The state-of-charge (SoC) column on the Leaderboard is an estimation of the cost associated with providing any given frequency response service. This cost is only associated with non-Balancing Mechanism-registered assets (non-BMUs). This is because, while we do not have visibility of their physical operation, they are required to manage their SoC when providing frequency response services. Because we have visibility of SoC management for Balancing Mechanism-registered assets (BMUs), we do not need to do any further calculations to determine the cost incurred for those.
To calculate SoC management, we estimate volumes of energy throughput on a settlement period basis. Energy throughput is estimated by modelling the contracted response for each service using the physical (measured) grid frequency provided by National Grid ESO. The corresponding system price (as published by ELEXON) is then used to calculate an estimation of the real-time cost of providing frequency response. We do this for each asset, multiplying the system price by the estimated energy throughput for each settlement period and aggregating the cost for the month.
There are a few further assumptions made alongside the ones outlined above, these include:
Round trip efficiency (RTE): we assume an RTE of 85%, with symmetric efficiency on both imports and exports (92% (√85)).
Grid frequency data: because grid frequency data for a given month is actually published a few days after the end of the month, and therefore after the publication of the Modo Leaderboard, we apply the corresponding month's figures from the previous year. This is done for both BMU and non-BMU registered assets.