No. 29: On storage equipment (December 14, 2011)

Storage equipment is vital to level off the supply-demand gap of power between the daytime and nighttime, given the fact that renewable energy susceptible to weather and geographically-distributed power generation are expected to spread in the future. At present, sodium sulfur storage battery is commercialized. It employs metal sodium for anode, sulfur for cathode, and ceramics called beta alumina for electrolyte. It charges and discharges at 300-350 degrees centigrade, and it has a life of about 15 years. It has an energy density of about 100 watts per kilogram comparable to that of a lithium-ion battery. It enjoys high expectations as a stationery large-scale storage at present. Currently, only NGK Insulators produces and markets this kind of storage battery. It has an annual production capacity of 150,000 kW on an output basis.

The sodium nickel chloride storage battery that uses beta alumina for electrolyte like the sodium sulfur storage battery is also a high-capacity storage battery that operates at a high temperature. It is expected to be widely used in the future for delivery trucks and taxies that have to bear continuous load. In addition, another storage technology is available for surplus power from large plants that generates power using renewable energy, such as large-scale photovoltaic power plant called mega solar power plant. It electrolyzes water using surplus power, and produces and stores hydrogen. The stored hydrogen is converted to energy with the help of a fuel cell as necessary. However, lots of technological issues, such as increasing the efficiency of electrolysis of water and securing safety production and storage of hydrogen, are need to be settled to spread this technology.