Introduction
A range extended ESS system refers to a fully integrated product where the battery, power conversion equipment, generator interface, and controller are designed as a single unit. This integrated approach allows for optimized cooling, reduced communication latency, and pre tested control sequences. Injet HanCang developed a five hundred kilowatt hour range extended ESS system prototype in 2024 and deployed six production units in 2025. This article details the integrated design architecture, component selection rationale, and performance data from the first year of operation.
Integrated System Architecture Description
The Injet HanCang range extended ESS system uses a common DC bus architecture. The battery bank consists of lithium iron phosphate cells arranged in a two hundred forty volt configuration. A bidirectional DC DC converter connects the battery to a one thousand volt DC bus. The generator, a variable speed diesel unit, connects to the bus via an active rectifier. The grid tie inverter connects the bus to the AC side. A programmable logic controller monitors battery state of charge, generator status, load power, and grid status. The controller issues start and stop commands to the generator based on state of charge thresholds. All components fit within a standard twenty foot shipping container. The battery occupies the left half of the container. The generator occupies the right rear corner. The inverter, rectifier, and controller occupy the right front section. Thermal management uses a liquid cooled plate for the battery and forced air cooling for the generator and power electronics.
Component Selection and Specifications
Each component in the range extended ESS system was selected based on specific performance criteria. The battery cells are prismatic lithium iron phosphate with nominal voltage of three point two volts and capacity of three hundred ampere hours. The battery bank contains one hundred forty four cells arranged in forty eight series groups of three parallel cells. The nominal energy is five hundred eighteen kilowatt hours. The generator is a four cylinder turbocharged diesel unit rated at one hundred fifty kilowatts continuous. The generator includes a twelve volt starting battery with automatic charger. The active rectifier uses silicon carbide MOSFETs and has a rated efficiency of ninety seven percent at full load. The grid tie inverter is rated at three hundred kilowatts continuous and five hundred kilowatts for ten seconds. The controller is a programmable logic controller with dual redundant power supplies and a real time clock for time of use scheduling.
Control Logic and State Machine Operation
The control logic in the range extended ESS system operates as a state machine with five states. State one is idle, where the system monitors load and grid but takes no action. State two is battery discharge, where the system supplies load from the battery. State three is battery charge from grid, where the system charges the battery during low cost periods. State four is generator charge, where the system starts the generator and charges the battery. State five is fault, where the system isolates the battery and shuts down the generator. Transitions between states are triggered by state of charge, time of day, and grid status. The state of charge thresholds are configurable. Injet HanCang ships systems with default thresholds of thirty percent for generator start and seventy percent for generator stop. The controller includes a deadband of five percentage points to prevent oscillation between states.
Prototype Test Results from Laboratory Environment
The five hundred kilowatt hour prototype underwent a twelve week laboratory test program before field deployment. The test program measured electrical performance, thermal performance, and safety response. Electrical performance tests measured DC bus voltage regulation within plus or minus one percent during generator start transients. Generator start to full power time was eight seconds, limited by engine warm up. Battery current ramp rate was limited to point two C to avoid voltage spikes. The system round trip efficiency from generator fuel to load, including all power electronics, measured at thirty four percent at full load. Standby loss measured at one point two kilowatts, primarily from the controller and battery management system. The range extender contributed thirty eight percent of total energy over the test period, with the remainder from grid charging.
Field Performance Data from Six Production Units
Six production range extended ESS systems were deployed at commercial sites across the United States in the first quarter of 2025. Injet HanCang collected performance data from these units for nine months. The combined dataset includes fifty four thousand operating hours. The average system uptime was ninety nine point two percent. The most common cause of downtime was scheduled generator maintenance. Unscheduled downtime averaged eight hours per system over the nine month period. The average generator start count per system was one hundred twenty. The average run duration was two hours. The average battery state of charge at generator start was thirty one percent. The average state of charge at generator stop was sixty nine percent. The average battery capacity degradation across all six systems was zero point eight percent. The system with the highest cycling had one point four percent degradation. The system with the lowest cycling had zero point three percent degradation.
Thermal Performance During Extreme Conditions
Two of the six production systems are located in regions with extreme summer temperatures. One system in Arizona experienced ambient temperatures of forty five degrees Celsius. The other system in Texas experienced forty two degrees Celsius. Injet HanCang analyzed thermal data from both systems during the hottest week of the year. The Arizona system maintained battery cell temperatures between thirty and thirty eight degrees Celsius. The cooling system consumed an average of five point two kilowatts, representing two point six percent of average system throughput. The Texas system maintained battery cell temperatures between twenty eight and thirty six degrees. The cooling system consumed four point eight kilowatts on average. Generator compartment temperatures reached a maximum of fifty eight degrees in both locations, which is within the operating specification of sixty five degrees. No thermal related shutdowns occurred in either location.
Maintenance Data and Service Intervals
Maintenance records from the six production systems provide data on actual service requirements. The generator requires oil changes every five hundred operating hours. The average generator operating hours across the six systems was two hundred forty hours over nine months, meaning each system required approximately one oil change during the period. The battery cooling system requires coolant replacement every four thousand hours or three years. No coolant replacements were needed during the nine month period. The air filters for the generator compartment required replacement every six months in dusty locations and every twelve months in clean locations. The Arizona system required two air filter changes. The Texas system required one. The remaining systems required none. The controller software was updated once across all systems to fix a state of charge calculation error. Total maintenance cost across all six systems for the nine month period was twelve thousand dollars, averaging two thousand dollars per system.
Safety and Protection System Performance
Each range extended ESS system includes multiple protection layers. A hardware based overvoltage trip disconnects the battery if DC bus voltage exceeds one thousand one hundred volts. A thermal fuse on each battery module opens at ninety degrees Celsius. Generator exhaust gas temperature monitoring shuts down the unit if temperature exceeds six hundred degrees Celsius. A flame arrestor is installed on the generator air intake. The battery compartment has a pressure relief vent and a thermal runaway detection system using gas sensors. During the nine month field period, no protection events occurred on any of the six systems. Injet HanCang performed a controlled test of the protection system on the prototype unit. A single cell was forced into thermal runaway using an internal heater. The system detected gas evolution within twelve seconds and isolated the affected module. No propagation to adjacent cells occurred.
Conclusion
The integrated range extended ESS system from Injet HanCang has demonstrated reliable operation across six production deployments. The prototype test results show thirty four percent fuel to load efficiency and eight second generator response time. Field performance data from nine months of operation show ninety nine point two percent uptime and average battery degradation of zero point eight percent. Thermal performance data from extreme heat locations confirm that the liquid cooling system maintains battery temperatures within specification. Maintenance data show average annual cost of two thousand dollars per system. Safety tests confirmed thermal runaway containment within twelve seconds. These results support the use of integrated range extended ESS systems for commercial applications requiring extended runtime.