ENERGY UNIT:
CALCULATING AND
METERING ENERGY
CALCULATING
ENERGY USE
APES VERSION
UNDERWRITERS
LABORATORIES
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ENERGY STAR
ENERGY STAR® is a joint
program of the U.S.
Environmental Protection
Agency and the U.S.
Department of Energy
helping us all save money
and protect the
environment through
energy efficient products
and practices.
USING A KILL-A-WATT
METER
Which appliances are using the most energy?
Where can we save energy?
BACKGROUND
INFORMATION:
HOW IS ELECTRICITY
MEASURED?
Electricity is measured in volts, amps and watts.
• Volts measure the “pressure” under which electricity
flows.
• Amps measure the amount of electric current.
• Watts, named to honor the inventor of the steam
engine,
James Watt, measure the amount of work done by a
certain amount of current under a certain pressure.
A kilowatt (kW) is 1,000 watts and a kilowatt-hour (kWh)
is the energy of 1,000 watts working for one hour.
=
CALCULATING .085883459
a Sample
YOUR ENERGYRead
• Bill
Cost/Energy
use = Rate per
Electric
and
Calculate
the
kWh
RATE
rate that the
customer would
have paid for the
• month’s
Example:
sample
bill
$45.69
532 kWh
USING A KILL-A-WATT
METER
• Used to calculate the
energy use of appliances
• Find out which of your
appliances, lamps and
computers are actually are
costing you the most!
• Just plug them into the KillA-Watt electricity usage
monitor and it will tell you
how efficient they are.
• The Kill-A-Watt’s easilyreadable LCD display
measures consumption by
the kilowatt-hour, just like
the electric company.
USING THE METER
• Plug into an outlet
• Plug the appliance into the
meter
• Leave in place for a
specified time – usually 24
hours
• Go Back next day – DO NO
UNPLUG
• Read the meter first
• Record time and kWh used
• Then unplug and return
• Use the information to
calculate the energy use
• You can calculate one time
use, hourly use, day use,
weekly use, monthly use, or
yearly use
• This includes power and
cost
• You need to know:
• Rate
• kWh used
• Time used
SAMPLE DATA #1
• A projector is plugged in for
30 minutes to a kill-a-watt
meter – it use 0.12kw of
energy
• Calculate the energy used
in one hour, one day and
one month (30days)
• If your energy company
charges you $0.25/kwh How
much will using the
projector cost for one
month. Assume the
projector was used for 24
hours.
• .12 x 2 = .24kW per hour
• .24 x 24 hours = 5.76 kW per
day
• 5.76 kW x 30 days = 172.8
kW /month
• 172.8kW x .25/kWh = $43.20
SAMPLE DATA #2
• A Kuerig coffee maker
uses .02kw in 30 minutes.
• Calculate the energy use
for 1hour, 1 day, and 1
month (30 days)
• Energy company
charges you $0.25 per
kwh How much will it cost
you per month to
operate your coffee
maker? Assume it is
always on
• A Household’s Electric
Bill is $123.45 and their
energy use for the
month was 675kwh
• What is the rate per
kWh they are charged?
CALCULATE THE
• A household
uses
FOLLOWING
734kWh of energy in
one month
• Their electric company
charges them .095
/kWh
• How much is this
monthly bill?
$0.18/kWh
$69.73
HOW DO YOU KNOW HOW
MUCH ENERGY A POWER
PLANT CAN PRODUCE?
• you don't measure electricity in megawatts per day, it's
just megawatts.
• A megawatt is a rate, not a quantity, just like miles per
hour is a speed, not a distance. You would never ask
someone how many miles per hour can your car travel
in a day. You would either ask how many miles in a day
or you'd ask how many miles per hour.
• A watt measures speed at which the electricity flows.
• The unit for measuring a quantity of electricity is the
watt-hour.
EXAMPLE
• If you run a 500 watt generator for 8 hours, the total
electricity generated is 4000 watt-hours, which is 4 kilowatthours, written 4kWh.
• In 1963 the United States Army built a nuclear power plant
which only produced 140kW. If you had a 140kW generator
running 24 hours a day it would produce 3360kWh, or
3.36MWh
•
A city of 50,000 people would probably use between 2 and 3
GWh per day. A 100MW plant could provide that much
power if it ran 24 hours a day but the peak demand would
likely be in the middle of the afternoon (especially in summer
time when air conditioners are running) and could easily top
200 or 300MW.
ENERGY UNITS
• kilo = one thousand
• Mega = one million
• Giga = one billion
• 1000 W = 1 kW (kilowatt)
1000 kW = 1 MW (megawatt)
1000 MW = 1 GW (gigawatt)
• 1Btu = 1055 joules or 1.055kj
• Joules = watts x seconds
• 1 watt = 1 joule/second
Enriched Uranium is used in nuclear reactors to generate electricity. The
Nuclear One nuclear power in Arkansas generates an average of 836MW.
Use the information provided to answer questions related to nuclear
energy and the production of electricity by Nuclear One.
• 1 uranium fuel pellet is approximately equivalent to 3 barrels of oil.
• 1 barrel of oil can generate 623 kilowatt hours of electricity.
• Assemblies are the groupings of fuel rods in a reactor. There are 75
assemblies in Nuclear One’s primary reactor.
• There are 450 fuel rods per assembly.
• A typical fuel rod contains 400 pellets per rod.
A. What does generating 836MW mean?
B. How much electricity in kWh can one uranium fuel pellet generate?
C. If Nuclear One power plant uses all 75 assemblies, how much energy
could it generate?
D. If Nuclear One is operating at full capacity, how much electricity is
generated in 24 hours?