Flow Battery Energy Storage Systems - An Emerging Energy Technology Grant Project
This project sought to install and demonstrate a zinc-bromine flow battery system at Kotzebue, investigating energy storage opportunities for rural wind-diesel systems in Alaska. Due to materials issues, commissioning problems, and manufacturer reorganization, the battery was returned and the project is currently on hold.
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 overall goal of this project was to test through demonstration advanced battery systems and their application to broader Alaska energy needs. Specific goals related to the installation of the system at KEA’s powerhouse in Kotzebue included (1) increasing voltage stability, (2) increasing the efficiencies of operating diesel generators and (3) capturing excess wind energy during off-peak hours. The technology specified for demonstration was a 500-kW, 2.8-MWh Premium Power Transflow 2000 zinc-bromine flow battery. Key project milestones included factory acceptance testing, shipment, installation and commissioning, and demonstration operation.
Pre-project activities including system characterization, modeling and site preparation commenced in 2009, with project activities formally commencing in March 2011. Factory acceptance testing of the battery was finalized in July 2011, and the battery system arrived in Kotzebue September 2011. Installation and attempted commissioning of the system commenced and continued through the spring of 2012, at which time the battery was returned to the vendor.
In factory acceptance testing, the battery exhibited approximately 2 MW-hours during charging, and provided only about 1.6 MW-hours in discharge, lower than its 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 (the project team was unable to commission the battery) of the project. Additionally, throughout the course of the short battery deployment, the battery had several unexpected leaks some of which could not be identified, but there was speculation that they were due to extreme temperatures affecting the hose clamps.
In the Spring of 2012, it was announced the manufacturer was undergoing a restructuring and the battery was recalled; it was shipped back at the end of the summer season in 2012. KEA is currently under discussion with Premium Power to provide a redesigned unit to site. Since the Denali Commission EETG program ended on September 30, 2012, funding will not be available for future project deployment. The future status of the various funding sources involved in this project is unknown at this time.
It is recommended that the re-engineered system should not be brought back to Kotzebue until it can produce the original power rating of 500 kW. The requirement to produce 500 kW, as originally specified, is critically necessary for the battery system to stabilize and balance the Kotzebue electric grid effectively; with additional new wind generation to the Kotzebue grid, the reduction of the battery power from the original 500 kW to 125 kW (after its redesign) would render it ineffective in providing both stability and balancing functions to the Kotzebue grid.
Because of the experience at Kotzebue, it is recommends that the re-engineered system meet the following milestones either at the Premium Power factory site or at a third-party test site:
- The system must operate according to a specified charge-discharge profile continuously for a period of 30 days. During this time, the system must meet a minimum efficiency of 70 percent and an availability of 90 percent.
- The 30-day test period should be completed without leaks from any component of the system, including the stacks, valves, pipes, connectors and couplings.
- The system must be remotely connected to the KEA SCADA (or its simulated equivalent) and respond to all commands it receives from it — including remote startup and shutdown — within the time frames specified during the 30-day test period.
In addition to these performance-related milestones, Premium Power should identify the physical location of all subsystems within the trailer and satisfactorily demonstrate that these are accessible for maintenance and repair in the field by Premium Power technicians, using equipment that would reasonably be expected to be available at the Kotzebue site.
Prior to shipping the system, Premium Power must satisfactorily demonstrate that it is capable of packaging, transporting and installing the system at Kotzebue in compliance with KEA requirements. It must also demonstrate that it is capable and willing to support the necessary technical staff at Kotzebue for a period of eight weeks if the system is reinstalled at Kotzebue.
There are two specific recommendations for future battery storage projects in other remote Alaska communities. The first is to continue tracking the progress of flow battery technologies by annual technology assessments and laboratory evaluations. The technology assessments should be geared to assessing the readiness of the technology for Alaska applications and report results of laboratory testing. Such assessments should be conducted for a period of three to five years.
The second recommendation recognizes the desire by the remote Alaska communities to introduce new battery technologies to reduce their dependence on diesel fuel and increase their utilization of renewable energy technologies. However, the selection of energy storage technologies and their integration into the community power grid needs careful and informed consideration. The emerging technology landscape of battery systems is fairly complex, and remote communities need technical support and guidance to determine when and if battery storage is the correct technical and economic solution for their specific conditions.
It is proposed that guidelines be developed that can be used by the communities to implement future projects. These guidelines would allow the communities to objectively evaluate suitable battery technologies on a project-specific basis. The guidelines would include assessing the maturity of the vendor’s product and evaluating the vendor’s ability to successfully support the project through the installation, startup and acceptance phases and address other technical issues that the community may otherwise overlook. Incorrect or misleading information about technology readiness and performance occurs frequently in emerging technologies, and these guidelines would help the communities make informed decisions that align with their project’s objectives.
Photo 1: Premium Power TransFlow 2000 at the Princeton Power factory. Courtesy of KEA.
Photo 2: Premium Power TransFlow 2000 Rendering. Courtesy of KEA
Photo 3: Battery Controls and SCADA interface in the KEA power plant. Courtesy of KEA.