Ty Christopher, Director of the Energy Futures Network at the University of Wollongong, explains some fundamental laws of physics and why solar has its limits.

What percentage of the grid can solar realistically provide? 

That is difficult to answer because if you start taking it at the total macro level, you're not being fair to things. 

I'll give you an example. 

Just think of it in terms of carbon footprint. 80% of the carbon footprint of the Illawarra is BlueScope Steel. So you could take all of the CBD, every single home, every business, the port, everything in the Illawarra to net zero carbon. And if you do nothing with BlueScope, at the end of all of that, you've still got 80% of your emissions. 

So asking as a percentage of the grid in total what solar can contribute is not being fair to what it can do in terms of impact. Because the grid is dominated by these big energy users that have to have different types of solutions applied to decarbonise their activities, the big energy solutions. 

So what I would say is that solar on homes and large solar arrays last year (2023) generated around 23% of the energy into the grid in total over the course of the year. 

At the moment, the rapid growth of both big solar and solar farms is starting to keep pace with home solar, now some of the Renewable Energy Zones are starting to unlock. But it's fair to say that, in volume, the amount of solar coming into the grid is still dominated by solar on homes, not big solar farms. 

There's 23 gigawatts of solar capacity on homes at the moment in the grid. And there's in the low teens of gigawatt capacity, in terms of big solar farms. So realistically, at this point in time, we've got a third of homes, give or take, and they're currently contributing, call it around 15% of the energy into the grid from those homes. 

So theoretically you could multiply that by another two times and you could get to say, 45% of the energy in the grid could come from solar on homes theoretically. 

But I think saying that starts to ignore some of the fundamental laws of physics. 

The fact of it is that all of this lovely solar is connected to the grid via the skinniest wires in the grid. 

The wires that connect your home to the grid are about as thick as your pinky at best. There's only so much energy can flow through that wire, regardless of the direction that it's flowing, whether it's being exported by the home or whether it's being imported by the home. 

And similarly, it connects to a not very much fatter wire in the street that is subject to those same fundamental laws of physics. 

So what that means is, even if you were generating this massive amount of energy on all of these homes, the wires aren't fat enough to get it to flow back up the grid to the high voltage components of the grid where it can transfer across and flow back down to big energy users, for example. 

So the important focus of home energy generation and distributed energy resources such as solar on homes and solar on businesses, needs to be consumption of that solar generated electricity within the business and home, and then consumption of the solar generated electricity within the local street or streets where the energy is generated, because you are working within the physical limits, the physics of the thickness of the wires and their ability to transfer power around. 

And what I think we'll start to see is a natural saturation point where before we get to 100 percent of homes having solar, we get to a point where we are actually generating enough solar for that suburb already. 

And the physics will actually dictate that you will hit the limit of what you can generate and use locally. The physics will probably kick in first, before we reach a point where every single home has solar. 

And are those skinny wires something that can never be changed? 

Of course, they can be changed – at great expense. 

More so than building offshore wind, or nuclear?

You would be surprised. Mobilising people and machines and rebuilding existing electricity grids is tremendously expensive, especially when you start getting into areas with underground electricity assets. 

As soon as you're digging in the ground, it’s literally dig a hole, start throwing money in it, and then throw a match in and set fire to it. 

It’s driveways restoration, people's gardens, think about all these new lovely suburbs with underground power and new landscaping, and going and just digging them all up and laying new and fatter wires. 

And then the question is, well, how, how much larger wires do you lay? What technology will come later on? 

So we're talking billions, many, many billions of dollars. 

There's been studies done in the past going back two decades where there's been calls for undergrounding all of the electricity grid and it came to tens of billions of dollars to underground the electricity grid just in New South Wales. 

So can it be done? 

The answer is: of course it can. I'm an engineer, throw money at me, I'll give you anything you want. The question is, is that really in the best interest of us all as a community? 

What's the invested carbon in doing all of that work as opposed to getting our suburbs to the point where, as I would call it, they're grid light in how they operate and they only propose a very modest electricity demand on the grid and that at a time when the electricity grid's more than able to cope or whatever. And I'm talking here in the hours between midnight and 6:00 AM.

So if you can get the suburbs so that, through the course of the day, they are running on the sun and storing unused electricity both thermally (in hot water) and chemically (in batteries) through a combination of home batteries, EV car batteries, and community batteries, then we could extend the solar window past when the sun's gone down right out towards eight or nine PM at night. 

And then only at that later point in the evening would the suburb start to be putting a little bit of energy demand on the main grid. 

And then the sun comes up in the morning, and rinse and repeat. 

That looks to me like the best economic, the lowest net carbon footprint. 

And if you're sharing the energy equitably, the best social outcome for all of this, if for no other reason than it makes maximum utilisation of the billions of dollars of grid assets that are already there.

Ty Christopher, Endeavour Energy’s former ‘chief engineer’, is an electrical engineer who brings 37 years of hands-on experience in the power supply industry to his current role as Director of the Energy Futures Network at the University of Wollongong.

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