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Energy Glossary

## Kilowatt Hour (kWh)

The kilowatt hour is used as energy unit. It is defined as

1 kilowatt hour = (the power of 1 kilowatt) x (1 hour duration)

#### Understanding the meaning of 1 kilowatt hour

A horse can deliver a (more or less) permanent power of 1 hourse power which is equivalent to 0.735 kilowatts. A horse delivers during 1.35 hours the amount of 1 kilowatt hour in terms of mechanical energy:

(1 horse power) x (1.35 hours) =
(0.75 kilowatt) x (1.35 hours) = ca. 1 kilowatt hour

Please observe that the kilowatt hour means kilowatt multiplicated by hour!

#### Usage

The kilowatt hour is mainly used to measure electric energy (= power, electricity) but can be used to describe the amount of energy for each type of energy.

As comparison a seleced list of fuels with their specific energy content is listet below.

Fuel/energy carrierEnergy in kWhEnergy in Joule
1 cubic meter nat. gas 10 36 000 000
1 litre of gas or diesel 10 36 000 000
1 kg of hydrogen 33 100 000 000
1 kg of dry wood 5 18 000 000
1 kg rechargeable lithium ion battery 0.1-0.3 330 000 - 1 000 000
1 metric ton of water in hoover dam (200m) 0.5 2 000 000
IMPORTANT NOTICE: The given values in the table are rough values and might depend on fuel quality etc.

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