How much energy do you use in a day?
How much does it cost?
How much carbon dioxide does it generate
On the ground – what does it mean to you and me?
Energy is the currency of life. It gets things done. Different
forms of energy have different costs, both direct and indirect.
This module is designed to get students to think about the
different forms of energy they consume, how much of each they
consume and the cost of this consumption, both in dollar and
greenhouse gas emission terms.
It is also hoped that it will highlight the fact that we happily
spend more on certain foods and yet only buy the cheapest
energy (unless a household purchases Green Power).
The types of energy generally consumed can be split into three
categories:
Why is where our energy
comes from important?
What makes a high
emissions fuel versus a low
emissions fuel? Why are
some fuels far cheaper than
others?
How much energy a student eats in a day helps to put in context the
energy they use elsewhere. All food bought commercially has energy
content information on it, per 100g and per serve. This allows
students to accurately assess how much energy they themselves eat.
The cost is calculated from the sale price of the food and the fraction
that was eaten.
Why are we willing to pay
large premiums for foods
that we like (personal
energy) but not for fuels that
we burn in the home or for
transport?
This includes both gas and electricity (and in some cases wood).
Calculating the energy that students consume indirectly through their
activities is a little more involved but still relatively simple. Electrical
appliances come with labelling that lists the maximum wattage. For
most appliances this wattage can be used as an approximate normal
wattage and energy consumed can be calculated using:
Energy = Power × Time (if you use the units kW and hours, this gives
you energy in kWh).
Example calculations as well as a listing of wattages that can be used
as approximate values for different appliances can be found at:
http://www.energysavers.gov/your_home/appliances/index.cfm/myto
pic=10040
2
Gas appliances are also required to have a label indicating power.
This is usually in the units MJ consumed/hr. Again:
Energy = Power × Time.
Hot water calculations are best done from scratch, although clearly
heat pumps and solar hot water complicate matters if they are
present. An example calculation is shown in Appendix 2.
Burning wood in theory does not generate net CO 2 emissions as
the wood will eventually break down and release its stored carbon.
This is essentially true in the case of a slow combustion stove that
is operated ‘hot and hard’.
(For the purposes of this exercise, this is confined to cars. Bicycles
fall under the ‘Food Energy’ category as the energy required to
pedal a bicycle has already been counted there.)
Change is
constant, yet
often we fight it.
The amount of energy a car consumes can be calculated directly
from the fuel consumed or estimated using distance traveled and
fuel consumption data. Students can keep track of how much
petrol they put into their cars or record their odometer readings
and calculate approximate fuel consumed using litres of
How can we view
the challenge of
climate change
and changes
science is telling
fuel/100km and values derived from websites such as:
http://www.greenvehicleguide.gov.au/GVGPublicUI/home.aspx
It is relatively straightforward to calculate both the cost and the
emissions generated from the three different energy use activities:
Emissions = Energy Used × Emissions Factor
Emissions factors are explained in more detail under ‘Key Terms’
us we must make,
as an opportunity
and also on the ‘constants’ worksheet of the ‘Everyday Energy
work book’.
rather than a
catastrophe?
Calculating emissions (mostly indirect in the form of input
fertiliser, fuel for transport or bi-products such as methane from
cows belching etc) is much harder. For the purposes of this
module, these emissions will not be calculated. If students are
interested, a number of links explore this topic further and are
found in the references section under ‘Indirect Emissions’.
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Different forms of energy have differing energy unit costs.
 How much money does your
family spend on energy in a
week (petrol, electricity,
natural gas)?
Different forms of energy produce different levels of carbon dioxide
emissions/unit of energy delivered.
When purchasing food, we consider a wide range of factors other
than cost or efficiency.
 How much energy does this
represent?
When purchasing energy (electricity or gas) we often don't think
about it much because the energy is largely invisible and also
because it is aggregated.
 How much does your family
spend on the grocery bill –
people energy?
By explicitly looking at how we consume energy, we can question
our assumptions of how we use energy.
By making choices, we can increase or reduce our energy use and
 How much energy does this
therefore our greenhouse emissions.
represent?
Emissions Factor: The amount of carbon dioxide generated per
Note to Teacher: the sample
unit of energy used. For direct use of fuels, these factors are
energy diary can be used to
relatively uniform. Burning a litre of petrol generates the same
generate plausible values if
amount of CO2 wherever you are in the world. However, for
students do not obtain the
electricity, these factors may vary widely from state-to-state and
above information.
country-to-country and are dependent primarily on how the
electricity is produced.
