there are four cardinal points, defined below, four export GSP Technical Limits will be calculated, and following agreement between parties, the largest figure given will be extrapolated across the entire year.

Alternative Export GSP Technical Limit =Maximum Observed Export at Defined Cardinal Points+(Unconnected Unrestricted Registered Capacity*Scaling Factors)

Definitions for formula:

Maximum Observed Export at Defined Cardinal Points = the maximum power exchange at the site from the previous calendar year, for each cardinal point, observed during the periods below:

Winter cardinal point – 01 Dec to 28 Feb

Access Period (maintenance period) cardinal point – 01 Mar to 31 May, or 01 Sep to 30 Nov

Summer Solar Max cardinal point – 01 Jun to 31 Aug (between 10:00-16:00)

Summer Solar Min cardinal point – 01 Jun to 31 Aug (between 04:00-06:00)

Unconnected Unrestricted Registered Capacity = all generation downstream of the GSP that is unconnected and not subject to transmission reinforcement works.

Scaling factors = specific to technology type, a value between zero and one that is multiplied by generator capacity to create assumed power output for scenario-based backgrounds. See Table 1 for Scaling Factors.

It should be noted that the formulae may need further revision as the ESO’s work to utilise revised Construction Planning Assumptions is implemented. Further analysis is required to understand the impact of this work, which will continue alongside the initial rollout.

 

How are generators informed?

Once it is established that a GSP can be allocated Technical Limits using the methodology described above, the DNOs will discuss with relevant Small and Medium Restricted Generators to establish their interest in receiving a curtailed connection offer. This process will typically involve an application through an Expression of Interest (EOI). The DNO will then issue a variation to the customer’s connection offer, containing an estimate of the export and import curtailment values for the relevant Restricted Generator, based on the GSP Technical Limits for the GSP, and the methodology the DNO is using to calculate the curtailment.

 

How is it managed?

GSP Technical Limits only become effective once the relevant DNO has signed their agreement with the ESO to add the terms and conditions of GSP Technical Limits into their BCA.

A DNO may only advance the connection and energisation of Restricted Generators behind GSP Technical Limits when their GSP Technical Limits Scheme has commissioned, and achieved necessary compliance sign off by the ESO.

The DNO will be required to monitor and control the pre-fault net power exchange at the Grid Supply Point (GSP) within the GSP Technical Limits specified in their technical appendices throughout the year. At some sites, this will be enabled through the provision of required data by the ESO, via a real-time data exchange link between DNO and ESO control systems.

It is the DNO’s responsibility to design an automated control scheme that manages the power contributions from DER that are connected under GSP Technical Limit terms, so that the GSP’s power flow does not exceed either the export or import GSP Technical Limits agreed with the ESO and is in accordance with the associated compliance process. The automated control scheme must be permanently armed, and this shall form part of the DNO’s System.

The GSP Technical Limit Scheme will be monitored by the ESO to ensure it is healthy at all times. The DNO shall inform the TO and the ESO of any issues related to the GSP Technical Limit Scheme that impacts on the operation of the Transmission System, and any proposed mitigating actions to ensure the GSP Technical Limits can continue to be met at all times.

If the GSP Technical Limit Scheme is not healthy, or fails to meet the requirements as described above, the ESO will notify the DNO as such, and the supporting Compliance Process will be followed. A remedial course of action will be sent by the DNO to the ESO in writing before a trilateral investigation between ESO, DNO, and TO is undergone to understand the causation for the scheme’s ill health/failure.

The ESO shall track the DNOs’ adherence to their GSP Technical Limits, and reserves the right to temporarily reduce or suspend the use of the GSP Technical Limits following consistent instances of non-compliance by the DNO.

 

When is a GSP Technical Limit changed?

The GSP Technical Limits may be changed periodically to reflect changes to the contracted background on both distribution and transmission systems. Triggers for this reassessment are typically as follows:

• Annual review. Each GSP Technical Limit will be reassessed annually, to take account of changes to GSP demand levels and changes to contracted generation background.
• Completion or removal of the need for transmission reinforcement works. 
• Termination of transmission connected capacity.

 

Reallocation of capacity following Termination

Where an Unrestricted Customer terminates their agreement with the DNO, the DNO may follow the Reallocation of Terminated Capacity process and reallocate that capacity to an alternative project. This must be done following the queue order, respective of connection application date, offering the potential to enable some previously Restricted Customers to move to an Unrestricted connection.

The following rules apply to reallocation of capacity:

Details of the supporting Compliance Process are currently under review, with drafting ongoing within the ENA.

• At sites where there is a fault level concern, capacity reallocation must be only on a like-for-like (or smaller) fault level impact basis.
• If reallocation causes a greater fault level impact, then a Project Progression will be required and the capacity for reallocation will not be utilised until the study and offer process concludes.
• Thermal capacity reallocation will either be on a like-for-like basis (or smaller) in terms of size and technology. If the reallocation is to a different technology, then a scaling factor will be used. For certain technology combinations, such as wind to battery, no reallocation is possible since differences in demand at Winter or Access Period cardinal points will add more demand to an already demand-restricted GSP.
• Multiple sites can be reallocated, provided the above rules are met.
• Reallocation of capacity for hybrid (co-located) sites can only progress on the basis of like-for-like technology mixes and ratios.
• Any unused and previously terminated capacity will remain with the DNO until the next annual reassessment of the GSP Technical Limits, at which point it will be reviewed.

You can find the full appendices here.