Electrical Power & Efficiency (12.7)
SNC 1D
Read pp. 530-535
Electrical Power & Electrical Energy
Define the following terms:
Term
Definition
Electrical Power
The unit of power is the __________(___)
kilowatt-hour (kW-h)
EnerGuide label
The Cost of Electricity
When dealing with the amount of electrical energy a customer uses over a period of time, the
electrical energy is measured in kilowatt-hours (kWh).
E
P t
E = energy (kWh)
P = power (kW)
t = time (h)
When determining the cost of the electrical energy used, we can use one of the following two
equations:
Cost of electrical energy
($)
=
Electrical Energy Used
(kWh)
x
Electricity Rate
($/ kWh)
OR
Cost of electrical energy
($)
=
Power
(kW)
Note: Always convert watts (W) to kilowatts (kW)
Time is always in hours (h)
x
time
(h)
x
Electricity Rate
($/ kWh)
Problem: Calculate the cost of operating each fluorescent light fixture during the past 6 weeks
for the closed ecosystems? Each light fixture uses two fluorescent tubes – each tube
is rated at 32 watts. The cost of electricity is 12 cents per kW-h.
To determine the cost to operate an electrical appliance uses over a period of time, we need
three pieces of information:
Power rating of the appliance
The power rating of an
appliance is usually printed on
the appliance
Always convert watts (W) to
kilowatts (kW)
watts =
1000
kilowatts
Time period the appliance was
used
Cost of electricity (per kW-h)
Always covert times to hours (h)
seconds
3600
=
hours
minutes
60
=
hours
days x 24
=
(12 cents = $0.12)
hours
𝑪𝒐𝒔𝒕 𝒕𝒐 𝒐𝒑𝒆𝒓𝒂𝒕𝒆 𝒂𝒑𝒑𝒍𝒊𝒂𝒏𝒄𝒆 = 𝒑𝒐𝒘𝒆𝒓 𝒓𝒂𝒕𝒊𝒏𝒈 × 𝒕𝒊𝒎𝒆 𝒑𝒆𝒓𝒊𝒐𝒅 × 𝒄𝒐𝒔𝒕 𝒐𝒇 𝒆𝒍𝒆𝒄𝒕𝒓𝒊𝒄𝒊𝒕𝒚
Solution:
Use the GRASS method of problem solving.
Given:
What information is given?
Use appropriate symbols and
units.
Required:
State what you are asked to find.
Analysis:
Explain how you will solve the
problem. Which equation will
you use?
Solution:
Substitute the values into the
equation, with units, and solve.
Statement:
Write a concluding statement.
Problem 2:
A laptop computer uses a 75 W adapter when it is plugged in. Electricity costs
5.6 cents per kW-h. Calculate the cost to operate the laptop for one year, 24
hours/day.
Solution:
Use the GRASS method of problem solving.
Given:
What information is given?
Use appropriate symbols and
units.
Required:
State what you are asked to find.
Analysis:
Explain how you will solve the
problem. Which equation will
you use?
Solution:
Substitute the values into the
equation, with units, and solve.
Statement:
Write a concluding statement.
Questions:
p. 535 # 2-7