Supercapacitors Spur Advances in Hybrid Public Transportation

Any driver who has watched walkers or cyclists speeding past his traffic-snarled car knows the benefits of mass transit. When fewer solo travelers take their cars out on the road, everyone gets where they need to go faster — not to mention cheaper and with less pollution. With recent advances in energy storage, the benefits of public transportation are even greater. Around the world, hybridized buses, trains and other mass transit options are making travel cleaner, more efficient and more available. Clean transportation is better for riders, funders and the environment, and it’s on the rise.

What factors are driving adoption of hybrid public transportation? Below are seven of the most significant:

1. Governments are loosening the purse strings to fund energy-efficient transportation projects.

Americans’ love for their own cars affects the environment, but mass transit in this country hasn’t been clean historically, either. To remedy that, the U.S. Department of Transportation has allocated $112 million to support 46 energy-efficient mass transit projects across seven states. And the interest from local governments is keen. Reuters reported that the Transportation Department received 266 funding requests worth $1 billion. The biggest bulk of the money available will go to initiatives in Pennsylvania, where the state is investing in hybrid buses and more vehicles fueled by natural gas. In California, the funding will go to electric, hydrogen fuel cell, hybrid and diesel-hybrid buses that emit fewer pollutants into the air and rely less on oil. Similar projects are underway in Florida, Illinois, Ohio, Texas and Washington.

Internationally, governments in Asia, South America and Europe are funding similar efforts. All of this official support to decrease the environmental impact of mass transit is bolstering the manufacturers and engineers charged with creating hybridized transportation options.

2. Supercapacitors are solving the energy storage problems batteries cannot.

A supercapacitor, also known as an ultracapacitor, can store a high amount of energy in a small container, leading to larger capacitance and longer stretches of time between parts replacement. For these reasons, supercaps are well suited to increase fleet efficiency. Engineers are adopting these components as part of an increased focus on hybridized asymmetric concepts, which combine an ultracapacitor and battery. Together, the battery and the ultracap shrink the carbon footprint of transportation applications such as hybrid buses and light rail trains.

3. Lower equivalent series resistance (ESR) meets the cooling requirements of hybrid buses.

The longer lifespan and higher power of supercaps trumps batteries, but there is another benefit for hybrid bus manufacturers, who have had to grapple with stringent cooling requirements that shorten cell lifespans and increase costs. Ultracaps can increase efficiency and power capabilities of the cell by parallel amounts. The resulting higher performance and reduced cooling requirements lengthen the operating lifespan of cells and reduce environmentally harmful emissions.

4. Advances in regenerative braking help hybrid applications capture, store and apply energy more efficiently.

Regenerative braking solutions harness energy that would otherwise be wasted and use it to re-accelerate. Supercapacitors have become a critical part of that process, providing power that is capable of quickly discharging to get vehicles moving without delay.

5. Supercapacitors are now less expensive and more durable.

The price of ultracaps has fallen by 90 percent in the past decade, while battery prices have fallen by only 30 to 40 percent during the same time. Why is this the case? Supercaps 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.

The rugged nature of the latest ultracapacitors is also important for mass transit innovation. Ultracapacitors on the market today are more rugged and durable in order to provide the best solution foracceleration, 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. Unlike batteries, these cells operate with high efficiency, high charge acceptance and cycle stability in a wide temperature range – from +65° Celsius to –40° Celsius.

6. Light rail application manufacturers are building on the successes of their peers in the hybrid bus market.

The same challenges and opportunities that exist in the hybrid bus market are true in light rail applications, but the stakes are higher. The cycles required to propel a train can reach as many as 350,000 per year, meaning a lot more heat and higher cooling requirements on the energy storage solution. Here, too, the lower ESR of supercapacitors is essential. When manufacturers can lower their cooling requirements, they boost the overall efficiency of their applications.

The regenerative braking lesson established by hybrid bus makers translates to rail, as well. Light rail applications rely on ultracaps to get the fast charge they need to pick up speed without the assistance of overhead wires, which can be costly. No other energy storage product has the volumetric power and longevity needed to achieve the high cycle life requirements of rail.

7. Pressures for cleaner vehicles in the consumer market extend to the overall transportation landscape.

Just as mass transit players turn toward the possibilities of hybridized buses and trains, their peers in the consumer market are pushing toward better electric vehicles (EVs). On that side of the industry, proposed corporate average fuel economy (CAFE) regulations and rising gas prices are catalysts for innovation from carmakers. As consumers make the switch to fuel-efficient personal vehicles, they will come to see it as the desired norm for public transportation, as well.

Cleaner future for mass transit

With governments around the world funding more efforts to limit the carbon footprint of public transit and reduce energy consumption, manufacturers are more eager than ever to embrace technology to get cleaner mass transit options on the roads and rails. And now is an opportune time for them to pursue that goal.

Advances in supercapacitor technology mean that manufacturers can lower the ESR and increase energy density by using ultracaps alone or in concert with batteries. Hybrid energy storage systems that pair an ultracapacitor and a battery yield increased energy and improved power density of the hybrid supply, which allows the battery to operate without large current spikes that would normally occur if the battery were used alone. This leads to a longer, more effective life for the battery and a more efficient energy supply for the application.

By 2022, the volume of supercapacitor production will increase by as much as 45 percent, making this technology almost as common as the city buses and light rail trains it will power. The shift to cleaner mass transit means more jobs for workers and lower costs for manufacturers. In every sense of the phrase, blue skies are ahead in the mass transit market. MT

Jeff Colton is vice president of sales, North America at Ioxus.

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