Vanadium Redox Flow Batteries

The vanadium radox battery energy storage system (VRB) is a flow battery that is capable of storing energy in multi megawatt ranges and for durations of hours or days - from any available input source such as the grid, renewable resources or a diesel generator. The stored energy can be returned to the grid or supplied to a load as required and directed. The VRB is capable of being charged as quickly as it was discharged and is able to respond to all forms of power quality variations and can be operated in a UPS mode as well. For loads which require reactive energy, the VRB can provide VARS on a continuous basis either when charging or discharging. Flow batteries are further described in this previous post.

The durability and wide design options of vanadium batteries promise large markets for many applications, such as load leveling, storage in renewable energy systems (e.g. wind and solar) and uninterpretable power supplies.

VRB's are based on the patented vanadium-based redox regenerative fuel cell that converts chemical energy into electrical energy. Redox is the term used to describe electrochimical reactions in which energy is stored in two solutions with electrochemical potentials sufficiently separated from each other to provide an electromotive force to drive the oxidation-reduction reactions. In the VRB energy is stored chemically in different ionic forms of vanadium in a dilute sulfuric acid electrolyte.  This creates a current that is collected by electrodes and made available to an external circuit.  The reaction is reversible allowing the battery to be charged, discharged and recharged.

The cost is quoted in $/kWh or $/MWh since the VRB is an "Energy Storage System" and should not be considered a UPS or even a generator. Although the VRB provides the full UPS capability, its primary use is for energy storage for long periods, which UPS and conventional technologies cannot provide. As an approximate cost, systems are priced between $350-$600 per kWh, sizes ranging from a few hundred kW's to MW size systems. As the size of the system in kWh increases, the cost per unit decreases significantly. For example, a system rated at 100MWh would have an installed cost of about $325 per kWh. The incremental cost of storage for large systems is approximately $150 per kWh.

Performance

• The VRB has an availability of greater than 98%. It is designed for unattended operation with very low maintenance costs.
• No degradation from repeated deep charges and discharges. The system can be discharged and charged greater than 13,000 times (20% to 80% SOC) without deterioration in system efficiencies.
• System round-trip efficiencies between 70% - 78%.
• The VRB-ESS has a charge/discharge window of 1:1 - allowing off-peak charging for on-peak dispatch - a fraction of the time required by other battery systems and ideal for wind generation applications.
• Cross mixing of electrolytes does not lead to contamination of electrolytes
• Indefinite life of electrolyte (no disposal or contamination issues).
• Once charged, the electrolyte remains fully charged with low self-discharge.

This technology is one of the only socially responsible energy storage options in existence. As a "green" technology, the VRB is characterized by the lowest ecological impact of all energy storage technologies and is unlike most other conventional energy storage systems that rely on toxic substances such as lead, zinc or cadmium. The electrolyte is a solution of vanadium mixed with a dilute sulfuric acid, with about the same acidity as in a conventional lead-acid battery. Unlike lead acid systems however the VRB electrolyte has an indefinite life span and is reusable.

The electrolyte in vanadium reflux batteries is known as an "Aqueous Solution of Sulphates of Vanadium". It is made up of sulfuric acid, and emulsified vanadium particles. The electrolyte is pumped from separate storage tanks into flow cells across a proton exchange membrane (PEM) where one form of electrolyte is electrochemically oxidized and the other is electrochemically reduced. 

The cell stacks are self-contained sealed devices that consist of many cells, each of which contains two half-cells that are separated by a membrane. In the half-cells, the electrochemical reactions take place on inert carbon felt, polymer composite, electrodes from which current may be used to charge or discharge the battery.

When charged electrolyte solution is allowed to flow through the stack, ionic transfer between the different forms of vanadium ions across a separating membrane will result in a balancing electron flow into an external circuit (DC current) and so complete the electrochemical path for discharge. Forcing current into the stack from an external source reverses the process and recharges electrolyte in the stack, which is then pumped back into the reservoirs.

The balance of components required for the installation of a VRB consists of PVC pipes for connection between the electrolyte storage tanks and the Cells Stacks, and pumps to circulate the electrolyte through the system. Where required, heat exchangers to maintain the operating temperature of the electrolyte are included. In cold climates the heat exchangers are not required.

Commercialization

VRB was pioneered in the Australian University of New South Wales (UNSW) in early 1980's. The Australian Pinnacle VRB bought the basic patents in 1998 and licensed them to Sumitomo Electric Industries (SEI) and VRB Power Systems.  UNSW has recently developed a variant of VRB, the vanadium bromide battery which is being developed by V-Fuel Pty Ltd.  This technology is not reviewed in this post.

VRB Power Systems Inc. of Vancouver, B.C. Canada is an electrochemical energy storage company that is commercializing the patented Vanadium Redox Battery Energy Storage System ("VRB-ESS") and has acquired the intellectual property rights and assets to the Regenesys Energy Storage System.  In May 2005, VRB Power acquired a world-wide license to SEI's patents and technology (excluding Japan).

