Do you ever wonder how power companies charge us for using our equipment, appliances, and computers? Do you know how to compute for the energy consumed by those? Do you know how to compute for the cost of our energy consumption?

In this article, I’m going to teach you how to calculate for the energy consumed by most equipment and appliances that we are using as well as its cost.

Power companies are not charging us for power, but for energy. In physics, energy is defined as the capacity of doing work. There are many forms of energy, but we are talking about electrical energy here.

Energy (W) is the product of Power and time.

In equation form, this is given as
E = P x t

Since Power is the product of current and voltage, we can also express energy using current, voltage, and time.

In equation form, this is given as
E = I x V x t

The cost for our energy consumption is determined by the product of the energy and rate per kilowatt-hour charged by the power companies.

Where
Cost = Energy x rate

The unit of energy used to calculate our energy consumption is the kilowatt-hour (kWh). Currently, the rate per kilowatt-hour for residential consumption in Cebu (VECO’s rate) is Php 11.89 or approximately Php 12 (0.23 USD).

Here in the Philippines, we are usually billed monthly. And to determine how much energy is consumed for a given period of time, an electric meter is being used.

Since most of our equipment, appliances and gadgets has a constant power rating, energy consumption depends on the number of hours these equipment and appliances are actually operated.

Below is the list of power ratings of the common equipment and appliances that we are using:

Household Appliances

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Household Appliances:	Power Rating
Washing Machine (non-auto)	280 W
Washing Machine (automatic)	585 W
Water Heater	1,500 W
Flat Iron	750-1,000 W

Lighting Fixtures

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Lighting Fixtures:	Power Rating
Fluorescent Lamp	20-40 W
Ceiling Fixtures (3-lamps)	120 W

Cooking Equipment

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Cooking Equipment:	Power Rating
Blender/Grinder/Mixer	300-700 W
Refrigerator Freezer, 12 cu. ft.	300 W
Refrigerator, 10 cu. ft.	170 W

Entertainment Systems

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Entertainment Systems:	Power Rating
DVD/VCD Player	300 W
T.V. Set Color, 16"	90 W
T.V. Set Color, 20"	110 W
Stereo Component	380 W

Cooling Equipment

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Cooling Equipment:	Power Rating
Airconditioning Unit (0.75 HP)	727 W
Airconditioning Unit (1.0 HP)	944 W
Desk Fan 10"	50 W
Stand Fan 16"	80 W
Ceiling Fan, 3-blader	140 W
Ceiling Fan, 4-blader	160 W

Computer

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Computer	Power Rating
PC with monitor	225 W
Desk Jet Printer	175 W
Scanner	12 W

Given the power rating of some equipment and appliances, we can now compute for the energy consumption with our assumption for the time that it is operated.

Let’s have the washing machine (non-auto) for our first sample computation.

Assuming that we are using it for 2 hours. Then, we can compute for its energy consumption and cost by using the formula stated above.

Energy = Power x time

Washing Machine (non-auto):

Power Rating	Time	Rate
280 W	2 hours	Php 11.89/kWh

Energy = (280/1000 kW) x 2 hrs
Energy = 0.280 kW x 2 hours
Energy = 0.56 kWh
Note: We divide 280 Watts by 1000 to convert it into kilowatts since 1kW = 1000 W

Computing the cost,
Cost = Energy x rate
Cost = 0.56 kWh x Php 11.89/kWh
Therefore, the cost for Washing Machine (non-auto) operated for 2 hours is Php 6.6584 (0.13 USD)

Let’s compute the cost for using PC with monitor for half day (12 hours):

PC with monitor:

Power Rating	Time	Rate
225 W	12 hours	Php 11.89/kWh

Energy = (225 /1000 kW) x 12 hrs
Energy = 0.225 kW x 12 hours
Energy = 2.7 kWh
Note: We divide 225 Watts by 1000 to convert it into kilowatts since 1kW = 1000 W

Computing the cost,
Cost = Energy x rate
Cost = 2.7 kWh x Php 11.89/kWh

Therefore, the cost for PC with monitor operated for 12 hours is Php 32.103 (0.62 USD)

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Assuming that every day, a household operates the following appliances with a specific duration. Let's compute for the total cost that they will pay in a month.

