Near the top of the Perth Basin 350 kilometres from Perth, a little-known energy storage facility plays a crucial role managing supply risks and providing flexibility in Western Australia’s energy market.  

Filling a sandstone reservoir of a former gas field almost three kilometres underground, the Mondarra Gas Storage Facility is connected to Western Australia’s major energy demand centres via APA’s Parmelia Gas Pipeline and the Dampier to Bunbury Natural Gas Pipeline. 

The importance of Mondarra was solidified following the 2008 Varanus Island explosion which wiped out 30% of Western Australia’s gas supply. The months-long energy crisis that followed shattered business and industry.  

The facility has a storage capacity of approximately 18 petajoules of gas, over 2,500 times the equivalent energy capacity of one of Australia’s largest grid-scale battery storage facilities, Synergy’s recently opened Collie big battery. 

The role of deep energy storage

As we head into the summer months, Mondarra will be there to provide flexibility and meet supply challenges. 

Surplus natural gas is injected into the reservoir during low demand, allowing it to be accessed quickly during peak demand or in the event of an energy emergency.  

Since 2023, there have been 76 days where Mondarra has stepped up to play this role and supply up to 150 terajoules a day into the network. This includes where unplanned outages impact supply from the North West Shelf or Perth Basin.  

At the peak of one market shortfall in January 2024, Mondarra delivered over a petajoule of gas over a 10-day period, keeping the gas flowing to both industry and power generation assets in the South West Interconnected System (SWIS).

In short, Mondarra kept industry and households going, without anyone knowing what was going on, which is the whole point of long duration energy storage.

Batteries and long-duration gas storage 

The ability of gas storage facilities to maintain energy supply for long periods emphasises the different role they play to grid-scale batteries.  

Synergy’s Collie big battery, one of Australia’s largest, plays a critical role in the SWIS providing grid stability and delivering energy during high demand periods. The battery cost around $1.6 billion and can support ~785,000 average homes for around four hours.¹  

But, unlike Mondarra, big batteries in Collie can’t support days or weeks of low renewable generation or unplanned outages.²  

Mondarra can store enough gas for the generation of electricity required for ~785,000 homes in the South West for ~35 consecutive days. The state would need approximately 210 big batteries to provide a comparative level of energy storage at a cost of more than $300 billion.  
 
The importance of Mondarra to Western Australia’s energy security cannot be understated.  

It’s a simplistic comparison and is not intended to undermine the important role batteries play, but it underlines how important gas is to a secure energy system and how efficiently gas infrastructure stores energy.   

Supporting energy transition

The role of gas storage will continue to be critical through the energy transition. Gas-fired power generation is essential to back-up renewable energy and support the State Government’s policy to retire all state-owned coal generation by 2030.  

The WA Parliament’s inquiry into the State’s Domestic Gas Reservation Policy in 2024 acknowledged the important role these storage facilities play and found this role is likely to become increasingly significant as Western Australia transitions towards net zero.³ 

Gas storage facilities like Mondarra provide the resilience our energy system needs – reliably and affordably.