Ultracapacitors: The Power To Change the Automobiles We Drive
CHICAGO (March 5, 2006) - Think of an ultracapacitor as a double shot of electricity, ready within your vehicle, for when you need it need it most. It is electrical energy that is clean, sufficient and available, but without any hangover effects.
Since the dawn of time, Mother Nature has shown us repeatedly how electrical energy can be stored and released in an instant. Every thunderstorm forms a natural capacitor, with the clouds and the ground being two electrical conductors separated by air. But when enough energy has been stored, the gap is closed with an arc of lightning - wherein massive electrical energy is unleashed, and transferred from one electrode to the other.
While not as old nor as powerful as the natural capacitor, manmade capacitors have been around since the invention of the Leyden jar in 1745 - approximately twice as long as automobiles have been. While not up to the storage capacity of lightning yet, capacitors have been getting there. Unlike batteries, which store electrical energy and release it as a continual flow of electricity, capacitors simply store an electrical charge and release in an instant. In their earliest days, capacitors were simple devices that stored miniscule amounts of electrical energy. Common in cameras, audio and other electronic devices, capacitors have found a willing host in automobiles, capable of supplying an extra burst of energy when needed in ways similar to the flash of a camera.
Capacitors have evolved over time as well, both in their construction and in their ability to hold ever more energy in reserve. The Leyden jar yielded to the electrostatic capacitor, which in turn gave way to the electrolytic capacitor, and more recently the nanogate capacitor. Each innovation increased the energy density of capacitors - the storage capacity of these devices - by increasing the surface area of the conducting surfaces within the capacitor, decreasing the separation distance between the conducting surfaces, or using newer and more efficient materials, such as carbon rather than earlier metal-only surfaces.
Today, the highest electrical storage capacity devices are known as super- or ultracapacitors (UCs), which can be stand-alone units, or grouped into banks or modules of multiple series-connected UCs, the collective having much more storage capacity. The combination of enormous surface area and extremely small charge separation gives the UC its outstanding capacitance relative to conventional capacitors.
A marriage of convenience: the best of both technologies
For most of the time that automobiles have existed, batteries have been the energy storage choice. As the demand for electrical supply has not only increased but accelerated over the years, batteries haven't been able to keep pace. John Miller, Maxwell Technologies' vice president of Advanced Transportation Applications says that the advent of UCs and advances in related technology and economics have enabled UCs to cut into the stronghold once dominated by batteries.
(Photo: Maxwell Technologies)
The key, he says, was to understand the pros and cons of batteries and UCs - in terms of cost, weight, energy stored and the cost of building vehicles - and putting each technology to its best use. With the inclusion of carbon electrodes, UCs are more efficient than batteries in several areas.
"The cost curve for UCs is coming down rapidly, relative to battery costs," says Miller. "In 1970, the cost was $1 per farad; whereas today it is one cent per farad and soon will be half of that." Harvesting, storing and releasing electricity from regenerative braking is done more efficiently with UCs as well.
"Ultracapacitors are lighter than nickel metal hydride (NiMH) or lithium-ion (LI). And unlike batteries, in cold temperatures ultra-capacitors won't lose power like batteries,' he adds. Miller also points out that unlike batteries, UCs are more compact and provide flexibility by being able to be positioned in smaller cavities in a vehicle where batteries won't fit: inside fenders or running boards, for example. From an environmental perspective, UCs are made of friendlier materials and more easily disposed of.
(Photo: Maxwell Technologies)
(Photo: Maxwell Technologies)
Even aftermarket applications, such as vehicle sound systems, have embraced UCs. Until recently, sound systems never prevented a car from starting. But with the advent of more power-hungry systems, it occurs more and more frequently. Miller explained the growth in using UCs in audio applications, saying that, "Two years ago in California, only one store used ultra-capacitors when installing 1Kw, 400-amp sound systems. Today, there are six stores."
Like the rise of telematics, computers, software and audio-visual infotainment systems, future vehicles will see an increasing use of UCs - be they hybrids or hydrogen fuel cell-powered vehicles, or crossovers between the two. Increasingly, the OEMs and aftermarket companies are finding that UCs fit the bill affordably and effectively.
According to Maxwell, several of its key innovations have contributed to this. Lowering the cost per farad for UCs made them an affordable and environmentally friendly power solution alternative. Maxwell has developed its own proprietary electrode using patented manufacturing techniques, which enables low cost, high performance and high purity. The modular integration design enables higher operating voltage and longer life. In addition, the longer life enables improved application life costs with zero maintenance.
The company's BMOD2600 family of modular products is the first specifying in excess of 1 million charge/discharge cycles. The integrated modules include internal cell-to-cell balancing, module temperature monitoring capabilities and module over-voltage indicators. If higher voltage systems are required, the modules are series-connectable and include module-to-module balancing cable interconnects. For example, the BMOD2600-48 module incorporates 18 MC2600 2.7 volt cells, which are individually balanced to provide increased reliability. With a 48.6 volt operating range, the module is ideal for applications in automotive subsystems, heavy-duty vehicle subsystems, rail system power and fuel cells.
