Utilities which must meet a continually growing demand for power, especially during peak periods, are often faced with very expensive investment options. In many cases, adding new generating capacity to meet these increasing peaks has been one of the only choices available. However, management at NGK Insulators in Japan now see a practical and comparatively low cost alternative to deal exactly with such a situation. According to Takashi Nakabayashi, General Manager of the Engineering & Technology Department at NGK’s Sodium
Sulfur Battery Division, improved battery technology offers the possibility for utilities to achieve load levelling in such cases and eventually at a lower cost than adding new generating capacity.
Nakabayashi explains that the initial development of the concept of load-levelling batteries actually came from the Tokyo Electric Power Corp. (TEPCO), Japan’s largest electric utility. In 1984, faced with a growing peak demand of about 5 per cent per year, TEPCO engineers were examining opportunities for adding new hydro-electric generating facilities, However, because of the height and storage requirements of any project to meet such a growth in demand, siting proved very difficult. “For them,” says Nakabayashi, “adding new power generation was really only necessary
to meet this peak demand requirement. Therefore they wanted to level their load factor if at all possible and began a study of different technologies for electric energy storage involving both rotating storage and chemical energy storage.”
The value of compactness of an NaS battery is one-third that of lead acid, or alternatively, its energy density is three times higher. The alternative battery technologies available at the time included lead acid and nickel-cadmium. However, compared to hydro pumping, the price of these types of batteries was considered too high and their energy density too low. In this respect, TEPCO engineers established targets for the price, durability and efficiency of a battery in order for it to be cost-competitive with hydro generation. The price target for the battery was calculated to be lower than ¥ 200,000 per kW and the criterion for durability was eight hours, based on the load curve of the utility’s distribution substations. Insofar as lifetime, the minimum was initially set at 10 years but later revised upwards to 15 years. Efficiency of the battery system was required to be higher than 75 per cent since hydro pumping has an efficiency of approximately 70 per cent.
