First of all, great idea! You would certainly not be the first person with that desire, but bear in mind that you consume A LOT of electricity throughout the year, the average Dutch citizen approximately 3500 kWh. Your solar panels will mainly generate electricity in the summer time, approximately 8 to 10 times as much as during a winter day, and hence you would need a storage capacity of almost 1000 kWh to go fully off-grid, without having backup capacity by diesel generators. If you use electricity for cooking and heating you will require even more energy storage capacity. And, that is expensive. Traditional batteries are not made for long duration storage, and when you increase capacity (kWh) you will get a high power capacity with it (kW). That makes storage unnecessarily expensive. When we launch our battery we will charge you for your desired kW and kWh capacity independently, and as our kWh’s offered are basically salty water, it will be much more affordable, safe and better for the environment.

We know that our energy density is not comparable to Li-ion technology and we will never even get close to such an energy density. Our technology does not focus on similar applications as Li-ion, we only focus on stationary applications, like the ones mentioned. Each storage technology has its advantages and disadvantages, that’s totally fine, and technologies can perfectly co-exist. Li-ion could for example focus on the larger power capacities, while we focus on the large storage capacities, and together we could make electricity supply a bit more sustainable!

Our product is still in development. Technology is still expensive today, and we’re working day (and sometimes even night as well) to make it more affordable. We do this along with the line of three pillars: 1) We look at the entire system price, sourcing cheaper materials with similar or even higher quality to reduce cost price and improve performance. 2) Membranes are a large cost component in our system (they generate the power). Buying larger quantities of membranes reduces the cost price of this, and hence we are building large(r) scale pilot projects to get this price down. 3) Improvement of performance. This aspect leads to a cost price reduction as well, as increasing the efficiency or power output of the system leads to less material needed for the same power output, and thus you as a customer will have to pay less for our battery. At the moment, our whole team is focussed on having a first product available by 2023. This will not be for the household market, we will only start developing a product for that market after 2025.

Energy storage, in general, provides added value in the sense that it allows increasing PV and wind capacity installed up to 100%, and allows the omission of power outages caused by the renewable energy production peaks. The efficiency of renewables is increased (by 30 up to 50% depending on the penetration rate), as the intrinsic instability and highly fluctuating output of solar and wind is annihilated. The Blue Battery removes this inefficiency by storing the electricity in times of peak production and delivering grid stability and enhances the share of own consumption of solar and/or wind energy. To put in a broader perspective, ion-exchange membrane technology is also utilised in other industries. Nowadays ED is perceived as one of the most economical processes of production of drinking water, especially with salt concentrations below 5 g/L (i.e. brackish water). More than 2000 plants have since then been installed with a total membrane area installed of more than 1.5 million m2. As the technology allows to concentrate and dilute streams of water (i.e. the charging process), the technology could in practice be useful for removing salt (e.g. sodium chloride, phosphate, nitrogen) from the ground- and/or surface waters. Furthermore, integration of a bipolar membrane allows to separate brackish water in an acidic and base stream, and as the technology is food-grade, it’s perceived as being the most suitable for acid and/or base production for food industry applications (e.g. removing the mesocarp in mandarins).

At the moment AquaBattery is still developing the Blue Battery technology on a pilot-scale level. The focus is on cost price reduction and improvement of performance in this first period. We are investigating already on how to further reduce the environmental impacts of our storage system, by using for example recycled materials (e.g. polymers from plastic waste). When the technology becomes large-scale and worldwide available, we deem important to reduce the total quantity of transportation. One of the core priorities by then is to use as many local materials as possible. Our storage system allows to do so. Reservoirs can be made from locally available materials, as long as the materials are able to withstand the concentrations under specific temperature conditions. The same holds for tubing and piping work. Depending on the country, pumps and sensors could be sourced locally as well, as long as they meet certain criteria set. When the moment is there, we aim to solely export our membrane stacks to the site, with an integrated power converter, and a battery management system to operate the battery.

