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Also referred to as low load or system low, and illustrated in the ‘Duck Curve’, Minimum Demand is a challenge facing energy networks around the world.

Minimum Demand is the lowest level of energy demanded from the grid at a point in time. Under certain scenarios it can present challenges that can place the grid under strain and make the energy system vulnerable.

Low demand typically occurs during daylight hours in autumn and spring, on cloud-free sunny days, when temperatures are mild enough that larger energy consuming devices such as heaters, air conditioners and pool pumps aren’t turned on. 

It is also more likely on sunny weekends or public holidays, when offices and large industry are off for the weekend and are not using power. The graph below is a clear example of this, with rooftop solar providing more than two-thirds (70%) of the State's electricity needs at that time. 

WEM operational demand fuel mix (25 September 2023)

WEM operational demand fuel mix graph

Image source: AEMO DPV Data Dashboard

With one in three households having their own rooftop solar generation, more solar is being exported than we can balance with demand.

At those times, we need to respond to the high quantities of solar being generated and exported into the grid to maintain and ensure grid stability. Without solar management measures, Minimum Demand could lead to widespread outages.

It’s critical that these measures are in place, as it takes far longer to fully restore a power system – a matter of physics, and not unique to Western Australia.

Aerial view of a houses in a suburban street which have solar panels installed on the roof

The SWIS is one of the largest stand-alone power grids in the world, around the same size as the United Kingdom and more than four times the size of Tasmania.

However, the number of electricity users is far lower than on other large grids, meaning we have a low density of customer connections.

The SWIS is also a fully islanded grid – it has no interconnectors to other grids. Most, if not all, other large grids rely on interconnectors to help them ride through system balance challenges.

As renewable energy supply increases, we are using fewer thermal generators that can be quickly dispatched to meet energy demand. This can make it difficult to maintain a secure balance when demand is very low.

However we have a number of short and long-term strategies in place to ensure we can manage Minimum Demand and continue to enable more rooftop solar uptake by residents and businesses.