Zwei Männer am Tablet in Forschungsabteilung
Vanadium Redox
Flow Technology
Redox Flow

Vanadium Redox Flow: Bulk-scale storage technology for your own home

Vanadium Redox Flow technology (VRF) has been successfully used for years as a large-scale storage technology for photovoltaic and wind farms. For the first time, VoltStorage takes this energy storage technology into your own home.

Operating principle of the Vanadium Redox Flow storage technology

The Vanadium Redox Flow (VRF) technology was already developed by the US space agency NASA in the 1970s. So far, it has only been used in bulk-scale storage systems – for example, in one of the largest batteries in Europe at the Fraunhofer Institute in Pfinztal.


Two separate tanks contain a vanadium-based electrolyte liquid with different oxidation levels, which is used as a storage medium.


The electrolyte liquid flows through two closed circuits into high-performance battery cells. If electrical energy is stored, the electrolyte is reduced in the negative half-cell and oxidized in the positive half-cell. This results in a conversion process from electrical to chemical energy.


A specially designed pumping system directs the electrolyte into battery cells. The pumping system is only activated when required.

Positively charged electrolyte tank

In the uncharged state, the positive electrolyte circuit contains vanadium ions with an oxidation state +4. In this state the electrolyte takes on a blue colour. Once it is supplied with the power that is to be stored, the vanadium ions oxidize and assume the oxidation state +5.

When the storage system is fully charged, the positively charged electrolyte circuit only contains vanadium +5. The electrolyte then shows a yellowish colour.

Negatively charged electrolyte

In the uncharged state, the negative electrolyte circuit contains vanadium ions with an oxidation level of +3. This causes the electrolyte to take on a blue-green colour. Once it is supplied with the power that is to be stored, the vanadium ions reduce and assume the oxidation state +2.

When the storage system is fully charged, the negatively charged electrolyte circuit only contains vanadium +2. The electrolyte then has a purple colour.

Battery stack

The positively and negatively charged electrolyte is fed into the battery to initiate charging and discharging processes. The membrane keeps both electrolyte liquids separate to ensure the efficiency of the battery system.

However, the membrane is ion-permeable, so that during charging and discharging the ions cross the membrane to complete the electric circuit.

This allows for electrical energy to be stored through a redox reaction, which converts electrical into chemical energy.

Pumping System

The positive and negative electrolyte circuits each have a pump system. This ensures that the electrolyte liquid is directed into the battery cells.

Advantages of Vanadium Redox Flow technology

Ecological and fully recyclable

VRF technology does not require the use of rare raw materials and conflict materials. The vanadium used as a storage medium is extracted during iron production – without exploiting nature. That’s why VRF technology is an ecological alternative to lithium energy storage systems.

100% non-flammable

Operational safety plays a key role in energy storage. The VRF technology offers a decisive advantage in this respect: The vanadium-based liquid electrolyte persists exclusively of non-combustible components, consisting mostly of pure water. VRF storage systems are therefore 100 percent non-flammable and offer more operational safety than other storage solutions.

100% capacity guarantee

Storage systems based on VRF technology can be charged and discharged at will without losing any capacity. Among all available storage systems,VRF batteries are the only solution able to maintain their initial capacity after 10,000 charging cycles. This makes VRF systems the most durable storage solution on the market.

VRF technology in VoltStorage SMART

Until now, VRF technology has been successful used in bulk-scale storage systems for years. The VoltStorage SMART is now the world’s first home battery that makes the VRF technology available for private households.

This was made possible by VoltStorage’s patent-pending production process, which for the first time allows an automated and cost-effective production of redox flow batteries.

VRF-Technologie im VoltStorage SMART Heimspeicher

Battery stack

The reduction or oxidation of the vanadium electrolyte takes place in the battery stack, which consists of 18 battery cells stacked on top of each other.

The patent-pending manufacturing process for the redox flow battery stacks is carried out at the VoltStorage headquarter in Munich – and is thus 100% Made in Germany.

Pumping system

The pumping system directs the vanadium electrolyte into the battery. The internal battery management in turn ensures that the low-noise pumping system is activated when required. This ensures an efficient pump usage.

Electrolyte tanks

Two seperate electrolyte tanks contain 220 litres electrolyte liquid in total.

Electronics & Battery Management

The electronics and battery management integrated in VoltStorage SMART have been developed by VoltStorage and specially designed for VRF technology.

Redox-Flow Batteriezelle von VoltStorage

Bipolar plate

The bipolar plate is used as the electrode of a Redox Flow battery cell. It is thus responsible for the electrical conductivity, which is increased on the material side by using particularly conductive and corrosion-resistant materials, such as graphite.

Ion exchange membrane

The transparent and thin layered ion exchange membrane separates the positve and negative charged half cell and ensures the separation of the two differently charged electrolyte circuits. It only allows an ion exchange between the half-cells, which is necessary for power storage or discharge.

Graphite felt

Via the liquid channels in the cell frame, the positve or negative charged electrolyte, which serves as a storage medium, is directed into the respective half cell.

There the electrolyte is taken up by the large-area graphite felt and distributed evenly in the two half-cells. This results in a charge exchange between the differently charged half-cells via the ion exchange membrane.

Cell frame with liquid channels

The cell frame of VoltStorage Redox Flow battery cells has several small liquid channels. These channels allow the electrolyte liquid to flow evenly into the battery cells.

Battery cells in the VoltStorage SMART

The Redox Flow battery cells of the VoltStorage SMART consist of two half cells each. Each half cell has a frame with liquid channels. In the middle of each half cell is a large-area graphite felt. The half cells are separated by an ion exchange membrane. Each battery cell is enclosed by two bipolar plates.

Why VoltStorage Home Battery?

The ecological alternative to lithium

Lithium-based power storage systems must be questioned in ecological terms. Thanks to Vanadium Redox Flow storage technology, we offer private housholds a sustainable and resource-saving alternative.

More about the ecological alternative

More energy independence

Use more of your self-generated solar power at home and thus save on your electricity bill – with our power storage device you and your family gain more independence from the energy market and rising electricity prices.

How to become more independent

Storing power - safer than ever

Conventional lithium- or lead-based power storage systems cannot guarantee full operational safety. Thanks to Vanadium Redox Flow technology, you can rely on the only storage system that is 100% non-flammable.

This is why VoltStorage is so safe

Energy storage Made in Germany

With the VoltStorage SMART home battery system you can rely on an eco-friendly energy storage solution that was fully developed in Germany. This provides you with high product quality “Made in Germany”.

Learn more about "Made in Germany"

Saving more CO2 with VoltStorage

With the VoltStorage SMART based on eco-friendly Vanadium Redox Flow technology, you can use C02-free solar energy around the clock – and make an important contribution against climate change.
How can I save CO2 with VoltStorage?

Free data monitoring via VoltStorage App

With the VoltStorage App you have access to all data around your energy storage system, your PV system, your power consumption and your C02 emission savings – at any time and on all devices.
Learn more about the VoltStorage App