Currently, the PowerCube™ is configured as a behind the meter resource. In essence this means that Axion acts as a virtual generator by curtailing load. When the PowerCube is commanded to take load from the grid it uses that power to charge its battery. When commanded to discharge, the battery is discharged into the plants load effectively reducing or curtailing its power consumption.

Energy Storage for the Grid

Tom Granville - Axion Power

Filed Under - Energy Storage - Storage Systems

Q: Can you give us a quick description of what the PowerCube™ is and how it works?

Ans:  The Axion PowerCube™ is a Battery Energy Storage System (BESS) that leverages our patented PbC® battery technology.  The PowerCube™ integrates the batteries, power electronics, safety systems and computer controls into a complete system module.  The current “building block” is rated at 500 kW but can be scaled to a 20MW system. The system can also be configured into smaller building blocks for residential or community storage initiatives.  Our PowerCube™ can be configured to participate in the utilities ancillary markets, such as the frequency regulation and energy markets.  Capabilities include providing power quality, back-up power, power smoothing and load leveling.

In the utilities ancillary markets, we have partnered with Viridity Energy, a curtailment service provider (CSP).  As an example, Viridity Energy bids the PowerCube™ into the frequency regulation market at various times during the day.  If our bid is accepted, Viridity receives a regulation signal (REGA) from PJM, the RTO in our area.  That regulation signal is transmitted to the PowerCube™ and commands the BESS to either charge or discharge.  The system is capable of responding to the signal in 250 milliseconds. 

Q:  How does the PowerCube™, with PbC® Technology, participating in the regulation market benefit the RTO, utilities and end user?          

Ans:  In October of this year, the Federal Energy Regulatory Commission approved rule changes that reduced the minimum required amount of resources to 100 kW, from the previous minimum of 500 kW.  This new minimum level for participation allows the PowerCube™ to participate in the utilities ancillary services.  The regulation services correct for short-term changes in electricity usage that could affect the stability of the grid.  It also helps PJM optimize the power generation and adjust the generation output to maintain the desired frequency of the grid.  Previously, system operators have relied on slow responding generating resources to vary output to balance system frequency. Now,with assets like the PowerCube, those generators could be re-tasked to focus on load generation. 

Follow on Question:  What is the response time of the PowerCube™ to the REGA signal and how does it benefit PJM.

Ans:  The PowerCube™ can respond to the REGA signal received from viridity in 250 ms.  The roundtrip communication time between PJM, Viridity and the PowerCube™ is on the order of 3 seconds.  Currently, utility assets (natural gas fired peakers) that are participating in the regulation market have 5 minutes to respond to the regulation signal.  Fast responding assets like Axion’s PowerCube™ will benefit PJM by providing them with the ability to control the frequency of the grid in real time. It should be noted that the further the frequency drifts out of balance, the more difficult rebalancing becomes. The amount of power required to move back into balance increases geometrically, so it is incumbent that the provider respond quickly.  

Q:  How does the PowerCube™ benefit renewable energy sources like Solar, Wind, Tidal, etc.?

Ans:  Incorporating renewable energy sources into the grid infrastructure is challenging.  Energy from solar panels, wind turbines, etc. is derived from unregulated natural resources (e.g. the sun is blocked by passing clouds; the push of the wind is inconsistent in both force and direction, etc.).  This intermittency makes it difficult for utilities to predict what their output will be, thus the importance of battery energy systems like the Axion PowerCube.  The PowerCube™ is charged or discharged as needed to smooth out these natural irregularities, increasing the quality of renewable energy output and the value of renewable expansion.  

Q:  The PowerCube qualified in the PJM market as a 100 kW resource.  What is the benefit to PJM?  Is the technology scalable to larger power ratings?

Ans:  PJM is able to re-task the generation assets that are currently being used for frequency regulation and optimize them for load generation.  Fast responding technologies, like the PowerCube™ can be used to maintain the frequency of the grid in real time.  The technology is scaleable in building blocks of either 500 kW or 1 MW.  

Q:  There are many battery technologies available, what makes the PbC® technology better choice over Li-ion, Na-S, traditional lead acid, flow batteries, etc.?

