calc.engineer / Solar & Power / Battery Autonomy

Battery Autonomy v1.0.0

Calculates how many days a battery bank can sustain loads without solar input — critical for off-grid and backup power sizing. Accounts for depth of discharge, round-trip efficiency (lithium vs lead-acid), minimum state of charge, and optional partial solar contribution during cloudy weather. Outputs autonomy in days and hours, usable capacity, and daily deficit. Use with avg_solar_contribution_pct = 0 for worst-case (no sun) scenarios, or 20-30% for realistic cloudy-day modeling. Chains from solar_sizing (battery_kwh) and solar_load_audit (daily_kwh).

← from solar_sizing.battery_kwh← from solar_load_audit.total_daily_kwh
Daily energy consumption in kilowatt-hours (kWh)
Total installed battery capacity in kWh
Depth of discharge (0-1), default 0.8 for lithium
Battery round-trip efficiency (0-1), default 0.90 for lithium, use 0.80 for lead-acid
Minimum state of charge percentage, default 20%
Average solar contribution during autonomy period (0-100%), default 0 for worst-case
Fill in the inputs and Compute to see the structured result.

From an agent (MCP) or the API

curl -X POST https://calc.engineer/api/battery_autonomy \
  -H "Content-Type: application/json" \
  -d '{"daily_kwh": …, "battery_kwh": …, "dod": …}'

MCP: connect to https://calc.engineer/mcp and call battery_autonomy.

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