Supplying the bulk of electricity in Western Australia by wind
This webpage explores the limits of the amount of wind generation
that can be installed on the South West Interconnected System or
Load versus Accumulated Hours a
Timestamp data for the South West Interconnected System
(SWIS) as shown in Figure 1 was obtained from Western Power for
one year, April 05 to March 06, at half hour intervals, to calculate
the graph in Figure 2.
Figure 1, Sample of Timestamp data for the
The load in MW was graphed against accumulated hours a year for
WA's electricity consumption on the SWIS - just under 15,000 GWh.
Figure 2, SWIS versus Accumulated Hrs/yr
From this graph, we can see that the baseload was just over a
third the maximum load, and the average just over half the maximum.
This means that the system already has load following capability
of two thirds the maximum load, ie just under 2000MW.
Windspeed Distribution and Power
Based on the 800kW Enercon E48 wind turbine, a typical powercurve
- if somewhat smaller than most modern machines.
Figure 3, Windspeed versus Power Output and Distribution
Wind distribution is based on a year's worth of wind data from
a mast on top of Mt Barker Hill, 70km north of Albany (and the
coast) on the highway. The electricity generated by the wind turbine
is the product of these two curves. The windspeeds have been doctored
to give a modest Capacity Factor, CF, of 0.35 ~ around 2,300 MWh/y.
Now, we can combine the two curves by recalculating the distribution
curve as accumulating hours a year and graphing it against the
corresponding power output for that windspeed. Ie at 6m/s, the
distribution is 1075 hours a year, including the hours at windspeeds
lower than 6m/s, we get 3716 accumulated hours, the output at
6m/s is 120kW.
At 12m/s, the accumulated hours are 8391 hours and
the power output is 750kW.
Combining the distribution curve and the power curve
provides a single curve for a single turbine ie output for one turbine
will look something like this. This is a single turbine supplying
electricity to roughly 500 people.
Figure 4, Power versus Accumulation Hrs/yr
Of course, more turbines, more windfarms more geographically spread
will give a flatter curve, it will be rare that the wind will
be strong or weak, everywhere.
An idea of how much flatter is given by looking at data from four
different sites. In this case, 1 years worth of half hourly data
at Bureau of Meteorology (BoM) sites around the SWIS, the wind speeds
were multiplied by a single factor selected to give a capacity factor
of 35% with an E48 power curve. It is assumed that the variation
in windspeed at the BoM sites will be representative of what would
be expected from a windfarm.
Figure 6, % Power versus Accumulated Hrs/yr
The average for all sites is shown below, however, we ought be
looking not at the average, but at the average of all the wind
farms every half an hour;
Figure 7, Average and Real Time Average
The resulting curve is somewhat different, and this illustrates
what we mean be geographical dispersion. Adding the production
from windfarms at all four sites at the same time gives a flatter
curve, as fronts pass through, one windfarm will be producing
when the other is not, similarly, it will be also rare for both
to be producing at full power or not at all. What is really interesting
are the very few hours above 80% of full output.
From a study of Nordic countries by H. Holttinen, Hourly Wind
Power Variations and Their Impact on the Nordic Power System,
2003, Helsinki University of Technology, come very similar looking
Figure 8, Nordic curves of wind production
vs accummulated hours
2000MW of wind plant
Back to the SWIS, from Figure 2 we see the system can cope with
nearly 2000MW of variable load. But 2000MW intermittant supply
of energy by the wind?! 2000MW is greater than our minimum of
1100MW so there will be times of the year when the wind plant
will need to be derated. How often and how much will the wind
The difference between the load and the energy generated
for each half hour for the year April 05 to March 06 is calculated.
Figure 9, SWIS Load vs 2000 MW of Wind Plant in
Figure 10, SWIS and 2000MW Wind Generation
From the above graph, the area between the two curves is the wind
energy generated. This is about 41% penetration. The area above
the blue curve and below the Accumulated Hrs/yr axis is excess
wind energy which occurs when the load is less than the wind plant
produces - this is around 1% of the overall wind generation. The
remaining electricity generation required is under the rest of
the blue curve.
Why the tiny excess?
Why, when the lowest load is almost half the 2000MW of wind plant,
is only 1% of the electricity generated by the wind in excess?
Figure 11, Combined Output vs Accummulated
Consider the curve of the combined output of the
2000MW of windfarm vs the accummulated hours a year, despite the
leveling impact of geographical distribution, for 70% of the year,
the total output is still less than 50% of maximum, ie for most
of the time, the impact of the 2000MW is less than 1000MW.
In addition, a look at the time of day curves, shows
that, on average, the output roughly matches the load.
Figure 12, SWIS and 2000MW Wind Generation Time
What does 2000MW look like?
- At 5MW/square kilometre, we need 400km2
- SWIS covers 322,000km2 (1 ½ size
- 400km2 could be 2km x 200km which
compares with a north south distance of the SWIS of some 1600km
Figure 13, Possible Windfarm Locations, 200MW sites
- Number of jobs in construction, 2,960 jobs for 5 years*
- Number of jobs in operation, 216 permanent jobs**
- Total job years = 16,160
- Equivalent to 733MW of coal (at 90% Capacity Factor)
Based on 20 year life
*assumes 7.4 job years/MW if job 100%
local, Dr Robert Passey , March 2003 Driving Investment, Generating
Jobs Report, p17
**assumes 37 job years / TWh Dr Robert Passey , March 2003 Driving
Investment, Generating Jobs Report, p17
Wind generated energy would now supply 56% of what is
consumed, an increase of 34% from the increase of 50% in capacity.
Excess is now 10% of wind generation but we now have 2000 hours a
year where the SWIS is supplied entirely by wind!
Figure 14, SWIS, 2000MW and 3000MW of Windplant
|% of total Load
Table 1, 2000MW and 3000MW of Wind vs Load
Figure 15, SWIS, 2000MW and 3000MW vs Time of Day
The two wind plant curves have had the excessive energy
removed. The shaded area is peak for weekdays. There is NO peak period
on the weekend or during public holidays.
An interesting dark horse is the possibility of the
electric vehicles which would easily soak up the excess electricity.
© Copyright 2010 SkyFarming Pty Ltd