A power system is a huge, complex machine. It gets energy from hundreds of large generators and delivers it to millions of households and businesses of all sizes, many of which are also generating their own power. At every millisecond, supply and demand in the system must be in balance. So how does an operator like AEMO keep control of such a complex system?

To run a power system and supply households and businesses with the electricity they need, system operators around the world need two things.

First, the power system has to be predictable. That way, we know what to expect and we are ready to do whatever is needed to keep the system balanced between supply and demand, and operating securely and reliably for consumers.

And, equal first, the power system must be dispatchable. That means we are able to pull any reins we need to, to maintain that balance and secure, reliable operation.

No matter how the power system changes, both these things are needed. Predictability and dispatchability make it possible to keep the system secure, maintain reliable supply, and operate the system efficiently.

Without these two elements, we could have problems leading to equipment tripping off or blackouts, or could spend too much money on resources and infrastructure the system doesn’t need.

What is dispatchability?

Dispatchability means we know we can rely on the resources in the system if we need to ‘dispatch’ or send instructions for them to act in a particular way at any time. ‘Resources’ can include generators and transmission assets that supply power into the system, and also 'demand resources', or consumers changing how much energy they draw from the system.

It helps to understand dispatchability if we break it down into some specific questions:

  • Is the resource controllable? If AEMO asks it to cut back to zero megawatts, or operate to its maximum capacity, or anywhere in between, can that be done? If not fully controllable, can the resource be controlled to any extent? For example, if a wind farm can’t produce more energy (because it can only do that if more wind blows), can it generate less or switch off if needed?
  • Can we be confident the resource will be available when it’s needed? (In the industry, we talk about this as how firm the resource is.) How far in advance can availability be guaranteed? How long can the resource stay available at the requested level? And how dependable is the resource? For example, what is the risk of it breaking down?
  • How flexible is the resource? How fast can it respond to new directions from AEMO when things change? Can it quickly increase or decrease, or switch on or off? Does anything technically restrict it from responding according to its capacity on paper?

For AEMO to operate the system so consumers get the power they need, there need to be enough controllable, firm, and flexible resources in the system to match supply to demand, and enough in reserve in case something major and unexpected happens.

Predicting the future

To have the right mix of resources available in the right place at the right time, we need to be able to predict what the system will need, when, and where. As you can understand, that is not easy. Operators have to know what is happening all the time, and anticipate what is likely to happen in the coming seconds, minutes, hours, days, weeks, years, and even decades.

Predictability means having accurate data about demand and supply, models that show how the system will react to a range of conditions and events, and forecasts everyone can have confidence in. That is a big challenge. For example, everyone knows how hard it is to accurately forecast the weather. But you might not appreciate how the famous unpredictability of weather has become one of the biggest challenges for the predictability of the power system.

To learn more about the link between weather and a reliable power system, listen to our podcast here.

We all use more energy when the weather is more extreme, for cooling and heating. So having a good idea what the weather will do makes it easier to predict demand for power and have enough resources ready. But whether the sun is shining or covered in cloud also makes a big difference to how much energy is generated from solar photovoltaic (PV) systems – big solar farms, and the small PV systems on over 1.5 million Australian rooves.

Did you know that rooftop PV across Australia now adds up to about 5.5 gigawatts (GW) of generating capacity? That’s more than the 2.9 GW Eraring power station in New South Wales (the biggest power station in the National Electricity Market). When rooftop PV is generating, those 1.5 million plus houses and businesses don’t need to draw power from the grid. And when they reduce or stop generation because the sun disappears, that can make a very big difference to demand from the power system.

For big solar and wind farms, of course, less sun or wind means less fuel to supply energy to the power grid.

Also, it’s not just weather that is making both demand and supply much harder to predict. Rooftop PV is managed by the households and businesses that own it, on their side of their electricity meters. These ‘distributed resources’, operated outside the power system, are growing all the time. And they will keep growing, because consumers quite rightly want more control over where their energy comes from and how they use it.

AEMO can’t dispatch these resources – we can’t even see when rooftop PV is being used, let alone predict what it might do. That’s a big deal now, and will have a bigger effect as distributed resources keep growing.

The more things change, the more they stay the same

As we welcome exciting changes in energy that benefit consumers and the environment, we can’t ever lose sight of the basic laws of physics and the things the power system will continue to need.

We are confident that with the right signals to the market, and the right planning, the power system can have the predictability and dispatchability it needs, and the power system of the future in Australia can be at least as secure, reliable, and efficient as the power system of the past.

For a more in-depth read, see our September 2017 advice to the Federal Government on dispatchable resources in the National Electricity Market.