Battery energy storage system

A system for providing balancing services to an electrical power distribution network to which it is connected, the system comprising:

• a storage battery with a detector adapted to monitor, either directly or indirectly, its state of charge (SoC);
• at least one non-battery asset (low) that is adapted to increase power supplied to the network relative to that withdrawn from it;
• at least one non-battery asset (high) that is adapted to increase power withdrawn from the network relative to that supplied to it;
• and
• a central controller adapted to be responsive to imbalances detected in the network, to receive information from the SoC detector and to generate signals for controlling operation of the battery and the assets;
• wherein the central controller is further arranged to respond to imbalances as follows:
• (a) By charging and discharging the battery to counter the imbalances when information received from the SoC detector indicates that the battery SoC is within an optimal range, the optimal range extending between a predetermined low threshold and a predetermined high threshold;
• (b) By operating asset (low) to increase power supplied to the network relative to that withdrawn from it when information received from the SoC detector indicates that the battery SoC is below the predetermined low threshold;
• and
• (c) By operating asset (high) to increase power withdrawn from the network relative to that supplied to it when information received from the SoC detector indicates that the battery SoC is above the predetermined high threshold;
• Wherein the low and high thresholds are determined such that:
• with SoC at the low threshold, the battery remains capable of discharging for a lag time equivalent to a time taken for the selected asset (low) to reach its operational capacity;
• and
• with SoC at the high threshold, the battery remains capable of charging for a lag time equivalent to a time taken for the selected asset (high) to reach its operational capacity.

A method of selecting non-battery assets from a portfolio of non-battery assets to supplement balancing services to a network provided by a battery, the battery having a detector adapted to monitor, either directly or indirectly, its state of charge (SoC) and, if the detector indicates the battery SoC exceeds a high threshold or falls below a low threshold, the method includes the steps of:

• (a) Identifying a number of combinations of aggregated assets from the portfolio, wherein:
• (i) If the method is triggered by exceeding the high threshold, each asset is operable to provide a balancing response equivalent to withdrawal of power from the network;
• (ii) If the method is triggered by falling below the low threshold, each asset is operable to provide a balancing response equivalent to supply of power to the network;
• and
• (iii) Each combination includes at least one asset and has a respective lag time, this lag time being a time taken for the respective combination of aggregated assets to reach its operational capacity;
• (b) For each of the combinations of aggregated assets identified, verifying that:
• (i) The combination is capable of operating at a power level sufficient to match that of the battery when carrying out its balancing service;
• and
• (ii) The battery threshold at which this method is triggered is such that the battery is capable of continuing either its charging or discharging balancing function without reaching either full capacity or full depletion for the lag time of the respective combination;
• (c) For all verified combinations found at Step (b), identifying the lowest-cost combination, taking into account operational costs and those associated with asset degradation;
• (d) Switching on the lowest-cost combination of aggregated assets identified and Step (c);
• and
• (e) After a delay of the lag time associated with this lowest-cost combination, and if the battery SoC has not returned to a level between the low and high threshold values, switching off the balancing service provided by the battery.