May 2021

Purpose. To signal that short-term fluctuations in the wind supply will create more problems for grid control as the installed wind capacity increases.

Background. As long as we have enough conventional power capacity to satisfy our needs, the vagaries of solar and wind power do not threaten the supply, just the stability in the grid.

It was known from the start that wind inputs would be intermittent but there was an expectation that the supply would become more even as the number and geographical extent of windfarms increased.

In 2012 Paul Miskelly published the first major analysis of the system with 2GW of installed capacity and he warned that the problem of wind droughts and rapid fluctuations in the wind supply might not be mitigated with more installed capacity.

Recently “Tony from Oz”, a long-term wind-watcher released a detailed report on fluctuations in the wind supply.

The most important observations.

Over the relatively short period of the study, significant falls in the supply of wind power, equivalent to the size of a typical coal-fired generator, became more prevalent, larger in size and the power loss occurred more quickly.

Over the two years of the study there were 107 separate entries for power losses of 500MW or more within one hour. The highest fall was 980MW on 09May 2020; that is equivalent to two coal power generators going off line in the hour. There were 16 occasions when the fall was 700MW or greater.

Comment. Frequent outages of coal-fired turbines would be regarded as a serious scandal and receive headline treatment in the media. Similar falls in the wind system pass without comment.

Recommendation. That the significance of short-term fluctuations be noted for further investigation and public discussion.


The data are sourced from the continuous record of output from all the registered generators that is kept by the Australian Energy Market Operator. Each wind farm is registered as a generator, likewise the individual generators, often four in number, in coal-fired power stations.

The observations cover 800 days from May 2018 to the end of June 2020.

The number of short-term falls of 500MW or more were counted in periods of one hour or less and in one to three hours. A separate report covered larger falls over longer periods.

The 500MW figure corresponds to the most common capacity of coal-fired generators, so the fall of 500MW can be compared with the impact of a coal-fired generator going off line.


Miskelly 2012

Introduction to the study of fluctuations.
Short-term fluctuations.