Were you one of those who thought maths was a waste of time in school? Well maybe you should think again…

This little bit of knowledge may seem minor, but it plays a big role in determining whether or not your lights come on every time you flick the switch.

We’re talking about Probability of Exceedance (PoE).

Never heard of it? Here’s a rundown of what PoEs are and why they are important in maintaining the energy demand and supply balance in Australia.

In simple terms, PoE is a method of measuring any data that can vary. By placing an upper and lower limit on the observations, PoE can be used to measure anything from traffic speeds to how much you weigh, or even how fast you ride your bicycle to work in the morning.

At AEMO, PoEs are used in a number of important forecasting functions, including to forecast energy demand, wind, and solar generation. These forecasts range from as little as five minutes ahead of real time, to days, weeks and years in advance.

A PoE is generally organised in a distribution curve and uses 90, 50, and 10 marker values to present and measure data. The 50 PoE mark is the average, or middle value, in any range of measurement and the most likely scenario to occur. This means 90% of the data will be greater than the 90 PoE marker and only 10% of the measured data will be higher than the 10 PoE.

Example of what a PoE curve would look like.

Confused? Well here’s an example to shed some light on how this works.

For instance, if the weather forecaster at AEMO notes that the 90, 50 and 10 PoE temperatures for tomorrow will be 25, 26 and 27 degrees, we can be fairly confident that the mostly likely temperature will be 26 degrees, resulting in relatively low electricity demand.

The PoE forecast as explained above.
Now imagine that the weather forecaster observed the 90, 50 and 10 PoE peak temperatures tomorrow at 32, 38 and 45 degrees. Based on the calculations, we anticipate the mercury to hit 38 degrees but not 45 degrees.
A forecast for higher temperatures that could lead to higher demand.

In this way, PoE helps us forecast the most likely scenario, and therefore ensure there is enough energy generation available to meet the likely electricity demand and manage any risk that it might peak higher.

AEMO’s role as Australia’s power system operator is to maintain the supply and demand balance in the system, and the use of PoE is just one of the many tools at work behind the scenes at AEMO to ensure your home and business is supplied with the energy you need, when you need it!