NewsMolten Salt for Energy Storage Gets Another Chance, Maybe

Molten Salt for Energy Storage Gets Another Chance, Maybe

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A team from the Pacific Northwest National Laboratory (PNNL) has created a new system for storing energy in molten salt. The group claims that their “freeze-thaw battery” is a step towards creating batteries that are that are suitable for storage during the winter months.

Anyone who is involved in the process of transferring energy from acquisition to use it is a three major elements to this path including storage and capture of energy, along with transmission back to load. This is the case regardless of the size that is being used, whether it’s a small-power intermittent load on a small IoT equipment or huge grid-scale configuration. Based on the particulars that the app is using and the size of it, your energy pathway will include these three components in various proportions, and each will have distinct challenges.

The storage component of the equation is extremely difficult particularly in the case of renewable energy sources like wind power and solar energy which are intermittent, whereas the demands of the user aren’t. Alongside cost and reliability, a key aspect of a sustainable storage plan is that it offers a high energy storage density in terms weight and volume. But this can be a risk also.

The PNNL team’s research, which was funded by Imre Gyuk Director of Energy Storage at the Department of Energy’s Office of Electricity, has produced a new molten-salt scheme to store energy. This isn’t the first time we have used the molten slats in this way however, as the concept and the various ways to implement it have been in use for decades.

The authors claim that the difference is the fact that they claim that their “freeze-thaw battery” is a step towards batteries that can be utilized to store seasonal energy: saving energy during one season, like spring, and utilising it in a different season like autumn. The battery is recharged by heating the battery up to 1800C that allows ions to move through the electrolyte’s liquid phase to store chemical energy.

The battery is then cool to room temperature which results in “locking in” the battery’s energy. The electrolyte solidifies and the ions which shuttle energy remain nearly stationary. The substance is fluid at temperatures higher, but it is solid at room temperatures. If the energy needs to be utilized by heating the battery likely due to natural seasonal warming which means that the energy stored is released.

I won’t get into the specifics of the salt materials or electrochemical processsince they are thoroughly described within the PNNL research paper, “A freeze-thaw molten salt battery for seasonal storage” which was published by Science Direct (plus – shhh! Chemistry isn’t my forte). The project examined three closely related activation techniques for the cathode of nickel their battery to determine if they are comparable This is an interesting view.

They have some top-quality figures from their hockey puck-sized test unit, which is illustrated in Figure 2. The storage blocks are passively storing the energy in a low-cost manner because their lack of mobility at room temperature eliminates self-discharge channels.

The researchers boast of a remarkable capacity recovery rate of 90% over a time of between one and eight weeks. The researchers also state they believe that “the cells could effectively retain energy with comparable or superior performance to contemporary room temperature Li-ion batteries, which have low self-discharge rates at 2%-5% per month.”

Figure 2: Thermal–cycling performance under various cathode activations. (Source: Pacific Northwest National Laboratory)

A major benefit of these designs is that they make use of commonly available materials instead of rare earths. The cathode and the anode are made of solid nickel and aluminum, while the separator is made of fiberglass instead of a costly ceramic that can crack in freeze/thaw cycles. In addition those components (especially those that contain electrolytes) aren’t a threat to the numerous risks that are associated with traditional batteries.

In reading their document (I’ll admit that a lot in the science is beyond my comprehension) I couldn’t find an accurate understanding of traditional energy storage statistics for batteries including energy density by volume , weight and open cell voltage current ratings and energy (rate of flow). This could be because of a inability to comprehend from my side or maybe other causes.

What are your thoughts on the feasibility of this kind of scheme for storage of energy? Do you think the concept of a seasonal freeze/thaw conceivable or is it only feasible in very specific circumstancesin any case? Are you of the opinion that it can be scaled up to size and capacity ? This is often the most difficult aspect of any concept of energy storage even if it’s been proven to be feasible in a small-scale test?

Michal Pukala
Electronics and Telecommunications engineer with Electro-energetics Master degree graduation. Lightning designer experienced engineer. Currently working in IT industry.