What is the Vanadium Redox Battery Energy Storage System ("VRB-ESS")?
The VRB-ESS is a device 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 diesel generator. The stored energy can then be provided back into the Grid or supplied to a load as required and directed. It is uniquely capable of being charged as quickly as it was discharged and is able to respond to all forms of power quality variations and so can be operated in a UPS mode as well. For loads which require reactive energy, the VRB-ESS is fully rated to provide VARS at nameplate on a continuous basis either when charging or discharging.
What are the Ranges of VRB-ESS Sizes Available?
Small units are used for communications and/or substation battery replacement - for any specified number of hours of storage. These units are NEMA cabinets for standalone indoor or outdoor use and adhere to cell phone tower, battery backup standards. Larger units are available in 50kW increments with any specified hours of storage. You can specify storage requirements separately from power rating.
What is the Energy Density of the Electrolyte? (Wh/litre?)
This is a function of the application requirement and can range from 16Wh/litre to 25Wh/litre as measured on a round trip charge/discharge cycle. These are actual measured and delivered values and should not be confused with ideal theoretical values which could be as high as 28 to 43Wh/litre. Other energy storage systems often quote theoretical values.
What is the Power Density W/kg
This is a function of the system cell stacks and electrolyte. For large systems this is 220 Watts/kg and for the small systems about 110-120 W/kg.
Does the Electrolyte Self-Discharge?
Once charged the Electrolyte has very low self discharge as it is circulated through the cell stacks. If charged and stored separately it will remain charged almost indefinitely.
How Many Hours are Required to Charge for Each Hour of Discharge?
You can charge the system as quickly as you discharge it. The system provides a roundtrip efficiency of approx. 80%. Therefore with the input of 20% additional power to cover the losses, you can get 1 hour of discharge for every hour of charge.
How Fast Can it Respond to Short-Term Events?
Transient response to millisecond events such as voltage sags or motor starts is a standard capability of the system. Its use as an UPS is thus possible.
What is the Footprint? What are the Weights of the System Components?
A unique factor of the VRB-ESS is that you can position or locate the electrolyte tanks separately from the Cell stacks and Power electronics. This allows you to design the system footprint to fit virtually any space. The largest area required is for the electrolyte storage tanks. This can be determined from the energy density in Wh/liter. You can then chose the shape of the tanks and hence footprint of the system. For example a 1 MW 8Hour storage system will require: 8,000 kWh x 1,000 (watts/kW) / 20 Wh/liter = 400,000liters of electrolyte. If 2 meter high square tanks are chosen then the footprint for the tanks will be 200 square metres. The cell stacks and Power conversion systems will add a further 10 to 15% to the space.
The electrolyte weighs about 1.4kg/liter and is usually over 90% of the total weight of the system.
What is the Life Cycle of the VRB-ESS?
The VRB-ESS can be discharged and charged greater than 12,000 times without deterioration in system efficiencies and suffers no degradation from repeated deep charges and discharges. The anticipated life of the system is over 15 years, and could be extended by replacing the membranes in the cell stacks. The electrolyte will retain a residual value close to its original cost as it is completely reusable.
What is the Time Required to Complete an Installation?
Delivery schedule is approximately 6 to 8 months from order to energisation, including environmental permitting.
What is the cost per kW? What is the Incremental Cost of Additional Storage Capacity?
The cost is quoted in $/kWh or $/MWh since the VRB-ESS is an "Energy Storage System" and should not be considered a UPS or even a generator. Although the VRB-ESS 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 $50 per kWh.
What are the O&M Costs Associated with the VRB-ESS?
There are only two moving parts in the VRB-ESS. These are low maintenance long life pumps, which require replacement every 5 to 7 years. All other operations and maintenance costs are limited to possibly two visits per year to check on overall status of the system. Detailed on line data is available to determine if any unplanned maintenance is required. Operations are automatic and programmed into the system controller. We estimate an O&M cost of $0.001/kWh is required. Reliability is thus very high.
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