Capacitors have the handy ability to store and release electrical energy very quickly—much more quickly than the batteries and fuel cells already being used in electric and hybrid-electric cars. Unfortunately, typical capacitors have been able to store only tiny amounts of charge, making them useless for driving the power-hungry engines these cars use. Not so ultracapacitors. While they still can’t store as much total energy as a fuel cell or a battery, ultracapacitors—also known as electrochemical capacitors—can supply the burst of energy needed to accelerate up a hill or around another car on the highway. They can also soak up energy that would otherwise be lost during braking, storing it for later use.
The focus of intense research by automobile makers in recent years, ultracapacitors are finally being tested on the road. AFS Trinity Power in Bellevue, Washington, recently displayed a modified hybrid SUV that uses ultracapacitors alongside batteries and an internal combustion engine, and major manufacturers such as Honda and Toyota have also been experimenting with the technology.