VRB Power Systems. electric storage systems (VRB-ESS) are intended for applications from 2.5kW's to 10MW's with durations of 2 hours and greater.  VRB's vanadium products are aimed at two markets:

1. The VRB-ESS is sized for telecom applications (2.5kW's to 10kW's - multiple hours) intended to replace lead acid battery backup systems.
2. The VRB-ESS is designed for Utility and Remote Area Power Supply systems (less than 25kW's - multiple hours).

Cellennium Company Limited- A team of European scientists created a novel design architecture of the vanadium battery.  This design is said to allow economical production for vanadium batteries in modular sizes as small as 3 to 5 kilowatts, thus potentially enabling wide­ spread use of energy storage for small, distributed applications. The technology of the new vanadium batteries is easily scalable to megawatt sizes.

This novel technology is now owned by Squirrel Holdings Limited; Cellennium Company Limited has acquired from Squirrel the rights of the use and development of the new vanadium batteries in Thailand. The Cellennium Company Limited has recently launched a program to commercialize these batteries. The new vanadium batteries are working successfully in the laboratory, and are giving excellent results. The unique features developed by Squirrel Holdings Limited are as follows:

• The electrolytes are fed through a stack of cells in series instead of in parallel as in other designs.
• The cells in a stack consist of pairs of high precision molded structural components designed for speedy "LEGO style" error ­free assembly with o­-ring sealing to prevent leaks.
• The electrodes, sandwiched between novel glassy carbon bipolar plates and the cell membranes, consist of carbon fiber mats permeated by a system of fine channels to distribute the electrolyte through the whole area with very small flow resistance.
• The cells are placed horizontally in a vertical stack to make a compact and structurally stable unit.
• A novel hydraulic feature within the system allows the battery to be "black started'' from a state of total inactivity without the need for priming of the electrolytes from outside sources.
• Production of the electrolytes can be done modularly and electrochemically, operating at room temperature, without the addition of chemicals.

Sumitomo Electric Industries, Ltd. (SEI) has been involved in the development of redox flow cells since 1985 in collaboration with Kansai Electric Power. They have successfully built demonstration scale units for grid load leveling applications and have been building and installing commercial scale units in Japan since 2001. 

Applications

SEI has 16 operational VRB systems in Japan, which include peak shaving, utility and renewable energy storage applications, and has developed a 42-kW cell stack.  A 3 MW x 1.5 sec. plus a 1.5 MW x 1 hr system for Tottori Sanyo Electric has been operating since 2001 at a large liquid crystal manufacturing plant as a combination of UPS for voltage sag compensation and a peak shaver to reduce peak load.

The VRB-ESS installation for PacifiCorp in Castle Valley, Utah, was the first large-scale commercial VRB-ESS in North America. The 250kW X 8 hour (2 MWh) unit which is connected to an 209 mile 25kV rural feeder, is being used as a load leveling (peak shaving) device to supply peak power capacity to a remote location in southeast Utah. The VRB-ESS enables PacifiCorp to assure the energy supply, while deferring the need for a new sub-station. The system includes innovative control interface applications and provides considerable impact on local voltage and power factor control. The installation site is in an environmentally sensitive area of national parks in southern Utah, and the VRB-ESS is unobtrusive and flexible.

The VRB-ESS installation for Hydro Tasmania on King Island in Australia was completed in November 2003. King Island is a small remote location off the south coast of Australia that supports and operates 5 wind turbines ranging from 250 - 850kW and Four Diesel generators at 1.5MW each that act as a remote grid to supply power to the local residents. The 200 kW x 4-hour (800 kWh) VRB-ESS installation has been integrated with the wind turbines and diesel generators to form a 3-way hybrid system that improves power supply and quality to the community of King Island.  The VRB-ESS is used to smooth the short term output variations in the wind generators and the customer loads while providing frequency and voltage control.

VRB Power Systems announced that it has sold a 30kW x 2 hour VRB-ESS to the South Carolina Air National Guard. The VRB-ESS will provide power quality enhancement and back-up energy supply for a tactical radar system in the event of grid disruption. The VRB-ESS system will improve energy efficiencies and economics by supplying backup power for 2 hours versus 10 minutes currently provided by a UPS system.  Additionally, the VRB system has an expected 10 year (or greater) system life and the flexibility to add hours of power supply by simply increasing the volume of electrolyte.

Suppliers:

VRB Power Systems Incorporated, Vancouver, B.C., Canada
Cellennium (Thailand) Company Limited, Bangkok, Thailand
Sumitomo Electric Industries, Ltd., Osaka, Japan (no information available on website)
V-Fuel Pty Ltd, Sydney, Australia (vanadium bromide battery)

Other Resource:

Electricity Storage Association, Vanadium Redox Batteries, Morgan Hill, CA
New Vanadium Batteries--A Breakthrough Solution for Electricity Storage, Exell, R.H.B., et al, University of Technology, Bangkok, Thailand and Cellenium Company Limited, Bangkok, Thailand

More blogs about energy storage, flow batteries, renewable energy, renewable, technology, energy

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