The home storage market is currently dominated by lithium-based systems. High-performance alternatives such as Vanadium Redox Flow (VRF) technology have not been able to establish themselves in the past despite major advantages, due to high production costs and end-customer prices. VoltStorage GmbH is now the first company in the world to successfully and cost-effectively launch VRF home batteries on the market, thanks to a patent-pending production automation.
Energy storage systems are considered to be a pioneering key technology for making renewable energies available around the clock. In the bulk storage segment, there are many approaches ranging from mechanical solutions, such as pumped storage or power-to-gas power plants, to electrochemical approaches based on lithium, redox flow or corresponding hybrid solutions. This technological diversity has not established itself in the home storage segment; lithium systems dominate the world market almost exclusively. The critical factor is the lack of innovative solutions boosting the cost-competitiveness of alternative high-performance technologies on the home storage market.
How Vanadium Redox Flow Battery Technology Works
The vanadium redox flow (VRF) technology, which has been successfully used in large storage facilities for years, is classified as a high-performance storage technology. In the summer of 2017, for example, Europe’s largest battery, put into operation at the Fraunhofer Institute in Pfinztal, southern Germany, was based on VRF technology. In contrast to conventional technologies, VRF technology relies on an electrolyte liquid as the main energy carrier. This liquid flows in two circuits with different oxidation levels and is pumped through specially designed battery cells – for this reason VRF batteries are also known as flow batteries. The battery cells consist of two half cells separated by an ion-exchanging membrane. During the charging process, the battery cells are supplied with electrical energy, which leads to an oxidation in the cathode half-cell and a reduction of the electrolyte in the anode half-cell – hence the term “redox flow”. The electrons released in the cathode half-cell migrate via graphite electrodes into the anode half-cell, which in turn is supplied by the ion-exchanging membrane with positive balancing ions from the cathode half-cell. Thus, a reversible conversion process from electrical to chemical energy takes place.
Advantages of VRF Technology
VRF technology has several advantages for home storage applications. VRF based systems guarantee maximum safety, as the electrolyte liquid used is 100% non-flammable. The liquid electrolyte is also the reason for the high durability of VRF storage devices, as it excludes the formation of dendrites. This formation is typical for many electrochemical processes and leads to capacity losses. VRF systems can thus be loaded and unloaded infinitely often without losing capacity, which is a significant advantage in providing charge-intensive grid balancing power. In addition, the vanadium dissolved in the electrolyte liquid is highly recyclable. After electrochemical oxidation, the electrolyte only needs to be heated to 70°C to absorb the dissolved vanadium pentoxide. A fact not to be underestimated in the context of global resource security and price stability.
First Successful Market Launch of VRF Home Batteries
Despite the advantages, no VRF storage system has been able to establish itself on the home storage market in the past. In 2016, the SCHMID Group was the first supplier to introduce a corresponding system at the ees trade fair. However, due to enormous purchase costs and the size of the overall system, which complicated the installation in private households, the hoped-for market success failed to materialize.
As the first supplier worldwide, VoltStorage GmbH accomplished to successfully launch VRF home storage systems this year, thanks to a patent-pending production process that, for the first time, allows fully automatic production of VRF battery stacks. Until now, this complex production process was always done manually, which made down-sizing for the home storage market unprofitable, as the example of the SCHMID Group shows. For the first time, automated stack production makes it possible to produce at low cost, notably lowering the end customer price. The compact 3-phase system (power: 3.0 kW | capacity: 6.8 kWh) with emergency power function has an LCOS of € 0.13 / kWh (incl. installation and integrated battery inverter). By coupling two or more systems, performance and storage capacity can be increased as required. So far, VoltStorage has been offering its VRF storage system on the German market. International expansion is planned for the coming years.
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