Capacitors

The world of motoring and motorsport is changing. How quickly we move towards a world dominated by all-electric passenger vehicles is uncertain, although it’s unlikely that we will decide that hybrids and electric propulsion were a big mistake and that it’s OK to continue either burning fossil fuels or growing crops to provide all our liquid fuel.

There is an increasing number of electric roadcars available (in Europe at least), some of which are very agreeable, with nice styling, good performance and reasonable driving range. They are finally becoming desirable and practical at the same time. Electric motorsport is also enjoying a steady rise. The motorcycle series TT-Zero and TTX-GP have enjoyed increasing popularity and success in recent years, and electric car racing is now firmly in the spotlight, with Formula E now an official FIA series with manufacturer backing from Renault.

Away from pure electric racing, of the various hybrid technologies available, electric hybrids have proven to be the most popular solution. While most teams and car manufacturers choose to use batteries as the method of storing energy, some have chosen capacitors. Even in non-hybrid motorsport, some teams choose to replace the car battery with a capacitor.

The most high-profile user of capacitors as stores of significant amounts of energy is Toyota, which has rejected the battery in favour of ‘supercapacitors’ on its hybrid LM P1 car for Le Mans and the World Endurance Championship. The Toyota hybrid system delivers an incredible 300 bhp (224 kW) to augment the 530 hp produced by the engine – almost four times the power delivered by the Formula One systems in 2013. In the Toyota, the proportion of the power-unit performance which is electric is even greater than will be the case in Formula One from 2014 onwards. The capacitor was chosen because of its ability to charge and discharge at a higher rate than batteries can manage for the same mass. Toyota had previous experience of supercapacitor storage for racing hybrid systems, having used them in a GT car application with success in 2007.

There is evidence to suggest that Red Bull has used supercapacitors as the energy storage on its Formula One car, with the capacitor packs mounted flat on the floor of the car. There is a natural link between Red Bull and supercapacitors. Renault, the engine supplier for Red Bull, is involved in many kinds of racing and runs several one-make series. The Formula Renault 2.0 and 3.5 cars have both rejected conventional batteries and replaced these with supercapacitors; in the Formula Renault one-make cars, the capacitor supplies only the power necessary for the vehicle electrical systems, rather than providing propulsion.

Outside motorsport, capacitors for hybrid applications are becoming more popular, despite their higher initial costs because, over the life of the vehicle, capacitors are said to prove less expensive. Battery reliability and life are still in question: battery life in a pure electric passenger car can be between four and eight years. At this point, it is often uneconomical to replace the battery, so some electric cars are supplied with batteries on a lease basis.

Supercapacitors have perhaps lacked the investment that batteries have enjoyed, and as a result are at a lower level of development. They are consequently likely to improve at a faster rate than batteries and, given their current competitiveness (no pun intended), we should not be surprised to see them become used more widely for automotive and motorsport applications. 

Written by Wayne Ward