A picture to illustrate the power of rooftop solar

Solar panels being installed on a roof (rooftop solar)
Image: Shutterstock

By Phil Kreveld

At the recent Australian Financial Review Energy Summit, AEMC chair Anna Collyer said it was always easy to ask why more has not been done, and there is always more to do, but Australia is so far ahead of the rest of the world with its take-up of consumer energy resources that “we don’t have any examples to follow here”.

“We are, step-by-step, inventing and implementing entirely new fields of policy and engineering,” Collyer said.

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She also acknowledged that integrating rapidly growing consumer energy resources, such as rooftop solar and household batteries, into the power grid is a huge opportunity that has not been grasped quickly enough.

And that is enough of a lead-in to the diagram of a typical distribution network with lots of rooftop solar (blue-coloured). According to Collyer “consumer energy resources will be at least 20% of our energy solution, but it is not getting 20% of our attention’’ and “that has to change.”

A short technical explanation for those interested. Rooftop solar inverters (blue coloured) are ‘grid following’ and therefore require a stable source of voltage. This is supplied by the grid-forming (voltage-forming) inverter (GFMI) connected to sub-transmission. When the distribution network is pushing out power the battery energy storage system (BESS) is being charged so that in that instance, the GFMI can provide reactive power to support stable voltage for the rooftop solar inverters, drawing virtually no real (useful) power. The BESS can also receive energy from transmission, therefore providing a virtual additional line. The GFMI, being equipped with droop-control, works in harmony with the generators connected to the transmission grid. In instances of black-out, the BESS-GFMI can restart the distribution network, and then resynchronise with the transmission grid when distant energy sources have restarted.

So, here’s a change! The red boxes-and big battery energy storage system, at the edge of the light-grey coloured distribution network, is what we should be putting into the distribution substations instead of ‘futzing around’ with community batteries, and ever-more complicated ways (marketing schemes) for solar owners to derive some commercial benefit from energy trading.

The benefit of the illustrated scheme is that it would make many distribution networks in the sunny states close to independent of transmission—and for instances where externally transmitted energy is often required, congestion would be relieved by the BESS as it is a virtual extra transmission link. Considering that transmission costs are rising and rising, dwarfing wholesale energy at times of surplus generation, a big economic advantage could be gained. But there’s more because in the event of a black-out, distribution networks could self-start, a bit like the under-desk, uninterruptible power supplies for desk-top computers.

Distribution networks in their entirety, per the above graphic example, would become ‘prosumers’. Of course that would require considerable capital expenditure in those networks but that could be offset by capital savings in transmission projects (defying the mantra of ‘no transition without transmission’). Yes, a whole-of-system analysis would have to support the proposed project described here in outline. Right now, the rules are that networks cannot be generators of electricity—only their millions of connected customers. However, the Australian Competition and Consumer Commission (ACCC) has just waved through Brookfield’s plan to acquire Origin with Brookfield becoming owner of generation and transmission—in the interests of the nation. And so is the scheme proposed here in the interests of the nation!

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Right now, a quagmire of rules, regulations, government interference and planning silos stuff up attempts at ‘whole of grid’ solutions. When AEMO was questioned on the possibility of rendering distribution networks more independent, the answer was evasive. More’s the pity! Any outsider’s view of the National Electricity Market is one of government-interfering complexity-one that is discouraging to investors, frustrating to owners of generating assets and of not making use of our rooftop assets. In short, shareholder interests in transmission investments, political expediency and wishful thinking as opposed to the hard yakka of real system planning might cater to short term interests but at the expense of a reliable, cost-effective national electricity system catering for sensibly-set renewable targets.

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