Kilojoules: (KJ) a unit of energy
Megajoules: (MJ) 1000 KJ = 1 MJ
Natural gas is typically sold per MJ
Kilo-watt hour: (kWh) another unit of energy
3.6 MJ = 1 kWh
Electricity is usually sold per kWh
Green Power: energy that produces no net greenhouse emissions,
as certified by the Australian government
Make a detailed list of what food you eat in a day – a food diary.
Keep an energy diary for the day – how much energy do you
consume in the form of electricity, gas, or petrol in a day.
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Did your energy diary and ‘low
How does the amount of energy you use in your body compare
carbon day’ make you think it
with the amount of energy you use in other aspects of your life?
would be easy or hard to reduce
What do you think an energy diary from someone who lives in
emission by 60% by 2020?
rural Bangladesh looks like?
http://en.wikipedia.org/wiki/List_of_countries_by_carbon_dioxide_
Do you think it is reasonable to
expect people to pay more for
electricity if it reduces
greenhouse emissions?
emissions_per_capita
Were you surprised by the relative costs of different types of
energy?
How do different students’ energy diaries compare? What
accounts for the differences (could be the amount of energy used,
fuel type, distance from school, lifestyle, etc.)
What are the emissions factors for electricity, natural gas and
petrol?
Why is the emission factor for electricity so high in Australia?
Does this mean that electricity is a bad form of energy? What
options are available to reduce its emissions intensity?
Gas is a lower emissions fuel than electricity, but still a fossil fuel.
How should it be viewed in the context of greenhouse emissions?
1. Prepare graphs comparing energy used, cost and emissions
generated from the three different activities
2. Hold a ‘low carbon day’ in which students and teachers aim to
minimise their energy usage and hence their carbon footprint
3. Draw up a ‘reflections board’ for the whole class coming out of:
a) What it was like to consciously choose activities that wouldn't
use energy/generate emission, and
b) Can you imagine living like this all the time?
4. Prepare another series of graphs showing the difference
between a normal day and the low carbon day
5. Prepare the same graphs using costs and emissions factors if
Green Power is purchased for all electricity use
Some of these activities could be used to produce 2020 Vision
competition entries.
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Indirect Emissions:
http://www.energysave.energyaus
tralia.com.au/carbon_emissions__
and__you/learn/3.0_your_emissio
ns/your_emissions
This is a back of the envelope calculation for carbon dioxide
emissions from eating food. It seems to align quite well with
various numbers on the web.
Most energy is derived from sugars, oils or starches; these will
typically have CH2 or CH2O as their main component.
In the case of oils, 12/14 of the mass is therefore carbon.
Emissions Factors:
http://aie.org.au/Content/Navigati
onMenu/Resources/EnergyData/E
nergy_Value_Greenh.htm
In the case of starches and sugars 12/30 of the mass is therefore
carbon.
100g of oil contains 3800 KJ of energy
(these values are
100g of starch contains 1460 KJ of energy
Costs:
http://www.actewagl.com.au/price
s/home/
packets)
100g of sugar contains 1700 KJ of energy
Emissions per MJ (Oil Calculation):
CH2 + O2
List of countries by carbon dioxide
emissions per capita:
from food
CO2 + H2O
14g
44g
In other words, 14g of oil produces 44g of carbon dioxide
http://en.wikipedia.org/wiki/List_
So how much does 100 g produce?
of_countries_by_carbon_dioxide_e
100/14 × 44 = 324g of CO2
missions_per_capita
100g of oil contains 3.8MJ of energy.
Therefore 324/3.8 = 82.7g of CO2/MJ of energy consumed.
As noted, indirect emissions from food are quite substantial, for
example in the case of eating meat or food that may have been
transported by air. The purpose of this module is not to provide
exact values, but to promote understanding around energy use and
emissions. If students are interested, they can be encouraged to do
further research.
Sample Calculation of Energy Used (Q) to Heat Water
m = mass of water in kg (same as litres); dT = the change in
temperature; Cp = specific heat capacity of water = 4.18 KJ/KgºC;
Q = Cp m dT
Lee has an 8 minute shower in the morning. He uses a low flow
shower head that delivers 9 litres of water per minute. Therefore
the mass of water used is 8 x 9 = 72 litres or kg. Average shower
temperature is 40 degrees Celsius (this can also be measured).
Cold water starts at an average temperature of 15 ºC.
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Therefore Q = 4.18 × 72 × (40-15) = 7524KJ