A range extended battery storage system integrates a primary battery bank with an auxiliary generator that recharges the battery during operation. This configuration differs from conventional battery storage because the battery never fully discharges. The generator maintains the battery within a mid range state of charge window, typically thirty to seventy percent. Injet HanCang has developed a range extended battery storage system platform that optimizes the interaction between battery chemistry, generator control, and load management. This article presents battery specific design considerations, cycle life data, and application examples.
The battery is the core component of any range extended battery storage system. Injet HanCang selects lithium iron phosphate chemistry for all systems due to four characteristics. The first characteristic is cycle life. Lithium iron phosphate cells typically achieve four thousand to six thousand cycles to eighty percent capacity retention, compared to two thousand to three thousand cycles for nickel manganese cobalt cells. The second characteristic is thermal stability. Lithium iron phosphate cells do not undergo thermal runaway until temperatures exceed two hundred seventy degrees Celsius, providing a wider safety margin. The third characteristic is flat voltage curve. The voltage changes slowly with state of charge between twenty and eighty percent, which simplifies the charging algorithm. The fourth characteristic is cobalt free composition, which reduces supply chain risk and material cost. The table below compares battery chemistries for range extended battery storage system applications. Parameter Lithium Iron Phosphate Nickel Manganese Cobalt Lead Acid Cycle life to 80 percent 4000 to 6000 cycles 2000 to 3000 cycles 500 to 1000 cycles Round trip efficiency 92 to 95 percent 90 to 93 percent 75 to 85 percent Operating temperature range minus 20 to 60 Celsius minus 10 to 55 Celsius minus 40 to 50 Celsius Energy density 120 to 160 watt hours per kilogram 200 to 250 watt hours per kilogram 30 to 40 watt hours per kilogram Cost per kilowatt hour 100 to 130 dollars 110 to 140 dollars 50 to 80 dollars Recommended state of charge window 20 to 80 percent 30 to 70 percent 50 to 80 percent For range extended battery storage system applications, lithium iron phosphate provides the best balance of cycle life and safety despite lower energy density than nickel manganese cobalt.
Sizing the battery in a range extended battery storage system requires different calculations than standalone battery storage. The key difference is that the battery is not required to provide the full daily energy. Instead, the battery provides energy between generator runs. Injet HanCang uses a five step sizing methodology. Step one determines the average load power in kilowatts. Step two determines the desired time between generator runs in hours. Step three multiplies load power by desired run time to get battery energy. Step four adds a thirty percent buffer for state of charge window constraints. Step five rounds up to the nearest standard battery module size. For example, a site with one hundred kilowatts average load and desired generator run interval of four hours requires a battery energy of four hundred kilowatt hours before buffer. Adding thirty percent gives five hundred twenty kilowatt hours. The nearest standard Injet HanCang module size is six hundred kilowatt hours. The generator will start every four hours under average load, run for approximately one hour, and recharge the battery from thirty to seventy percent state of charge.
A range extended battery storage system extends battery cycle life by avoiding deep discharges and high state of charge holding. Injet HanCang conducted a cycle life test comparing three operating regimes. The first regime cycled batteries from ten percent to ninety percent state of charge, representing standalone battery operation. The second regime cycled from thirty percent to seventy percent, representing range extended operation. The third regime cycled from forty percent to sixty percent, representing aggressive range extended operation. All tests used the same lithium iron phosphate cells at twenty five degrees Celsius ambient temperature. The results showed that the ten to ninety percent regime reached eighty percent capacity retention after three thousand two hundred cycles. The thirty to seventy percent regime reached eighty percent after five thousand four hundred cycles, a sixty nine percent increase. The forty to sixty percent regime reached eighty percent after six thousand eight hundred cycles, more than double the standalone regime. The range extended battery storage system therefore effectively doubles or triples battery life compared to standalone operation. Additional testing examined the effect of charge rate on cycle life. The range extended battery storage system typically charges at a C rate of point five to one. The test compared point five C charging to one C charging within the thirty to seventy percent window. The point five C charging group achieved five thousand six hundred cycles. The one C charging group achieved five thousand cycles. Slower charging provides a twelve percent cycle life benefit.
