No. 30: On small storage equipment (December 15, 2011)

Families equipped with a solar battery were able to use power in the daytime and give their neighbors an opportunity to take a bath in the disaster-stricken areas during the Fukushima disaster. As this story shows, generation equipment and storage equipment allow households to use the minimum amount of electricity necessary for daily life even though power supply from an electric power company is shut down. In this sense, household storage equipment and movable storage equipment will grow more important for the construction of a future energy system. In addition, operating such a distributed energy system as fuel battery that generates electricity from hydrogen requires storage equipment to allow for self-sustained operation of the system.

The current four major secondary chargeable batteries are lead battery, sodium sulfur battery, lithium-ion battery, and lithium air battery. The theoretical energy density is 165 kW, 786 kW, 583 kW, and 11,700 kW, respectively. Lithium-ion batteries are most popular at present, but excess voltage and low voltage greatly affect them. After the Fukushima disaster, household storage systems using a lithium-ion battery were commercialized by consumer electronics makers. They are mostly sold for 400,000-500,000 yen per kW. A household storage system is supposed to be put on the market for a little higher 100,000 yen per kW in 2012. Because a standard family with three members consumes about electricity of 3 kW per day, the price range a little higher than 100,000 yen is supposed to make a storage system spread wider.