It is quite common to share the power, energy and demand without distinguishing between the three. Because this practice can lead to confusion, the differences between these three measures will be discussed.The power is an instant reading. The power provided by a meter reading is the present flow of Watts. The power is immediately measured just as current.In many digital meters, the power value is measured and is actually calculated on a second interval because it takes a certain amount of time to calculate the values of the RMS voltage and current. But this time interval is kept small to preserve the instant nature of power.The energy is always based on a certain time increment; It is the integration of the power on a time increment.
Energy is an important value because almost all electric bills are based, in part, on the amount of energy used.Typically, electrical energy is measured in units of kilo Watt-hour (Kwh). A kilo watt-hour represents one constant load of one thousand Watts (a kilo watt) for one hour. Stated another way, if the energy delivered (the instantaneous Watts) is measured as 1,000 Watts and load it was served during a time interval of one hour, then the load would have absorbed an energy of a kilo watt-hour. A different load can have a requirement of constant power of 4,000 Watts. If the load was served during a time he would absorb four Kwh. If the load was served for 15 minutes it would absorb a total deese or 1 Kwh. To give an illustration, assume that the power level is maintained constant for each minute when a measurement is taken, if we could represent in a graph would do that each line represents the power of the load for the time of one minute increment. In real life the value of power moves almost constantly.With these data we could illustrate the calculation of energy.