Environmental Evaluation of Batteries for Electric Load Leveling

Abstract

Objective. The batteries spread mainly on a lead-acid battery for cars. A nickel-metal-hydride battery and a lithium-ion battery were put to practical use in 1990's, and then these new batteries have spread rapidly because of high energy density. Recently, large-scale batteries for electric load leveling are attracted a great deal of attention for global environment. We have estimated the effects of batteries for electric load leveling as a case study. Energy and environmental loads on four types of batteries of lead-acid（PbA）, nickel-cadmium（NiCd）, nickel-metal-hydride（NiMH）and lithium-ion（Li-ion）batteries were analyzed for high-efficiency usage of electricity using a life cycle assessment method. The net total efficiency was estimated considering loads on the material process such as production, manufacturing and use. This total efficiency was calculated with the ratio of the life cycle discharged energy to the life cycle input energy. The CO₂ emission intensity was also analyzed for the electric-load leveling.

Results and Discussion. In case of using the nighttime electricity, the CO₂ emission intensity for the battery system decreased to almost the same level for the CO₂ intensity of the daytime electricity. In particular, the lithium-ion battery showed the smallest loads. The effects of use conditions for the battery such as the depth of discharge（DOD）and the discharge rate（C rate）were then analyzed. It was clarified that the CO₂ emission intensity was varied according to the use condition.

Conclusions. Large-scale batteries for electric load leveling are expected to use widely for not only industrial sector but also electric vehicles and residential photovoltaic system. It is promised that large-scale batteries are going to play an important role in electric load leveling in the near future.