The Unrealized Key to Higher Fuel Efficiency

by | Nov 13, 2012

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Fleet managers and operators are searching for ways to combat rising fuel prices and meet government fuel economy regulations. The current corporate average fuel economy (CAFE) standards call for an average of about 29 miles per gallon, with a gradual increase leading to 35.5 mpg by 2016. With the new mandate, the government standards require automakers to almost double the average fuel economy of new cars and trucks by 2025 – calling for an average fuel economy of 54.5 mpg.

With the demands of fleet managers and operators voiced, vehicle manufacturers are scrambling for a way to increase the fuel efficiency of their vehicles. There are many steps to take to increase fuel efficiency: start stop technology, recovering energy from shock absorbers and regenerative braking, but some provide a bigger bang for the buck than others. Micro hybrids, or vehicles using start stop technology, and recovering energy from shock absorbers improve the vehicles’ fuel efficiency by only about 2 to 3 percent. The clear leader is regenerative braking, which can improve fuel efficiency by a whopping 20 to 30 percent. Evaluating the primary energy storage solution for these initiatives is typically the best place for carmakers to start, as choosing the right energy storage technology will further increase the fuel efficiency gain and position the vehicle to be attractive to buyers. Vehicle manufacturers are concluding that using ultracapacitor technology, as opposed to batteries, is the best way to achieve this high fuel efficiency and offer vehicles that consumer want to buy. Here’s why.

Choosing the Right Energy Storage Solution

Ultracapacitor technology enhances the operation of hybrid vehicles as compared to lithium-ion or nickel metal hydride battery solutions. Ultracapacitors are perfectly suited for hybrid vehicles using regenerative braking and offer the best solution to capture and then reuse the energy from braking.  Ultracapacitors are the only technology able to capture the high peak power levels of regenerative braking in a compact, low-weight package. And, for carmakers looking to do anything possible to increase fuel efficiency, the small light-weight form factor makes a big difference.

Ultracaps have a high cycle life and are able to handle more than one million charge and discharge cycles. This is drastically higher than what batteries can handle, and the longer lifespan is a draw for manufacturers and users. Since no chemical reaction occurs when ultracapacitors charge and discharge, they have a long cycle life. On the other end, batteries consist of electroactive material, so for every charge and discharge, the electroactive material begins to wear out. Because of this, batteries can only cycle a few thousand times, a major drawback.

Beyond the long lifespan, ultracaps have a high charge acceptance rate of 95 percent, a wide temperature operating range and an instantaneous recharge capability. Ultracaps absorb and release energy much more rapidly and efficiently than batteries, they’re more powerful and they can charge faster. All of these qualities make ultracapacitors the ideal energy storage solution for hybrid-electrical applications. Choosing ultracaps with low weight, low equivalent series resistance (ESR), and high power density means manufacturers can meet customers’ demands for a low-cost solution that is easy to install and will reduce operating costs at a vehicle or fleet level.

Ultracaps allow the end user to enjoy driving the vehicle as they do today, with no operational changes.  Because batteries have poor charge acceptance and poor charge efficiency compared to ultracapacitors, the hybrid driver would need to drive differently to maximize the recovery of braking energy. Specifically, the driver must remember to brake much earlier when coming to a stop so the battery can slowly absorb the braking energy. Vehicles using ultracaps can be driven hard, as ultracaps can absorb all the energy – even from the quickest stop – and the driver can accelerate quickly without negatively impacting the hybrid energy recovery system. Unlike batteries, the ultracapacitors can rapidly discharge their stored energy and act as a turbo boost for the driver.


One way ultracapacitors are used in a hybrid-electrical system is when an electric motor is added to the drivetrain. The ultracaps send their captured energy to that motor, which uses that as a recycled energy to power the vehicle in concert with the gas, CNG or diesel engine.

In this application, the vehicles that will benefit most from regenerative braking are the ones that operate in frequent braking conditions. It makes sense; the vehicles that drive routes that require frequent braking will be able to capture more energy from that braking. This may include city buses or garbage trucks, both of which may stop every block or so. With the use of ultracapacitors, a hybrid-electrical system can extend the life of brake pads anywhere from 50 to 100 percent. This coupled with increased fuel mileage and reduced maintenance requirements, means fleet operators can see a payback in as little as two to three years.

Where Market Is Headed

The market for ultracapacitor hybrids is expected to grow rapidly, particularly in Japan and Europe. Several automakers are working on ultracapacitor-based hybrid systems with a goal of reaching the required fuel efficiency. While other factors are considered, ranging from driving patterns, sourcing lower-weight materials and more, using ultracapacitors to power regenerative braking systems is the key to achieving the desired performance.

By 2020, ultracapacitors are expected to be a $7 billion market, which represents a 56 percent compound annual growth rate. The high growth means material and manufacturing costs and overall pricing will fall significantly, making this an even more attractive energy storage solution. On the customer end, fleet managers will look to ultracaps to increase the fuel efficiency of their fleets, thereby benefitting their business’ bottom line.

Jeff Colton is vice president of sales, North America at Ioxus.  He is responsible for managing and growing the company’s North American sales operations in multiple alternative energy sectors. Previously, Jeff held executive roles at companies including General Electric Corporation, Sanyo Electric Corporation and Saft Battery Corporation. Jeff can be contacted at [email protected] or 858-663-1609.


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