Introduction
A range extended energy storage system combines a primary battery with a secondary power source that recharges the battery during operation. This configuration differs from conventional storage because the secondary source does not supply the load directly. Instead, it activates only when the battery state of charge reaches a lower threshold. Injet HanCang has deployed multiple range extended energy storage systems in industrial and remote area applications. Field data from these installations provide measurable evidence of performance improvements. This article presents the architecture, component sizing methods, and operational results from real world deployments.
Definition and Core Architecture
A range extended energy storage system consists of three main elements. The first element is a rechargeable battery bank, typically lithium iron phosphate chemistry. The second element is an auxiliary power unit, usually a diesel or natural gas generator. The third element is a controller that monitors battery state of charge and commands the auxiliary unit to start or stop. The auxiliary unit connects to the system through a rectifier that converts its AC output to DC for battery charging. The load always draws power from the battery and inverter path, never directly from the generator. This arrangement allows the generator to operate at a fixed optimal power point regardless of load variations.
Component Sizing Guidelines
Proper sizing of a range extended energy storage system requires analysis of the expected load profile. The battery bank must be sized to handle the average load for a target duration without generator support. Injet HanCang uses a four hour baseline for most commercial applications. The generator is sized to match the average load, not the peak load. For example, a site with an average load of one hundred kilowatts and peak load of three hundred kilowatts would receive a generator rated at one hundred to one hundred twenty kilowatts. This sizing ratio keeps the generator operating between seventy and ninety percent of its rated capacity when running, which is its most efficient range. The battery capacity in kilowatt hours is then calculated as average load multiplied by desired autonomy hours minus the expected generator contribution.
Performance Data from Field Installations
A range extended energy storage system installed at a telecommunications facility in Northern Canada provided twelve months of operational data. The site had an average load of eighty five kilowatts and experienced grid outages lasting four to six hours, twice per week. The battery bank was sized at five hundred kilowatt hours. The auxiliary generator was rated at one hundred kilowatts. Over the twelve month period, the generator started one hundred four times. Average run duration was two hours and twenty minutes. The battery state of charge remained between thirty and seventy percent for ninety three percent of the operating hours. Battery capacity degradation measured at two point one percent, compared to a projected five point five percent for a non extended system under similar cycling conditions. Total fuel consumption was three thousand two hundred liters, representing a sixty percent reduction compared to a generator only solution.
Economic Analysis Based on Real Costs
The levelized cost of storage for a range extended energy storage system depends on the ratio of battery cycles to generator hours. Injet HanCang developed an economic model using component prices from 2025. For a system with daily discharge duration of six hours, the levelized cost per kilowatt hour delivered was one hundred fifteen dollars. A standalone battery system under the same load profile produced a levelized cost of one hundred fifty five dollars. The difference comes from two factors. First, the range extended system uses a smaller battery bank because the generator provides recharge during long discharge events. Second, the battery experiences less depth of discharge per cycle, extending its useful life from seven years to eleven years. The generator adds maintenance costs of approximately eight hundred dollars per year, which is included in the model.
Application Examples for Different Industries
Range extended energy storage systems suit three main application categories. The first category is remote telecommunications and monitoring sites where grid power is unavailable or unreliable. These sites typically have constant low loads and occasional high loads from heating or cooling equipment. The range extended design prevents battery depletion during multiday cloud cover events when solar PV is also installed. The second category is electric vehicle fast charging stations in areas with limited grid capacity. The battery handles the peak charging demand, and the generator recharges the battery between vehicles. The third category is industrial peak shaving where demand charges are high but grid connection capacity is limited. Injet HanCang has deployed systems in all three categories with documented uptime exceeding ninety nine percent.
Maintenance Requirements and Schedules
A range extended energy storage system requires maintenance on both the battery and the generator. The battery requires annual capacity testing and passive balancing of cell voltages. Injet HanCang recommends replacing the battery when capacity falls below eighty percent of nameplate rating. The generator requires oil changes every five hundred operating hours, air filter replacement every two hundred hours in dusty environments, and fuel filter changes annually. The controller software should be updated every eighteen months to incorporate improved state of charge algorithms. Total annual maintenance cost for a two hundred kilowatt system is approximately two thousand dollars, based on data from twelve Injet HanCang installations.
Limitations and Design Constraints
Range extended energy storage systems are not suitable for every application. The generator adds complexity and requires fuel storage, which may be prohibited in some jurisdictions. The system produces exhaust gases and noise during generator operation, limiting indoor installation options. The response time of the generator from start command to full power output is typically ten to thirty seconds. Applications that require instantaneous backup power during the first seconds of an outage need an additional uninterruptible power supply or larger battery buffer. Injet HanCang recommends a minimum battery buffer of fifteen minutes at full load to cover generator start up and stabilization.
Conclusion
A range extended energy storage system provides a practical solution for applications requiring discharge durations beyond the economic limit of standalone batteries. Field data from Injet HanCang installations show a sixty percent reduction in fuel consumption compared to generator only systems and a forty percent reduction in levelized cost compared to battery only systems. Proper sizing of the battery to generator ratio is critical. The data presented in this article confirm that range extended energy storage systems achieve their intended benefits when designed according to load profile analysis and maintained according to recommended schedules.