Practical guide
Compare battery capacity with inverter demand
A battery size and an inverter rating answer different questions. LoadDay shows both the energy needed across the planning horizon and the power peaks entered for the load list.
Translate nominal battery energy
The default 1,000 Wh battery is reduced by the 85% usable fraction and 90% inverter efficiency. That produces about 765 Wh delivered for this estimate, below the 1,230 Wh daily load.
delivered Wh = battery Wh x usable fraction x inverter efficiency
Review planning horizon coverage
Required battery energy divides daily Wh multiplied by planning days by usable fraction and efficiency. The default one-day plan needs about 1,607.84 nominal Wh, so the 1,000 Wh input covers about 62.2% of the selected horizon.
required battery Wh = daily Wh x planning days / (usable fraction x efficiency)
Check continuous and peak ratings
The default running load is 125 W and the entered peak sum is 220 W. Compare those values with the 1,200 W continuous and 2,400 W surge inputs, then follow the actual equipment documentation for connection and installation decisions.
Check your own scenario
Replace the illustrative inputs with measured values and dated specifications.
Open LoadDay Power PlannerMethod and references
Read the full calculation method and its limits
- U.S. Department of Energy home energy worksheet
- U.S. Consumer Product Safety Commission generator and carbon monoxide safety
Method and examples reviewed 2026-09-30. Examples are illustrative; input values and specifications are not independently verified.