Battery energy storage deployment in Western Australia’s Wholesale Electricity Market (WEM) is rapidly accelerating. Five projects are operational today, totalling 1.4 GW, with a further 1 GW expected to come online over the next three years.

As the system transitions away from coal and the demand for energy storage increases, the delivery of battery energy storage systems will be critical to maintaining system reliability and supporting renewable generation.

This article provides an update on battery energy storage deployment in the NEM, highlighting newly commissioned assets, trends in system size and duration, and how this could change in the future.

Executive summary

• Grid-scale battery capacity reached 1.4 GW in 2025, representing a 2.5× increase over the past 12 months.
• Government-owned batteries make up the majority of the fleet, accounting for ~60% of installed capacity, although this share is expected to fall to about 34% by the end of 2028.
• The average installed battery is 230 MW with a duration of 3.86 hours, while the development pipeline is mostly systems with four hours or more of storage.
• Operational battery capacity could reach 2.5 GW by the end of 2028.

If you are new to the WEM, it’s worth reading our introduction to the market, available here.

WEM grid-scale battery energy storage capacity reached 1.4 GW and 5.3 GWh in Q4 2025

Grid-scale battery energy capacity in the WEM was limited until mid-2024. The first project, Kwinana Stage 1, entered commercial operations in Q2 2023 and remained the only grid-scale battery for more than a year before Kwinana Stage 2 was commissioned.

Since then, three additional systems have reached commercial operation, all located in Collie, south-western Australia. Over the past two quarters, 841 MW of battery capacity has come online, marking two consecutive record quarters for deployment. All projects except Kwinana 1 are four-hour systems, lifting total storage capacity to 5.3 GWh.

360 MW of battery projects are under construction, with a further 700 MW in the pipeline

360 MW of battery capacity is now under construction, with 200 MW expected to commission in the next 12 months. The remaining capacity is scheduled to follow in early 2028.

A further 704 MW of projects sit in the development pipeline across various planning stages. Delivery remains uncertain, but if these projects proceed, installed battery capacity would reach around 2.5 GW by the end of 2028.

​​Wagerup 1, initially scheduled for commissioning in late 2024, has experienced significant delays after former contractors withheld key equipment. Since then, Alinta have engaged with Genus to deliver the remainder of the project. This project is expected to come online by April 2026.

The WEM is seeing a shift towards larger and longer-duration battery energy storage systems

Very large batteries (>200 MW) are the norm in the WEM, with four of the five commissioned systems exceeding this size. This continues a trend that began in late 2024 with the commissioning of the 225 MW Kwinana 2 battery.

Battery durations are also increasing. The average duration across the WEM battery fleet now stands at 3.86 hours. The pipeline is shifting toward longer-duration systems, as batteries must defend a six-hour dispatch window to earn flexible capacity credits. Falling costs for long-duration storage and anticipated coal retirements are also increasing demand for assets capable of sustained load shifting, rather than short-duration peak shaving.

Longer-duration storage receives higher flexible capacity credits

Historically, storage assets were awarded capacity credits based on their ability to sustain output over a four-hour window. In the 2027–28 Reserve Capacity Mechanism, four-hour batteries were accredited at 97% of nameplate capacity for both flexible and peak capacity, whilst two-hour batteries received only 46%.

For the same cycle, the Electric Storage Resource (ESR) Duration Requirement increased to 12 trading intervals (six hours) for assets in the 2027-28 Reserve Capacity Cycle, further strengthening incentives for longer-duration storage.

Synergy has reclaimed its lead as the largest BESS owner after deploying its 500 MW Collie BESS

Synergy is a government-owned gentailer (generator–retailer) that owns the bulk of dispatchable generation in the WEM. Its battery portfolio includes the pilot project at Kwinana and the subsequent expansion, Kwinana Stages 1 and 2.

Neoen briefly overtook Synergy as the largest BESS owner after commissioning its two-stage Collie battery project, Collie Stages 1 and 2, with a combined capacity of 560 MW and 2,240 MWh. Synergy regained the lead when its 500 MW Collie BESS entered commercial operation in Q2 2025.

Several new developers are expected to enter the WEM by the end of 2028. Notable among them is Alinta Energy, which is developing the 250 MW Reeves Plains BESS Stage 1 in the NEM, with construction scheduled to commence in early 2026.

Even with the entry of new participants, Synergy is expected to retain its position as the largest BESS owner beyond 2028.

Buildout has been backed by a combination of government funding and contracts

Three of the five operational batteries are owned by Synergy and sit on the government balance sheet. This helped support deployment when market signals alone were insufficient to underpin investment.

Three assets have also received contracts for Non-Co-optimised Essential System Services (NCESS). These contracts address system and network requirements that existing market mechanisms do not meet. This can include system restart capability and support during minimum demand conditions.

NCESS contracts are procured on a case-by-case basis and can be quite lucrative. Collie 2 is a good example of this, earning $591k/MW/year for 2025-27. Several assets in the pipeline have progressed past FID after winning a CIS agreement.

These contracts partially define battery operational profiles

Battery dispatch in the WEM is largely driven by arbitrage of the midday-to-evening price spread. Most assets charge during low-priced daytime periods and discharge into the evening peak, despite the relatively low spread compared to the NEM.

At the same time, most batteries are subject to contractual obligations that constrain behaviour during specific periods:

• NCESS-contracted batteries are required to follow AEMO dispatch instructions during predefined seasonal and daily obligation windows.
• CIS-contracted batteries must make contracted capacity available during high-demand periods but otherwise operate on a merchant basis.
• State-owned batteries are generally operated to support system reliability rather than to maximise commercial returns.

The Capacity Investment Scheme could bring another 400-600 MW of capacity by 2030

There are two ongoing CIS tenders relevant to the WEM:

• Tender 5, targeting 1,600 MW of renewable generation (including hybrid projects), and
• Tender 6, targeting 2,400 MWh of dispatchable capacity.

Submissions for both tenders closed in November 2025, with successful bids expected to be announced in March–April 2026.

Tender 6 is explicitly focused on dispatchable capacity and could deliver an additional 400–600 MW, depending on the system's duration. While Tender 5 does not directly target battery storage, it may drive additional battery capacity through co-located systems. We saw this in CIS Tender 4, where 3.5 GW / 11.4 GWh of battery capacity was approved despite the tender seeking only generation capacity.

Strong battery deployment in the WEM lays the foundations for reaching 2.5 GW by 2028 year-end

Battery deployment in the WEM continues to scale rapidly, with record capacity additions in Q4 2025 and a clear shift toward larger, longer-duration systems. 1 new project added 500 MW of capacity, pushing the total operational fleet to 1.4 GW and 5.4 GWh.

Construction activity remains high, with 364 MW of capacity progressing toward completion. There are another 700 MW of battery capacity in various stages of pre-construction, which could bring operational battery capacity to 2.5 GW by the end of 2028.

The WEM’s battery sector continues to mature, driven by larger systems, longer durations, and a stronger focus on commercial outcomes.