What is kilowatt-hour (kW / h)

The life of modern mankind is impossible without the development and consumption of energy. However, it was like this at all times. The first kind of energy, mastered by people, became warm. Dwellings - though caves, even structures - should be heated, cooking required fire, and for this burned products of vegetable origin, in other words, wood, were used. By their volume, it was approximately possible to judge the possible amount of heat released during combustion.

But time passed, and now energy is produced by mankind in an industrial way. It became a commodity, it began to be sold and bought. And where there is industrial production, one can not do without control.

The era of electricity required a new unit of accounting for this product, produced and sold to consumers. It became kilowatt-hours (kW / h).

The kilowatt-hours are more convenient than joules

Generally, the energy - both worked out and consumed - is measured in joules. This unit is adopted in the international measurement system of SI and is the main one. One joule corresponds to the energy consumed by a source with a power of one watt for one second. The unit is simple and intuitive, but it has a significant drawback: in the scale of consumption of even one single apartment, it is extremely small for calculations. Paying energy consumed when billing even in kilojoules (kJ) would be difficult because of the large number of characters. Therefore, a general decision was taken to increase the unit to kilowatt-hour (kWh). This is the historical origin of this extra-system unit.

Transfer of kilowatt-hours to joules and back

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

After switching to kilowatt-hours, it became much easier for the consumer to perceive psychologically the meaning of what he pays for. Since at first time electricity was used mainly for lighting residential and industrial premises (there was even the concept of "paying for light"), he should simply understand that a 10-hour light bulb would "screw" exactly 1 kWh.

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

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

Energy and power in the GHS system

There is one more unit that is used to measure the energy produced - calorie, it is used in the GHS system. For most of our fellow citizens (especially women), calories are known from the annotations explaining the nutritional value of food. In fact, this is the amount of energy needed to heat one gram of water per degree Celsius at an initial temperature of 19.5 ° C. It would be convenient if not for a small value (it is only about 4.19 times larger than the joule). But it's not only that. It is rather inconvenient to translate it into familiar watts-watches, and with the unit of power measurement everyone has already got used to it. However, sometimes kilocalories and megacalories are still used to determine heat consumption. To translate Gcal / h into kW is not difficult, it is enough to know that 1163 kilowatts correspond to one gigacalorie. It should be remembered that there is another rule. Calorie is a unit of energy, and power is measured in watts. Therefore, through this ratio one can equate Gcal and kW / h or Gcal / h and watts. Do not confuse energy with power!

Counter Device

To measure the amount of electricity consumed, electricity meters are used, which are kind of integrators that multiply power for a time using a mechanical or electronic system. The easiest way to understand the principle of their operation is to use the example of the device of old-type meters. The active power is equal to the product of the mains voltage (it is standard and equal to 220 volts) by the current value. The speed of rotation of the disk is proportional to the power consumption, and the faster it rotates, the more often the numbers on the wheels driven by them move.

Counter as an integrator

Accounting for consumed energy is similar to the process of integration. If the abscissa is located on the abscissa and the ordinate is postponed to consume power (which may be different during the accounting period), then you will have to pay for the "area", bounded by the curve from above, and the segment of the reporting period along the edges. This will be the consumed electricity, kWh is the unit that expresses its physical essence, and to calculate the debt, it only remains to multiply the received number by the current tariff.