[Units]
[Using the Bill]
[Reading a Meter]
[The Cost]
[The Environmental
Cost]
[How it is Produced]
Use The Above Links To Navigate To A Specific
Part Of The Electric Bill Project
The watt (W) is a unit of electrical power, which is the rate
at which we use energy. We pay the electric company for the use
of energy. A kilowatt (kW) is equal to 1000 watts: kilo is a prefix
that means 1000. (Note that k is the normal prefix for kilo, W
is the normal abbreviation for Watts and h is the normal abbreviation
for hours). A watthour (Wh) and a kilowatthour (kWh) are units
of energy, where 1000 Wh= 1 kWh. The equation relating energy and
power is:
Energy = Power x Time
For example, if a 75 W bulb (power) is turned on for 2 hours
(time), it will use 150 Wh or 0.15 kWh of energy (energy = power
x time).
The cost for each unit of energy we use is measured in cents
(c) or dollars ($) per kWh. The typical cost per unit of energy
is 10 c/kWh or $0.10/kWh. Using the equation below, we can determine
the cost of our energy use:
Cost of energy use = Energy used x Cost per unit of energy:
Using our example above, the cost of using a 75 W bulb for 2
hours is:
Cost of energy use = 0.15 kWh x 10 c/kWh = 1.5 c.
[Units]
[Using the Bill]
[Reading a Meter]
[The Cost]
[The Environmental Cost]
[How it is Produced]
Make a list of the total cost of monthly electricity use as
written on the bill. Discuss/calculate the minimum, maximum and
average of the classes' electricity bill. Bar graphs could be made
of the number of bills totaling less than $30, $3040, $4050,
$5060, $6070, $7080, $8090, $90100 and greater that $100.
Discuss with your class the reasons why some bills are higher than
others. Perhaps the difference is related to the size of the home,
number of refrigerators, freezers, TVs, computers etc. at the home
or whether or not they have a pool or spa.
Consider a typical sample electric bill which contains the following
information.
Total Usage 
647 kWh 
Baseline Allowance 
266 kWh 
Baseline Usage 
266 kWh @ $.10077 
NonBaseline Usage 
381 kWh @ $.12039 
Amount 
$72.67 
Next discuss that electricity
use is measured using units of kilowatthours, abbreviated
as kWh on the bill.
Each kWh costs
a certain amount of money that is specified on the bill. Up to
a certain amount of electricity use, called the baseline usage,
the cost of a kWh is one amount, which on the sample bill is
$.10077/kWh or 10.077 c/kWh. This can be used to introduce the
concept of less than (<)  for electricity usage less than the
baseline allowance of 266 kWh, the cost is $.10077 per kWh. For
amounts greater (>) than the baseline usage, the cost is higher
 $.12039 per kWh. Ask your students why SDG&E makes it cost
more for you if you use higher amounts of electricity. Explain
that this is a way that higher costs are used to try to discourage
people from using excessive amounts of energy.
Next have your students calculate the total electricity used
by adding their baseline usage (266 kWh) and their nonbaseline
usage (381 kWh). This should agree with the amount denoted as
total usage (266 kWh + 381 kWh = 647 kWh). Then have them determine
their electricity bill amount. First have them multiply their
baseline usage (266 kWh) by the baseline rate ($.10077/kWh) to
determine their baseline cost (266 kWh x $.10077/kWh=$26.80).
Second, have them multiply their nonbaseline usage (381 kWh)
by the nonbaseline rate ($.12039/kWh) to determine their nonbaseline
cost (381 kWh x $.12039/kWh=$45.87). Now they should add the
baseline cost and the nonbaseline cost ($26.80 + $45.87 = $72.67)
to obtain their total electricity cost for the month.
The gas usage and cost could
be similarly determined. Students could also calculate the
state surcharge
tax and the state regulatory
fee, given the rates specified on the bill and teachers could
discuss the concept of taxes and how taxes are used. For example,
as stated in the SDG&E "A Guide to Understanding Your Gas & Electric
Bill, " the state surcharge tax is used for various energy management
programs as well as the development of energy resources. The
state regulatory fee pays for the operation of the California
Public Utilities Commission, which determines the rates that
the utilities are allowed to charge their customers.
