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Energy Harvesting Europe 2015
Energy Harvesting Journal

Supercapacitors to the rescue

ZoomSupercapacitors to the rescue
They call it the Bad Dreamliner because the new Boeing jet has been beset with electrical problems. When new, the Airbus A380 also had electrical problems but they were caught at an early stage. This time it has been more dramatic. In one instance a fire raged in the belly of a Boeing 787 parked at Logan International Airport in the USA. Flames were doused that emanated from the lithium-ion battery compartment. Investigations continue to determine the precise origin of that problem but the air industry is acutely aware that lithium-ion batteries have caused extreme incidents before. A UPS plane crash landed with its cargo of lithium-ion batteries on fire, the two pilots dead from asphyxiation.
 
In Europe, Airbus rejected a design of electric nosewheel from the German Aerospace Agency DLR. This would have made airliners into electric vehicles when on the ground, saving huge amounts of noise, cost and pollution. Airbus did not like the fact that the fuel cell in the device needed a large lithium-ion battery across it to manage load variation. Ironically, Boeing has gone ahead with electric nosewheels to an alternative design that obtain power from the existing Auxiliary Power Supply APU, a jet engine for lighting, aircon and so on that is used when the main turbines are switched off.
 
Lithium-ion batteries have been associated with a number of explosions and fires in electric vehicles in China. Often lithium-ion incidents are not caused by defective cells, such as those badly made by some of the proliferating small suppliers in China. It may be the sophisticated battery management system required by the difficult characteristics of such batteries or it may be bad battery pack assembly for example but, for designers and regulators, lithium-ion batteries now signal, "Pay attention!". For example, lithium-ion batteries do not last for the life of a vehicle and replacement can be very expensive and even dangerous given the rather unpredictable nature of the state of charge.
 
Supercapacitors, sometimes called ultracapacitors, are electrostatic, not electrochemical devices. Unlike batteries, they can be fully discharged for transport and maintenance. Their behaviour is more predictable and they are more tolerant of faults and damage. In the past, they have been little used because they are expensive and they hold one tenth of the electricity per unit of volume or weight. Self-discharge was rapid and troublesome in many envisaged applications.
 
However, in the modern world, up front price is less important than cost over life and supercapacitors are usually fit and forget with guaranteed life of up to ten years and actual life of over 20 years. Safety is now much more of an issue, with regulations tightening in this respect. Low maintenance is also sought in order to reduce down time and scope for error. The crash of a Concorde airliner that marked the end of that era was down to bad maintenance on the plane in front that shed a large section of metal in the path of the supersonic airliner. Even car manufacturers now seek 15 year guarantees for parts and batteries have no hope of complying with this. For emergencies such as opening electric bus doors after an accident or backing up regenerative brakes in a hybrid car supercapacitors are now specified because they are reliable. Supercapacitors provide emergency feathering of blades in large wind turbines and their magnitudes superior charge-discharge performance and reliability now sees them across batteries in electric cars, buses and other vehicles or completely replacing batteries in the Toyota racing car, the MAN hybrid bus, the Riversimple car and much more. Hassle free, safe and fit-and-forget are now very powerful drivers of the supercapacitor business, another example being capturing 30% of the energy of a train when it brakes, supercapacitors having almost completely deposed lithium-ion batteries in this application.
 
Supercapacitors are improving much faster than lithium-ion batteries and their marketing is now more imaginative, many applications not involving batteries being opened up. They are not perfect of course, with voltage changing over discharge, that self-discharge and the use of toxic liquids. However, flammable acetonitrile, which has been associated with cancer, birth defects and emitting hydrogen cyanide when burning is no longer used by nearly all supercapacitor manufacturers. Greener, safer versions are now offered by nearly 50% of suppliers and they are less inferior in performance. Indeed in some respects they have improved performance over traditional supercapacitors. These use more benign organic or inorganic solvents or they use ionic liquids where there is no solvent and solute. Anyway, acetonitrile has little regulatory constraint or problem when in small quantities in small devices.
 
Last year, Maxwell Technologies in the USA, current market leader in supercapacitors, did its largest business in supplying them for battery protection and increased performance in electric buses. However, East Asian sources supplied the largest order for supercapacitors last year, that for capturing braking energy of trains in Hong Kong. By contrast, little Evans Capacitor in the USA is prospering selling specialist supercapacitors with high energy density and other attributes into US military vehicles including aircraft. Here reliability, long life and performance are paramount and batteries are nowhere near to offering adequate characteristics. Indeed, these are often electronic rather than electrical components.
 
Little wonder that the leaders in supercapacitors are growing sales at 30% yearly nowadays. That growth is predicted to continue by leading analysts IDTechEx. Uniquely, it has major three reports on the subject. They are the wide ranging, "Electrochemical Double Layer Capacitors: Supercapacitors 2013-2023",and the drill down studies, "Supercapacitor/ Ultracapacitor Strategies and Emerging Applications 2013-2025" with extensive interviews and analysis of technological trends and, at the smaller end, " Batteries and Supercapacitors for Smart Portable Devices 2013-2023: Markets, Technologies, Companies".
 
The future of supercapacitors may involve rivalling the size of the lithium-ion battery market within twenty years particularly as use in vehicles and grid applications take off. Graphene can theoretically give higher energy density in a supercapacitor than that planned for lithium-ion batteries. Printing of the electrics and electronics offers huge gains in cost and performance. It is therefore significant that IDTechEx has Europe's largest event on Printed Electronics coming up in Berlin Printed Electronics Europe, Berlin, Germany, April 17-18 2013  External Link. This year, it will have streams on supercapacitors , electric vehicles land, water and air, graphene and many topics in printed electronics and electrics - one stop shopping for the key future technologies with many potential end users declaring what they need.
 
Top image: Private Jets
 
 

Author

Dr Peter Harrop

Dr Peter Harrop

Dr Peter Harrop is the Founder and Chairman of IDTechEx.
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