PacifiCorp is a utility based in Portland, Oregon with operations in six Western states. The Castle Valley site was serviced by a 25 kV feeder over 85 miles long, with 209 miles of total line. The length of the feeder led to complaints of low reliability and power quality. In addition, the feeder could not supply any significant amount of new load without causing low voltage to existing customers. Traditional alternatives to add capacity and improve service in this area are costly and environmentally difficult, so that PacifiCorp has sought viable alternatives to meet these goals. The Castle Valley VRB System was built and commissioned for this purpose.

Vanadium redox flow batteries store energy in two electrolytes which are pumped from separate storage tanks across proton exchange membranes in the cell stacks, producing a DC current. The reaction is reversible, so that the battery can be charged and discharged repeatedly with high efficiency. The VRB-ESS™ at Castle Valley was built by VRB Power Systems of Vancouver, British Columbia. The system was sized to provide 250 kW for 8 hours, with a round-trip efficiency when fully operational of between 65% and 80%. The system incorporated a power converter which converts the DC power provided by the battery to AC power during discharge, and vice versa during recharge. The power converter was also capable of providing reactive power compensation and overload capability for short periods of time. The system was commissioned in November 2003, operational in May 2004, and was decommissioned in Spring 2008.

Vanadium Redox Flow Battery