Battery/Diesel Grid-connected Microgrids: A Case Study of Future Microgrid Capabilities
Introduction
As large scale battery technology and economies of scale continue to improve, many industrial utilities are investigating the use of battery technology as the basis for Grid Energy Storage Systems (GESS) which will likely be part of future microgrid systems. Based in Victoria, Australia, AusNet Services, the state’s largest energy delivery service owning and operating approximately $11 billion of electricity and gas distribution assets that connect into more than 1.3 million Victorian homes and businesses, began investigating GESS in 2013. AusNet Services chose to trial the technology to explore the ability to manage peak demand with the potential to defer investment in network upgrades.
Through a competitive tender process, AusNet Services awarded the contract to design, construct and deliver a GESS to a consortium led by ABB Australia and Samsung SDI, with ABB in Australia providing the integration technology and design and Samsung SDI taking the role of battery supplier.
Situated in the northern suburbs of Melbourne, the system is located at an end-of-line distribution feeder in an industrial estate. The GESS is the first Australian system of this type and size. A two-year trial is currently underway to investigate the capabilities of grid-connected microgrids to provide peak demand support. The trial will explore the benefits to peak demand management, power system quality and network investment deferral that large-scale, grid-connected energy systems can provide.
The GESS At-A-Glance
- Commissioned in December 2014
- 1 MWh 1C lithium battery system which interfaces to the microgrid through a 1 MVA PowerStoreTM (an inverter-coupled energy storage system)
- 1 MVA PowerStore diesel generator
- Grid connection substation consisting of a 3 MVA transformer and sulfur hexafluoride (SF6) filled ring main unit and power protection devices
- SF6 gas-circuit breaker-based ring main unit with associated power protection systems
- Portable system components, with the generator, batteries and PowerStore housed in shipping containers, and transformer and RMU housed on skid-mounted platforms
System Outcomes, Future Works and Applications
While the GESS is currently in its two-year trial and investigation period, the capabilities of the system as demonstrated show promise for future microgrid applications. With islanding capabilities and a compact portable design allowing it to be positioned near to customers, the GESS will strengthen the power grid while enabling power system upgrades to be postponed or eliminated. Energy Storage systems such as the GESS also present an effective method of managing temporary feeder disconnection in times of need (line maintenance, bushfire prevention), because the system can support the connected microgrid for time periods sufficient to allow the system interruption to be dealt with.
Historically, the PowerStore has used a flywheel-based energy storage system with a capacity of 5 kWh in microgrid applications. The increased and customizable energy storage capacity of the Samsung lithium-ion battery-based system compared to flywheel-based systems shows promise for increasing the contribution of renewable energy sources by over-sizing the renewable resource with respect to the microgrid load to charge the batteries during times of renewable generation, for discharge during times of intermittent/no generation (e.g. using solar generation stored in battery based systems for night time supply). This increased contribution would result in increased diesel savings and reduced emissions in such applications, with the possibility of eliminating the need for backup diesel generation.
Battery-based energy storage systems also show promise for increasing the penetration and contribution of solar generation into larger traditional Macrogrids. The longer duration of intermittencies caused by solar generation compared with wind generation necessitates a support system with a larger energy capacity suited to battery-based storage systems such as the GESS. With such support systems, larger distributed sources of solar generation could be integrated into Macrogrids as their intermittency would be smoothed by a GESS or similar system. Support provided by systems such as the GESS would not be limited to solar generation as any distributed sources of generation could be supported, given the power system supply and stability capabilities of the GESS.
The islanding capabilities of the system also show promise for reducing the severity and duration of outages in larger macro-grids as serious faults can be isolated and rectified, while the supply to interrupted areas is maintained by a GESS. Given the prevalence of bushfires in Victoria, the islanding and ‘bumpless’ reconnection capabilities of systems similar to the GESS may be used to mitigate the effect of such fires on the supply to remote and rural areas. In such cases, a feeder would be de-energized just prior to a bushfire passing through the area with any disconnected communities supplied by the GESS. Once the fire had passed through and the feeder checked for damage, the line would be re-energized before the GESS would perform a ‘bumpless’ transition, and the area could then be supplied by the feeder.
The dual functionality of systems with respect to both network supply and stability such as a GESS also show promise in reducing the CAPEX required to integrate high penetration levels of renewable generation into grids. As the one system functions in the same way as both an energy storage device and a STATCOM, the supply and stability issues associated with renewable intermittency (e.g. voltage and frequency variations caused by renewable intermittency) can be mitigated at a reduced CAPEX level in comparison to investing in a stand-alone energy storage component and a standalone STATCOM system component. This is especially important for microgrids, as the smaller power rating of such grids (and economics resulting from related power purchase agreements) usually results in a smaller CAPEX and higher targeted penetration, making effective integration of the renewable resource vital to the success of such projects.
Advances in lithium-ion battery technology with respect to charge and discharge ratings (the ‘C’ rating) are currently 4C pulsed (whereby a 250 kWh system would be able to discharge at 1 MW for 5 minutes). This opens exciting possibilities for energy storage systems in microgrid applications as the smaller footprint of such systems without a degradation in power rating make them attractive for smaller, remote systems. Increasing ratings also are attractive in larger grid connected systems for local intense peak load support, such as that needed to support arc furnaces, large cranes and hoists and other large, intermittent industrial loads.
Click here to read the full whitepaper, which presents these results and discusses the future applications for the demonstrated technology. The results of the two-year trial period will be published at its completion.
