The estimated monthly electricity consumption is calculated as a multiplication of the nominal power of the electrical device, expressed in kW, with the number of monthly consumption hours and the demand factor.
The following mathematical expression can be used for estimating the monthly electricity consumption:
Ec=Pw*Tore*Fc (1 )
where:
Ec – is the estimated quantity of electricity consumed during a month in Wh (wattora) or in KWh (kilowattora); (1kWh= 1000Wh or 1KWh= 1000W*1hour);
Pw – is the nominal power of the electrical device expressed in W(watt) or KW (kilowatt);
Tore – is the monthly period of the device use, expressed in hours;
Fc – is the demand factor, also called demand coefficient.
The nominal power (Pw) is the power marked on the device or on its identification label (fridge, vacuum cleaner, TV set, radio, light, electrical engine, etc.).
The demand factor (Fc) is 1 in all cases, except the powerful devices (electrical engines, electrical ovens, weld devices, etc.) where the factor is between 0,4 -1, in accordance with the nature of the devices and their average functioning conditions.
The monthly working period of the devices (Tore), expressed in hours, is estimated by each owner in accordance with the real number of hours in which the device is working.
It has to be taken into account that the device can be connected to a power outlet through a power cable, but it should consume energy only when it is powered on (either automatically, like the fridge, or by a button, like the TV set, the hair dryer, etc.)
Example of estimated monthly electricity consumption
We take the example of a household, having one exterior light of 40W, 5 lights of 60W each in two rooms, 4 lights of 40W each in the other spaces of the apartment, one radio, one iron, a washing machine and a fridge.
We use the expression (1) to estimate the monthly electricity consumption.
We have the following values:
-exterior light: 1 pc x 40W x 180hours = 7.200Wh
-room lights: 5 pcs x 60W x 100 hours = 30.000Wh
-lights in the other rooms: 4 pcs. X 40W x 30 hours = 4.800Wh
-radio: 1 pcs x 40W x 200hours = 8.000Wh
-iron: 1 pcs x 450W x 30 hours = 13.500Wh
-washing machine: 1 pcs x 450W x 20 hours = 9.000Wh
-fridge: 1 pcs x 140W x 500 hours = 70.000Wh
Total = 142.500Wh
The monthly estimated consumption will be approximately 142,5 KWh (1KWh=1000Wh)
The fee per KWh applied by the supplier is the controlled fee in effect, approved by the Autoritatea Naţională de Reglementare în domeniul Energiei (ANRE), for the type of consumption program chosen by the consumer.
If we consider, for the example above, a monom CD fee (low voltage), we will take then its value of 0,4330 lei/KWh.
The estimated value of the monthly consumption in the above example will be:
142,5KWh x 0,4330 lei/KWh = 61,70 lei
We add to this value the VAT and the tax for non-commercial consumption, which is calculated on the basis of the euro exchange rate on October 1st of each year and is in effect during the following year.
The VAT for 2011 is 24% and the consumption tax for the same year is 0,004265 lei/KWh.
Please note that the real value is the one registered on the invoice received from the supplier, as the real consumption is the one registered by reading the watch.