Blue Sky Energy offers saltwater-based residential solar storage


pv magazine: Blue Sky Energy offers a salt water-based home storage system as an alternative to common lithium-ion batteries. How does the basic principle of this technology work?

Helmut Mayer: The basic principle is very simple. The technology is similar to lead-acid batteries, except that only natural materials are used. The ions move in the electrolyte to the anode or cathode, thereby charging and discharging the battery. The electrolyte consists of salt water and is therefore also the namesake. This storage technology allows a 100% over-discharge (100% DoD) without damaging the battery. Thus, 100% of the storage capacity can be used. Due to the materials used, the battery is completely non-toxic and neither flammable nor explosive.

Where does the technology come from?

Some companies are working on saltwater technology. Blue Sky Energy uses Aquion's saltwater technology and Benan Energy's new generation of saltwater technology from China.

What are the advantages and disadvantages of saltwater-based home storage?

Advantages: It is safe and environmentally friendly, does not use hazardous materials and rare earths, low self-discharge, maintenance-free and robust, being 100% deep-discharge capable and able to last longer without loading. The storage tanks have a wide temperature range of -5 degrees to +50 degrees Celsius for the new generation. They are also easy to install. Disadvantages are the energy density – twice as large as a comparable lithium product – and the C rate, which is limited at 0.5C.

What is the market price of your systems?

In terms of price, they are close to those of comparable lithium products.

Since when is the company active in the market, and how many of its systems have been installed?

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Blue Sky Energy has been working with power storage technologies for over six years. For four years, we have been actively selling the saltwater technology, which we developed further in 2017 into the complete “Greenrock” system. To date, we have successfully installed around 300 storage tanks.

Were these only for photovoltaic home storage or also for commercial storage?

Primarily home storage, and occasional commercial storage with around 100 kWh.

The market share is still rather low. What are your perspectives for this technology?

We see great potential for the home storage market as we notice that the issue of safety and environmental friendliness is becoming increasingly important in this segment. Our distribution partners usually offer our “Greenrock” saltwater storage tank as an alternative to conventional products (mostly lithium). One in three end customers then opt for the saltwater technology. The market share is still low, as the sales partner network is also small.

Here we focus on finding further good distribution partners. We see further potential for the off-grid market, this means classic stand-alone systems. Here we are strong due to the wide temperature tolerance, freedom from maintenance and the robustness and reliability of the technology.

Are you actively working on the further development, for example on improving the energy density of the storage systems?

We work with our partners to improve the system's energy density and C-rate. Furthermore, we are developing the “Greenrock” saltwater storage tank into a ready-to-connect commercial solution. With the integrated energy management system (EMS) for our “Greenrock” product line, we were recently able to successfully conclude a product development that offers the end customer many options with regard to integration with electric charging stations, peak shaving or hot water generation.

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