Nanotech 2010

Lead-acid Battery to Lithium-ion Battery for Load Leveling of Renewable Energy

M. Hiratani
Shin-Kobe Electric Machinery Co., Ltd., JP

Keywords: battery, lithium-ion, lead-acid


Electric power generation using natural energy resources such as wind power and photovoltaic power has an advantage to supply electricity without greenhouse gas emission. But the drawback is fluctuation in the power output depending on the weather. A promising solution is a large-capacity battery system which can stabilize voltage and frequency of the power grid in which the renewable energies are incorporated. We developed a 2000 Ah valve-regulated lead acid battery system from two hundreds of 1000-Ah cells, and have been applying it to 1200-kW wind turbine generators over eight years. The output fluctuation of the wind power generation can be compensated with the discharge output of the battery (Fig. 1). The capacity was maintained to larger than 85% of the initial one even after the seven-year use (Fig. 2). The practical lifetime was estimated to be nine years. Based on the above results, we have already developed a new battery with a life expectancy longer than seventeen years, and the battery system is operated in MW-class wind power generation at present. Another prospective energy storage device is a lithium ion battery. We launched mass-production of cylindrical 90 Ah cells for electric vehicles, ten years ago. We have improved the battery chemistry and performance for industrial applications like construction machines and fork lifts. Using a Mn-based cathode, the 90-Ah cell (67 mm x 410 mm) gives energy densities of 104 Wh/kg and 237 Wh/L. Figure 3 shows current dependence of discharge profile at 25 ºC. The 90-% capacity of the standard one is available at a rate of 2 CA (180 A) (Fig. 3), and moreover the 70-% capacity can be discharged at 1 CA even at a low temperature of -30 ºC (Fig. 4). This cycle-use cell is also expected for the load leveling, as it shows good performance at a typical low rate of 1/3 CA in the energy storage.
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