20 August 2006

Baby Steps Along the Plug-in Path

As I mentioned in my last post on the drawbacks of hydrogen, it has problems with production, storage, and distribution. It is well known that electric vehicles thump hydrogen on production efficiency. With regards to storage, the problems for batteries are greater than hydrogen but are still technical rather than theoretical in origin. Distribution is not a problem at all for electrics and plug-ins.

Not only does the electrical grid already exist, but also progress towards a full-fledged plug-in hybrid can be made in small baby steps that do not require any massive investments of capital.
  1. The battery capacity can be tailored to the user. Ideally a plug-in hybrid should have enough electric range for the daily commute. Since battery storage is expensive no one will want to buy more then is economical for them
  2. As transportation energy consumption is shifted to electricity the proportion of hydrocarbon fuel that is derived from biomass or synthetic sources can be increased at the expense of fossil fuels. This does not benefit climate change greatly but does have a major mitigating impact on the problems of peak oil.
  3. Improvements in hybrid technology that boost the tank-to-wheel efficiency of cars can be gradually introduced. This includes adding ultracapacitors to increase the power that can be recouped by braking, lightening of the body, etc.
It is easy to imagine the battery capacity of the plug-in advancing in small steps. Right now the biggest markets for high power batteries is power tools and laptops. Widespread introduction of hybrids with their large battery packs should drive the price down (as long as it doesn't cause any material shortages). The Toyota Prius currently carries a 1500 Wh battery pack. Assuming it can discharge 50 % of its capacity and it consumes 160 Wh/km then the electric range is already almost 6 km. The main reason the Prius doesn't have an all-electric switch (in North America) is that the battery and transmission can't provide enough power to achieve high speed. That requires a series hybrid setup, where there is no transmission: the propulsion is provided solely by electric motors.

Switching from a parallel to a series hybrid is a big step. It transforms the engine into a generator, which implies that it runs at a constant speed. This will benefit diesel engines significantly on the side of pollution emissions. It also means that the size of the internal combustion generator component of the car can shrink substantially. The engine only needs to be able to provide enough power to keep the vehicle at highway cruising speed. For a car such as the Prius traveling at 110 km/h that's only about 15 kW (or 20 hp) to overcome the drag and rolling resistance. Note that is power needed at the tires, not what's developed on the crankshaft. All of the surge acceleration can be handled by the stored electrical energy. The torque of electrical motors is extremely high.

I exaggerate a touch but the hydrogen path benefits little from hybrid technology. One can't take all the benefits of the hybrid path and then at the end of the road decide to switch to the less efficient hydrogen vehicle. Does not compute, QED.

One reaction to the general malaise around hydrogen hype lately comes from Hydrogenics, which has joined the Plug-in Development Consortium (hat tip to Green Car Congress). This is a fairly major step down for a major Proton Exchange Membrane fuel cell equipment manufacturer. The plug-in concept marginalizes the on-board generator by attempting to use battery capacity to its maximum.

At some time in the far future we might find ourselves in the situation where electricity can be produced extremely cheaply in prodigious quantities. The most likely candidate would be solar power that uses thin-film technology that can be produced without high vacuum manufacturing. In this case the efficiency of energy storage might become irrelevant. One might assume that a hydrogen vehicle could be produced for significantly less, even if it consumed 2-3 times more energy. Currently the Honda H2 fuel cell vehicle costs about $2000000 so they have a long way to go. In fact the concept is so far into the future, what possible business does a commercial company have doing research on the subject? It's futurist stuff, which is why we see hydrogen often talked about in the same breath as carbon nanotubes and superconductors. The path to improving the status quo clearly lies along the path Toyoto chose of the hybrid vehicle. We have to keep kicking car builders in the pants so they continue to move forward.


Alex said...

Not only does the electrical grid already exist, but also progress towards a full-fledged plug-in hybrid can be made in small baby steps that do not require any massive investments of capital.


That requires a series hybrid setup, where there is no transmission: the propulsion is provided solely by electric motors.

I really find it hard to see why, having made the step to having batteries, motors and generators in a car, anyone has kept a mechanical transmission. It's just weight, friction and complexity. And it forecloses so much of the vehicle design.

Just killing the mechanical transmission would be an achievement. As you point out, the engine can be operated at its best efficiency speed all the time. Power is used much more efficiently. Regenerative braking is there. So is full-time all-wheel drive. With the motors mounted at the wheel, there's no need for an axle either - there goes another great lump of steel. There's no reason not to have four-wheel steering, for that matter, and everyone (not just Michael Schumacher) can have traction control, in software.

And the chassis design can be transformed. There being no reason not to put the wheels at the optimal location (the corners of the car). The battery pack is most of the weight, and that obviously goes right in the middle under the floor. Ferrari handling for everyone. No axles, no bonnet and no transmission tunnel means all the load space you can eat. If all the power transmission and control functions are wires with standard connectors, modular design gets serious. The possibilities are spectacular.

Robert McLeod said...

The primary reason why the hybrids still use a mechanical transmission is that its more efficient in transferring power to the wheels. An electrical transmission needs an electrical generator (your alternator might hit 90 % efficiency) attached to an electric motor (97 - 99 % efficient). The drop-off in the eletrical system needs to be clawed back by being lighter than its mechanical equivalent and running the heat engine at its optimum rate.

chaindropz said...

I enjoyed your post. I have been invested in ultracapacitors since about mid 2000. It looks like it will be a little longer to see the ramp.

chaindropz said...

I did not understand your comment on why the transmission remained mechanical. Don’t bother trying to explain it again. I probably would not understand. I like your blog and will be back when I have more time. I am sure you know about Oshkosh truck corporation propulse that do not have a transmission ,torque converter or batteries. I also think you make a good point about condensation and old gas.

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