Formula One battery design
The introduction of hybrid systems to motorsport has been somewhat laboured, especially since there have been some successful roadcars that have used the technology for more than a decade now. Although the introduction of hybrid technology in Formula One had been considered seriously since about 2005, it wasn’t raced until 2009.
Dubbed KERS (kinetic energy recovery system), it was scrapped for 2010, but has been a permanent feature since. In 2014, hybrid technologies will be a key part of the Formula One power unit, with double the power of the current systems, greatly increased energy storage allowed and a much higher duty cycle. If a driver has a KERS system failure in 2013, the penalty is serious but perhaps not disastrous. In 2014, with a great deal of the power unit’s performance coming from electric motors, the loss of the ERS (energy recovery system) in 2014 will be much more serious.
With the change in power and duty cycle for the electrical machinery in the power unit, the battery will have a very important part to play. As has been discussed previously, lithium ion cells are the usual choice for any modern electrical energy storage application. Supercapacitors have been used, but remain a niche choice.
The Mercedes KERS system was featured in RET issue 67 (December 2012/January 2013), and the pictures show that the battery and power electronics are in a single module. The equivalent battery for 2014 will be considerably larger, so they will present much more of a challenge in terms of packaging.
The amount of stored energy allowed is 4 MJ, ten times that which can be stored under the 2013 rules. If the current KERS cells are limited in terms of volume by their energy capacity, and if the same cells are used, the battery volume will be ten times the size. The larger battery and the new power electronics, combined with the complexity of the new turbocharged power unit, with its attendant charge coolers, will make packaging all of this hardware a real challenge for those designing the new generation of Formula One cars.
Lithium ion cell chemistry is the subject of rapid development. With the automotive industry pushing hard to produce long-lived cells with higher energy and power densities, racing is able to benefit from and contribute to such development. In developing cell technology, there is generally a trade-off between energy storage density and power density. With a doubling of power output and a tenfold increase in energy storage capacity, the energy density of the cell will become more important compared to the cells used in 2013.
The increasing focus on energy density may give the cells an easier life; with less incentive to charge and discharge a small cell mass at a high rate, cell lifetime may improve. Cell charge capacity is known to suffer when charged at high rates, which means that using the cells at the higher end of their power capacity will lead to a fall in their storage capacity over time.
If we can rely on the FIA to maintain a fixed set of rules for Formula One ERS in terms of the key parameters, cell development will lead to ever more compact and reliable batteries.
Written by Wayne Ward