Origin Energy has moved the 300 MW / 650 MWh Mortlake battery into commercial operation in southwest Victoria, turning an existing gas-fired peaker site into one of Australia's more interesting storage hybrids. The project is not the largest battery in the National Electricity Market, and it is not the longest duration asset now entering service. Its importance is more specific. Mortlake sits beside a 566 MW open-cycle gas plant, connects through AusNet's 500 kV switchyard, and uses grid-forming inverter capability. That combination puts battery storage directly inside the operating footprint of thermal peaking infrastructure. AI-generated image Mortlake pairs grid-scale batteries with an existing gas peaker site and a high-voltage connection in southwest Victoria. 300 MW battery output 650 MWh energy storage 500 kV switchyard link 2026 commercial start What started operating Origin confirmed that the Mortlake battery energy storage system has commenced commercial operations after commissioning. The asset is located at the Mortlake Power Station site, about 200 kilometers west of Melbourne. Origin approved the battery in January 2024, began site work later that year, and contracted Fluence as the primary construction partner. The headline numbers place Mortlake in the two-hour class: 300 MW of power and up to 650 MWh of stored energy. That makes it a fast-response capacity resource for evening peaks, contingency events, frequency control, and renewable shifting. It is not designed to carry the grid through multi-day weather patterns. It is designed to move quickly when the NEM needs firming capacity. The siting is the strategic part. Building at an existing power-station location can reduce some of the friction that slows greenfield storage projects. There is already transmission infrastructure nearby. There is an operating team with power-market experience. There is a known grid node. The battery still needed its own works, including a purpose-built substation, but it did not have to invent a power site from scratch. The core news Origin Energy's Mortlake BESS in Victoria is commercially operating. The project adds 300 MW / 650 MWh of battery capacity beside the company's existing Mortlake gas-fired power station, with a direct connection to AusNet's 500 kV switchyard. Why a battery beside gas matters Gas peakers and batteries are often presented as rivals in reliability planning. Mortlake shows why the relationship is more complicated. A gas turbine can run for longer scarcity periods if fuel is available. A battery can respond in milliseconds, absorb surplus renewable output, and avoid burning fuel for short peaks or system services. Placed at the same grid location, the two resources can cover different pieces of the reliability job. That matters in Victoria because coal retirements, renewable growth, and transmission constraints are reshaping how firming capacity is valued. Batteries can reduce the number of hours when gas is needed, but they do not erase the planning problem that appears when demand is high and renewable output is low for a sustained stretch. The near-term grid will likely use both technologies, with batteries taking the fast and frequent work where they have a clear edge. Mortlake also gives Origin a cleaner way to use a legacy thermal site. The company can participate in storage revenue streams while keeping existing peaking capacity available. For investors, that is a practical transition model: add storage to sites that already have grid access, then let market dispatch decide which asset earns in each interval. AI-generated image Two-hour batteries can handle fast balancing, peak support, and ancillary services while larger firming portfolios cover longer events. Grid-forming capability is the technical test The project has also been described in public reporting and project documents as using grid-forming functionality. That detail matters because the battery is not only a box of stored energy. Inverter controls decide how the asset behaves when voltage, frequency, and system strength become difficult. Most conventional grid-following inverters synchronize to an existing voltage waveform. Grid-forming inverters can help establish voltage and frequency references, which becomes more valuable as synchronous coal and gas units run less often. In practical terms, a battery with grid-forming controls can support system stability in ways that look more like traditional rotating machines, even though the asset is power electronics and battery cells. Australia has been one of the most active proving grounds for that shift. High renewable penetration in South Australia, Victoria, Queensland, and New South Wales has pushed storage developers and network operators to care about more than arbitrage. The value of a battery is now tied to how well it can support a weaker, more inverter-heavy grid. What Mortlake can prove Hybrid siting: storage can be added to thermal power sites with existing transmission access. Fast firming: the battery can respond to short peaks and grid events faster than thermal units. Inverter services: grid-forming controls can support stability as synchronous generation retires or runs less often. Portfolio value: Origin can operate battery and gas assets around different market signals at the same node. Australia's storage buildout is becoming operational Mortlake is part of a wider Australian shift from announcements to live assets. The NEM has already added enough batteries to change intraday price behavior, and developers are now commissioning larger projects with longer durations, stronger controls, and more sophisticated contracting structures. That can be uncomfortable for merchant battery owners because successful storage suppresses the same price spreads that helped justify early projects. The answer is not fewer batteries. It is better market design and better use of services that batteries can actually provide. Energy arbitrage is only one revenue line. Frequency control, reserve markets, system strength, network support, capacity contracts, and tolling agreements are becoming more important as the fleet grows. A battery like Mortlake can compete across several of those roles if the market rules recognize the services. Australia's storage pipeline also shows why location now matters as much as size. A 650 MWh battery at a useful transmission node can be more valuable than a larger asset stranded behind weak grid access or delayed connection studies. Mortlake's power-station setting gives it an advantage there. The next question is how often the market calls on the battery and how its operating data changes future peaker-site storage decisions. AI-generated image Australia's next storage phase is less about headline capacity and more about where batteries connect, what services they provide, and how they are paid. What to watch next The first marker is dispatch behavior. If Mortlake earns heavily from short-duration price spikes, it will reinforce the value of batteries at peaking nodes. If grid services become a larger share of revenue, it will strengthen the case for grid-forming requirements and stronger inverter specifications in future projects. The second marker is how Origin uses the battery alongside the gas plant. Batteries can reduce cycling on thermal equipment, reserve gas generation for longer events, and create optionality during tight market intervals. The most valuable strategy may not be maximum battery cycling. It may be coordinated operation that protects the site from fuel risk, outage risk, and volatile spot-market exposure. The third marker is replication. Other utilities and generators own sites with grid access, operating history, and changing economics as coal and gas fleets age. If Mortlake performs well, storage retrofits at existing power-station sites become easier to finance. That would speed deployment because the industry would be reusing part of the old grid to suppo