What array and battery cover this load?

Off-Grid and RV Solar Calculator: Solar calculator for an off-grid or RV system. Load list to panels, battery amp-hours, charge controller, and inverter.

How long will this battery run?

Battery Runtime Calculator: Battery life calculator with inverter efficiency, depth of discharge, and Peukert’s exponent for lead-acid.

What does this electricity cost?

kWh Calculator: kWh calculator and electricity cost from watts, hours, and a rate you enter. No live utility tariff.

Solar calculators: off-grid sizing, battery runtime, and kWh cost

Solar and battery calculators

Daily watt-hours, the array and the battery that cover them, how long a battery actually runs, and what the kilowatt-hours cost.

How these calculators work

The off-grid calculator adds a load list into watt-hours per day. Panel watts are that total divided by peak sun hours and by one minus the system loss. The loss starts at 14%, the PVWatts historical default, and it does not include battery round-trip loss. That loss is applied when the battery amp-hours are sized, along with depth of discharge and days of autonomy. Charge-controller amps are the installed array watts divided by battery voltage, times 1.25, the continuous-current factor in NEC 690.8. The inverter is the simultaneous watts, with a surge multiplier. Peak sun hours are a number you type. The city buttons are approximate annual averages, not a station lookup.

Battery runtime draws current from the battery after inverter efficiency, then limits the usable amp-hours by depth of discharge. Lead-acid also takes Peukert’s exponent against the 20-hour rating. A lithium exponent of 1 leaves the runtime at the energy limit. The kWh calculator is watts × hours × days ÷ 1,000, times a rate you enter. There is no live tariff.