Microgrid Islanding Runtime Calculator
Estimate how long a microgrid can sustain critical loads while islanded by balancing usable battery energy with renewable and generator support.
Preliminary engineering aid. Validate results against detailed load profiles, protection settings, and operational procedures before committing to run plans.
Examples
- 400 kWh bank at 85% SOC with 20% reserve, 60 kW critical load, 150 kW PV for 6 h/day, 50 kW generator for 4 h/day ⇒ Islanding endurance: 16.88 hours (0.70 days) before reaching the reserve limit. Net load to supply: 14.17 kW.
- 280 kWh battery at 90% SOC with 30% reserve, 45 kW load, 80 kW wind for 10 h/day, generator off ⇒ Islanding endurance: 13.25 hours (0.55 days) before reaching the reserve limit. Net load to supply: 11.67 kW.
FAQ
How should I choose the state of charge and reserve values?
Use the real-time SOC at the moment of islanding and the minimum reserve your battery management system enforces to protect cycle life.
What if renewable production is intermittent?
Enter the average output during the window it is available and adjust the availability hours. For storm conditions, lower the output or hours to stress-test the runtime.
How do I include generator fuel constraints?
Limit the generator runtime hours per day to reflect available fuel or noise restrictions. The calculator averages the contribution across the day.
Can I account for inverter or distribution losses?
Yes. Reduce the round-trip efficiency percentage to include extra losses through inverters, cabling, or transformers.
Additional Information
- Result unit: hours of autonomous operation before batteries hit the reserve threshold.
- Usable energy applies both depth-of-discharge and round-trip efficiency to the nominal capacity.
- Generation inputs are averaged over 24 hours so intermittent sources reduce net load proportionally to their availability window.
- If support generation equals or exceeds the critical load, the calculator reports continuous islanding capability.