POSCO, a large steel-maker in Korea, says it has succeeded in developing a sodium sulfur (NaS) battery for large capacity energy storage. With the goal of commercializing by 2015, POSCO has been developing a large capacity energy storing battery since January with RIST (a research institute wholly owned by POSCO).
This is a first for Korea, although, NaS battery technology is already in widespread use in Japan at more than 190 sites, totaling more than 270 MW (according to the Electricity Storage Association) and POSCO. The largest NAS installation in Japan is a 34 MW, 245 MWh unit for wind stabilization. U.S. utilities have deployed 9 MW for peak shaving, backup power, firming wind capacity and other applications; and project development is in-progress for an equal amount, according to the ESA.
POSCO claims its NaS battery has more than 3 times higher density than existing batteries with a lifespan of more than 15 years. In addition, unlike lithium ion batteries used as secondary batteries, materials are not particularly high in cost.
Prior to POSCO, Japan`s NGK has been the sole provider. As you can see in the chart, courtesy of NGK, NaS compares favorably to other energy storage systems.
As the smart grid business expands, the energy storage battery market which includes core technologies such as NaS batteries is forecasted to grow from approximately 450 million USD in 2010 to 10 billion USD in 2020, an average yearly growth of more than 35%, according to POSCO.
A NAS battery consists of liquid (molten) sulfur at the positive electrode and liquid (molten) sodium at the negative electrode as active materials separated by a solid beta alumina ceramic electrolyte. The electrolyte allows only the positive sodium ions to go through it and combine with the sulfur to form sodium polysulfides. During discharge, as positive Na+ ions flow through the electrolyte and electrons flow in the external circuit of the battery producing about 2 volts. This process is reversible as charging causes sodium polysulfides to release the positive sodium ions back through the electrolyte to recombine as elemental sodium. The battery is kept at about 300 degrees C to allow this process. NAS battery cells are efficient (about 89%).
Caption: NaS compared to other battery types, such as lead-acid, lithium ion and NiH. (Source: NGK).
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