Graphic by Annabel Driussi for ODP

When you get your electric bill every month, your utility company bills you for kilowatt-hours. But do you actually know what a kilowatt-hour is, or how many of them it takes to power your home and appliances?

Taking a step back, do you know the difference between energy and power? 

As we begin to have more in-depth conversations about a green energy revolution, it’s important to understand the basics. So, today’s #ExplainItToMe brings it allll the way back to your high school physics class.

First, energy is the capacity to do work—the application of a force to an object. In the case of your lightbulb, it’s the surge of electricity that’s applied to the wire in the bulb which then converts that electricity into light and heat.

Power, in turn, is how much of that energy is applied over a period of time. A watt is a unit of power, or the rate of energy transfer. A kilowatt is 1,000 watts. The wattage of a lightbulb, for instance, tells us how much electrical energy it converts into heat and light per second. For instance, if you leave a 50-watt lightbulb on for 20 hours, you’ll be billed for 1 kWh (1,000 watt-hours) of energy.

Which brings us back to kilowatt-hours. A kWh is a unit that tells us how much energy an appliance consumes or a fuel source produces over a period of time. One kilowatt-hour is something operating at a power of one kilowatt for one hour.

Here’s a quick analogy to sum things up:

 Think of your bathtub faucet,

Power = Gallons per minute, or the flow rate. The power is how quickly or slowly the tub fills.

Energy = Total gallons consumed. This is what you are billed for. Even if you filled the tub slowly over an hour or quickly in a few minutes, you’ll be billed for however much water (energy) you used, not the rate (power) at which you used it.