The other important factor affecting viability of these systems is the lifetime of the energy storage system. The extra cost of replacing an energy storage system too soon defeats the cost-saving goal of the system. Ultracapacitors are rated to handle up to 1 million charge/discharge cycles in a lifetime. For a hybrid-electric bus this can equate to an energy storage system lifetime of 10 years or longer. Battery life in these systems have been reported as only four to five years in comparison.
More than 12,000 hybrid buses are in daily service in China with ultracapacitors. All these buses use 25 percent less fuel than traditional buses and produce significantly less pollution. The number of buses continues growing, with manufacturers aiming to ultimately sell hybrid-electric buses without a subsidy due to continued growth and technology. The Chinese government subsidy program is an enormous success and should be viewed as a model for other countries to emulate.
Brian Eichler is the director of sales and marketing for Maxwell Technologies ultracapacitor products in the Asia Pacific and Americas regions. He has 20 years of technology sales experince.