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Exit capacity

This page provides an overview of exit capacity, including the types of capacity that are available, the different types of applications (and the capacity available in each), and the responsibilities of both users and National Grid.

Exit capacity gives shippers the right to take off the National Transmission System (NTS). Capacity is often also referred to as ‘rights’ or ‘entitlements’. A shipper needs to buy one unit of capacity in order to flow one unit of energy. This is known as the ‘ticket to ride’ principle. Units for both capacity and energy are in kWh/day.

Types of capacity

We make firm and off-peak capacity available to the market at each offtake point.

Firm capacity

The volume of firm capacity made available at each offtake point consists of the following amounts:

  • baseline exit capacity (obligated) – as defined by our Gas Transporter Licence;

  • incremental exit capacity (obligated) – firm capacity made available over and above baseline, in response to market demand and supported by user commitment. This increase in capacity is permanent; and

  • incremental exit capacity (non-obligated) – we can release additional firm capacity at an offtake point over and above obligated levels.

Off-peak

Off-peak capacity can be made available to the market at offtake points where firm capacity is not being used. The volume of off-peak capacity available at an offtake consists of three parts:

  • use it or lose it (UIOLI) – any firm capacity that hasn't been used over recent days can be resold to the market as interruptible capacity;

  • unutilised maximum network exit point offtake rate (MNEPOR) – during D-1 at 13:30 the NTS demand forecast is published. Where this demand forecast is less than 80% of the annual peak 1 in 20 demand forecast, we are obliged to release any remaining capacity up to the MNEPOR level as off-peak capacity; and

  • discretionary – we can make additional off-peak capacity available to the market.

If there are low pressures on the network, we may curtail off-peak capacity rights, without any compensation for the users affected.

Acquiring capacity

Once a shipper has obtained a shipper licence then they can be considered a user of the NTS under the terms of the Uniform Network Code (UNC). Shippers can obtain exit capacity by making applications or bids on the Gemini exit system, through a number of application windows and auctions. These applications or bids are allocated in accordance with UNC, and with consideration to our incentive schemes. You can find details of the exit capacity application windows and auctions within Section B of the UNC, published on the Joint Office website.

Applications

Long-term applications

There are three types of long-term exit capacity application windows:

  • Enduring annual exit (flat) capacity increase (EAFLEC) - This application window is for capacity covering the period Y+4 to Y+6. The capacity bought in this application window is enduring and can be increased or decreased in a later application window (subject to user commitment). The application period for this auction is 1 to 31 July where the bid window will be open from 8am to 5pm on each business day.

  • Enduring annual exit (flat) capacity decrease (EAFLEC) - This allows a user to decrease their enduring capacity holdings from Year Y+1 (October following the July window). Further decreases and increases can be requested in subsequent application windows. The application period for this auction is 1 to 15 July where the bid window will be open from 8am to 5pm on each business day.

  • Annual NTS (flat) exit capacity (AFLEC) - This is for capacity covering the period Y+1 to Y+3. The capacity allocated in this application window is not enduring and therefore cannot be increased or decreased. If capacity is requested in this application window for Y+2, in the following year's application window the capacity will show as Y+1 and any further annual capacity requested will be in addition to the original Y+2 capacity. The application period for this application window is 1 to 31 July where the bid window will be open from 8am to 5pm on each business day.

All submitted requests are subject to analysis by us. Successful applications submitted in the AFLEC window will be allocated within ten business days of the application window closing. Successful applications submitted in the EAFLEC window will be allocated on or before 30 September.

The unit price (p/kWh) for capacity brought in both AFLEC and EAFLEC is published on the Joint Office of Gas Transporters website. All conditions and requirements for all of the above mentioned application window can be found in UNC Transportation, Section B, Sub Section 3

Short-term applications

There are two auctions that run daily for the sale of firm exit capacity. Bids may be evergreen or reducing. An evergreen bid remains fixed throughout the day. A reducing bid reduces by 1/x with each hour that passes where it remains unallocated (where x is the number of hours remaining in the gas day at time the bid was placed). 

There is also one auction that runs daily for the sale of off-peak capacity. All these are detailed below: 

Day-ahead daily exit capacity (DADNEX)

Unsold obligated firm exit (flat) capacity will be made available in the DADNEX auction and is a 'pay as bid' auction. 

Bid Window: D-7 05:00 to D-1 14:00

Allocation Window: D-1 15:00 to D-1 16:00

Charges: For information, please refer to the Joint Office website

Within-day daily exit capacity (WDDNEX)

Any remaining unsold capacity after the allocation of the DADNEX auction will roll over and be made available in the WDDNEX auction which, is a 'pay as bid' auction. 

Bid Window: D-1 14:00 to D-0 00:00

Allocation Window: D-0 08:00, 14:00, 18:00, 22:00 & 01:00

Charges: For information, please refer to the Joint Office website

Daily off-peak exit capacity (DONEX)

In addition to firm NTS exit (flat) capacity users may also bid for and purchase daily off-peak exit capacity. This product is sold via the DONEX auction. This amount depends of the prevailing forecast total system demand for the gas day being less than 80 per cent of the 1-in-20 peak day demand. 

Bid Window: D-7 05:00 to D-1 14:00

Allocation Window: D-1 15:00 to D-1 16:00

Charges: For information, please refer to the Joint Office website

General pricing

All auction bids will be allocated based on price (highest first) until all unsold capacity has been allocated (in line with the allocation principles as described in UNC Section B – Annex B1). Where bids exceed the available unsold quantity, National Grid may allocate these but will do so at their own discretion.

Constraint management

We operate the system in accordance with the System Management Principles Statement. We take steps to physically optimise operation of the system to avoid constraints. When needed, we use a range of commercial tools to help alleviate constraint situations known as Constraint management actions.

Long-term-use-it-or-lose-it (LTUIOLI)

We will monitor use of users' available system capacity at interconnection points (IPs). After each six-month period (1 April to 30 September and 1 October to 31 March), we will then, in accordance with the CMP LTUIOLI Guidance Document, identify whether or not a user at an IP has underused its available system capacity and provide notification to that user.

Overruns

If a user's flow exceeds their capacity entitlements for any given gas day, a shipper will incur an overrun charge. The overrun charge is the shipper's financial incentive to buy all the capacity that it needs. 

For more information relating to overruns, please refer to the Uniform Network Code Transportation Principal Document - Section B3.13, System Use & Capacity.