How Long Will Your Solar Battery Actually Last?
Estimate runtime after protecting a reserve state of charge, then test how duration changes when the actual backup load moves below or above its nominal level.
Why battery runtime is not a fixed number
Runtime depends on both available energy and the rate at which the loads consume it. A battery supplying a refrigeration system, pump or HVAC load may experience large demand changes during an outage.
Reserve SOC reduces available runtime
Protected reserve is intentionally excluded from the current outage energy budget. A larger reserve improves preparedness for a later event but reduces energy available now.
Use the critical-load demand
For backup planning, use the load of the circuits that will actually remain energized. Whole-property average consumption can significantly misrepresent a critical-load panel.
Efficiency and standby power
The efficiency input accounts for broad conversion losses. Detailed planning can additionally include inverter idle consumption as part of the load.
FAQs
Can a battery with 10 kWh capacity deliver 10 kWh to the load?
Not necessarily. SOC limits and conversion losses reduce delivered energy.
Does this check inverter surge capacity?
No. Continuous runtime and instantaneous power capability are separate design checks.
Can load profiles be more accurate?
Yes. Interval or event-based load data are better than a single average for detailed outage planning.
Can I use this for commercial storage?
Yes, provided the inputs represent the actual critical-load configuration.