Ans:  The PbC® battery represents the best value/performance fit for battery energy storage applications.  It overcomes the significant performance limitations of lead–acid batteries (traditional and advanced) that include low cycle life and low charge acceptance, as well as lead-acids high module variation seen within battery strings.  PbC® batteries are fully recyclable and a fraction of the cost of non-recyclable chemistries such as Li-ion.  Both Li-ion and Na-S have significant safety issues, each with recent fire incidents garnering national attention.  While Na-S batteries contain inexpensive materials, they are operated at extremely high temperatures and are especially unfit for mobile applications.  In addition, they require hours to re-charge compared to our fast rate of charge – minutes or even seconds depending on the application.


Q:  Is the PowerCube™ a behind or in front of the meter resource and does it have any impact of the system design?

Ans:  Currently, the PowerCube™ is configured as a behind the meter resource.  In essence this means that Axion acts as a virtual generator by curtailing load.  When the PowerCube is commanded to take load from the grid it uses that power to charge its battery.  When commanded to discharge, the battery is discharged into the plants load effectively reducing or curtailing its power consumption.  The PowerCube can easily be configured as a behind or in front of the meter resource.  The main impact is on system layout and interface with the power systems. 

Q: What other markets does the PowerCube bring value to?

Ans:  In addition to the portfolio of grid services, the PowerCube is capable of (frequency regulation, load leveling, power quality, backup power and renewable smoothing), it has uses in other markets that require dynamic power storage and utilization.  Power back up for oil drilling platforms is one example.  A modified version of the design is in the final stages of deployment in the hybrid locomotives market.  We are preparing to release a smaller scale version of the technology for improving power quality in large residential homes and in community storage.

Q: What type of battery management and/or remote monitoring is available?

Ans:  Axion utilizes our proprietary Battery Management System (BMS).  The system allows us to monitor the health and State of Charge (SOC) of each battery.  With this information, the computer algorithms can make intelligent decisions on how to operate the BESS.  The PowerCube can be monitored and controlled remotely through a secure VPN tunnel.

Q: Why is the charge acceptance and module variation of the PbC® technology important to the end user?

Ans:  The charge acceptance of a battery determines how fast it can be recharged and how many cycles it can participate in over a given period of time.  The PbC® battery’s proprietary carbon negative electrode does not sulfate as does the lead negative electrode in a lead–acid battery. The result is a PbC® battery that can cycle much longer (3 to 4 times) and much faster (2 to 3 times).  In grid applications, this translates into a significantly longer life product that bumps up against the utilities “length of life” requirements.  Furthermore, in 2012 FERC and PJM will begin “pay-for-performance” market participation compensation. The exceptional response time of the PowerCube will provide an increased financial benefit to the Owner.

In a series string of individual batteries, the overall string capacity is limited by the lowest performing battery.  The module-to-module voltage variation of PbC® battery strings is ten times lower than that of lead–acid battery strings, which require frequent equalization charges and/or battery replacements to maintain system capacity over time.  The end user of a PowerCube gets more capacity output with less variation, cost, and downtime – all contributing to improved ROI.


Q: Does Axion provide the entire contents of the PowerCube™ or just the batteries?

Ans:We currently provide the entire piece of equipment as a plug in module. In the future we will have others assemble this for us and in some circumstances we may just provide the batteries for an application.

Q: Are there any installations currently using PowerCube™ technology?

Ans:The PowerCube on our site is the first deployment of this technology. We have purchase orders for batteries and have other PowerCube proposals in various stages right now, but everyone wants to be able to see one and touch one that is actually operating in the marketplace. That's why we’re so excited to see our PowerCube in action.

Q: Where does Axion go from here with this technology?

Ans:As mentioned already, we have applications in numerous markets that alllend themselves to the unique characteristics of our product namely – increased cycle life; high state of charge acceptance; fast re-charge capability and low voltage variation in large string applications. The hybride vehicle stop/start market; hybrid trains; solar and wind storage; oil rigs; residential storage – are but a few of these market applications


Thomas Granville has been Chairman of the Board of Axion Power International since 2003 and President and CEO since April of 2005. Prior to joining Axion, Mr. Granville served as managing or general partner for startups and emerging companies in the construction, commercial real estate, multi-family housing, and cable television industries. Mr. Granville also served as president of the National Elevator Industry Inc., a leading trade association representing elevator manufacturers and contractors.

Comments (1)

Posted by wm Byers on 01/05/12, 06:56 PM

Excellent article. It is hard to believe that a product like the Axion PowerCube can actually cost less than other UPS systems and then get paid by the grid for behind the meter services it employs. Congratulations Axion on achieving the holy grail. A UPS system that pays for itself. How cool is that.

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