Methodology
Make the estimate inspectable.
The planner keeps energy reserve, solar recovery, continuous output, startup demand, and controller current as separate checks, with every pressure assumption shown beside the result.
Core equations
Daily energy: running watts × hours × quantity, separated into critical and optional classes.
Battery range: total daily energy × reserve days ÷ 90% usable fraction ÷ 92% conversion allowance. The pressure edge adds 15% load uncertainty; the critical-only value remains visible as the load-shedding boundary.
Solar recovery range: total daily energy ÷ planning sun hours ÷ delivered-energy factor. The baseline uses 72%; the pressure edge combines 15% additional energy with a 60% factor.
Multi-source charging: solar contribution is array watts × planning sun hours × the shared 72% delivered-energy factor; DC–DC, shore, and generator contributions are entered delivered watts × realistic daily hours. Recovery time is the energy-to-restore target ÷ the positive energy left only after the full daily load.
Continuous inverter check: simultaneous running load × 1.25.
Startup surge check: the larger of running peak or momentary startup demand × 1.10. The load inventory models one selected appliance starting while the other selected peak loads run.
Battery-side current boundary: continuous and momentary inverter checks ÷ nominal voltage ÷ 90% inverter efficiency. Use both time ratings when checking BMS, conductors, and overcurrent protection.
Controller current check: array range ÷ nominal battery voltage × 1.25. PV open-circuit voltage, temperature correction, and exact controller input limits remain separate datasheet checks.
First-constraint ordering: compare full-load versus critical-only daily energy, startup versus running power, reserve days versus one day, and low-sun recovery versus the editable 4.5-hour reference. The largest multiplier above 1.05× sets the next verification; otherwise component compatibility comes next.
Use the result
Use the range to decide which optional loads can be shed, then verify component time ratings, battery BMS limits, monthly solar production, PV voltage, site conditions, mounting, wiring, protection, permits, and local requirements.
Continue planning
Apply the reviewed assumptions to a load plan.
Editorial record
Maintained by Make Your Own Tools to turn “Size off-grid power” into a defined daily wh, battery reserve, panels, and inverter. The references below provide the technical context for this planning path. Its calculation rules and planning assumptions are documented in the methodology, and affected calculations pass regression checks before the review date advances.
- Last reviewed
- Evidence set
- 4 primary references