In addition, the company recently introduced its new line of 16 Power-type BOOSTCAP ultracapacitor cells and multicell modules specifically designed and constructed for the most demanding automotive and transportation applications. Miller notes that these ultracapacitors provide a alternative to battery-based solutions for all types of hybrid drive systems, idle stop-start, power network stabilization and other automotive applications. "Automakers are turning to ultracapacitors for solutions that optimize efficiency, ensure reliable cold-starting, better manage power flows, stiffen and smoothen the power distribution network and provide fail-safe backup for critical safety systems," Miller says. The new products will provide the lowest equivalent series resistance and highest efficiency available to the automotive industry today, he adds. The company's CEO Richard Balanson comments, "With more than 60 million new cars produced annually around the world and the proliferation of power-consuming functions in current and future vehicles, the automotive market is real. It represents the single largest opportunity for ultracapacitor-based solutions, so we are moving aggressively to capitalize on Maxwell's position as the global technology leader."Gaining traction In addition to conventionally powered cars and trucks, Maxwell's ultracapacitors are currently used in several concept vehicles, such as the BMW X3 Concept Hybrid SUV, as well as current production models of the Toyota Prius and the Honda FCX hydrogen fuel cell vehicle. The BMW X3 was displayed at the 2006 NAIAS, and in addition to several other innovative technologies, it featured orange-colored UCs embedded in the running boards. More information on the X3, in video or podcast format, is available from BMW at http://vodcast.bmw.com/stories/1424704/.(Photo: BMW)The Toyota Prius gasoline-hybrid employs the use of Maxwell's UCs, notably in smaller out-of-the-way places, freeing up space for other features and amenities. Amongst other uses, the UCs capture and store electricity harvested from regenerative braking for use later, such as when accelerating. In the Honda FCX, Maxwell UCs serve as a supplementary power source to the main power source - the fuel cell stack - and provide extra energy under various driving conditions. Honda says that the modular Maxwell UC bank combines the electrical storage capacity needed for high output and high responsiveness with solid reliability. It stores energy produced during deceleration and braking and provides powerful drive assist during startup, acceleration, climbing hills and at other times when an extra electrical boost is required. The ultra-capacitor's internal resistance is lower than that of a battery, and moreover, because the UC stores and discharges electricity in response to fluctuations in the fuel cell stack, it doesn't require a converter for voltage regulation as in a battery system, so it delivers higher output. The result is improved drive-power performance and higher system efficiency. In short, says Miller, "The UC does everything the fuel cell can't do, and the fuel cell can do everything a UC can't."
BOTTOM: A cutaway of the UC used in HondaFCX.
(Photos: Honda)
Honda notes that while the improved Maxwell UC retains the same high-performance activated-carbon electrode that was used previously, an increase in the number of wraps around the electrodes resulted in improved electrode charge density and a significantly 10 percent higher energy storage capacity and output.
Good things come in small packages
Advances in both supercapacitors and batteries seem to be announced daily. The National Resource Energy Laboratory and similar work at other facilities on LI battery development has been substantial. The same holds for UCs. The use of carbon and nanotechnology is driving UCs to increased energy storage capacity and improved efficiencies.
Ongoing research in developing UCs on a compact nanotech scale is also leading to products that deliver more energy than ever before, but in a more compact product form: thinner and smaller. Using carbon-based nanotubes as an electrode material, companies and academics are developing UCs with electrodes that are smaller than a postage stamp, yet have surface area of hundreds of square meters - resulting in geometric increases in energy storage capacity. These new nanotube-based UCs can be made in any of the sizes currently available and also can be produced using conventional technology.
MIT's Joel E. Schindall, associate director of the Laboratory for Electromagnetic and Electronic Systems (LEES), recently announced that LEES has developed a UC in which the researchers progressed from traditional electrodes made of activated carbon and irregular porous material, and instead employed vertically aligned, single-wall carbon nanotubes to increase the surface area and hence the storage capacity of the UC. "Nanotube-enhanced UCs would combine the long life and high power characteristics of a commercial UC with the higher energy storage density normally available only from a chemical battery," he says.
A commercial company, JEOL, recently announced its development of the Nanogate Capacitor, which has an energy density of 50 to 75 watt-hours/kg, meeting or exceeding that of many conventional batteries.
With the current traction that UCs have, and reinforced by emerging research and development of enhanced UC efficiencies and capabilities, the future for UCs in the automotive industry has huge potential. But as the industry migrates to hybrids and hydrogen, automakers still have to be cognizant of and aligned with consumer expectations: excellent performance, long vehicle operating life, environmental friendliness and low maintenance costs. UCs fit the bill today and, says researchers, will be integral in powering the vehicles of tomorrow.
(Sources: Maxwell Technologies, Honda,
MIT)
