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Calculation of the N – 1 formula 1. Definition of the N – 1 formula The N – 1 formula describes the ability of the technical capacity of the gas infrastructure to satisfy total gas demand in the calculated area in the event of disruption of the single largest gas infrastructure during a day of exceptionally high gas demand occurring with a statistical probability of once in 20 years. Gas infrastructure shall cover the gas transmission network including interconnections, as well as production, LNG and storage facilities connected to the calculated area. The technical capacity of all remaining available gas infrastructure in the event of disruption of the single largest gas infrastructure shall be at least equal to the sum of the total daily gas demand of the calculated area during a day of exceptionally high gas demand occurring with a statistical probability of once in 20 years. The results of the N – 1 formula, as calculated below, shall be at least equal to 100 %.

2. Calculation method of the N – 1 formula The parameters used for the calculation shall be clearly described and justified.

For the calculation of the EPm, a detailed list of the entry points and their individual capacity shall be provided.

3. Definitions of the parameters of the N – 1 formula ‘Calculated area’ means a geographical area for which the N – 1 formula is calculated, as determined by the competent authority. Demand-side definition ‘Dmax ’ means the total daily gas demand (in mcm/d) of the calculated area during a day of exceptionally high gas demand occurring with a statistical probability of once in 20 years. Supply-side definitions ‘EPm ’: technical capacity of entry points (in mcm/d), other than production, LNG and storage facilities covered by Pm, LNGm and Sm, means the sum of the technical capacity of all border entry points capable of supplying gas to the calculated area. ‘Pm ’: maximal technical production capability (in mcm/d) means the sum of the maximal technical daily production capability of all gas production facilities which can be delivered to the entry points in the calculated area.

‘Sm ’: maximal technical storage deliverability (in mcm/d) means the sum of the maximal technical daily withdrawal capacity of all storage facilities which can be delivered to the entry points of the calculated area, taking into account their respective physical characteristics. ‘LNGm ’: maximal technical LNG facility capacity (in mcm/d) means the sum of the maximal technical daily send-out capacities at all LNG facilities in the calculated area, taking into account critical elements like offloading, ancillary services, temporary storage and re-gasification of LNG as well as technical send-out capacity to the system. ‘Im ’ means the technical capacity of the single largest gas infrastructure (in mcm/d) with the highest capacity to supply the calculated area. When several gas infrastructures are connected to a common upstream or downstream gas infrastructure and cannot be separately operated, they shall be considered as one single gas infrastructure.

4. Calculation of the N – 1 formula using demand-side measures Demand-side definition

‘Deff ’ means the part (in mcm/d) of Dmax that in the case of a disruption of gas supply can be sufficiently and timely covered with market-based demand-side measures in accordance with point (c) of Article 9(1) and Article 5(2).

5. Calculation of the N – 1 formula at regional level The calculated area referred to in point 3 shall be extended to the appropriate regional level, where applicable, as determined by the competent authorities of the Member States concerned. The calculation may also extend to the regional level of the risk group, if so agreed with the competent authorities of the risk group. For the calculation of the N – 1 formula at regional level, the single largest gas infrastructure of common interest shall be used. The single largest gas infrastructure of common interest to a region shall be the largest gas infrastructure in the region that directly or indirectly contributes to gas supply to the Member States of that region and shall be defined in the risk assessment.

The calculation of the N – 1 formula at regional level may replace the calculation of the N – 1 formula at national level only where the single largest gas infrastructure of common interest is of major importance for the gas supply of all Member States concerned in accordance with the common risk assessment. On the level of the risk group, for the calculations referred to in Article 7(4), the single largest gas infrastructure of common interest to the risk groups as listed in Annex I shall be used.