Prudent Energy is the only provider of a full range of Energy Storage products for use by end users and utilities. This comprises four product lines:

The VRB-ESS for small systems sized for telecom applications intended to replace lead acid battery backup systems from 5kW (multiple hours).

The VRB-ESS for larger applications up to 10MW's (multiple hours).

You can specify storage requirements separately from power rating.

This is a function of the system cell stacks and electrolyte. For large systems this is 100-150 Watts/kg and for the small systems about 80 Watts/kg.

You can charge the system as quickly as you discharge it. The system provides a roundtrip efficiency of 65 - 75%. A practical charge discharge ratio for optimal economic performance is about 1.7 to 1.

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. In a DC application it is always "on" so instantaneous response is provided. There is no need for any bridging device as fuel cells require.

A unique factor of the VRB-ESS is that you can store the electrolyte 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 8-Hour storage system will require 1MWx 1,000,000 x 8hours / 15 Wh/liter = 540,000liters of electrolyte. The cell stacks and Power conversion systems will add a further 20% to the space. The electrolyte weights about 1.4kg/liter and is usually over 90% of the total weight.

The VRB-ESS electrolyte can be discharged and charged any number of times at 100% DOD and suffers minimal degradation from repeated deep charges and discharges. The anticipated life of the system is over 10 years, and could be extended by replacing the cell stack. The electrolyte will retain a residual value close to its original cost as it is completely reusable.

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 calculate and have measured an O&M cost of $0.008/kWh is required. Reliability is thus very high.

Each VRB-ESS consists of four major components.

a- Balance of plant (frames and plastic piping, pumps, valves and controls)

b- PCS

c- Cell stacks

d- Electrolyte and tanks

At the end of the project life the electrolyte can be reused or reprocessed to extract the vanadium. In general Prudent Energy will offer to buy back the electrolyte for reuse. The BOP and tanks are required to be disposed of as low grade hazardous waste given that they have been in contact with sulphuric acid and electrolyte. This is a simple task and well quantified. Cell stacks will be recovered by Prudent Energy for rebuilding or disposal as these will contain several tens of litres of electrolyte in their internal felt layers.

The PCS and transformer will be scrapped or reused as conventional electrical equipment.