## 1 Introduction  
Wind turbines have already seen widespread use in both grid-connected and remote electricity generation. Large grid-connected wind farms are currently in operation and in development all over the world. The major economic and practical drawback of wind energy is its intermittent nature. Wind energy demands not only that the wind is blowing, but also depends on cut-in and cut out wind speeds--the wind speeds at which generation begins and is stopped to avoid damage respectively. Despite careful consideration given to site selection in order to ensure a relatively stable wind source and strength, the wind and its strength still cannot be guaranteed. This has a number of implications. Firstly, wind turbines have an average production of only about 33% [1] of their rated power meaning wind farms need to be oversized in order to accommodate reduced wind speeds, greatly increasing capital costs. Secondly, wind power is afforded only limited grid penetration before grid instabilities can occur. At or below the limit of penetration a cut out in wind can be compensated for elsewhere on the grid, but above the limit of penetration the grid is too reliant on wind, so without some means of storage can be very vulnerable to power shortages. Thirdly, for non-grid connected systems, an additional power source such as a diesel generator or a means of storage is required. Power generation systems in remote areas typically rely on diesel generators and as such are susceptible to the upward trend in the price of diesel. In order to overcome this, many remote communities are installing wind turbines to reduce their dependence on diesel. The use of an electrochemical energy storage system as an integration technology can potentially further increase the renewable penetration of these wind/diesel systems and in doing so offer long-term tangible monetary and environmental benefits. There are several types of electrochemical energy storage technologies currently in existence, from lithium ion batteries to lead-acid batteries. Redox flow cells are another type of battery that exhibits excellent potential for use as energy storage devices due to a number of desirable properties. Redox flow cells employ a half-cell arrangement and utilise electrolytes with different electrochemical potential to store and discharge energy. Flow cells have significant benefits over other batteries including a long operating life, lower capital and operating costs and greater capacity due to the separation of energy and power rating. The Vanadium Redox Battery (VRB) [2; 3; 4; 5], pioneered at the University of New South Wales (UNSW) is proving to have the desired properties required for successful energy storage. Currently two types of VRB are in differing stages of development. The Generation 1 VRB, also referred to as the All-Vanadium Redox Flow Battery, employs a V\({}^{2+}\)/V\({}^{3+}\) redox couple in the negative half-cell and a VO\({}^{2+}\)/VO\({}_{2}^{+}\) redox couple in the positive. In contrast, the Generation 2 VRB utilises Br\({}^{-}\)/ClBr\({}_{2}\) or Cl\({}^{7}\)/BrCl\({}_{2}\) and VBr\({}_{2}\)/VBr\({}_{3}\) redox couples in the negative and positive half-cells respectively [6; 7]. The distinguishing feature of both types of VRB over other flow cells is that the VRB employs a single vanadium electrolyte on both sides of the cell. This eliminates the problem of cross-contamination inherent in other types of redox flow batteries, gives an indefinite electrolyte life, reduces maintenance costs and results in excellent storage properties. The Generation 1 VRB has already seen extensive field testing and demonstration in a range of energy storage applications, with several VRB wind storage systems currently installed in Japan and Australia. In 2003 a 200 kW/800 kWh VRB was installed on King Island, Australia to store energy for a wind diesel grid thereby reducing diesel fuel consumption on the island.