[Units]
[Using the Bill]
[Reading a Meter]
[The Cost]
[The Environmental Cost]
[How it is Produced]
You can also teach your students to read their electricity
meters, which read in kilowatthours. Have their parents help them
find out where their meters are located. Then have them read their
meters as follows. Read from left to right. If the dial hand is
between numbers, use the lower one. If the dial hand is exactly
on a number, look at the dial to the immediate right. If its dial
hand has not passed zero, record the lower number. Students could
make tables or graphs of their daily usage (by subtracting successive
days' meter readings) or tabulate or graph their cumulative usage
on a daily, weekly or monthly basis. They should also compare their
reading to the electricity meter reading on their bill. They should
obtain a reading somewhat higher than the reading on the bill,
since the reading taken for the
bill occurred earlier.
[Units]
[Using the Bill]
[Reading a Meter]
[The Cost]
[The Environmental Cost]
[How it is Produced]
The SDG&E booklet "How Much Are Your Appliances Running" provides
a way for students to understand why their electric bill costs
as much as it does. Each student should be given a copy of the
booklet. They should then go home and make a list of all of the
electricity using appliances in their home and how often they are
used per month. They can then use the costs stated in the booklet
to calculate the monthly use cost of these different appliances.
This will require the use and understanding of many different units
 such as costs per load of running the washer, dryer, dishwasher,
etc., costs per hour, costs per day and costs per month. Their
total electricity cost per month should approximate the cost shown
on their
electric bill.
The students can also be challenged to try to reduce their energy
usage. Have them suggest ways that they might affect the energy
use of their home. Perhaps they will turn off the pool heater,
turn down the thermostat in winter or turn it up in the summer,
turn off light bulbs, wash dishes more efficiently, turn off
a rarely used second refrigerator, etc. They can do this for
a day or more ( if they read and record their meter reading on
a daily basis) or for a month and then try to see if they reduced
their monthly electric bill.
Another interesting concept can be discussed at this point,
namely the cost of buying or purchasing an appliance versus
the cost of using or operating an appliance. Ask the students
to determine the cost of buying an appliance of their choice
(by having them go to a store, look at ads in the newspaper or
asking their parents). Then have them determine the hourly, daily,
monthly or yearly cost of using the appliance (using the SDG&E
booklet). Have them determine how long it takes for the operating
cost to equal the purchased price.
For example, suppose a 100 watt
regular or incandescent light bulb costs 50c and will last
(called the
average lifetime or
avg. life on the box) for 1000 hours. According to the SDG&E
booklet, it costs 1c/hour to operate a 100 watt. Therefore, in
50 hours, the cost of using a light bulb will equal 50c, which
was the purchased price of the light bulb. Over the 1000 hour
lifetime of the light bulb, it will cost 1000c or $10 to operate
the light bulb, which is 20 times the cost of the light bulb.
A compact fluorescent bulb is more expensive than a regular
incandescent light bulb. Have the students determine how much
more expensive it is. It also lasts much longer. The compact
fluorescent bulb also is less expensive to operate than the incandescent
light bulb. Over the course of a lifetime of a fluorescent bulb,
have the students determine the total purchase price of the one
fluorescent bulb, the price of the many incandescent light bulbs
that will last as long as the incandescent bulb, and the price
of operating the two types of bulbs. Which is cheaper to use,
considering both the purchasing cost as well as the operating
cost?
Let's do an example. Suppose
the compact fluorescent bulb, that has a light output equivalent
to a 100
watt incandescent bulb,
lasts for 10,000 hours and costs $10. It costs about 1/4 c per
hour to operate according to the SDG&E booklet. So, over 10,000
hours, the compact fluorescent bulb costs 10,000 hours x 1/4
c/hour = 2,500 c or $25 to operate. For 10,000 hours of use,
the total cost is $10 to buy one bulb and $25 to use the bulb,
for a total of $35.