Appliances	Power Rating	Time
T.V. Set Color, 20"	110 W	12 hours
Flourescent Lamp	20 W	6 hours
Refrigerator Freezer, 12 cu. ft.	300 W	20 hours
Desk Fan 10"	50 W	10 hours
Ceiling Fan, 3-blader	140 W	10 hours
Washing Machine (non-auto)	280 W	2 hours
Flat Iron	750 W	2 hours
PC with monitor	225 W	8 hours

COMPUTATION:

T.V. Set Color, 20":

Power Rating	Time	Rate
110 W	12 hours	Php 11.89/kWh

Energy = (110/1000 kW) x 12 hrs
Energy = 0.110 kW x 12 hours
Energy = 1.32 kWh

Computing the cost,
Cost = Energy x rate
Cost = 1.32 kWh x Php 11.89/kWh

Cost = Php 15.6948 (0.30 USD)

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Flourescent Lamp

Power Rating	Time	Rate
20 W	6 hours	Php 11.89/kWh

Energy = (20/1000) kW x 6 hrs
Energy = 0.020 kW x 6 hours
Energy = 0.12 kWh

Computing the cost,
Cost = Energy x rate
Cost = 0.12 kWh x Php 11.89/kWh

Cost = Php 1.4268 (0.027 USD)

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Refrigerator Freezer, 12 cu. ft.

Power Rating	Time	Rate
300 W	20 hours	Php 11.89/kWh

Energy = (300/1000 kW) x 20 hrs
Energy = 0.3 kW x 20 hours
Energy = 6 kWh

Computing the cost,
Cost = Energy x rate
Cost = 6 kWh x Php 11.89/kWh

Cost = Php 71.34 (1.36 USD)

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Desk Fan 10"

Power Rating	Time	Rate
50 W	10 hours	Php 11.89/kWh

Energy = (50/1000 kW) x 10 hrs
Energy = 0.05 kW x 10 hours
Energy = 0.5 kWh

Computing the cost,
Cost = Energy x rate
Cost = 0.5 kWh x Php 11.89/kWh

Cost = Php 5.945 (0.11 USD)

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Ceiling Fan, 3-blader

Power Rating	Time	Rate
140W	10 hours	Php 11.89/kWh

Energy = (140/1000 kW) x 10 hrs
Energy = 0.14 kW x 10 hours
Energy = 1.4 kWh

Computing the cost,
Cost = Energy x rate
Cost = 1.4 kWh x Php 11.89/kWh

Cost = Php 16.646 (0.32 USD)

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Washing Machine (non-auto):

Power Rating	Time	Rate
280 W	2 hours	Php 11.89/kWh

Energy = (280/1000 kW) x 2 hrs
Energy = 0.280 kW x 2 hours
Energy = 0.56 kWh

Computing the cost,
Cost = Energy x rate
Cost = 0.56 kWh x Php 11.89/kWh

Cost = Php 6.6584 (0.13 USD)

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Flat Iron

Power Rating	Time	Rate
750 W	2 hours	Php 11.89/kWh

Energy = (750/1000 kW) x 2 hrs
Energy = 0.75 kW x 2 hours
Energy = 1.5 kWh

Computing the cost,
Cost = Energy x rate
Cost = 1.5 kWh x Php 11.89/kWh

Cost = Php 17.835 (0.34 USD)

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PC with monitor:

Power Rating	Time	Rate
225 W	8 hours	Php 11.89/kWh

Energy = (225/1000 kW) x 8 hrs
Energy = 0.225 kW x 8 hours
Energy = 1.8 kWh

Computing the cost,
Cost = Energy x rate
Cost = 1.8 kWh x Php 11.89/kWh

Cost = Php 21.402 (0.41 USD)

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The summation of cost is:

Appliances	Cost
T.V. Set Color, 20"	Php 15.6948 (0.3 USD)
Flourescent Lamp	Php 1.4268 (0.027 USD)
Refrigerator Freezer, 12 cu. ft.	Php 71.34 (1.36 USD)
Desk Fan 10"	Php 5.945 (0.11 USD)
Ceiling Fan, 3-blader	Php 16.646 (0.32 USD)
Washing Machine (non-auto)	Php 6.6584 (0.13 USD)
Flat Iron	Php 17.835 (0.34 USD)
PC with monitor	Php 21. 402 (0.41 USD)
Total =	Php 156.95 (2.997 USD)

That is the total cost as operated in one day. Since we are assuming that a household operate those appliances with a specific duration every day, then, we can compute their monthly consumption.
Monthly bill = Php 156.95 (2.997 USD) x 30 days
Monthly bill = Php 4708.44 (89.55 USD)

Obviously, the cost of our consumption varies with the power rating of the equipment/appliances and the period of time that it is operated.
The greater the power rating the greater the cost. And the greater the duration that the equipment or appliances is operated the greater the energy consumption and the cost.

So that’s how to compute for the energy consumption of our equipment and appliances as well as the cost for the energy consumption.

For further questions and/or inquiries about this article, please feel free to leave a comment.

Written by:
Jemarie S. Fuentes
Registered Electronics Engineer

Image Source: 1, 2, 3

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