What is a kilowatt hour (kWh)


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What is a kilowatt hour (kWh)
What is a kilowatt hour (kWh)

The life of modern mankind is impossible without the production and consumption of energy. However, this has always been the case. The first type of energy mastered by people was heat. Dwellings - even caves, even buildings - had to be heated, cooking required fire, and for this, combustible vegetable products, in other words, firewood, were used. According to their volume, it was approximately possible to judge the possible amount of heat released during combustion.

But time passed, and now humanity produces energy in an industrial way. She became a commodity, they began to sell and buy her. And where there is industrial production, control is indispensable.


The era of electricity required a new unit of account for this commodity, produced and sold to consumers. It became kilowatt-hours (kWh).

Than kilowatt-hours are more convenient than joules

Actually, energy - both generated and consumed - is measured in joules. This unit is accepted in the international system of measurements SI and is the main one. One joule corresponds to the energy that is consumed by a source with a power of one watt for one second. The unit is simple and visual, but it has a significant drawback: on the scale of consumption of even one single apartment, itextremely small for calculations. It would be difficult to pay for the energy consumed when billing even in kilojoules (kJ) due to the large number of characters. Therefore, a general decision was made to enlarge the unit to a kilowatt-hour (kWh). This is the historical origin of this off-system unit.

Conversion of kilowatt-hours to joules and vice versa

1 kWh

The correspondence between joules and kilowatt-hours is easy to calculate. There are 3600 seconds in 1 hour, 1000 watts in a kilowatt, so it turns out that 1 kWh is the same as 3.6 million joules (or 3.6 megajoules).

After the transition to kilowatt-hours, it has become much easier for the consumer, psychologically, to perceive the meaning of what he pays for. Since at first electricity was used mainly for lighting residential and industrial premises (there was even the concept of “paying for light”), he should have simply understood that a hundred-watt light bulb would “wind up” exactly 1 kWh in ten hours.

If its power is 40 watts, then the amount of the same tariff can be "burned" two and a half times longer. True, and there will be less light.

Electric heaters used for space heating consume much more power than light bulbs, therefore, they spend as much per hour as other lighting equipment per day, especially since modern energy-saving technologies are progressing, LED and neon lamps have appeared, durable and economical. Incandescent lamps use most of the energy they use to heat the air.

Energy and power in the GHS system

There is another unit that is used to measure energy produced - calorie, it is used in the GHS system. Most of our fellow citizens (especially women) know the calorie from annotations that explain the nutritional value of food products. In fact, this is the amount of energy that is needed to heat one gram of water by one degree Celsius at an initial temperature of 19.5 ° C. It would be convenient if it were not for the small value (it is only about 4.19 times the joule). But it's not only that. Converting it to the usual watt-hours is rather inconvenient, and everyone has already got used to the power unit. However, sometimes kilocalories and megacalories are still used to determine heat consumption. Converting Gcal / h to kW is not difficult, it is enough to know that 1163 kilowatts correspond to one gigacalorie. It must be remembered that another rule applies here. A calorie is a unit of energy, while watts are a unit of power. Therefore, through the indicated coefficient, one can equate Gcal and kW / h or Gcal / h and watts. Don't confuse energy with power!

electricity kWh

Counter device

To measure the amount of electricity consumed, electric meters are used, which are kind of integrators that multiply power by time using a mechanical or electronic system. The easiest way to understand the principle of their operation is to use the example of an old-style metering device. Active power is equal to the product of the mains voltage (it is standard for us and is equal to 220 volts) by the valuecurrent. The speed of rotation of the disk is proportional to the power consumed, and the faster it spins, the more often the numbers on the wheels that drive it flicker.

gcal h to kW

Meter as an integrator

Energy metering is like an integration process. If you place time on the abscissa, and plot the power consumption on the ordinate (which may be different during the accounting period), then you will have to pay for the “area” bounded by the curve on top and the segment of the reporting period at the edges. This will be the consumed electricity, kWh - a unit that expresses its physical essence, and in order to calculate the debt, it remains only to multiply the resulting number by the current tariff.

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