Supercaps and ultracaps have been "sexy" for decades now. People look at their cycle life and fast charging ability and their first thoughts are usually "Eureka! The perfect battery!"
A supercap's specific energy is typically around 6-10 wh/kg, with some claiming up to around 40 wh/kg. A few years ago, lab prototypes were getting 80-85 wh/kg. I don't follow this stuff closely, so maybe it's 100 wh/kg in the lab now. Meanwhile, a good mass-production Panasonic 18650 lithium ion battery such as the type Tesla uses has a specific energy of 250+ wh/kg. I'm not a EE, but it appears to me that supercaps are a good choice where your energy storage needs are minimal, cycle life is critical, weight isn't, and the rapidly falling voltage as they discharge isn't a problem. None of these reallly applies to an EV, not even an RC car, as far as I can tell. One good use for supercaps is keeping the processor running in portable devices while the user changes the (disposable) battery. The needed capacity is quite small, and the cap (usually) lasts the life of the device. I think they've also been used instead of a battery in some programmable home HVAC thermostats. Supercaps can level an EV's battery load, and thus improve the battery's apparent capacity. In the early 2000s, Solectria used supercaps experimentally as current levelers in EVs, in an effort to get more range out of lead batteries. They worked, but the rapid voltage fall meant they needed a DC:DC converter, and its (in)efficiency was a problem. Also, the range improvement was highly dependent on how the vehicle was driven. http://www.evdl.org/docs/supercap_leveler.pdf The report linked above doesn't discuss the system's cost, but it was very high for the small amount of benefit it returned. If increased range is the objective, it's cheaper and more practical to just increase the EV's battery capacity. That's why you don't see supercaps replacing lithium ion cells in Teslas. David Roden - Akron, Ohio, USA EVDL Administrator = = = = = = = = = = = = = = = = = = = = = = = = = = = = = EVDL Information: http://www.evdl.org/help/ = = = = = = = = = = = = = = = = = = = = = = = = = = = = = Note: mail sent to "evpost" and "etpost" addresses will not reach me. To send a private message, please obtain my email address from the webpage http://www.evdl.org/help/ . = = = = = = = = = = = = = = = = = = = = = = = = = = = = = _______________________________________________ UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub ARCHIVE: http://www.evdl.org/archive/index.html INFO: http://lists.evdl.org/listinfo.cgi/ev-evdl.org Please discuss EV drag racing at NEDRA (http://groups.yahoo.com/group/NEDRA)
