The Solar Guide's Guide to a Kilowatt hour
This is what you pay for when you buy energy from the local utility company.
A kilowatt-hour (kWh) is a unit for measuring energy. It is, as its name suggests, one kilowatt of power used over a period of one hour.
A light bulb is typically 60 watts; leave it on for an hour you have used 60 watt hours, or .06 kWh
A typical personal computer uses approximately 70 watts. In addition, a 17" monitor uses another 80 watts. That comes to 150 watts in an hour, or .15 kWh. If you have the same computer on for only 4 minutes (say, to check your e-mail), that would come to .01 kWh.
With an LCD monitor that uses only 35 watts, an hour of usage will come to .105 kWh.
Did you know?
In Britain, a kilowatt hour is commonly referred to as a unit.
Joules and Megajoules
Another term related to the kilowatt-hour is the joule. The joule is a watt-second. Since this is such a small measure, it is impractical for most uses.
For example, 1 kWh = 3.6 million joules.
Some utility companies do measure in the megajoule, 1 million joules. 1 kW = 3.6 joules.