Interest in the development of redox-flow batteries (RFBs) for large-scale grid storage is growing, and considerable investments have been made into the research and development of RFBs over the past few decades. Unfortunately, practical implementation has been hampered by various cost and performance issues typical of an immature state of development. One critical factor for the competitiveness of this technology is the installed cost. In this work, we incorporate recent developments in all-vanadium RFB research and present an analysis of the associated cost factors. The major components of a RFB that affect installed cost are identified and used as variables to create a capital cost function. The function is then used to calculate the rate of change of the capital costs with respect to the major components. The capital costs are also calculated for a range of component values and plotted. Key findings include a high sensitivity of system capital cost to purity of vanadium and substantial fractions of the cost associated with perflurorosulfonic acid membranes currently used for proton transport. (C) 2012 The Electrochemical Society. [DOI: 10.1149/2.041208jes] All rights reserved.