Why does inverter efficiency only apply to AC loads?

DC loads draw straight from the battery with almost no conversion loss, but AC loads run through an inverter that wastes 8 to 15 percent of the energy as heat. The tool divides AC load energy by the inverter efficiency so the battery drain reflects that real loss.

What is the difference between daily Wh and peak power?

Daily watt-hours is total energy used over 24 hours and sizes your battery and panels. Peak power is the highest wattage drawn at one instant if everything runs together, and sizes your inverter. They are different numbers and both matter.

How do I find an appliance's wattage?

Check the nameplate, the manual, or a plug-in power meter. Resistive loads like heaters draw their rated watts, while motors and compressors surge well above rating at startup, which your inverter sizing must allow for separately.

Should I add a safety margin to the total?

Yes. Real usage varies and components age, so add 15 to 25 percent to the daily Wh total before sizing panels and batteries. Phantom standby loads and cable losses also add up and are easy to underestimate.

Does runtime have to be a whole number of hours?

No. Enter fractional hours for short-duty appliances, such as 0.25 for a microwave used fifteen minutes a day. The tool multiplies watts by hours regardless of whether the figure is whole or decimal.

Off-Grid Load Audit Calculator

Every off-grid solar design starts with an honest load audit: how much energy each appliance uses in a day. This calculator lets you list appliances with their wattage and daily runtime, then sums the watt-hours and applies inverter losses so your battery and panel sizing rests on real numbers.

How it works

Each appliance contributes watts × hours/day watt-hours. DC loads add to the battery drain directly. AC loads pass through the inverter, so their energy is divided by the inverter efficiency to account for conversion loss:

DC daily Wh = Σ (watts × hours)            for DC rows
AC daily Wh = Σ (watts × hours) ÷ efficiency   for AC rows
Total daily Wh = DC daily Wh + AC daily Wh

Peak power is the sum of every appliance’s wattage, the worst case where all run at once, used to size the inverter.

Example

A 60 W laptop for 5 hours is 300 Wh. A 1200 W kettle for 0.2 hours is 240 Wh; at 90 percent inverter efficiency that draws 240 ÷ 0.9 ≈ 267 Wh from the battery.

Tips

Add a 15 to 25 percent margin before sizing panels and batteries.
Hunt down phantom standby loads — routers and chargers run all day.
Peak power sizes the inverter; daily Wh sizes the battery and array.