should be noted that air conditioners, refrigerators and other machines using CFC gas as a refrigerant should be treated carefully when discarded, as CFC gas causes the greenhouse effect several thousands times more intensively than carbon dioxide, and therefore a release of CFC gas into the atmosphere would be devastating, possibly voiding our efforts for reducing $ CO_{2} $ emissions.)

However, the introduction of such effective technologies has not yet been promoted thoroughly. But it means there exists a large potential: the introduction of state-of-the-art energy-saving machines and equipment or operational optimization of existing equipment could reduce $ CO_{2} $ emissions considerably. Thus, in order to effectively promote emission reduction, not only technology development but also the efforts to expand thorough utilization of available technologies is extremely important.

## Column : Technologies with High Potentialities

Here are some examples of potential technologies that are currently at the RD&D stage but are expected to produce substantial effects to mitigate global warming in the future, especially in the commercial, residential and transport sectors.

(1) Storage technologies (for electricity and heat)

Electricity is being widely used today. Although this energy is very convenient in general, it has an efficiency problem, since it is difficult to use electricity in a remote location from a power plant or supply line, as it cannot be stored easily. Therefore, it is hoped that high-performance batteries or condensers for accumulating an electric charge (lithium battery, sodium-sulfur battery, large-capacity capacitor, etc.) will be developed. For example, it would be quite useful if there were a durable large-capacity capacitor that can be recharged quickly and would scarcely deteriorate even after repeated charge and discharge. Such capacitor would make it possible to commercialize plug-in hybrid vehicles or other high-performance, high-efficiency electric vehicles that people dream of.

Heat is generated in various energy-consumption activities, and a potential for energy efficiency improvement exists here too. An effective heat storage device would make it possible to use stored heat regardless of time and place. An idea of a “TransHeat Container” is a technology to store and transport heat without time/space restrictions, such as day and night, cold place and hot place, and winter and summer. The development and commercialization of such technology as well as peripheral supporting systems are pending.

Fuel cells, which can convert chemical energy directly to electricity, are also potential electricity storage devices, where electricity could be stored in the form of hydrogen with the utilization of water electrolysis technology for hydrogen production. Early commercialization of such fuel cells is also pending.

Electric double layer capacitor

Photo: courtesy of Nippon Chemi-con Corporation

TransHeat Container Photo: courtesy of Sanki Kogyo Co., Ltd. This container carries a tank equipped with a latent heat-storage system, and is used to supply heat to a remote place by road transportation.

## (2) Utilization of cryogenic heat or unused heat

Consumption of thermal energy leads to a reduced heat temperature, which means a lower value of “exergy” (available energy). For example, high-temperature vapor has a high exergy, and can thus be used as a power source or for power generation. On the other hand, when the temperature of the water vapor lowers to that of the surrounding air, the low-temperature water is not able to provide energy. In the process of a temperature shift from high to low, waste energy is released into the atmosphere, and the idea of collecting such waste energy at every state of temperature shift would be quite