The Technical Limits will be implemented through an scheme owned by the DNO. NGESO will provide the DNO with the appropriate limits for power flow through the supergrid transformers (SGTs) at the GSP. The DNO will monitor the power flow through the SGTs and will control the output of customers connecting under the Technical Limits scheme, so that the limit is never exceeded. There will be a LIFO (Last In First Out) stack, to put customers in commercial queue order, in terms of who is curtailed in which order.

There will also be a requirement for customers and DNOs to provide visibility and control of distribution generation connecting under Technical Limits to NGESO. This will be done via links between the DNO and NGESO control systems.

Technical Limits will only be rolled out at GSPs which meet the criteria for each of the phases of the roll-out:

• Phase 1a. Transmission Thermal Enabling Works must be required at the GSP, with no fault level works. It will be a single user GSP, with customers with long connection timescales.
• Phase 1b. Transmission Thermal Enabling Works must be required at the GSP, with the fault level headroom <1kA. It will be a single user GSP, with customers with long connection timescales.
• Phase 2. Site with two or more transmission customers (so two or more DNOs, or one DNO and one or more direct transmission connections). These are complex sites and require interaction with multiple parties.

Phase 1a. DNOs are currently writing to customers with accepted offers on Phase 1a GSPs, asking them to provide an Expression of Interest (EOI) in October and November 2023 to be included in the process. It is unknown when the DNOs will issue the revised offers.

Phase 1b. DNOs and NGESO will agree revised Bilateral Connection Offers (BCAs) in Q4 2023, with DNOs writing to customers in November / December 2023 asking for an EOI.

Phase 2. Sites will begin to be selected in Q1 2024 for review.

Curtailment

The headline of Technical Limits is great—connect early without waiting for transmission reinforcement. The downside is that a site will be curtailed (i.e. have a reduced output – see our ‘What is curtailment in electricity networks and how does it work?’ explainer). It is unknown what the curtailment will be for each site until the DNO issues the revised offers with associated curtailment reports. The actual curtailment will of course depend on which sites actually proceed to connection.

Transmission costs and securities

An earlier connection date via a Technical Limits connection won’t change the cancellation liabilities, securities and SGT reinforcement charges associated with the connection however an earlier connection date may mean customers face some of these liabilities (such as the wider cancellation charge) earlier.  Once connected, transmission liabilities for distribution connected generators fall away and so while  customers should assume that whatever works were presented to them through the Project Progression process will still apply, the timing of the liabilities may make a significant difference.

DNO connection works

Whilst Technical Limits will allow some sites to connect prior to transmission reinforcement works, the DNO will still need to undertake the connection works on the distribution system, including any distribution reinforcement works. The higher the voltage, the longer the works take to schedule and complete. And of course, DNOs have a limited resource for delivery, so will not be able to do everything at once.