Air vs Liquid, the age old debate petrolhead debate between the purists and the performance junkies, you want to see the epitome just listen to any BMW Motorrad aficionado.
No mater, a new chapter has entered the liquid vs air debate and its relevant to us, active cooling on EV vehicles. See Tesla uses active liquid cooling for their batteries, modules and motors, the Volt uses active cooling although the Volt is technically a PHEV. However the notable absentee is the Nissan Leaf and thats because the Nissan Leaf does not use Active Cooling. What DOES the Nissan Leaf have? How about a cooling controversy in one of the hottest American markets. There are about 20 Nissan Leafs, most clustered in Arizona, that have seen thermal degradation of their battery packs almost exclusively due to the high temperatures these vehicles operate in daily. These owners are seeing an average of 15% capacity loss within 1 or 2 years of ownership, which is an age away from Nissans assurance of only 20% degradation over 5 years. This from Green Car Reports:
I live in Dallas, TX,” wrote one reader in an email to us. “Exactly a year from purchase and 20,206 miles I lost my first capacity bar. It happened yesterday.”
“It is no longer ‘isolated’ to Arizona or a few cars,” they told us. “I have pictures of the gauge if you want them. And it is a far cry faster than the ’20 percent in five years’ Nissan states.”
Looking deeper, we discovered yet more cases of Leafs with lost capacity bars, including unsubstantiated reports that at least two cars in Arizona have now lost not one, but two capacity bars.
Now whats interesting is that back in 2010 just prior to the Leafs launch Wired Magazine actually accused Nissan of cutting corners in getting the Leaf to market so quickly. If you remember Nissans EV program was still nascent when the Leaf burst onto the scene in late 2010, and that's because just 2 years prior Nissan was not even a factor in the EV conversation. Quoted from Wired:
It also appears Nissan has cut corners on the most critical aspect of electric vehicle technology — the battery pack. The key engineering trade-off Nissan has made is opting not to include active thermal management, where the temperature of the pack is controlled by an HVAC system similar to what cools the passenger cabin on a hot day. Instead, Nissan has opted to use only an internal fan that circulates the air within the sealed pack to evenly distribute the heat, which escapes by passive radiation through the pack’s external case.
Thermal management in lithium-ion battery packs is critical to the long-term performance and quality of the battery. The manganese oxide pack is sensitive to high temperature and the primary consequence is that the pack will degrade more rapidly than one with active thermal management. This problem will be worse in hotter climates such as Phoenix, which Nissan has selected as one of its launch cities.
Which is interesting when you consider the quip Ghosen uttered to Bloomberg in early 2010:
"The engineers will always tell you, ‘Wait a little more,’ and if you keep playing this game, you never launch any product"
Right so enough of that, how does this relate to the e-Golf? Well VW has decided to not include an active cooling system on the e-Golf. Their rationale is that because the system has been designed for gentle charge and release it does not need an active cooling system as opposed to rapid charge systems seen on Teslas.
The company’s engineers have tested the e-Golf’s battery pack in places like Death Valley and Arizona, as well as cold-weather climates, and found no dramatic impacts on performance. VW’s Darryll Harrison recently told AutoblogGreen that the Panasonic lithium nickel manganese cobalt oxide cells used in the e-Golf had “the lowest self-warming tendency and the lowest memory effect of all cells tested. The need for a cooling system wasn’t there.”
Of course, this doesn’t mean that VW has given no thought to temperature issues. The company says it has developed a Battery Management Unit with an intelligent thermal control that allows the pack to remain within an optimal temperature window, and that waste heat is quickly directed into the chassis, away from the battery.
VW’s engineering goal for the e-Golf was to develop a highly efficient system, as opposed to one that focused on charge time or capacity. The e-Golf’s cells are designed for “gentle” charge and discharge, which helps to reduce heat, compared to cells designed for rapid charging. The lack of a cooling system also translates into weight savings.
Do keep in mind that the GTE will have active cooling, which VW explains is because of the performance nature of the GTE. However now consider the Nissan Leaf, not a single person in their right mind would confuse the Leaf for a performance vehicle yet the Leaf is still vigorously degrading itself in hot climates.
I have to imagine the Germans will be keeping an extremely close eye on these developments, especially as the e-Golf will likely have a similar appeal to the Leaf in similar markets...