Supercapacitor Bus Service Shanghai
China is experimenting with a new form of electric bus (capabus) that runs without powerlines using power stored in large onboard supercapacitors, which are quickly recharged whenever the electric bus stops at any bus stop (under so-called electric umbrellas), and fully charged in the terminus. A few prototypes were being tested in Shanghai in early 2005. In 2006, two commercial bus routes began to use supercapacitor buses; one of them is route 11 in Shanghai.
In August 2007, a research team at RPI developed a paper battery with aligned carbon nanotubes, designed to function as both a lithium-ion battery and a supercapacitor (called bacitor), using an ionic liquid, essentially a liquid salt, as the electrolyte. The sheets can be rolled, twisted, folded, or cut into numerous shapes with no loss of integrity or efficiency, or stacked, like printer paper (or a Voltaic pile), to boost total output. As well, they can be made in a variety of sizes, from postage stamp to broadsheet. Their light weight and low cost make them attractive for portable electronics, aircraft, automobiles, and toys (such as model aircraft), while their ability to use electrolytes in blood make them potentially useful for medical devices such as pacemakers. In addition, they are biodegradable.
Capacitors are electronic devices. Conventional capacitors have enormous power but store only tiny amounts of energy. Batteries can store lots of energy but have low power . they take a long time to be charged or discharged. Supercapacitors offer a unique combination of high power and high energy.
How It Works Batteries are charged when they undergo an internal chemical reaction. They deliver the absorbed energy, or discharge, when they reverse the chemical reaction. In contrast, when a supercapacitor is charged, there is no chemical reaction. Instead, the energy is stored as a charge or concentration of electrons on the surface of a material. Advantages Supercapacitors are capable of very fast charges and discharges, and apparently are able to go through a large number of cycles without degradation. Applications Supercapacitors found their first application in military projects . for example, starting the engines of battle tanks and submarines or replacing batteries in missiles. Common applications today include starting diesel trucks and railroad locomotives, actuators, and in electric/hybrid-electric vehicles for transient load leveling and regenerating the energy of braking. NASA has used 30 large supercapacitors in its turbo-electric city bus.
Shanghai China has a system of buses based on Supercapacitors rather than batteries. They can be charged much faster than batteries (even the Nanosafe), but hold less energy (at the current time). It is quite possible that supercaps will be superior to the Nanosafe batteries in this application, as they charge faster, withÂ the ability to do many more charge/discharge cycles. Currently, they have somewhat poor energy/weight ratio compared to Lithium batteries. Their fast recharge time, however allows them to be charged at every, or every other stop without inconveniencing the passengers or driver.
The ideal system, would then be to combine the high capacity of Lithium batteries, with the faster charge and higher cycles of Super Capacitors. Between these two technologies, it would seem that the Nanobus is now practical and feasible.
Over the next few years, with new emphasis on EV and Plug-in Hybrids, that the differences between Super Capacitors and Advanced batteries will likely converge