Rooftop solar and battery storage take centre stage in W.A energy transition

Rooftop solar and battery storage take centre stage in W.A energy transition

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Rooftop solar and battery storage to play central role in WA energy transition, but the state’s new 20-year blueprint does not include stretch climate targets.

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Western Australia has unveiled its first 20-year blueprint into how the clean energy transition may evolve in its uniquely isolated grid, and it seems clear that rooftop solar PV and battery storage will take centre stage.

The Whole of System Plan – an 18-month piece of work led by a specially formed task-force, with input from the Australian Energy Market Operator, the state government and the state’s main utilities – is similar to AEMO’s Integrated System Plan for Australia’s main grid, but it applies only to WA’s South West Interconnected System, possibly the world’s biggest isolated grid.

That makes it both an interesting and challenging exercise, and there are a couple of key takeaways from the document: In all four scenarios modelled – confusingly given movie names such as Cast Away, Groundhog Day, Techtopia and Double Trouble – renewables account for at least 70 per cent of installed capacity and sixty per cent of generation.

But the WOSP does not include stretch “climate” targets that form a key part of the ISP. The emissions reductions over the next 20 years are comparatively modest – no more than 50 per cent in absolute terms. There are no scenarios that model the complete exit of coal, and two of the scenarios that represent low operational demand assume little or no new large scale wind and solar projects over the next decade.

Instead, rooftop solar and battery storage, along with demand management, form the core of the two low demand scenarios, Cast Away and Groundhog Day. For reasons not entirely clear to this reader, rooftop solar plays only a minor role in the higher demand scenarios, where larger scale wind and solar assume a greater role and where new transmission and gas fired generation is also required.

The taskforce makes clear that it does not believe any of these scenarios described will be the actual outcome. Instead, it says they are  the best bets that can be made for now on how the transition may evolve, and what actually happens is likely to be an amalgam, and the WOSP will be updated as the future becomes clear.

The key message from state energy minister Bill Johnston, who launched the WOSP on Monday, was that renewable generation is expected to triple by 2040, rooftop solar will continue to displace traditional forms of generation, particularly coal, and battery storage will also play a big part in the state’s future, not just filling in the gaps in generation but also providing key grid services.

“It’s the most comprehensive modelling study ever undertaken into the future of WA’s electricity system and it will support our transition to low-cost electricity,” Johnston said in a statement before a briefing on Monday.

“Our state is embracing renewable generation, with one in three households having rooftop solar panels, this signifies that battery storage will play an important role in our future.”

But there is bad news for aspiring developers of large scale wind and solar projects. The state is just now completing a rush of new installations including the 214MW Yandin wind farm, the 180MW Warradarge wind farm and the 100MW Merredin solar farm. But according to the WOSP, that’s about it for the next few years.In the two low demand scenarios, there is room for only one smallish wind farm out to 2030, and no large scale solar. The outlook changes in the high demand scenarios, but only because the modellers assume that rooftop solar growth will not be as strong because the large scale wind and solar will reduce power prices and so reduce the incentive for rooftop solar.

But then the document says this about rooftop PV.

“The modelling assumes rooftop PV systems automatically form part of the lowest cost to supply. The reason for this is two-fold. Firstly, there is no cost attributed to installing new rooftop PV capacity – the systems are paid for and installed by individual customers.

Secondly, the surplus energy produced by rooftop PV systems spills out into the network throughout the day, meaning it is effectively ‘dispatched’ ahead of all other capacity, displaces all forms of large-scale generation and imposes additional ESS requirements on the system.”


That seems slightly contradictory. In any case, the various scenarios assume that the level of rooftop solar PV in the SWIS increases from 1,291MW in 2020 to 2,258MW and 5,037MW by 2030 – anything from a doubling to a more than four fold increase (see graph above).

“The growth in rooftop PV in Groundhog Day outstrips what is required to meet both end-user and peak demand,” it says. “This has allowed the WOSP to test the implications of extreme rooftop PV growth, levels of curtailment and impact on power system security.” Significant curtailment of solar PV is likely to occur when its capacity exceeds 2,700MW from 2025.

While this sounds deeply problematic, it also notes this: “Under all scenarios, a common theme is that the volume and density of rooftop PV in the grid provides an opportunity for large numbers of individual systems to be aggregated and coordinated to provide energy and ESS (system services), where capable, into the WEM.”

And it notes that this is  a validation for the DER roadmap that was unveiled earlier this year, flagging tighter standards on inverters and protocols that would allow either the introduction of “dynamic exports”, or the switching off of rooftop solar when needed. As it turns out, South Australia is entering that regime already.

The outlook for battery storage appears to be stronger and has more clarity, with a mix of two hour and four hour battery storage. But that may be a moot point now, given that since this document was delivered to the government in August, the government has already announced its intention to build a 100MW battery, with likely two hours storage, in the next year.

So that mandate would appear to take care of the forecasts considered in the table above, although it should be noted that W.A. is also installing a significant amount of household and “community” scale battery storage, which should be able to absorb some of the local network issue of soaring rooftop solar PV.

Unlike AEMO’s ISP, the WOSP does not envisage the complete elimination of coal by 2040, but it does admit that it may struggle to survive. In some scenarios, half of the coal capacity could be removed within five years.

In the high demand scenarios, the remaining coal plants may operate at only half their capacity, but in the low demand scenarios – where rooftop solar PV becomes the dominant player – then coal struggles to be economic at all. Some observers have expressed surprise that the WOSP should assume that coal remains in the grid in all scenarios.

“In Cast Away and Groundhog Day, the amount of end-user demand being met by rooftop PV systems continues to increase. As a result, there is less opportunity for coal to operate as baseload generation and fewer coal-fired generation facilities can be run continuously,” it says.

“Therefore, in the Cast Away or Groundhog Day scenarios, where operational demand has plateaued or is in decline, coal-fired generation becomes economically marginal.”

Like coal, gas has a better future in the high demand scenarios than the low demand scenarios. In low demand, there is no gas for any new gas generators, because the gas generators already built to back up the existing fossil fuel fleet are enough to support the transition to renewables. Only in the high demand scenarios is there need for new gas generators, but these will be fast start units used more sparingly.

Where does this leave emissions? WA already has a lower level of emissions per unit of power (emissions intensity) than the grid on the eastern states, and also the scenarios suggest at least a halving in emissions intensity over the next 20 years. The biggest falls in emissions intensity comes with the higher demand scenarios, because of the amount of new large scale wind and solar into the grid.

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