| Energy storage
stores in use – but not for hydrogen. One apparently obvious solution is to use existing natural gas storage and convert it for hydrogen. The existing natural gas storage in northern Europe is extensive – and the invasion of Ukraine has put it under the spotlight. Can natural gas caverns be used for hydrogen? It is an attractive idea. There is huge capacity existing, and they take up little land space. Existing caverns are away from the biosphere and hydrosphere and they are leak-tight – although that assumption would have to be redetermined for hydrogen. The technical implications were discussed at a second meeting, also held in March at the IMechE, with the support of the University of Nottingham and the UK’s Energy Research Accelerator. On the critical question of whether caverns could be repurposed, delegates heard that it was possible. But the process has 15-20 steps that involve: removing equipment suitable for methane storage and installing a series of temporary well
heads and other equipment; successively flooding the caverns with brine (to remove the remaining methane) and nitrogen; several steps in between, such as carrying out sonar surveys; installing wellheads and other equipment to handle the new hydrogen stock; and finally filling the cavern. As for the cost and time involved, that is not clear. Dollars or euros, it starts at several million for the technical conversion process summarised above. But there are non-technical questions. What happens to any gas inventory that is currently in the cavern? Who pays for the hydrogen needed to fill the cavern? To that might be added the cost of transporting the hydrogen to and the cavern to fill it, and from the cavern to potential customers, if the local gas grid is not ready to support it. What is involved in maintaining the high purity levels of the hydrogen used in industry, given that caverns may have water or other contaminants?
The timescale is another open question.
The technical conversion might take up to 18 months, the meeting heard. But permitting and licensing may be much slower, especially if the existing cavern does not already have permits for processes such as meeting water requirements or disposing of brine. That can take years. It should be said that existing caverns are not the only option for underground hydrogen storage. Another option presented at the conference envisaged a series of engineered caverns where hydrogen was stored at high pressure and shallow depths. The ‘cavern’ is a void encased in successive layers of rock, drainage, reinforced shotcrete and high-grade steel. These would have the advantage that they could be used at many more sites – but they are at the demonstration stage, with just one in operation in Sweden to store methane. At the moment, most of these options are speculative. The war in Ukraine may see them move to a more active investigation phase.
Fluence projects stack up worldwide
Recent Fluence projects include battery systems for Broken Hill in Australia (with advanced grid forming capabilities), for a substation in Taiwan and a community wind farm in Ireland
Fluence has been chosen by AGL to deliver a 50 MW / 50 MWh battery facility with what are described as advanced grid-forming capabilities, for the Broken Hill battery energy storage system in New South Wales, a project funded by ARENA (Australian Renewable Energy Agency). The project will use Fluence’s Gridstack technology and be part of AGL’s planned 850 MW battery rollout in Australia, as well as demonstrating the capability of the latest inverter technology to support stable operation in areas of low system strength. A partnership between AGL, ARENA, University of NSW and Fluence has enabled the first system of this level of complexity to be realised. It will provide a range of system security and reliability services to the grid at Broken Hill.
Unlike grid-following or other grid-forming energy storage systems in Australia’s National Electricity Market (NEM), AGL’s Broken Hill energy storage system will start and remain in grid-forming mode, with all inverters operating as a voltage source. The system will inherently resist changes in voltage and frequency on the grid and provide synthetic inertia, also known as Virtual Synchronous Machine (VSM) mode, and fault current contribution, along with standard energy storage services like FCAS (frequency control ancillary services), FFR (fast frequency response) and PFR (primary frequency response). The project will also provide storage
and firming capacity to the NEM and may assist AEMO (Australian Energy Market Operator) to connect other inverter-based renewables nearby, supporting the West Murray region. AGL chief operating officer, Markus Brokhof said the Broken Hill battery project was another step forward in AGL’s aspirations to become a leading orchestrator of energy storage deployments in Australia.
“As Australia moves forward with its energy transition, we know that firming technologies like energy storage will be the backbone of renewable energy supply”, Brokhof said. Aaron McCann, Fluence general manager for Australia commented: “Broken Hill battery is the first project Fluence is delivering to AGL within the framework agreement announced in January 2021…The Broken Hill battery project’s full power dispatches instantaneously to quickly respond to large changes in voltage and/or frequency, delivering the fastest response of all battery-based energy storage systems currently available in the market. This fast response will enable the system to operate stably and damp voltage oscillations after a fault in weak grid areas like the West Murray region, which will enhance the system strength on the grid.” The project, with expected completion in 2023, will be delivered by Fluence in conjunction with its local consortium partner, Valmec and in partnership with EPC Power, which is supplying its latest grid-forming inverters.
Taipower’s storage plans Meanwhile, Fluence and TECO Group have been awarded a contract for a battery-based energy storage system to be located at Taiwan Power Company’s Taoyuan Longtan EHV substation. There are 29 such substations in Taiwan managed by the state-owned Taiwan Power Company (Taipower). Taipower plans to install a total of 160 MW of energy storage at these sites, with Taoyuan Longtan being the largest project, having a capacity of 60 MW/96 MWh, representing an investment of over TWD 2.6 billion. To mitigate potential risks, safety features are incorporated throughout the energy storage system hardware architecture, including ground- fault monitoring, emergency shutdown circuit, fire detection and suppression systems, and incipient gas detection, among others. For instance, upon detection of smoke, the system will trigger an emergency shutdown and deploy suppressant
Above: Fluence Gridstack energy storage system
www.modernpowersystems.com | May 2022 | 29
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