The Netherlands has a strong base in the development of water (membrane) technology, and together with company partners as FujiFilm Europe, Wetsus, TU Delft and REDstack we are strengthening this position even further. Progression in the development of the Blue Battery improves the water-technical knowhow and offers high potential as an export product.

As the technology allows to concentrate and dilute streams of water (i.e. the charging process), the technology could in practice be useful for removing salt (e.g. sodium chloride, phosphate, nitrogen) from the ground- and/or surface waters. In Figure 1-1 below it is visualised how the membranes separate specific salts within the stack. The cation exchange membrane only allows permeation of positive ions (e.g. Na+, P+, N+), while the anion exchange membrane only allows permeation of negatively charged ions (e.g. Cl-). The membranes can be tuned in such a way that they are more favourable to permeation of a specific type of ion. Hence, membranes are available that allow for example only phosphorus.

Figure 1-1. Conceptual visualisation of energy conversion schemes using Electrodialysis (left) and Reverse Electrodialysis (right) with 3 cell pairs (Nm=3). A is an anion-exchange membrane (AEM), C is a cation-exchange membrane (CEM). See Appendix B. Adapted from Strathmann (2004a).

To tackle salinisation, specifically, stacks could be build that has salt (or brackish) water as inlet stream. The water stream is then split in a concentrated stream of salt water, the other in a freshwater stream. The more power is put into the process, the larger the concentration difference that is being created. From the saline water stream, specific ions could be removed by further refinement processes, and sold onto the market (e.g. magnesium for fire extinguishers). The fresh water can be mixed with the natural water streams subsequently.

Energy storage using our technology has scalability as one of the unique selling points: power and storage capacity are decoupled and both can be independently up- or downscaled. Membrane stacks provide the power capacity, the storage capacity is retained in the water reservoirs (and more specifically in the concentration difference between the water reservoirs). A good way to compare is the analogy with a warehouse and a warehouse’ door. The total volume in the warehouse compares to the storage capacity, the size of the door with the power capacity. Traditional storage systems possess a specific volume to door ratio, wherein our battery we can make a small warehouse with a big door or a huge warehouse with a tiny door. The latter case matches the need for neighbourhoods, farms, solar- or wind parks to buffer seasonal fluctuations and increase with that the self-consumption of own generated electricity: power capacity can be fairly low, while large storage capacity is required.

The bipolar membrane allows storing electricity not only in a concentration difference between fresh and salt water but in a concentration difference between acid and base. In a fully charged system, 1 M acid and 1 M base is stored in a total volume approximately 1/3 of the salt water reservoir. The addition of the membrane allows improving the energy density of the system. While the Blue Battery stores electricity with an energy density of ~0.5 kWh/m3 of water, the energy density can be increased by a factor of 10 (i.e. 10x less volume needed for the energy storage capacity). The technology is not that far yet, for the first pilot we aim at 1.0 kWh/m3. In addition to that, the bipolar membrane increases the power output per membrane stack, by an approximate factor of 10 as well. This reduces the total membrane area by a factor 10, or in other words, instead of using ten stacks we only need to use one for the same power output. The last advantage is that the system produces a more stable voltage in time, allowing power conversion hardware to be more ampere and Volt-specific, reducing the cost price concurrently. At the first pilot the power capacity is 1.0 kW.

We strive for using as many natural materials as viably possible, but not in the initial development phase. Ideally, we would fill our battery from locally available water sources. 2/3 of our planet is covered by water, of which 97% is salinated. Filling the battery on an island with water from the sea would reduce transportation and appurtenant emissions. In that case, we would ship together with our stacks a dedicated membrane stack for filtrating seawater and making it suitable for our battery. Furthermore, as indicated previously, the polymer membranes we hope to source in a later moment in time from recycled sources, or from biological sources (e.g. sugarcane, maize) if technology allows.

Thanks for showing interest in doing so, and thanks even more for nice jokes about cations, join the club! While we could have chosen to write some nice words on that here, we prefer you reach out to us in person! Click here to redirect yourself to our beloved e-mail address magically OR please use the contact form at below.

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