BESS modeling: investigating the role of auxiliary system consumption in efficiency derating

Large-scale Battery Energy Storage System (BESS) capacity installed for stationary applications is rising in the first decades of 21
^st
century. Business models related to BESS highly depend on BESS lifetime. BESS lifetime can be preserved only if accurate thermal management of the assets allows to keep it at design temperature. Auxiliary systems' needs for cooling and heating the BESS cannot be disregarded while modeling the real-world operation of these facilities. In this paper we propose an improved protocol for organic modeling of large-scale BESS grid-connected. We assess the share of losses and the operational efficiency related to the provision of ancillary services to the network by BESS in different seasons and different working conditions. We highlight that BESS efficiency increases in case the system is constantly exploited, avoiding time idle or at low power. The model proposed, with respect to standard techniques, allows to better represent BESS performance. Indeed, just by disregarding the losses related to thermal management of the assets (as it is for standard modeling techniques), errors committed are up to 10%.