Electric vehicles (EVs) are having their time in the spotlight with several models from makers such as General Motors, Tesla and Nissan on the market today and more to come in the future. The cost of fuel continues to rise, and there is pressure from the government – through proposed legislation like the corporate average fuel economy (CAFE) regulations – for automakers to reduce vehicle emissions and improve fuel efficiency. Automakers are calling for more efficient power sources to meet these demands. In short, the market need for EVs will only increase with time and more consumers will make the switch to fuel-efficient vehicles.
The growing demand for EVs is spurring the automotive industry’s search for sophisticated components to extend the longevity of these vehicles while simultaneously improving their performance capabilities. Research and advancements in efficient components over the last several years has led to a hybrid energy storage system consisting of an ultracapacitor and battery pairing. This pairing increases energy and improves the power density of the hybrid supply, which allows the battery to operate without large current spikes that would normally occur when using just a battery. When the battery can operate without current spikes, it has a longer, more effective life. The hybrid system reduces the cycling of the battery under heavy load conditions, in turn extending the life of the hybrid supply and providing a more efficient energy supply.
Ultracaps offer compelling benefits over batteries
Ultracapacitors store energy electrostatically, whereas batteries produce energy via a chemical reaction. For automotive manufacturers, this difference means an economical, versatile power delivery technology more beneficial than batteries. Coupled with batteries in a hybrid system, ultracapacitors improve the range and performance of trucks, passenger and delivery vehicles.
An important step in improving fuel efficiency is reducing the gross weight of vehicles. Using an ultracapacitor helps with this, as the size and weight of the battery used is greatly reduced. Batteries are heavy and large, so implementing a system where ultracapacitors provide the power allows the battery to be sized for energy instead of power. This results in a smaller-size, higher energy density battery that achieves the same performance.
Beyond size and weight reduction, ultracaps offer other benefits over batteries. They operate with high efficiency, high charge acceptance and cycle stability in a wide temperature range – from +65° Celsius to –40° Celsius. Batteries can’t perform well below 0° Celsius. Ultracaps also boast a high cycle life; often their life cycles are longer than the machines into which they are built. Ultracaps can go through charge and discharge cycles more than a million times, which meets the requirements of hybrid vehicle start/stop applications. The long lifecycle makes for little to no required maintenance, ultimately resulting in cost savings.
In further demonstration of their cost savings, ultracapacitors’ prices have fallen by 99 percent in the past decade, while battery prices have fallen by just 30 to 40 percent in the same period. Mass volume savings possible with ultracapacitors just aren’t achievable with batteries. Ultracapacitors are a relatively new introduction to the industry, and as they are further developed and adopted, their prices are likely to keep dropping. Batteries, though, have been on the market for more than 100 years and their prices are for the most part stabilized.
One final advantage over batteries is the increased efficiency and power ultracaps provide. They are 95 to 98 percent round-trip efficient compared to an average of 60 to 80 percent efficiency for various batteries. An important benefit, especially to vehicle acceleration applications, is that ultracapacitors have up to 1,000 times the power density of batteries. Higher power means a higher fuel savings since a hybrid system can power starting and ignition systems at a lower voltage regulation.
Numerous automotive applications powered by ultracapacitors
Ultracapacitors on the market today are more rugged and durable in order to provide the best solution for acceleration, energy recapture, peak load shaving and other high power applications. Durable cells are able to operate in demanding environments such as hybrid drive technology and meet an industry need for high performance. In addition, ultracapacitors are increasingly built for easy integration so auto manufacturers can easily install the cells without additional engineering teams.
Automotive and transportation manufacturers employ ultracapacitor technology in several applications. Ultracaps improve the fuel economy and reduce harmful emissions in hybrid buses. By redefining the hybrid architecture with ultracapacitors, engineers enable stop-and-go driving for large vehicles such as urban transit buses and delivery trucks that typically rely on diesel engines. Using smaller engines with generators and operating them at constant, efficient RPMs and power output levels increases energy efficiency. Also, temporary increases in power demand and support for voltage bus stabilization can be met by drawing power from hybrid energy storage systems.
Ultracapacitors store and provide energy far faster than batteries, allowing for several uses of ultracapacitors in hybrid automotive applications. They can harvest energy that would otherwise be lost in applications such as regenerative braking. Regenerative braking systems recapture kinetic energy and convert it into electricity – energy that is typically converted to heat by friction in the brake pads, and is therefore wasted, in traditional braking systems. Regenerative braking systems are commonly found in hybrid or electric vehicles, and the electricity output is used to charge the battery or hybrid system.
In a regenerative braking system employing a motor-generator set with a capacitor bank, the generator is driven when braking is required, which charges the capacitors. When the vehicle accelerates, the motor delivers assistance. In addition to HEVs and EVs, this system can be applied specifically for mass transit applications including light rail and buses.
Hybrid capacitors are used to back-up computer systems in EVs as well as for safety communication such as GPS, signal horns, optical warning units, and airbag and security power. They also power windows, locks, emergency brakes and lights. The hybrid capacitor’s high cycle life provides power if the vehicle computer loses power when the battery is disconnected. In the case of power outages, ultracapacitors also cover peak power demands and support of switch drives. They can activate the tilting systems of advanced tilting trains as well as deliver cold start support and power boost.
Automakers can achieve greater fuel efficiency with start/stop technology, which shuts off the engine while a car is stopped in traffic or at a red light. Ultracapacitors are the only technology that has the power and cycle life needed to provide the quick start to re-launch the vehicle, all while contained in a small density package.