Nissan Diesel Motor Co. Deploys Hybrid Bus With Double-Layer Capacitor

Nissan Diesel Motor Co. Ltd. (Japan) has deployed a hybrid bus combining a natural gas engine and an electrical double-layer capacitor. The double-layer capacitor is used to store the electricity regenerated from braking energy.The firm appears to be aiming for production later this year or in 2001. If commercialized, it will be the first vehicle in the world to use a double-layer capacitor. Route buses rarely travel at high speeds and brake often, making efficient recovery of braking energy a key issue. Nissan Diesel has believed that double-layer capacitors are an excellent choice for this application due to the charge/discharge cycle and collision safety requirements for commercial vehicles. In the past, however, these capacitors offered a weight/energy density of only about 0.5 to 3Wh/kg, preventing practical use.The new capacitor used by Nissan Diesel has a weight energy density of 6Wh/kg and an average and maximum output density of 450W/kg or 680W/kg, respectively. The mounted weight is 220kg. The charge/discharge cycle performance is said to be sufficient to handle normal travel distances of 500,000 to 600,000km and charge/discharge efficiency is over 90 percent.