The life of modern mankind is impossible without the generation and consumption of energy. However, this has been the case at all times. The first type of energy mastered by people was heat. Dwellings - even caves, even buildings - should be heated, cooking required fire, and for this we used combustible products of plant origin, in other words, firewood. By their volume it was approximately possible to judge the possible amount of heat released during combustion.
But time passed, and now mankind produces energy in an industrial way. She became a commodity, they began to sell and buy it. And where there is industrial production, you can not do without control.
The era of electricity has demanded a new unit of accounting for this product produced and sold to consumers. It became kilowatt-hours (kW / h).
Than kilowatt hours are more convenient than joules
In fact, energy - both generated and consumed - is measured in joules. This unit is accepted in the international SI measurement system 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. It would be difficult to pay for 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 kilowatt hours (kW / h). This is the historical origin of this extra-systemic unit.
Convert kilowatt hours to joules and vice versa
The correspondence between joules and kilowatt hours is not difficult to calculate. In 1 hour, 3600 seconds, in kilowatts - 1000 watts, so it turns out that 1 kW / h is the same as 3.6 million joules (or 3.6 megajoules).
After switching to kilowatt hours, it became 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 “pay for light”), he should just understand that a ten-hour light bulb “wraps” exactly 1 kW / h 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, there will be less light.
Electric heaters used for space heating consume much more power than light bulbs, therefore, they consume as much as other lighting equipment per day in an hour, especially since modern energy-saving technologies are progressing, LED and neon lamps have appeared, durable and economical. Incandescent lamps spend most of the energy consumed on heating the air.
Energy and power in the GHS system
There is another unit that is used to measure the generated energy - calorie, it is used in the GHS system. Most of our fellow citizens (especially women) know calories from annotations explaining the nutritional value of food. In fact, this is the amount of energy that is needed to heat one gram of water per degree Celsius at an initial temperature of 19.5 ° C. It would be convenient if it were not for a small amount (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, but everyone has already got used to the power unit. However, sometimes kilocalories and megocalories 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 should be remembered that a different rule applies here. Calorie is a unit of energy, and power is measured in watts. Therefore, through the specified coefficient, Gcal and kW / h or Gcal / h and watts can be equated. Do not confuse energy with power!
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 work on the example of the device of metering devices of the old model. Active power is equal to the product of the mains voltage (it is standard with us and is equal to 220 volts) by the current value. The rotation speed of the disk is proportional to the power consumed, and the faster it spins, the more often the numbers on the wheels driven by it flash.
Counter as an integrator
Accounting for energy consumption is similar to the integration process. If you set the time on the abscissa axis and put off the power consumption on the ordinate (which may be different during the accounting period), 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, kW / h - a unit expressing its physical essence, and in order to calculate the debt, it remains only to multiply the received number by the current tariff.