Advanced Electricity Storage Technologies Program Smart Energy Storage (Trading as Ecoult) Final Public Report Introduction Ecoult, working with CSIRO as its principal subcontractor, was provided $1,825,440 under the Advanced Electricity Storage Technologies (AEST) program to demonstrate the capability of a storage solution using advanced algorithms and the CSIRO-developed UltraBattery to modify the short-term intermittency of electricity produced by wind generation and improve integration into the grid. The AEST program aimed to maximise the value of renewable energy from intermittent electricity generation through the development and application of energy storage technologies. Globally, the renewable energy industry has recognised grid integration as one of the key constraints to the continued growth of renewable energy as a major contributor in the power industry. The Ecoult storage project at the Hampton Wind Farm aimed to improve the integration of wind energy by applying energy storage in an effective manner to help control changes in the power delivered from wind turbines to the grid. Rather than simply storing energy for later use or backup, the storage was used to smooth the output of electricity, and in particular to control the rate of change. The objective was to have the maximum impact toward improving grid integration, while applying the minimum amount of storage. The key benefits of the project have been: - Demonstration of significant reduction in short-term variability from the wind farm through the use of storage, improving the quality of the wind power provided. - Smoother power delivery to increase the amount of wind power carried on transmission lines and its penetration on the grid, along with increased flexibility in siting of wind farms. - Further technical development of the CSIRO UltraBattery a super capacitor integrated within a lead-acid battery which had already been proven in hybrid vehicle applications. - Advanced battery monitoring and management to further prolong the working life of the UltraBattery. - Development of advanced smoothing algorithms. - Modular (containerised) construction to allow flexibility of deployment.
The Hampton project entailed a phased implementation whereby an initial 100kW system was commissioned and operated while a 1 MW system was developed and implemented in parallel. Phase 1 allowed the integration and operation of the control environment, with the grid, turbine and batteries completed, tested and refined for the introduction of the Phase 2 MW-scale UltraBattery storage solution. Phase 1 also allowed for a string of UltraBatteries to be run alongside a number of standard lead acid chemistry batteries for the purposes of comparison and for CSIRO to advance the qualification of a number of different algorithms. Phase 1 and Phase 2 were compatible, to allow the CSIRO algorithms to be implemented on the Phase 2 hardware. The project has fully met its aims with the successful commissioning of both the Phase 1 and Phase 2 systems and with significant research conducted by CSIRO to refine and demonstrate the algorithms. The completion of the Phase 2 system provided a platform for the extension of the research and development toward direct commercial application and was a stepping stone toward the award to Ecoult of contracts to supply two substantial (MW scale) US based energy storage systems that will utilise the UltraBattery. Demand for Energy Storage Grid integration is one of the key constraints to the continued growth of wind energy. The problems lie both in the electrical characteristics of the wind farms and in the intermittency of the energy production. While it is possible to take measures to ensure wind farms comply with network requirements, it is more difficult to deal with the inherent variability in the energy generation. This variability covers a broad range of time-scales from seconds to hours and beyond. Both short and long time-scales create different problems and can benefit from distinct storage solutions. Short-term variability (sub-one hour) in power line flow can be quite substantial where sizable wind generating facilities are present. This creates significant problems of voltage support and frequency control, as well as causing excessive peaking on transmission lines (thus reducing carrying capacity) and increasing demand for backup systems. This is particularly important where substantial wind generation is present at the extremities of the grid or on relatively small capacity power lines as is often the case. The challenge, however, is that battery technologies for large-scale storage are either economically unfeasible or, in the case of standard lead-acid technology, unable to cope with the extreme cycling demands while delivering sufficient longevity. The integration of the UltraBattery into renewable energy systems could solve this problem, increasing the potential penetration of intermittent renewable energy into the grid. This project provided a path toward a solution to this short-term variability problem and toward providing output smoothing and peak-shaving in the sub-one-hour domain as well as conventional voltage stabilisation and frequency control. Algorithms are applications that run on system controllers that drive the charging and discharging of the batteries to smooth the wind turbine output. CSIRO is optimising the algorithms to achieve the maximum impact (value) on the quality (grid acceptability) of the output of the energy from the combined system while making the minimum impact on the longevity (cost) of the battery asset.
