Battery and panel assumptions
The calculation, in plain terms
Energy to add = battery Wh × (target charge − starting charge) ÷ 100. Adjusted solar input = the lower of panel rating and station input limit × solar yield factor. Net charging power = adjusted input − AC load ÷ 90% inverter efficiency.
Equivalent charging hours = energy to add ÷ net charging power. Solar days = equivalent charging hours ÷ peak-sun-hours/day. The conservative model applies losses after limiting rated input. It is a screening estimate, not a time-series simulation.
What a solar day means
Four peak-sun-hours is an energy-equivalent input, not four guaranteed hours of maximum output. Weather, shading, panel angle, temperature and time of year change production. Use a location-specific estimate from NREL PVWatts; do not treat the default as a local forecast.
Appliances overnight are a different calculation
The connected-load input is subtracted only during the equivalent solar-charging window. It does not account for night-time consumption or prove indefinite backup. Build your full daily energy budget in the outage planner.
Check electrical compatibility
A wattage match does not prove that panels are compatible. Verify open-circuit voltage in cold conditions, current, MPPT voltage range, connectors and the station’s pass-through charging rules in its manual. This calculator does not validate wiring or panel strings.
Product evidence
Sourced model inputs come from the manufacturer-linked dataset. The yield factor and 90% AC conversion efficiency are planning assumptions, not physical tests. Compare solar-input ratings across models.