This project assessed the functionality of integrating a flow battery with Kotzebue's wind farm and diesel generators to stabilize loads, increase wind penetration, and increase the efficiency of diesel generators. After being awarded the EETG grant, the Kotzebue Electric Association purchased and installed a flow battery system.
Energy storage remains one of the fundamental barriers to the feasible deployment of most renewable energy technology and the integration of multiple energy resources into power generation. For this reason, energy storage is considered a critical area of needed research. Large scale batteries for wind diesel systems that could provide village utility grid stabilization and load shifting are currently being developed by several suppliers. If these batteries become commercial products at the price currently being anticipated, they could provide significant diesel fuel savings in communities with wind resources.
A battery is an electromechanical method of storing energy. Energy is stored by chemical changes in a system, often between a metal and an oxidized state of that metal (ex: lead acid batteries have lead plates). Flow batteries use materials with multiple valence states so that electrons can be stored in an electrolyte solution which contains several ionic species. Since battery degradation often involves undesirable stray reactions that occur at the metal-electrolyte interface, these systems avoid those degradation mechanisms, and are projected to have very long lifetimes.
The stated intent of the project was to 1) increase voltage stability, 2) increase the efficiency of operating diesel generators, and 3) capture excess wind energy during off-peak hours. Specific to (1), KEA stated that they have seen wind penetration levels of over 60%; an installed battery system would allow KEA to provide frequency regulation and spinning reserve to utilize higher penetration levels and maintain system stability. Furthermore, a battery system would allow for more efficient diesel generator dispatch and would allow KEA to capture off-peak wind generation, ultimately reducing expensive diesel fuel consumption by KEA for power production. Kotzebue Electric Association's also hoped to analyze and demonstrate flow battery systems and their potential for energy storage in rural wind systems.
Before shipping and installation occurred, the battery went through lab testing at the manufacture's lab due to delays, the battery missed the 2010 barge season, and did not arrive in Kotzebue until the following year. The location for the battery was prepared and the battery moved into place under supervision of a premium power Representative.
The Premium Power Transflow 2000 is a 500 kW, 2.8 MW-hour battery based on a Zinc-Bromide technology. The TransFlow 2000 is the lowest cost utility-scale energy storage system. It is a fully integrated system that comprises energy storage, power conditioning, system control and thermal management subsystems packaged into a portable, turn-key, building block to be placed wherever it is needed for immediately dispatchable on-line energy storage. Each TransFlow 2000 provides up to 500kW of power and 2.8MWh of energy storage capacity in a single enclosure that fits onto a 53' trailer for mobility. The long term operation has been demonstrated (over 30 years for laboratory systems), indicating that this battery might prove to be cost effective for use in Wind-Diesel hybrid systems. Long term operation has been demonstrated (over 25 years for laboratory systems), indicating that this battery might prove to be cost effective for use in Wind-Diesel hybrid systems.
Advantages of Flow Batteries
The key reasons that private companies and the US DOE selected the Zinc/Bromine flow battery technology for development for electric utility stationary applications were:
- Low cost, non-hazardous materials that make the Zinc/Bromine battery a lower cost product to manufacture and dispose of at the end of its life.
- Flow batteries offer larger energy storage capacities that are not feasible by other battery technologies. Hence, Zinc/Bromine batteries are called “energy” batteries because they are suitable for applications where longer than 4 hours of energy storage are required.
- It is possible to increase storage capacity after commissioning the battery as needed by adding additional storage tanks for the liquid electrolyte.
- Full capacity depth-of-discharge is theoretically possible in routine operation of Zinc/Bromine batteries. Such deep discharges are not desirable or feasible with most other battery technologies.
Disadvantages of Flow Batteries
These are the disadvantages of Zinc/Bromine flow batteries:
- Zinc/Bromine flow batteries require substantial auxiliary systems, such as pumps and cooling to circulate the liquid electrolyte. There is also significant piping to transport the liquid from storage tanks to the stack and back, which if not designed and engineered correctly could lead to a leaking system.
- Metallic Zinc is deposited in the stack of the battery during the discharge cycle and this deposit needs to be removed by a periodic “stripping” cycle. This requires external energy and contributes to the other auxiliary losses leading to lower efficiency of the overall battery system.
Data and Analysis
In lab tests, the battery exhibited approximately 2 MW-hours during charging, and provided only about 1.6 MW-hours in discharge, lower than it's advertised 2.8MW-hour capacity. Additionally, there was significant variability in the measured efficiency of the battery from cycle to cycle. In none of the cycles was a charge rate of 313 kW maintained for 10 hours—the average charge time was about 6 hours at 313 kW. Discharge times were also shorter than anticipated.
Upon arrival in Kotzebue, it was also found that the battery had been improperly packaged and was damaged by corrosion due to salt water. This may have led to many of the commissioning woes of the project. Additionally, throughout the course of the project life, the battery had several unexpected leaks some of which could not be identified, but there was speculation that they were due to extreme temperatures effecting the hose clamps.
In the Spring of 2012, it was announced the the manufacturer was undergoing a restructuring and the battery was recalled, it was shipped back at the end of the summer season in 2012.
To access more detailed analysis, quarterly reports, the final report, please continue to the Resources, Links and Documents section of the page.
Funding and Partnerships
This project is a Denali Commission EETG Program project. The funding goal of the EETG program is to develop emerging energy technology that has the potential of widespread deployment in Alaska and has the long-term goal of reducing energy costs for Alaskans.
The Alaska Center for Energy and Power (ACEP), an energy research group housed under the Institute of Northern Engineering at the University of Alaska, Fairbanks, is serving as the program manager of the EETG solicitation. As the projects deal with emerging energy technology and by nature are high risk, high reward, ACEP’s technical knowledge and objective academic management of the projects, specifically for data collection, analysis, and reporting, is a vital component to the intent of the solicitation, i.e., providing lessons learned and recommendations.
Kotzebue Electric Association is a rural electric utility cooperative, based in Kotzebue, Alaska. KEA has 840 members, and generates over 18 million kilowatt hours per year.