Mobilizing a Global Energy Storage Fleet of Zinc Bromide Flow Batteries

Author(s):

Ryan Talbot - Primus Power
Hossein Kazemi - Primus Power
Janey Ward - Primus Power

A New Approach for Long-Life Energy Storage

When using renewable power sources, the energy flow depends on wind or sun activity. For example, energy surges can occur due to changes in cloud movement, which cause jumps and lags in generation. As a result, the entire grid infrastructure—stations, substations, transformers, and all the interconnections—suffers from this variability.

Energy storage systems help to smooth out this variability by storing energy when supply is high and demand is low, and by injecting power when the reverse is true. Utilities can use long-duration batteries to satisfy peak power needs, defer costly system upgrades, and shift midday oversupply of renewable photovoltaic generation to evening peak periods. However, achieving this effectively requires multiple hours of battery power. Batteries for grid-scale applications must last decades and deliver long-duration energy discharge on demand.

Primus Power’s mission is to make 100 percent renewable energy possible worldwide by delivering safe, low-cost, and long-life energy storage solutions. The core technology behind these solutions is Primus Power’s EnergyPod, a groundbreaking long-duration flow battery system. The proprietary EnergyPod flow battery uses only one flow loop (versus two for conventional designs) and advanced metal-based electrodes that enhance performance and extend durability. Furthermore, the EnergyPod has eliminated the use of a costly separator, which is a typical failure point of other flow systems. Unlike lithium ion batteries, flow batteries deliver uniform power without fade for decades. The rechargeable electrolyte liquid lasts indefinitely and cannot catch fire like lithium ion batteries. These innovations support a safer and lower cost energy storage platform that also features increased lifetime and a smaller footprint. This is why large-scale solar and wind power plant operators have chosen to partner with us for energy storage.

With this innovative flow-battery design, we were challenged to capitalize on a narrow window of time to get our product to market. The market for energy storage is evolving quickly. We recognized that we did not have time to develop our own control boards from scratch and also achieve the quality we require for mass, reliable industrial deployment. Our goal was to effectively balance time and cost for the successful release of our next generation of energy storage systems, the EnergyPod 2.

Evaluating Embedded Control Options

When evaluating options for designing the EnergyPod 2 control system, we considered a few alternatives. We could develop a custom control board in-house, or we could purchase another commercial off-the-shelf (COTS) System on Module (SOM) or single-board computer. We ruled out a custom board design since building the control boards in-house would require significant development effort that was outside of our core expertise and would likely delay getting the product to market. Additionally, we knew other COTS SOMs and single-board computers would require a significant amount of low-level development before getting to a minimum viable product.

To meet our time and quality demands, we chose to use the CompactRIO platform to control the EnergyPod 2 for the power conversion, signal conditioning, flow control, and network communication subsystems. Unlike other SOMs and single-board computers, CompactRIO controllers ship with fully validated middleware and drivers, which lowered risk and reduced development time by a third. We chose to program our control system using LabVIEW, so that we could accelerate development and leverage a single software platform to program our entire control system and user interface. The CompactRIO platform allowed us the flexibility and control to quickly test out new concepts and rapidly deliver solutions. We got the basics of our system up and running quickly, so we could spend most of our development effort iterating on designs and adding a richer feature set.  

System Overview

Primus Power’s EnergyPod 2 is a modular 25 kW x 125 kWh battery that can be arranged in series and parallel to form a multi-megawatt array. Users can put up to four EnergyPods in series to form an EnergyPack with the power and energy rating of 100 kW x 500 kWh, which then can be paralleled with other EnergyPacks for larger power and energy ratings. Figure 3 shows Primus Power’s EnergyFarm architecture.

Each EnergyPod 2 contains a signal conditioning board (SCB), which is a customized board powered by an integrated CompactRIO SOM. This board gathers, processes, and conditions data from the system’s sensors and actuators. The SCB communicates all the information to and from the battery management system (BMS), which is controlled by a CompactRIO General Purpose Inverter Controller.

Throughout development, we took advantage of the large community of LabVIEW developers and the vast library of troubleshooting guides and support resources. We also had a great experience working with JKI, a well-respected consulting company and NI Alliance Partner. JKI helped get us established rapidly for our first design with the NI platform.

Delivering the Solution

Using NI technology, we increased our level of integration and reduced our software development time by about a third. We used two internal engineers for this project. We would have needed more engineers if we had gone with a custom design approach or used programming languages other than LabVIEW. Embedded design teams typically require at least six engineers for this kind of project. The ability to program an FPGA and a real-time controller, and create PC executables from the same development environment allowed for greater code reuse and easier development and debugging. Ultimately, we saved money on costly development time and engineering costs. We also got the EnergyPod to market in only 10 months, which was approximately five months less than it would have taken otherwise.

Tom Stepien, CEO of Primus Power, said, “In my experience developing complex electromechanical products, it is usually the control system that is the long pole in the tent – gating the product release. Since standardizing on the CompactRIO platform, our NI-based controls system has not been on the EnergyPod critical path. This has been a welcome difference!”

Moving forward, Primus Power looks forward to accelerating shipments around the world and being a part of the rapid evolution toward renewable energy.

Author Information:

Ryan Talbot
Primus Power
3967 Trust Way
Hayward, CA 94545
Tel: (510) 342-7600