The other days I heard an interesting lecture at Xerox Parc by Dr. John Hsu of GM’s Advanced Programs office in Palo Alto on GM’s ideas about electric cars. He presented quite a bit of interesting material, a lot of which I hadn’t heard presented before in this form. First of all he distinguished between different kinds of hybrid cars. First, there is the conventional hybrid, like the Prius, where both motors are used together most of the the time and there is very limited electric only range. He contrasts this with GM’s ideas about extended range hybrid vehicles. In these cars a reasonable driving range is achievable on electric power only, and they are assumed to be pluggable, i.e. you can recharge the battery by plugging them in, in addition to turning on the gasoline engine. He distinguished between two types within this category. First, is the urban capable vehicle. This has sufficient range to cover every day driving without recharging the battery, but still relies on kicking in the gasoline engine to achieve peak performance. The second category is the “extented range electric vehicle” which achieves its full performance on the battery and only turns on gasoline engine at all if the battery gets discharged. The rationale behind these categories is that they use progressively less gasoline than a conventional hybrid. They do in this large part by having a bigger battery than a conventional hybrid and being pluggable. The “extended range” category is exemplified by the Volt. The urban capable hybrid by another model which GM plans to introduce (this was to have been a Saturn Vue derivative, but the sale of Saturn has scuppered that plan.). GM has both categories, because the urban capable designs currently allow a broader range of potentially bigger platforms than the Volt design does. He then went on to show a most interesting analysis, as to whether the pluggable hybrids actually reduce CO2 in comparison to regular hybrid. It turns out that the answer depends on the characteristics of the local grid. In California where a lot of electric power is clean, the pluggable hybrids significantly reduce CO2. On the east coast, where a lot of electricity comes from coal, in fact they increase CO2 consumption. Another chart showed the actual fuel savings. Basically the VOLT saves the average driver about half a gallon of fuel per day over, say, a Prius.
So this was a lot of good data, but what does it all mean? First of all, the economics of these designs are still a little odd. A 1/2 gallon a day will not compensate for the sticker shock of the Volt. Particularly as you are getting a glorified commuter car. This will not compete with the Japanese designs. Honda has intentionally priced the Insight to be affordable. Nissan is coming out with an economy priced pure electric car. And remember, today’s Prius is actually quite a large car, good for long trips and carrying lots of cargo. The Volt is not a replacement for that, and much pricier.
An interesting question is the relative sizing of the drive trains. Dr. Hsu pointed this out, that one option is to simply have redundant drive trains, with either electric of gasoline motors having equal power. Obviously, this is very inefficient. The compromise is either to make one motor much smaller than the other, or simply make them both small. The Toyota hybrids go for the later option – and simply use all the motors together for peak acceleration. This means thought that even with a bigger battery, performance is limited without turning on the gasoline engine. Admittedly, with a bigger battery, you won’t have to run the engine as much to recharge the battery, and can only run when you need to accelerate more. So making a Prius pluggable will make it get much higher gas mileage, but without retuning the propulsion system, to drive a significant distance at 70mph will require some gasoline. The Volt’s option is to allow you to go full tilt on the electric motor, but then suffer a big performance penalty when you’re out of battery. This is much what happens in the Prius if you drive at freeway speeds in the mountains – once you kill the battery your acceleration drops way off. With the Prius one learns to take advantage of momentum and give the battery enough time to recharge either from the motor or from a descent so that you do have enough power for the up hill sections. Driving to Yosemite or up I-80 in Sierras gives one lots of practice with that. The question will be if similar behavior will make the Volt palatable too at the outer limits of its range.
Some people wondered why bother with the gasoline motor at all if 80% of all trips are short range, and the Volt can handle that range? The answer of course is that people do need to take the other 20% of trips, and a range constricted car will force people into having a more conventional second vehicle, which dilutes its impact per household. People also asked about ideas for exchanging batteries. Dr Hsu responded that it’s like with changing batteries in latops: it used to be much more common than it is today, few people are doing it, and increasingly there is simply enough battery life not to do that. So from his perspective by the time such a battery swapping scheme came to market, it would likely be obsolete.
So what’s it all mean? I know I want to get a pluggable car for my next vehicle. It’s fairly obvious this will by a hybrid, with a gasoline engine in it, rather than a pure electric. I demand a practical car that can do I anything I want. It will also need to be affordable – I won’t pay an absurd premium simply for unusual technology. So, what will it be? Will I buy one of the GM electric cars? Honestly, at this point I don’t know. I don’t really see a convincing feature set there at an appropriate price. Of course, with all the new players entering the market practically every month (the latest being Nissan), I’m sure this will all change over the next two years. In any case this was a good, informative talk, even though I still haven’t figured out which electric car to get.
