Watts is the amount of instantaneous electrical power required to support a load, and is a product of the voltage and current. Watt hours is the amount of energy a load has consumed over time, and is a product of power and time. As an example: a 13W light bulb that has been left on for 4 hours has used 52Wh. Kilo Watt hours (kWh) is just 1000 Wh. So in the above example the 52Wh could also have been expressed as 0.052kWh. Understanding the difference is extremely important