http://www.legislation.gov.uk/eur/2015/1222/article/21/adoptedCommission Regulation (EU) 2015/1222 of 24 July 2015 establishing a guideline on capacity allocation and congestion management (Text with EEA relevance)Commission Regulation (EU) 2015/1222Commission Regulation (EU) 2015/1222 of 24 July 2015 establishing a guideline on capacity allocation and congestion management (Text with EEA relevance)2020-12-11King's Printer of Acts of Parliamenthttps://webarchive.nationalarchives.gov.uk/eu-exit/https://eur-lex.europa.eu/legal-content/EN/TXT/?uri=CELEX:32015R1222texttext/xmlen TITLE II <Strong>REQUIREMENTS FOR TERMS, CONDITIONS AND METHODOLOGIES CONCERNING CAPACITY ALLOCATION AND CONGESTION MANAGEMENT</Strong> CHAPTER 1 <Strong> <Emphasis>Capacity calculation</Emphasis> </Strong> Section 3 <Strong> <Expanded>Capacity calculation methodologies</Expanded> </Strong> Capacity calculation methodology Article 21 1 The proposal for a common capacity calculation methodology for a capacity calculation region determined in accordance with Article 20(2) shall include at least the following items for each capacity calculation time-frame: a methodologies for the calculation of the inputs to capacity calculation, which shall include the following parameters: a methodology for determining the reliability margin in accordance with Article 22; the methodologies for determining operational security limits, contingencies relevant to capacity calculation and allocation constraints that may be applied in accordance with Article 23; the methodology for determining the generation shift keys in accordance with Article 24; the methodology for determining remedial actions to be considered in capacity calculation in accordance with Article 25. b a detailed description of the capacity calculation approach which shall include the following: a mathematical description of the applied capacity calculation approach with different capacity calculation inputs; rules for avoiding undue discrimination between internal and cross-zonal exchanges to ensure compliance with point 1.7 of Annex I to Regulation (EC) No 714/2009; rules for taking into account, where appropriate, previously allocated cross-zonal capacity; rules on the adjustment of power flows on critical network elements or of cross-zonal capacity due to remedial actions in accordance with Article 25; for the flow-based approach, a mathematical description of the calculation of power transfer distribution factors and of the calculation of available margins on critical network elements; for the coordinated net transmission capacity approach, the rules for calculating cross-zonal capacity, including the rules for efficiently sharing the power flow capabilities of critical network elements among different bidding zone borders; where the power flows on critical network elements are influenced by cross-zonal power exchanges in different capacity calculation regions, the rules for sharing the power flow capabilities of critical network elements among different capacity calculation regions in order to accommodate these flows. c a methodology for the validation of cross-zonal capacity in accordance with Article 26. 2 For the intraday capacity calculation time-frame, the capacity calculation methodology shall also state the frequency at which capacity will be reassessed in accordance with Article 14(4), giving reasons for the chosen frequency. 3 The capacity calculation methodology shall include a fallback procedure for the case where the initial capacity calculation does not lead to any results. 4 All TSOs in each capacity calculation region shall, as far as possible, use harmonised capacity calculation inputs. By 31 December 2020, all regions shall use a harmonised capacity calculation methodology which shall in particular provide for a harmonised capacity calculation methodology for the flow-based and for the coordinated net transmission capacity approach. The harmonisation of capacity calculation methodology shall be subject to an efficiency assessment concerning the harmonisation of the flow-based methodologies and the coordinated net transmission capacity methodologies that provide for the same level of operational security. All TSOs shall submit the assessment with a proposal for the transition towards a harmonised capacity calculation methodology to all regulatory authorities within 12 months after at least two capacity calculation regions have implemented common capacity calculation methodology in accordance with Article 20(5).