After Gutenberg

There are trolleybuses in many cities around the world. Two poles are required in order to accommodate the return current. According to Wikipedia, in Shanghai testing began in 2005 with large on board super capacitor modules, which are quickly recharged at bus stops.

As early as 1993, engineers under a NASA contract demonstrated that a transit bus could enhance fuel efficiency and performance by the application of ultra capacitors. Last year at this time, this blog first relayed information about a company called EEStor. Leonardo ENERGY now wants to know whether the ultra capacitor that EEStor has under development is “Game-changing technology” or “Much Ado About Nothing?”

EEStor claims to be on track for producing an energy-storage system for electric vehicles:

• Weighing less than 50 kilograms
• Allowing a 300-kilometers driving range
• Able to recharge in less than 10 minutes.

While ultra capacitors can absorb and release power in a very short time and in a virtually endless cycle with little degradation, a big drawback compared to electrochemical batteries has been the energy they can store. EEStor claims to have overcome such limitation.

EEStor now claims that it can make a ceramic ultracapacitor with a barium-titanate dielectric that can store 280 watt hours per kilogram. If true, this is more than double the 120 watt hours per kilogram of a lithium-ion battery.

Such assertions result from the ability of barium-titanate to store “static electricity”, i.e., very pure barium-titanate can have an extremely high permittivity.

Leonardo Energy notes that there remain difficulties to overcome:

1. How on a mass-production scale can high purity be maintained?
2. How will a proper temperature range be obtained? (“The performance of the barium-titanate dielectric is dependent on temperature; it won’t work at low temperatures.”)
3. While able to undergo significantly more life cycles than batteries, the ceramic structure is subject to micro fractures caused by the thermal stress leading to premature failure. Has EEStor been able to overcome stress fracture tendencies inherent with their material?
4. What will happen when a car with a 3,500 V energy system crashes?

While EEStor is under development, Maxwell recently announced their new 125VDC Maxwell Ultra Capacitor Module that incorporates proprietary balancing, monitoring and thermal management and is designed to perform reliably through one million or more deep charge/discharge cycles, which equates to more than 15 years of operational life.

A fifth concern cited in the post is a somewhat different design issue. The ability to charge rapidly is a decided advantage, particularly with recapturing kinetic energy from braking or suspension. This quality also means that high-voltage capacitors self-discharge quickly, and thus require regular recharging. Which means supply from a range extender, as with the Oshkosh ProPulse Drive, or in combination with deep cycle batteries, as with Azure Dynamics urban delivery vans. A third possibility is a trolley bus situation, where the energy comes from a supply line except when the vehicle’s route leaves the power source for short excursions using stored electricity.