Watt-Hour

A watt-hour (Wh) is a unit of energy equal to one watt used for one hour. One thousand watt-hours make one kilowatt-hour.

Watt-hours let you compare batteries of different voltages, and match a battery to a solar panel or a load. A 100 Ah, 12 volt battery holds 1,200 Wh. Used to 50% depth of discharge, it gives 600 Wh, enough to run a 100 watt load for 6 hours in the battery runtime calculator.

Solar math works in Wh too. A 200 watt panel at 75% system efficiency delivers 150 Wh per peak sun hour, so refilling 600 Wh takes 4 peak sun hours. The solar charging time calculator does the conversion for you.