# What is a kilowatt hour? Understanding home energy use

(music) Welcome to the Enphase homeowner video series. If you've ever taken a glancing look at your electricity bill you know you are being billed for kilowatt hours. But what does that mean exactly? In this video we tackle that question. A watt is a common unit of measure
for electrical power. So if a watt is a measure of electrical power,
what exactly is power? Power is a measure of the instantaneous electricity
being used when you turn on any electrical appliance. You see power requirements called out
in watts on labeling for everything, from light bulbs to microwaves. Kilo means one thousand
so a kilowatt is 1,000 watts. However, both watts and kilowatts are only
a snapshot of instantaneous electrical usage. Energy, which is what we really care about,
and what the utility company charges you for, is that accumulated amount of power
being used over some period of time. Energy is expressed in kilowatt-hours. Here's an analogy that might help simplify the concept. Imagine you are driving a car. Your speed, or rate of travel
when you look at the speedometer, is the equivalent of power,
or rate of energy consumption. But you know that looking at the speedometer
doesn't tell you anything about how far you've gone.

For that, you need to look at your speed
over the time you've been driving. Energy is the equivalent of distance in this analogy. To understand how much energy you've used, you need to know how long you've been consuming
a specific amount of power. Energy is power over some period of time. In small amounts, we measure energy in watt-hours. Energy sized for a household, we measure
in thousands of watt-hours, or kilowatt-hours. Let's illustrate this with a couple of examples. A kilowatt-hour is 1,000 watts used over one hour. If you burned 10 100 watt bulbs for one hour
you would use 1 kilowatt-hour of energy.

Or, if you forgot to turn off
a single 100-watt bulb for 10 hours, you would also burn a kilowatt-hour of electricity. Taking that last example a step further, if you left that bulb on every day while at work or school, you would burn 260 kilowatt-hours per year. At 25 cents per kilowatt-hour,
that single bulb left burning each workday would cost you \$65 per year. You definitely want to turn off
all the lights before leaving the house. And switch to low-wattage LED bulbs. Now you know. Kilowatt-hours are a measure of energy,
which is power over time. Your utility bills you for the energy,
or the electricity you consume in kilowatt-hours. Visit our video page at