ENERGY UNIT: CALCULATING AND METERING ENERGY

CALCULATING ENERGY USEAPES VERSION

UNDERWRITERS LABORATORIES

• “Since 1894, UL has been testing, verifying, validating and inspecting thousands of everyday things to keep your family safe and give you peace of mind. We are an independent product safety certification organization. That means we have no affiliation with a brand, product or company – our only concern is your safety”

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 METERWhich 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 electricityflows.

• 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 acertain 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 YOUR ENERGY RATE

• Cost/Energy use = Rate per kWh

• Example: $45.69

532 kWh

Read a Sample Electric Bill and Calculate the rate that the customer would have paid for the sample month’s bill

= .085883459

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 Kill-A-Watt electricity usage monitor and it will tell you how efficient they are.

• The Kill-A-Watt’s easily-readable 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

CALCULATE THE FOLLOWING• 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?

• A household uses 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 kilowatt-hours, 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?