© 2021 by XOLTA
10
Figure 2.2:
Illustration of the
XOLTA outdoor BESS
BPU front view
Each XOLTA outdoor BESS has a battery protection unit (BPU). Figure 2.2 is an illustration of the BPU
consisting of a communication section and a power section.
The site controller is installed in the BPU and is connected to the XOLTA Cloud using the Ethernet port shown
in Figure 2.2. The Ethernet port ensures communcation between neighboring racks if operating in unison.
The site controller communicates with Lithium Balance’s n-BMSs via the CAN bus.
The DB9 Modbus port is used for communication with peripherals (e.g. energy meters).
The RJ45 port marked SPI is used for communication between the n-BMS MCU and the n-BMS CMUs (which
are located in battery packs). An additional DB15 plug is used for activation of the thermal management
system, sensing outdoor air temperature, LED diodes control and communication with the humidity sensor-
The Modbus TCP port is used for communication with the power conditioning unit (PCS) and communication
with neighboring racks if operating in unison.
The BPU is powered by single phase 230V AC and is protected by a 1.5A fuse located in the power entry connector.
2.3 System safety
2.3.1 Safety measures
The XOLTA outdoor BESS is protected by Lithium Balance’s state of the art n-BMS. The system
monitors essential parameters of the battery system (cell voltage, current, temperature) to
ensure safe operation. The n-BMS also monitors the battery main parameters, e.g. State of Charge
(SoC) and performs battery cell balancing to ensure maximal energy utilization and performance.
The XOLTA outdoor BESS is equipped with a battery protection unit (BPU) which protects the
battery and the inverter from conditions which can be detrimental to the BESS. It includes redundant
relays controlled by the n-BMS and redundant fast battery fuses.
In addition, in order to assure system longevity and safe operation (maintaining correct operating
temperatures), each of the XOLTA outdoor BESS battery packs is equipped with 12 temperature
sensors (two sensors per battery module). These give a total of 96 temperature sensors per battery
rack. This number of temperature sensors allows for quick detection of local temperature gradients
and thus ensures system safety and equal cell performance during the system lifetime. Furthermore,
temperature sensors are located on all battery safety-related PCBs
The thermal performance of the XOLTA outdoor BESS is also monitored by the site controller and
allows for power/current derating whenever the cell temperature or the ambient temperature is
outside a strictly determined range. The site controller also allows for converter error handling and
automatic connection/disconnection of battery racks.
NTC, LED,
thermal
management
BAT-
BAT+
CAN
Modbus RTU
Power
entry port
SPI
INV+
INV-
Ethernet
Modbus TCP
