Electrical Energy Use in the Home

- Lesson 14

Electrical Energy Use in the Home

- Last week we calculated how much energy

appliances use and how this correlates to the

length of time that they are used. - Energy power x time
- Now we are going to look at how much it costs to

use the electricity.

- Just like meat at the Northern has a price per

pound, electricity has a cost per kilowatt hour

(kWh). - If the cost of a kilowatt is 0.08, all we need

to know is how much energy is used to find out

how much it will cost. - Cost of energy used amount energy used (kWh) x

price per kWh

Example 1

- If a 500 W refrigerator/ freezer uses 75 kWh of

energy, and it costs 0.08/kWh. How much does it

cost to operate the refrigerator for one month? - Cost of energy used amount energy used x price

per kWh - Cost of energy used 75 kWh x 0.08 / kWh
- 6.00
- Therefore, it costs 6.00 dollars a month to run

the fridge.

Example 2

- A 200 watt TV is used 12 hours a day for 30 days.

How much will it cost to run if each kWh costs

0.08? - E P x t
- E (200W 1000W) x (12 h x 30 days)
- E 0.2 kW x 360 h
- E 72 kWh
- Cost of energy used amount energy used x price

per kWh - Cost of energy used 72 kWh x 0.08/kWh
- Cost of energy used 5.76

Practice questions

- Try the 4 questions, if you need help just ask
- A microwave oven uses 15kWh a month. How much

does it cost to run for one month? - Cost of energy used amount energy used x price

per kWh - Cost of energy used 15 kWh x 0.08 kWh
- Cost of energy used 1.20

- A toaster uses 5kWh hours of electricity per

month, what would it cost to use? - Cost of energy used amount energy used x price

per kWh - Cost of energy used 5kWh x 0.08 kWh
- Cost of energy used 0.40

- A 60 W incandescent bulb uses 30 kWh a month. How

much does it cost to run for one month? - Cost of energy used amount energy used x price

per kWh - Cost of energy used 30 kWh x 0.08 kWh
- Cost of energy used 2.40

- A 500 W clothes dryer uses 150 kWh of electricity

a month. How much does it cost to run for one

month? - Cost of energy used amount energy used x price

per kWh - Cost of energy used 150 kWh x 0.08 kWh
- Cost of energy used 12.00

Efficiency and Conservation

- Although the cost of one incandescent light bulb

is relatively inexpensive, it is important to

remember that there are multiple light bulbs in

every house and many are left on for multiple

hours a day. The cost of lighting can quickly add

up when you calculate all of the light bulbs in a

house.

- Fluorescent bulbs cost much more to use than

incandescent light bulbs do but they use less

energy for the same amount of light. Which one is

more cost effective in the end? A few factors

must be looked at cost of the bulb, life of the

bulb and power usage. We will compare the bulbs

over the life of one fluorescent.

- Bulb 1 60 watt incandescent
- Cost 0.50
- Life 1 000 h
- Power 60 W
- Since incandescent bulbs burn out faster we will

need to calculate the cost of all of the bulbs.

10 000 h 1000 h 10 bulbs. - 10 bulbs x 0.50 5.00

- Energy used
- E P x t
- E (60W 1000kW) x (10 000 h)
- E 0.06 kW x 10000 h
- E 600 kWh

- Cost of energy used amount energy used x price

per kWh - Cost of energy used 600 kWh x 0.08 kWh
- Cost of energy used 48.00
- Total cost for 10 00 hours of light
- Cost of bulbs cost of energy
- 5.00 48.00 53.00

- Bulb 2 13W fluorescent
- Cost 10.00
- Life 10 000 h
- Power 13 W

- One bulb provides 10 000 hours of light so we

only need to buy one bulb. - Total bulb cost 10.00

- Energy used
- E P x t
- E (13W 1000kW) x (10 000h)
- E 0.013 kW x 10000 h
- E 130 kWh
- Cost of energy used amount energy used x price

per kWh - Cost of energy used 130 kWh x 0.08 kWh
- Cost of energy used 10.40

- Total cost for 10 00 hours of light
- Cost of bulbs cost of energy
- 10.00 10.40 20.40

- Now we can calculate how much the fluorescent

bulb would save us after 10 000 hours. - Savings total cost of low efficiency appliance

total cost of high efficiency appliance - 53.00 - 20.40
- 32.60 .

Methods of conserving energy

- Thawing frozen food in the refrigerator
- Using a microwave instead of a conventional oven
- Cleaning dust from light fixtures
- Replacing light fixtures and appliances with more

efficient ones when they wear out. - Drying laundry on a clothes line

Methods of conserving energy

- Blocking sunlight with shades and blinds to

reduce air conditioning use - Using timer switches and programmed thermostats
- Turning down the heat in the winter by 1and

turning up the air conditioner by 1. - Turing off lights when leaving a room or reducing

the time lights are on. - Sealing up drafts around the house.

Calculating the Cost of Power Worksheet