Electrical Power

Electrical PowerSection 12.2

Important DefinitionsElectrical Power • the rate at which an appliance uses electrical energy• measured in watts (W) or kilowatts (kW)

Electrical Energy• the amount of energy used by an appliance• measured in kilowatt-hours (kW·h) or watt-seconds (W·s)• sometimes expressed in joules (J).

1 Joule = 1 W·s.

Consumer Energy Needs1. Consumers are billed based on

how much electrical energy (in kW·h) they consume. The amount of energy a customer uses depends on three factors:A. the power rating of appliances

usedB. the setting of the appliancesC. the amount (duration) of use

Power Rating• Appliances that consume more energy

have higher power ratings.

• Examples: LCD Television 0.12 kWStove 3.2 kW

 2. Why do you think the stove

consumes so much more energy?

3. Power can be measured in watts, but it is usually more suitable to use kilowatts (kW).

• What is the conversion between watts and kilowatts?

Conversion: __________ W = 1 kW

Device SettingsActual Power vs. Power Rating• The actual power used differ from the power rating. • This is because the actual power will depend on the setting of

the device.

4. Examples:▫Clothes washer

Wash cycle requires more power than spin cycle

▫Hair dryer High setting requires

more power than low setting

Amount of Use• The longer an appliance/device is used,

the more energy it consumes!

• Energy use:▫measured in kilowatt-hours (kW·h)▫ calculated by multiplying the power rating of a device

(in kW) by the number of hours it is used (in hours, h)

Energy (kW·h)

Power (kW) Hours used (h)

EnerGuide labels• All Canadian appliances have an EnerGuide label. • allows consumers to make informed decisions when

purchasing appliances

Scale compares the appliance to the most- and least-efficient models in the same class

Annual energy consumption of the model

5. Interpret the graphic:a. How much energy does this appliance consume, per

year?

b. Approximately how much energy does it use, per day? (Round to two decimals)

c. In terms of energy consumption, how does this appliance compare to other, similar appliances?

Scale compares the appliance to the most- and least-efficient models in the same class

Annual energy consumption of the model

300 kW·h

0.82 kW·h

Pretty good – on low end of scale

Sample Problem: Determining energy consumption & Cost6. A hair dryer is rated at 1200 W. On average, it used for

5 min each school day in the morning, when the cost of electrical energy is 10.9¢/kW·h.a. How much energy, in kW·h, is consumed each school

day, by the hair dryer?b. How much energy is consumed over all five school days

in a week?c. Calculate the weekly cost of using the hair dryer all five

days.

Time-Of-Use Pricing• Time-of-use pricing - A system of pricing, where the

price that is charged per kW·h of energy is different depending on the time of the day or week.▫ three different time of use prices:

off-peak, mid-peak, on-peak▫ intervals are adjusted twice a year (summer and winter)

• Energy consumption is monitored by a smart metre, which records hourly energy usage.

Summer weekdays Winter weekdays Price

Off-peak hours

Mid-peak hours

On-peak hours

7. Interpret the graphic. Use correct units, where appropriate.

Discuss with a partner...8. a. In general, why do you think the

peak hours change depending on the season?

b. What needs make up the major electrical demands in the summer?

c. What needs make up the major electrical demands in the winter?

Energy demands change with the seasons

Cooling/Air conditioning

Heating and lighting

d. Describe one way you could use your knowledge of time-of-use pricing, to save money.

Phantom Loads9a. Phantom load - The electricity that is

consumed by an appliance or device when it is turned off.

b. Example: TV– Always in standby mode, “waiting” to receive a signal to turn on

c. Features of typical devices with phantom loads:▫ remote controls (TV’s, stereo systems)▫ continuous display (like the clock on a stove)▫ feature rechargeable batteries (cordless phones)▫ external power supplies (like phone chargers)

What can you do to combat the phantom load?

Homework• Pg. 496 #1-4• Pg. 495 #1-5