WHAT ARE THE APPLICATIONS OF ULTRACAPACITORS IN VEHILCES?

Moscow saw a revolution in 1995 when a small fleet of buses started running on a 15 minute route. The bus was powered by ultracapacitors instead of batteries. China introduced Capabus in 2004, a 41 seater bus powered by ultracapacitors, which could be charged on select stops en route in half a minute. World saw trams and trains powered by ultracapacitors in different parts of the world. Energy stored in these capacitors was so substantial, and charging so fast, that Taiwan started using ultracapacitors for metro trains.

Today, ultracapacitors serve several applications in vehicles due to their unique properties. Their fast response, high energy storage capacity and quick charge / discharge capability make them ideal and preferred choice in large number of vehicles today. Ultracapacitors can serve several functions in vehicles. 

Benefits of ultracapacitors

Reasons for use of ultracapacitors over a battery-based solution for automotive power needs are as follows: 

1. Levelized cost of investment (LCOE) are far lower than comparable batteries.
2. They are “fit and forget” components and outlast the vehicle life.
3. Superior power delivery and reliability at cold temperature (where most batteries have problems).
4. Round trip efficiency is far superior to battery systems.
5. Battery-plus-ultracapacitor system is usually smaller, lighter, and cheaper than battery alone.

Event	Energy needed
Start –stop launch assist	15-25 Wh
4% grade @35MPH x 1min	170 Wh (Regen)
2% grade @35MPH x 1min	70 Wh (Regen)
Accessory 1KW x 1min	16.7 Wh

Cold start is expected to dictate the size of battery, but it is not so for ultracapacitors. If the size, weight, maintenance costs, replacement and downtime costs are considered, it makes sense to use ultracapacitors by themselves or as back up with batteries in many applications. EDLCs are much lighter than batteries, and weight is an important criterion in vehicle designs.

Ultracapacitor functions in vehicles

• Regenerative braking
• Battery backup
• Start-stop systems
• Power steering (needs about 2KW power)
• Air conditioning systems
• Accessories – radio, horn, etc.
• Subsystems with ultracapacitors improve fuel efficiency & reliability
• Electric drive, Hybrid vehicles

 About 100 million passenger vehicles p.a. produced worldwide, so the potential for ultracapacitors in vehicle applications is enormous.

What makes ultracapacitors ideal for vehicles?

• High power energy storage
• Fast charge / discharge
• High round trip energy efficiency above 95%-98%
• Long life in millions of charge/discharge cycles (lasting for decades)
• No maintenance
• Wide service temperature range: from -55⁰C to +70⁰C.
• Well suited for remote location usage

Some typical energy requirements where ultracapacitors are currently deployed:

Event	Energy needed
Start –stop launch assist	15-25 Wh
4% grade @35MPH x 1min	170 Wh (Regen)
2% grade @35MPH x 1min	70 Wh (Regen)
Accessory 1KW x 1min	16.7 Wh

Cold start is expected to dictate the size of battery, but it is not so for ultracapacitors. If the size, weight, maintenance costs, replacement and downtime costs are considered, it makes sense to use ultracapacitors by themselves or as back up with batteries in many applications. These are much lighter than batteries, and weight is an important criterion in vehicle designs.

Battery backup

Ultracapacitor modules are connected directly across battery terminals with proper polarities. Since the module delivers energy instantly, all surges and transient loads are served by the module, and battery is a saved of severe shocks and overloads. This helps extend the battery life by 4 to 5 folds. Even large IC engines of hundreds of HPs can be started with these modules.

Ultracapacitors as battery backup has been dealt with in detail here.

Regenerative braking

Ultracapacitors have another advantage over batteries in a vehicle. The high rate at which they can accept charge, enables them to do a much better job at capturing energy from regenerative braking systems. This technology turns a vehicle’s forward motion back into electricity when brakes are applied. Ultracapacitors make regenerative braking more practical, being able to accept charge at matching fast pace.

Start-Stop operations

Batteries face severe limitations when frequent start-stop becomes necessary- at signal crossings or in congested traffic. Their life fades quickly under such onerous conditions. Ultracapacitors take over this function and ensure vehicle starts smoothly under all conditions, saving the battery from frequent surge loads.

Ultracapacitors extend life of batteries in two major areas.

1. Substantially reduce battery replacement costs in vehicles.
2. Extend battery run time over 400%

Most critical factor is engine starting reliability in all conditions. Every time a lead-acid battery starts an engine, it is one step closer to end-of-life. A bank of U-caps relieves battery from engine starts. Starting with ultracapacitor enables greater reliability in colder temp.

Jump Start

There are situations where an IC engine does not start easily. For example, in extreme cold conditions like high on mountains or cold regions, battery capability goes down drastically, and it cannot give required torque and power to jump start the engine. Ultracapacitor comes in handy to give required power to engine, and its high power delivery for a short duration easily starts the vehicle under such conditions.

As temperature goes down, engine demands more power to start, while battery power delivery goes down significantly. In cold icy weathers, specially designed ultracapacitor modules located at bus or truck depot can start number of vehicles in succession. The battery then takes over and vehicle can run normally.

Voltage stabilization

Ultracapacitors help save battery from peak loads and surges by supplying these needs locally, thereby smoothing out all fluctuations and keeping battery voltage stable. This saves entire electrical system from sags and transients. This decouples short high power local requirements from vehicle supply system.

Power train solutions

Power supplies of hybrid vehicles may use ultracapacitors with distinct benefits. ultracapacitors are placed in parallel with primary power source to handle peak loads and recover braking energy. They can also improve HEV mechanical design. Use of more powerful, smaller, and lighter ultracapacitors causes an overall reduction in battery and system size, weight and cost. This also obviates the need of separate batteries for individual operations.

As main energy storage source

Buses, minibuses, golf carts, trams and other vehicles are using ultracapacitors as the sole energy source, replacing batteries in these vehicles.

These vehicles can be charged in very short time, are more energy efficient, and are benefited from reliability and long life of ultracapacitors. These will be subject of a separate article.