E NE RG Y MAT TER S
FACT SHEET 6:
UNDERSTANDING ENERGY DEMAND
The energy load is simply a measure of
how much energy (usually electricity) that
a user requires. It is normally measured in
kilowatt-hours (kWhr), being the standard
way to measure electrical energy
consumption (gas consumption is
measured in megajoules).
There are a number of ways that it can
be characterised.
Base Load
This is the minimum energy demand for a
facility (house, office, factory etc). Except
in the circumstances of complete
shutdown, it is very unlikely there will be a
time that a facility will turn every single
energy-consuming item off.
Actual Load
This is the amount of electricity being used
at any given time, and reflects the number
of devices that are switched, and how
much current they are drawing.
Exercise 2
Classify the following domestic electrical
devices are high, medium or low load.
Oven
Clothes dryer
Computer
Light
Exercise 1
When you go to TAFE and the house is
empty – electricity is still being used. What
are some examples of devices using
power when no one is there?
TV
Kettle
Microwave
Exercise 3
What data would you need to identify the
load demanded by a new electrical
device?
Where would you find this information?
Identifying just what is contributing to the
base load can help in reducing energy use
because it may be that some of these
devices can be conveniently switched off
when not in use.
Average Load
This is not surprisingly the total energy
used divided by the time period, and
allows you compare usage from different
time periods, eg KWhr/day. For example,
electricity bills often show average daily
usage from other billing periods (see Fact
Sheet: Understanding your Electricity
Bill). Since the billing period is not always
the same, the total load will be different, so
the average is provided.
Exercise 4
What is the average daily load if the total
electricity usage is 1742.8 kWhr for a
period of 94 days?
Peak Load
This is the maximum actual load required
for a given time period, and indicates that
more devices, especially the high-demand
ones, are being used at the same time.
Exercise 6
Why is this event – not enough electricity
to meet demand – called a brown-out?
A brown-out will create bad publicity for
the energy supplier, and the “demand” to
create more capacity. Building more a
power station costs a lot of money, and
since it won’t be needed most of the time,
it would be wasted money.
The way that suppliers try to cope
with this is to encourage users to spread
their usage out, (as well as reducing it
overall of course). For households, offpeak electricity for water heating is an
example of this. A different strategy is
used for large-scale users (eg aluminium
smelters, office blocks), and is explained in
the next section.
Load Factor
This is a calculated value, as shown below.
Exercise 5
Identify average, peak and base load on
the graph of actual load on the next page.
For domestic households (at this time), it
is not important, as it simply adds more
kWhr to the bill. For electricity suppliers
it is a problem, and large industrial and
commercial users, it is a cost issue.
For electricity suppliers needing to
meet the total load for all users on the grid,
sudden surges in load stretch their ability
to meet demand. They need to have the
capacity to supply the peak, but that
capacity may not be required for the rest of
the time.
For example, on a very hot summer’s
day, when everyone comes home and turns
on their air conditioner, the total
electricity required is high. If there is not
enough being generated, no one will get
enough electricity and a “brown-out” will
occur.
Energy Matters 6: Understanding Energy Demand
Load Factor =
Average Load
Peak Load
Exercise 7
Calculate the load factors for the following
two users.
User A
20
15
80
20
25
25
50
30
35
User B
20
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Exercise 8
Which is the better situation for the energy
supplier: a low or high load factor? Why?
Exercise 9
How much electricity units would Users A
& B from Exercise 7 be charged for?
User A
User B
For large-scale energy users, their
electricity costs are not simply a matter of
the number of kWhr (as with households),
but are dependent on their load factor.
Instead of paying for how much they use,
they are charged on the basis of their
maximum demand during the billing
period! The bill “assumes” usage
equivalent to the peak for the entire
period.
Energy Matters 6: Understanding Energy Demand
Therefore, it makes economic sense to
avoid times where high demand
equipment is switched on simultaneously,
minimising the peaks.
This does requiring a metering system
which is capable of recording more than
just the total load. The new meters can
record, store and upload electricity usage
at 15 minute intervals, and these are not
just intended for industrial users, but are
being rolled out for households as well.
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