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Energy (kWh) vs. Power (kW)

There is sometimes confusion about the difference between "electrical power" and "electrical energy". The following article should help clear up the differences.

Power

Power is measured in watts (W), kilo-watts (kW), mega-watts (MW), and giga-watts (GW). The power of a load can change quickly, especially if the load is turning on and off.

Examples:

A graph of power shows swings up and down (sometimes to zero) as things turn on and off.

Energy

Energy is measured in kilowatt-hours (kWh), megawatt-hours, and sometimes (less commonly) in watt-hours or watt-seconds. Energy is the primary measurement used by the utility company to determine your bill each month (although demand and power factor are also sometimes used). Unlike power, energy does not change quickly, but instead accumulates gradually.

Examples:

Unless you are generating electricity with PV or wind power, a graph of energy over time will always go up. It will go up faster when you are using lots of power, and it will level off if you stop using any power. But it will never go back down unless you generate electricity.

Water Analogy

If you consider electricity as though it is water:

Speedometer Odometer Analogy

You can imagine that power (W) is like your speedometer (current speed), while energy (kWh) is like your odometer. The speedometer can quickly go from zero to sixty and back to zero, but the odometer only slowly counts up: faster if your speed is faster. The speedometer tells you how fast you are going right now (how much power you are using right now), while the odometer tells you how far you've gone (how much energy you've used in total).

Energy vs. Power
 

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