Now, let's determine how much it will cost to buy enough incandescent
light bulbs to last 10,000 hours and how much it will cost to
use them for that length of time. Since a light bulb lasts for
1000 hours in our example, it will take 10 of them to last for
10,000 hours. Since each light bulb costs 50c, then it will cost
10 x 50 c =500 c or $5 to buy all 10 of the light bulbs. Since
it costs 1c/hour to use a light bulb, over 10,000 hours, it will
cost 10,000 c or $100 to use the light bulb. So, for 10,000 hours
of use, the total cost is $5 to buy the bulbs and $100 to use
the bulbs, for a total cost of $105.
Therefore, for 10,000 hours of use, the compact fluorescent
bulb will save a total of $105  $35 = $70 compared to the incandescent
bulb!
[Units]
[Using the Bill]
[Reading a Meter]
[The Cost]
[The Environmental Cost]
[How it is Produced]
Students should "think globally and act locally" in
regards to environmental issues. They should understand that using
energy
results in pollution of our environment. Energy is used by power
plants to make electricity. It is also used when we drive cars,
take airplanes, mow the lawn
and cook our food.
Many types of pollutants are produced by power plants. In San
Diego County, both oil and gas are burned during the production
of electricity. On average, the following pollutants are produced:
 852 pounds of CO2 per megawatthour of electricity produced.
CO2 contributes to the global warming of the environment.
(Note that 1000 kilowatthours = 1 megawatthour, or 1000 kWh = 1 MWh)
(Recall that 1000 watthours = 1 kilowatthour or 1000 Wh = 1kWh)
 0.048 pounds of particulates per megawatthour of electricity
produced.
Particulates are small particles that can contribute to smog.
 0.024 pounds of oxides of sulfur per megawatthour of electricity
produced.
Oxides of sulfur contribute to acid rain pollution.
The average SDG&E customer uses 5649 kilowatthours of electricity
per year or 5.649 megawatthours of electricity per year. How
much electricity does each student's family use each year. They
can estimate this amount by multiplying their one month electricity
usage by 12. Have them convert their family's usage from kilowatthours
to megawatthours. How does it compare to the average SDG&E customer?
In our example energy bill, the total electricity use was 647
kWh in one month. The average annual usage is therefore about
12 months x 647 kWh/month = 7764 kWh = 7.764 MWh. Therefore,
this household will generate 7.764 MWh x 852 pounds of CO2/MWh
= 6615 pounds of CO2 per year. It will also generate 7.764 MWh
x 0.048 pounds of particulates/MWh = 0.37 pounds of particulates
per year. Finally, it will generate 7.764 MWh x 0.024 pounds
of oxides of sulfur/MWh = 0.18 pounds of oxides of sulfur per
year.
Given their annual usage in megawatthours, have the students
calculate how much pollution of each type their household causes
at the power plant. Have them discuss the tradeoffs between their
polluting the environment and the convenience/safety/health/enjoyment
of appliances such as refrigerators, freezers, washing machines,
TVs, computers, video games, etc.
[Units]
[Using the Bill]
[Reading a Meter]
[The Cost]
[The Environmental Cost]
[How it is Produced]
Electricity is produced at power plants that convert energy
from one form into a second form, namely electrical energy. Electricity
can be produced by burning coal, oil, natural gas or wood. The
flow of wind or water can also be used to produce electricity.
Sunlight can be harnessed to produce electricity, either by heating
water or by direct conversion to electricity using solar cells.
The heat of the earth can be used to produce electricity at geothermal
power plants. The energy produced by the heat generated by nuclear
fission is used in nuclear power plants to produce
electricity.
All of these power plants have advantages and disadvantages.
Have your students perform a research project to investigate
how these different power plants work. Have them determine:
 What is the source of energy?
 How is the energy converted into electricity?
 What types of pollution are produced by this source of energy?
 What is the cost of electricity produced by this form of
energy?
 Where does this energy source come from? Is it imported?
Is it readily available at all times and in all places?
 What percentage of our nation's electricity is produced by
this form of energy? Why? What about other nations that might
have different natural resources?
Break your class into study groups. Have them write a report
about their topic and present it to the class. Next, have a debate
discussing the relatives advantages and disadvantages of all
of the different types of power plants.
[Units]
[Using the Bill]
[Reading a Meter]
[The Cost]
[The Environmental Cost]
[How it is Produced]
