# Kilowatt Hour Definition

This is a very simple question but something that I'm not able to wrap my head around. This Energy report states generated electricity. But what does "generated killowatthours" mean? I know that can't mean that the US produced that much electricity every hour...but what exactly does it mean?

• If you produce one kilowatt for an hour, that's a "killowatt-hour". It's about 3.6 million joules, says Google. – The Photon Mar 15 '13 at 21:55
• "In 2011, the United States generated about 4,106 billion kilowatthours of electricity. " in ONE year. – placeholder Mar 15 '13 at 22:00
• As there are about 8000 hours in a year, that means an average power generated of half a billion kilowatts, or 500GW. That suggests several hundred large (1-2GW) power stations - plausible. – Brian Drummond Mar 15 '13 at 22:13
• @The Photon With the knowledge that a joule is a watt-second (Ws) you wouldn't need to ask Google to know that one kilowatt-hour is exactly 3600000 joule. – starblue Mar 16 '13 at 15:32
• @starblue, totally right. Brain freeze on my part. – The Photon Mar 16 '13 at 15:39

You are confusing kilowatt hours with kilowatts per hour (which is a fairly useless measure of anything).

A kilowatt is a measure of the rate at which energy is delivered (also known as power). One kilowatt means that 1000 joules of energy is being delivered every second.

A kilowatt hour is a measure of total energy delivered.

kilowatt      = energy/time

kilowatt hour = kilowatt x time
= (energy/time) x time
= energy


So if your water heater draws 6 kilowatts when it is on, and is on for 30 minutes, then it has consumed 3 kilowatt hours.

According to the report:

In 2011, the United States generated about 4,106 billion kilowatthours of electricity. About 68% of the electricity generated was from fossil fuel (coal, natural gas, and petroleum), with 42% attributed from coal.

kilowatt hours = 4,106,000,000,000 kWh

hours          = 356.25 days * 24 hours/day
= 8766 hours

kilowatts      = (kilowatt hours) / hours
= 4,106,000,000,000 kWh / 8766 hours
= 468,400,639 kW


So we can see that during 2011, if you were to measure the power being generated in the USA, it would be about half a Terawatt.

• The ONE valid use I have seen for kilowatts per hour is for a factory making e.g. solar cells : if it makes one panel per hour, and it can generate 1kw, their output is 1kw/hour! – Brian Drummond Mar 16 '13 at 14:45