What units are used to measure energy?

If the energy a body possesses is revealed by doing work, the value of this work will be a measure of the energy it possesses. If, on the other hand, we have carried out work on a body and it has stored it in the form of energy, the measure of the work carried out on the body will give us the value of the energy that remains latent in the body. Therefore, the energy released or accumulated will have the same units as the work magnitude.

In the International System of Units (SI) the unit of work and energy is the July (J) defined as the work done by the force of 1 newton when it displaces its point of application by 1 meter, or what the same, to raise a mass of 101 g one meter.

In nuclear physics the electron volt (eV) is used as a unit, defined as the energy that an electron acquires when passing from one point to another between which there is a potential difference of 1 volt.

Its relationship with the unity of the International System is:

1 eV = 1,602 x 10-19 J, or 1 July = 6.2 x 1018 eV

For electrical energy, the kilowatt-hour (kWh) is used as the production unit, defined as the work carried out for 1 hour by a machine with a power of 1 kilowatt. Its equivalence with the unity of the International System is:

1 kWh = 3.6 x 106 J, or 3.6 million joules

so, the energy consumed by a 40-watt light bulb lit for 25 hours. In the accepted symbology for kilowatt hours, kW-h or kWh can be used interchangeably, but never kW / h that does not make any physical sense.

In order to evaluate the energy quality of the different energy sources, units based on the calorific value of each one are established. The most used in energy economy are kcal / kg, tec and toe.

• kcal / kg applied to a fuel indicates the number of kilocalories that we would obtain in the combustion of 1 kg of that fuel.
  1 kcal = 4.186 x 103 J
• tec: equivalent ton of coal. Represents the energy released by the combustion of 1 ton of coal (coal).
  1 tec = 29.3 x 109 J
• toe: tonne of oil equivalent. Equivalent to the energy released in the combustion of 1 ton of crude oil.
  1 toe = 41.84 x 109 J

The relationship between these units is

1 toe = 1,428 tec