Peak Shaving and Demand Charge Avoidance: 

Prudent Energy Vanadium Redox Battery Energy Storage System (VRB-ESS®)

Name of Project:
Peak Shaving and Demand Charge Avoidance:  
Prudent Energy Vanadium Redox Battery Energy Storage System (VRB-ESS®)
Oxnard, CA  
Peak Shaving  
Prudent Energy Service Corporation, a Delaware Corporation  
Prudent Energy Corporation  
Prudent Energy—600kW / 3.6MWh VRB-ESS®  
Private, with portions of project costs reimbursed at completion by state energy efficiency programs.  
Commissioned April 26, 2012 


Gills Onions operates one of the largest, most innovative and sustainable fresh-cut onion processing plants in the world. Its Advanced Energy Recovery System (AERS) that went into operation in July 2009 converts all of the plant’s daily onion waste into a combination of renewable energy and cattle feed. The result is increased energy independence, elimination of a significant waste stream, reduced operational costs and a smaller carbon footprint.


Gills Onions’ main economic motivation for using a VRB® system is to lower costs by shifting electricity generation from off-peak to on-peak periods.  The electric utility, Southern California Edison (SCE), uses rate tariffs that increase the cost for energy during high use periods, typically during a six hour period in the afternoon. Most of the electricity on the SCE system is provided by power plants that operate around the clock, like nuclear and combined cycle natural gas plants. as the load increases during the afternoon, SCE is forced to call on more expensive generators, like simple cycle natural gas turbines. This additional cost is passed through to the customer in Time Of Use (TOU) rates. Although Gills generates its own electricity, the company still depends on SCE for additional energy beyond what is produced by the onsite fuel cells. In addition, electricity usage at Gills tends to increase during the most expensive on-peak periods, which is typical of many industrial customers. Therefore, by charging the VRB-ESS® at night, and then discharging that power during the afternoon, Gills reasons it will be able to reduce the cost of expensive on-peak power from SCE. SCE also has a demand charge that varies by TOU. Unlike the charge for energy, the kW demand charge is assessed for the peak use during the month, as measured in 15 minute intervals. For example, the Gills plant may have a fairly steady power usage, which is typical for a 24 hour food processor. However, starting large pieces of equipment or whole processing lines can cause spikes in usage. these short spikes in power then set the demand charge for the entire month. Prudent energy storage can thus be used to protect against power fluctuations—discharging VRB® Power on Demand to avoid these unnecessary utility charges.


The VRB-ESS® at Gills Onions consists of three 200kW modules with enough Vanadium electrolyte to provide six hours of storage during the expensive on-peak utility rate period. In addition, the VRB® will respond to spikes in usage to reduce demand charges, with the full 600 kW available 24 hours per day. Moreover, if permitted by the local utility, the system can pulse an additional 50%, to 900 kW, for 10 minutes each hour, providing additional capacity for other events. Together, these reductions in on-peak energy costs and demand charges are estimated to save Gills Onions hundreds of thousands of dollars per year in lower electricity bills. Prudent Energy Services Corporation, a subsidiary of Prudent Energy Corporation, will own, operate, monitor and maintain the VRB-ESS® to ensure its safe and reliable performance. remote, automated system controls allow gills to focus its time on the food processing business, not on keeping its utility bills in check. This project creates the foundation for economies of scale in delivering large “flow battery” systems it provides a sustainable, commercially viable example of how advanced energy storage technologies are bringing our centuries-old electric grid into the modern era—reducing costs and improving reliability for power producers and consumers throughout the United States.

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