Dispatchability: Deception on demand

[Post updated July 9 2024 to include the AEMO definition of dispatchable capacity and a couple of other minor edits]

This post is all about dispatchability. You will have heard that as coal plants close we need more dispatchable electricity generation.

Here is the AEMO definition of "Dispatchable capacity" from the Glossary in the 2024 Integrated System Plan (emphasis added):

The total amount of generation that can be turned on or off, without being dependent on the weather. Dispatchable capacity is required to provide firming during periods of low variable renewable energy output in the NEM.

In October 2023, Chris Bowen put out a press release: “Joint media release: Registration opens for dispatchable renewable energy projects in SA and Vic”. There are others in other states. They are all part of the Capacity Investment Scheme. The body of the release uses the word dispatchable 7 times but also demonstrates that Bowen (and whoever else wrote the release) has a very poor grasp of the concept.

The folks at Australian Energy Market Operator (AEMO) know exactly what dispatchability means. And yet they occasionally seem to misuse it in mysterious ways in the Integrated System Plan (ISP) that match the Bowen concept. For example, the AEMO 2024 ISP has a chart showing the current amount of dispatchable electricity and its “growth” as we move toward 2050. But the chart uses a very different definition on its left hand side to the definition on its right hand side; at the 2050 target.

First let’s explain the concept.

Get it when you want it

Firstly, the dispatchability is about the generation of electricity; not its delivery.

Think about water. Taps are generators. Pipes and garden hoses are delivery. Electricity delivery is typically split into transmission, the big towers and cables operating at high voltages, and distribution, the smaller stuff operating at lower voltages along your street.

Household taps are almost always dispatchable. Meaning you always get water out when you turn them on; unless you have received a letter telling you the water will be off between such and such times, or someone with a back hoe has seriously misread their plan of where the water pipes run and put a digger through them.

But what about a tap on a tank in your back yard?

Suddenly we have a complication. My tank taps are mostly dispatchable in winter when we have rain in Adelaide, but definitely not dispatchable toward the end of summer. So the concept starts to look a little vague.

The tap is dispatchable if the tank has water, but not if it doesn’t. A tap on a big tank might be reasonably expected to be dispatchable more often than one which is on a small tank.

Electricity is the similar. A coal/gas/nuclear generator is dispatchable if it’s fuel source is reliable. A hydro dam is dispatchable when there is water in the dam. A battery is dispatchable when it is charged but not when it isn’t.

Best to split the concept: AEMO dispatchability and Bowen dispatchability.

Can we replace coal, which is AEMO dispatchable, with something like a battery which is only Bowen dispatchable?

But there is another complication which matters. The where of it.

Get it where you want it

An AEMO dispatchable source of electricity is one that is always available when you need it. But it’s actually better to say “always there” than “always available”. It’s no good having a generator in working condition in Queensland when you need the electricity in South Australia.

There is a spatial component to dispatchability.

You can subscribe (at no cost), to an AEMO service that will email you notices whenever it expects the grid in a region to be short of dispatchable electricity.

These notices might be thought of as planning information when they are a year or so into the future; which they can be. But when they are for next week, or tomorrow, then they are deadly serious warnings for generators that they’d better finish whatever has taken them off line and get ready to rock ’n roll.

Transmission lines can certainly move power between states, say from Victoria to South Australia (SA), but, like water pipes, they come in different sizes and the flow is limited.

Transmission lines let you add dispatchability by using a tap somewhere else.

For example, the new interconnector between South Australia and NSW (called Project EnergyConnect (PEC)) was supposed to cost around $2.3 billion; but that has blown out.

It’s supposed to come on-line in 2027 and reduce the potential for SA to be isolated from the rest of the grid in the event of one of the other transmission lines going down. Without these transmission lines, SA is burnt toast. We no longer have enough dispatchable power to cover renewable shortfalls.

How much power can PEC transmit? About 800 megawatts (MW).

The Australian Financial Review (AFR) article I linked to reckons that PEC will all the connection of 2,000 MW of renewables to the grid.

Did any lights flash in your brain?

Can you spot the difference between 800 and 2,000? It doesn’t matter how hard the wind is blowing or how brightly the sun is shining, you won’t deliver more than 800 MW of those 2,000 MW to South Australia. It’s pretty likely that those 2,000 will also be choked off going in the other direction as well.

What’s it for?

We rely on dispatchable power to cope with peaks, but we also need it to get us through a still night, or a run of still nights.

On the night of March 12, 2024, SA had 8 hours where the wind power averaged about 166 MW; about 12% of the maximum 8 hour average during that week. A 1, 2 or even 4 hour battery is useless for dealing with such nights. Household batteries are not dispatchable. Utility batteries with 1, 2, 4, or even 8 hours of storage are not dispatchable. They will not get us through one still night, let alone a string of such nights.

If you look at the Bowen press release I mentioned at the start of this piece you will see that Bowen hasn’t got a clue what “dispatchable” means. He thinks a 2 hour battery is dispatchable. It isn't. It is weather dependent. Is he lying? Of course not, that would imply he understood the concept.

The AEMO ISP

I said before that AEMO knows exactly what dispatchable means, so when they use the term wrongly, its reasonable to think there is a reason; perhaps political interference, perhaps sucking up to the Government of the day. Whatever the reason, it shouldn’t happen.

Now consider the following figure from the 2024 AEMO ISP. It shows the evolution of the capacity (which means power and not energy) as AEMO envisages it.

Note the line showing a steady increase in dispatchable electricity out to 2050. By the time we get to 2050, most of that electricity isn’t dispatchable; it’s home batteries that will run for an hour or two.

Batteries are at best, Bowen dispatchability, but not AEMO dispatchability. If you have a battery charged by a gas power plant, or nuclear reactor, then it is still dispatchable because it isn't dependent on the weather, but if your battery is charged by a weather dependent source, then it isn't dispatchable. As you can see, on the left hand side dispatchability means

hard dispatchability, but by 2050, it means something else.

Now here’s a corrected graph showing the actual dispatchable capacity in the system

envisaged by AEMO.

So did Bowen instruct AEMO to mislead people with their graph? I’ve no idea, but I’m

quite sure that everybody in AEMO knows exactly what dispatchable means.