Introduction
A range extended ESS incorporates a recharging source that is not the primary grid connection. This configuration is distinct from simple backup generator integration because the range extender operates based on battery state of charge rather than load demand. Range extended ESS is particularly useful in locations where grid power is available but unreliable, or where renewable generation has predictable daily intermittency. Injet HanCang has designed and commissioned sixteen range extended ESS units for commercial and industrial clients. This article presents configuration guidelines, test results, and observed performance data from these installations.
Standard Configuration for Range Extended ESS
A standard range extended ESS includes five main components. The first component is a lithium ion battery bank sized for four to six hours of average load. The second component is a diesel or gas generator sized at one third to one half of the inverter power rating. The third component is a bidirectional inverter that manages power flow between battery and load. The fourth component is a rectifier that converts generator AC output to DC for battery charging. The fifth component is a controller with state of charge based logic. Injet HanCang uses a DC coupled architecture for most installations. In this architecture, the generator connects to the DC bus through the rectifier, and the inverter connects the DC bus to the AC load. DC coupling improves efficiency by avoiding double conversion. In a five hundred kilowatt system with a two hundred kilowatt range extender, DC coupling improved overall system efficiency by four percentage points compared to AC coupling.
Sizing Methodology Based on Load Analysis
Proper sizing of a range extended ESS requires detailed load analysis over a minimum of one year. Injet HanCang uses a seven step methodology. Step one collects load data at fifteen minute intervals. Step two identifies the average daily energy requirement. Step three identifies the peak power requirement. Step four calculates the required battery capacity as average daily energy multiplied by desired autonomy days minus expected generator contribution. Step five sizes the generator as the average load during the longest expected discharge event. Step six selects the inverter rating as the larger of peak load or generator rating plus battery contribution. Step seven validates the sizing using simulation of historical load data. For a commercial building with average load of one hundred fifty kilowatts and peak load of four hundred kilowatts, this methodology produced a battery size of six hundred kilowatt hours and a generator size of one hundred fifty kilowatts.
Test Results from a Grid Support Application
A range extended ESS installed at a commercial building in California underwent a six month testing program. The building had a two hundred kilowatt average load and a four hundred fifty kilowatt peak load from air conditioning. The grid connection was limited to three hundred kilowatts. The range extended ESS used a four hundred kilowatt hour battery and a one hundred fifty kilowatt generator. The test program measured three performance categories. The first category was peak shaving effectiveness. The system successfully limited grid draw to two hundred eighty kilowatts during all peak events, representing a ninety five percent success rate. The second category was generator usage. The generator started on forty two occasions, with an average runtime of one hour and fifteen minutes. Total generator operating hours were fifty three hours over six months. The third category was battery cycle life impact. The battery completed one hundred two full cycle equivalents with a measured capacity degradation of one point one percent.
Demand Charge Reduction Data
Demand charges based on the highest fifteen minute average power draw are a major cost for commercial customers. A range extended ESS can reduce these charges by providing power from the battery during peak periods. However, if multiple peaks occur in rapid succession, the battery may deplete. The range extender recharges the battery between peaks, enabling multiple peak shaving events within the same demand interval. Injet HanCang analyzed fifteen minute demand intervals at a manufacturing site over twelve months. The site had an average of three demand peaks per day. Without range extension, the battery could shave only the first peak before depleting below the minimum state of charge. With the range extender operating between peaks, the system shaved all three peaks on ninety one percent of days. The average demand charge before installation was seven thousand two hundred dollars per month. After installation, the average demand charge was two thousand eight hundred dollars per month, a reduction of sixty one percent.
Grid Outage Bridging Capability
Range extended ESS provides bridging power during grid outages without relying on grid restoration time. The battery handles the first outage period. If outages recur before grid power returns, the range extender starts and recharges the battery during the brief grid on windows. Injet HanCang tested this scenario using a simulated grid profile with ten consecutive five minute outages separated by three minute grid on windows. The test used a three hundred kilowatt hour battery and a one hundred kilowatt generator. The load during the test was a constant one hundred fifty kilowatts. The battery provided power during the first outage, depleting from eighty percent to sixty percent state of charge. During the first grid on window, the grid recharged the battery to seventy five percent. The second outage depleted the battery to fifty five percent. The generator started during the second grid on window and recharged the battery to seventy percent. This pattern continued for all ten outages. The range extended ESS maintained load supply throughout without any interruption. A standalone battery of the same capacity would have depleted after the fourth outage.
Fuel Consumption Data Across Different Load Profiles
The fuel consumption of a range extended ESS varies significantly with load profile. Injet HanCang measured fuel consumption across three different load profiles using the same hardware platform. The first profile was constant load at one hundred kilowatts. The second profile was variable load with daily pattern of low night load and high day load. The third profile was intermittent load with random spikes. For the constant load profile, the generator consumed two point eight liters per hour of operation, and operated for three hours per day, resulting in daily consumption of eight point four liters. For the variable load profile, the generator consumed three point one liters per hour and operated for two hours per day, resulting in daily consumption of six point two liters. For the intermittent load profile, the generator consumed three point four liters per hour due to more frequent start stop cycles, and operated for one point five hours per day, resulting in daily consumption of five point one liters. The constant load profile had the highest absolute consumption but the lowest consumption per kilowatt hour delivered.
Installation Requirements and Site Considerations
Installing a range extended ESS requires consideration of several site specific factors. The generator requires exhaust ventilation to outdoors. The exhaust pipe must be rated for temperatures up to five hundred degrees Celsius and must be separated from combustible materials by at least eighteen inches. The generator requires a fuel storage tank with secondary containment. The tank size should provide for at least seventy two hours of continuous generator operation at full load. The battery requires a climate controlled space with temperature maintained between fifteen and thirty degrees Celsius. The inverter and controller require clearance of at least three feet on all sides for maintenance access. Injet HanCang provides a pre installation checklist that includes verification of these requirements. Sites that fail to meet any requirement receive a modified design.
Conclusion
Range extended ESS provides a configurable solution for commercial and industrial sites requiring both peak shaving and outage bridging. The configuration guidelines from Injet HanCang specify a battery sized for four to six hours of average load and a generator sized at one third to one half of inverter rating. Test results from a commercial building showed ninety five percent peak shaving success and one point one percent battery degradation over six months. Demand charge reduction data showed a sixty one percent reduction after installation. The grid outage bridging test demonstrated successful operation through ten consecutive five minute outages. Fuel consumption data showed that the intermittent load profile had the lowest daily consumption at five point one liters. These results confirm that range extended ESS is a mature option for commercial users.