As of 2010[update], the best ultracapacitors can only store about 5% of the energy that lithium-ion rechargeable batteries can, limiting them to a couple of miles per charge. This makes them ineffective as a general energy storage medium for passenger vehicles. But ultracapacitors can charge much faster than batteries, so in vehicles such as buses that have to stop frequently at known points where charging facilities can be provided, energy storage based exclusively on ultracapacitors becomes viable
China is experimenting with a new form of electric bus, known as Capabus, which runs without continuous overhead lines (is an autonomous vehicle) by using power stored in large onboard electric double-layer capacitors (EDLCs), which are quickly recharged whenever the vehicle 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 electric double-layer capacitor buses; one of them is route 11 in Shanghai. In 2009 Sinautec Automobile Technologies, based in Arlington, Virginia, and its Chinese partner Shanghai Aowei Technology Development Company are testing, with 17 forty-one seat Ultracap Buses serving the Greater Shanghai area since 2006 without any major technical problems. During the Shanghai Expo in 2010, however, 40 super-capacitor buses were being used on a special Expo bus service and owing to the super-capacitors becoming overheated some of the buses broke down. Buses in the Shanghai pilot are made by Germantown, Tennessee-based Foton America Bus Company Another 60 buses will be delivered early next year with ultracapacitors that supply 10 watt-hours per kilogram.
The buses have very predictable routes and need to stop regularly every 3 miles (4.8 km) or less, allowing quick recharging at charging stations at bus stops. A collector on the top of the bus rises a few feet and touches an overhead charging line at the stop; within a couple of minutes the ultracapacitor banks stored under the bus seats are fully charged. The buses can also capture energy from braking, and the company says that recharging stations can be equipped with solar panels. A third generation of the product, which will give 20 miles (32 km) of range per charge or better is planned.
Sinautec estimates that one of its buses has one-tenth the energy cost of a diesel bus and can achieve lifetime fuel savings of $200,000. The buses use 40% less electricity even when compared to an electric trolley bus, mainly because they are lighter and have the regenerative braking benefits. The ultracapacitors are made of activated carbon and have an energy density of six watt-hours per kilogram (for comparison a high-performance lithium-ion battery can achieve 200 watt-hours per kilogram, but the ultracapacitor bus is about 40% cheaper than a lithium-ion battery bus and far more reliable).
There is also a plug-in hybrid version, which also uses ultracaps.
RATP, the public-owned company that manages most of Paris' public transport system, is currently performing tests using a hybrid bus outfitted with ultracapacitors. The model, called Lion's City Hybrid, is supplied by German manufacturer MAN.
Other companies from the public transport manufacturing sector are developing electric double-layer capacitor technology: The Transportation Systems division of Siemens AG is developing a mobile energy storage based on ELDCs called Sibac Energy Storage  and also Sitras SES, a stationary version integrated into the trackside power supply. Adetel Group has developed its own energy saver named ″NeoGreen″ for LRV, LRT and metros. The company Cegelec is also developing an ELDC-based energy storage system.
University of Southampton spin-out Nanotecture has received a Government grant to develop supercapacitors for hybrid vehicles. The company is set to receive £376,000 from the DTI in the UK for a project entitled “next generation supercapacitors for hybrid vehicle applications”. The project also involves Johnson Matthey and HILTech Developments. The project will use supercapacitor technology to improve hybrid electric vehicles and increase overall energy efficiency
Sinautec is in discussions with MIT's Schindall about developing ultracapacitors of higher energy density using vertically aligned carbon nanotube structures that give the devices more surface area for holding a charge. So far they are able to get twice the energy density of an existing ultracapacitor, but they are trying to get about five times. This would create an ultracapacitor with one-quarter of the energy density of a lithium-ion battery.
The FIA, the governing body for many motor racing events, proposed in the Power-Train Regulation Framework for Formula 1 version 1.3 of 23 May 2007 that a new set of power train regulations be issued that includes a hybrid drive of up to 200 kW input and output power using "superbatteries" made with both batteries and supercapacitors.
Ultracapacitors are used in some electric vehicles, such as AFS Trinity's concept prototype, to store rapidly available energy with their high power density, in order to keep batteries within safe resistive heating limits and extend battery life. The Ultrabattery combines a supercapacitor and a battery in a single unit, creating an electric vehicle battery that lasts longer, costs less and is more powerful than current technologies used in plug-in hybrid electric vehicles (PHEVs).
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