Outcomes The Hampton project has successfully demonstrated smoothing of energy produced by wind turbines for use on the grid. The work completed at the Hampton site was supportive to the award of two US Department of Energy grants for major storage demonstration projects in the United States that will use UltraBattery technology. The first of these projects will use the UltraBattery to smooth output energy from a 500KW solar photovoltaic farm on the PNM network in Albuquerque, New Mexico. The second of these projects will use UltraBattery to provide 3MW of electricity regulation services directly on the PJM network in Lyons, Pennsylvania. Algorithm development and analysis is continuing toward maximising contribution against cost for the storage systems. In May 2010, CSIRO and East Penn Manufacturing Co Inc.,(East Penn) of Pennsylvania in the United States reached an agreement whereby East Penn acquired Ecoult and licensed the UltraBattery technology from CSIRO (under a royalty-bearing commercial licence). Ecoult has, in parallel to the Hampton project, progressed longevity analysis of the UltraBattery and, with East Penn, capability for manufacturing the UltraBattery at volume. Successful completion of the Hampton project has given the UltraBattery and Ecoult a sound platform to continue to build success in utilising the UltraBattery to contribute toward accelerating the adoption of renewable energy and providing grid stability. System Implementation The Hampton Phase 1 system was rated at 144kW and utilised four banks of various VRLA lead acid batteries (including one bank of UltraBatteries) and Phase 2 used a single 1MW capable inverter and a single string of UltraBatteries (rated at 500kWh at 50% Depth of Discharge). By following the two-stage implementation, Ecoult was able to develop and refine the smoothing algorithms (and also implement comparative testing of the UltraBattery) using the Phase 1 system while implementing the Phase 2 MW-scale production system. The larger, Phase 2 UltraBattery energy storage system was successfully commissioned on site and grid connected on 29 th June 2011. Grid connection of Phase 2, combined with the implementation of the Phase 1 system and the testing and research conducted on it, completed the full scope of this AEST project. Research utilising both systems will continue with Ecoult and CSIRO working together and looking forward, trialling of enhanced algorithms will be transferred across to the Phase 2 system while utilization of the Phase I system will become increasingly oriented at the objectives of the performance comparison of the UltraBattery against the other lead acid technologies. The Phase 2 system implementation process provided valuable experience and supported important objectives including:
- The ability of East Penn to manufacture UltraBattery cells in large format for grid power applications. Modular construction of the energy storage solution. Site installation experience. Electrical assembly and monitoring experience. Battery installation in accordance with the IEEE 1187 standard. Ecoult UltraBattery Energy Storage Solution at Hampton Wind Farm System Operation, Lessons and Results While the principles of the hardware system are reasonably straight forward, the control algorithm and optimising system to maximise life of the battery bank can be highly complex. The battery state of charge is kept within operating limits. A schematic of the system is shown below with the four banks of 60 batteries, each from a different manufacturer to enable performance comparison against the UltraBatteries. The system is coupled through to the 690V 3-phase AC Bus via the inverter/charger systems.
Hampton Schematic The initial control algorithm used proportional plus integral control principles to smooth electrical power. The parameters selected for the controller must suit the physical constraints of the system, for example maximum charge/discharge rates of the system and the storage capacity. The parameters can be varied in real time, for example to allow for a soft landing when the storage system is approaching its designated maximum or minimum capacity. The Phase 1 inverter banks have a total power throughput of 144kW and so are too small to deliver the equivalent power of the wind turbine (660kW). To provide testing over the full range of conditions, a divider is applied to the turbine input signal to enable it to be bought within the operating range of the inverter banks. The divider can be varied so that the inverter power capability represents a range between approximately 25% and 100% of the turbine maximum output. To prolong the life of the lead acid cells, and to decrease the chance of exceeding the cell voltage limits, the system is operated in a partial state of charge mode. At Hampton, this means that during standard operation the average state of charge should not exceed the operating range. The operating range for the Hampton testing was set at 25% to 75%. Initially, the storage target value is divided evenly between the battery banks. Some adjustments are then made based on each bank s state of charge to keep them from drifting too far apart, and compensates for variations in the battery manufacturer s stated battery capacity while maintaining the total storage target power. Results Phase 1 of the system was commissioned in mid-2010 with continuous testing, improvements and modifications. Ecoult has selected a number of periods for analysis where the system was running with consistent parameters for the explanation below. Smoothing
The figure below shows an example of the smoothing system in operation on a day of very mixed conditions. The signal multiplier was set to 0.25 and the maximum turbine output is recorded as approximately 170kW which is reached in the isolated strong wind event around 18:00 hrs. The line in red illustrates that the output was successfully smoothed with the full capacity of the inverters of 144kW able to absorb the fluctuating signal - the PI controller settings also result in a time shift of just less than 1 hour. Smoothed Output against Target 26/12/2010 More dramatic is the control demonstrated over the rate of change (ramp rate) as shown in the figure below where the 5 min average ramp rate is very significantly reduced. In this figure the controlled ramp rate (the blue line centred around 0 on the right hand axis) reaches a maximum of less than +/- 3kW per 5 minutes as compared to the uncontrolled output (the red line centred around 0 on the right axis) which ranges as wide as +/- 30 kw per 5 minutes. In simple terms the ramp rate has been constrained by an order of magnitude. 700 40 storage.powerin storage.powerout storage.targetpowerout 5 min Ramp rate In 5 min ramp rate out 600 30 500 20 400 kw 300 0 200-10 10 Ramp rate kw per 5 min 100-20 0-30 0:00 2:24 4:48 7:12 9:36 time 12:00 (hh:mm) 14:24 16:48 19:12 21:36 0:00 Ramp Rate reduction with smoothing system 26/12/2010
To achieve the smoothing results above, the algorithms turned over approximately 40% of the capacity of the store each day. The design life of the UltraBattery systems is of the order of 4000 full capacity cycles indicating a significant life at this duty cycle. It is hoped that more advanced algorithms will reduce the capacity cycling even further while achieving greater impact. Conclusions The project has been successful against the AEST project grant objectives. The work at Hampton will continue with the focus moving to development and trialling of enhanced algorithms on the 1MW Phase 2 system while the performance comparison of the UltraBattery against the other lead acid technologies continues on the Phase 1 system. Ecoult continues to quantify the outperformance of UltraBattery over alternate storage technologies and in particular to quantify its longevity when used for various grid and renewable ancillary applications. The experience and market readiness of the product and solutions that has been gained was very important in supporting the attainment of the two MW scale storage solution projects that are currently being implemented in the United States by Ecoult which will utilise the UltraBattery and continue the platform for commercialisation that has been established.