Operating a range extended battery storage system requires specific battery management settings. The first insight is that the state of charge estimation algorithm must account for generator charging current ripple. Generator rectifiers produce a small AC component on the DC bus. This ripple causes current measurement errors of up to two percent. Injet HanCang added a low pass filter to the current measurement circuit, reducing error to zero point three percent. The second insight is that the battery balancing circuit operates less frequently in range extended systems because the battery stays within the mid state of charge region where cell voltages are more uniform. Balancing can be scheduled weekly rather than continuously, reducing energy consumption from the balancing resistors. The third technical insight for range extended battery storage system design is that the battery cooling demand is lower than in standalone systems. Deep discharges generate more heat due to higher internal resistance at low state of charge. By avoiding deep discharges, range extended operation reduces average cell temperature by three to four degrees Celsius. Lower temperature directly reduces the rate of solid electrolyte interface growth, extending calendar life. Injet HanCang measured calendar aging at forty five degrees Celsius and at forty degrees Celsius. The five degree reduction reduced capacity fade by thirty percent over eighteen months.
A range extended battery storage system can be integrated with solar PV or wind generation. The integration adds complexity because renewable generation is variable. Injet HanCang has developed a control algorithm that prioritizes renewable charging over generator charging. When solar power exceeds load demand, the excess charges the battery. The generator remains off. When solar power is insufficient, the battery supplies the deficit. The generator starts only when battery state of charge falls below thirty percent and solar power is forecast to be low for the next two hours. Data from a solar plus range extended battery storage system in Arizona shows the effectiveness of this approach. The site has a one hundred fifty kilowatt solar array, a six hundred kilowatt hour battery, and a one hundred eighty kilowatt generator. Over a twelve month period, the generator supplied only eight percent of total energy. Solar supplied fifty two percent. The grid supplied forty percent during maintenance periods. The generator started on sixty two occasions, each run averaging one point eight hours. Without solar, the generator would have supplied an estimated forty percent of energy based on the same load profile.
A remote telecommunications tower provides an ideal application for a range extended battery storage system. The tower consumes a constant load of fifteen kilowatts for radio equipment and five kilowatts peak for air conditioning. Grid power is not available. A standalone battery system sized for two days of autonomy would require nine hundred sixty kilowatt hours, costing approximately one hundred twenty thousand dollars with a replacement every five years. A generator only system would consume fifteen thousand liters of fuel annually at a cost of twenty thousand dollars. Injet HanCang installed a range extended battery storage system with a two hundred kilowatt hour battery and a twenty kilowatt generator. The battery provides twelve hours of autonomy. The generator runs for eight hours per day, recharging the battery while also supplying the load. Annual fuel consumption is four thousand liters, an seventy three percent reduction from the generator only solution. The battery is projected to last eight years based on the thirty to seventy percent cycling window. The payback period compared to generator only operation is three years. The table below summarizes the comparison. Solution First Cost Annual Fuel Cost Battery Replacement Every Ten Year Total Cost Generator only 25000 dollars 20000 dollars Not applicable 225000 dollars Standalone battery 120000 dollars 0 dollars 5 years 240000 dollars Range extended battery storage 85000 dollars 5000 dollars 8 years 135000 dollars The range extended battery storage system has the lowest ten year total cost despite having both battery and generator components.
In a hybrid system, the generator can supply the load directly. In a range extended system, the generator only charges the battery. The load always draws from the battery. This difference allows the generator to operate at its optimal power point regardless of load variation.
Injet HanCang designs range extended battery storage systems to operate between thirty and seventy percent state of charge. The maximum depth of discharge from seventy percent to thirty percent is forty percent, compared to eighty to ninety percent in standalone systems.
Yes, an existing battery system can be converted by adding a generator, rectifier, and controller. Injet HanCang offers retrofit kits for battery systems up to five years old. The existing battery management system must support external charging control.
Based on Injet HanCang customer data, the payback period for adding range extension ranges from two to five years depending on generator runtime and local fuel costs. The payback is shortest when the alternative is a larger battery bank.
No, standard lithium iron phosphate cells work well in range extended applications. However, cells optimized for partial state of charge cycling are available from some manufacturers. Injet HanCang can supply either type.
A range extended battery storage system from Injet HanCang uses lithium iron phosphate batteries operating within a thirty to seventy percent state of charge window. Cycle life testing shows that range extended operation achieves five thousand four hundred cycles to eighty percent capacity retention, a sixty nine percent increase over standalone operation. Technical insights include current ripple filtering, reduced balancing frequency, and lower cooling demand. Integration with solar PV is supported through a control algorithm that prioritizes renewable charging. A remote telecommunications application example shows a ten year total cost of one hundred thirty five thousand dollars for range extended storage compared to two hundred twenty five thousand dollars for generator only and two hundred forty thousand dollars for standalone battery. Potential customers can request a battery sizing proposal from Injet HanCang.