Discussion of "Review of usage-based transmission cost allocation methods under open access

Abstract

The authors present an interesting comparison of methods to determine the use of transmission lines, the charges for such use in bilateral transactions as well as in multilateral or open access conditions, as well as alternative tariff schemes. The subject is of growing relevance in the discussions on transmission open access taking place worldwide, and we congratulate the authors for their work. We would appreciate if the authors make a critical assessment of these methods, as well as an indication of the advantages and disadvantages of each method as compared to the others. The results shown in the paper1 give very similar cost assignments for the compared methods, so it is difficult to choose one against the other. What do the authors propose and why? Even though several methods are briefly analyzed in the paper, their implementation is not fully explained. It is not clear the use of equation [7] that the authors indicate corresponds to the original MW-mile cost allocation method. It seems to correspond to the power flow decomposition method, rather than the MW-mile one. We understand equation [2] better represents that method, or even equation [8] as an application. We tried to reproduce the calculations of the flow contributions that are reported in Tables IV and V, but we were not successful in obtaining the same costs. In fact, it is not clear to us why the total transmission cost incurred by each generator is expressed as a variable cost ($/MW). The cost assignment to each generator should be a distribution of the total system transmission cost. The data in the example is expressed as a DC load flow, without including losses. However, the two tracing methods by Bialek and Kirschen discuss how to include losses and perform the assessment using an AC load flow. Since the MW-mile method uses a DC load flow to assign responsibilities in the use of a line, we are interested to learn what the authors assumed for this assignment in the two indicated methods. We are also interested in the assessment of revenues reconciliation for the example transmission system, in the case of bilateral transactions and the one charging generators. Is it possible to conclude on the percentage of transmission cost recovery of the different presented methods?