Thursday, May 07, 2009

Today's Brilliant Idea

Chevy is coming out with the Chevy Volt, which is supposed to be the first "series hybrid" in mass production. A "series hybrid" is different from a "parallel hybrid" (the Prius is a parallel hybrid). In a parallel hybrid, there are actually two engines in the car: one is an internal combustion engine (ICE), and the other is electric. Roughly speaking, these two engines work at the same time, or in parallel (this isn't quite true in the Prius, but close enough).

A "series hybrid" only has one engine: an electric engine. The "hybrid" part comes from the fact that there is a generator onboard that produces energy from some sort of fuel. The basic idea is that there is a store of batteries than can be charged at night from a regular electrical outlet, the car runs for about 40 miles on the batteries, and then the generator kicks in if you need more electricity than that for your trip.

The advantages of a series hybrid are that it is more efficient and more simple (it only has one engine rather than two). The disadvantage of the series hybrid is that it requires batteries. Right now, the only practical solution are big, heavy (but cheap) lead acid batteries. These take up so much space that only die hards (like me!) are really willing to work with them, but they do work really well.

The solution is to develop small, light lithium ion batteries. The chemical properties of these batteries allow them to store much more energy per unit mass, which is why they are smaller and lighter - you just need less mass for the same amount of energy. These are popular in small items like laptops, but this is largely because laptops don't remember much energy, so the batteries are pretty small and cheap. Cars require a lot of energy, and there require a lot of battery to run them. This can be done in two ways: make a really expensive (but awesome) car, or figure out a way to make the batteries cheaper.

Chevy believes it can produce the batteries cheaply. Toyota does not believe that anyone can yet. I tend to trust Toyota on this one, due to their success with the parallel hybrids and their relative success in the overall car industry.

So what can be done now, assuming that Chevy doesn't come up with small, light, cheap batteries? This is where my brilliant idea comes in (I am probably not the first, though). Why not build a series electric car without the battery? You would have an electric motor on the car, but this motor would be run by a gasoline generator (for now) rather than batteries. Here are the advantages of such a car:


  • Electric engines are much, much simpler than ICEs.
  • All of the technology that would be used is proven. These electric motors are currently running our fridges, computers, golf carts, and electric cars. There isn't a lot of risk, since we are removing the only risky unknown (the batteries).
  • This appears to be much, much more efficient than an ICE. A typical ICE is roughly 20-25% efficient. That is, if you have a 10 gallon tank of gas, you are actually only using about 2 of those gallons to make the car go forward. The other 8 gallons go toward making the car noisy and hot (which can be good in the winter, but it would be much better to only create heat when you want it and not in, say, August). On the other hand, a home electric generator is roughly 80-85% efficient (it converts one gallon of gas into 30 kilowatt-hours of electricity, which ends up being 83% efficient, since one gallon of gas contains roughly 36 kilowatt-hours of energy). Even accounting for losses at other stages in the engine, it seems like we would immediately have a car that is 2-3 times as efficient as an ICE.
  • These cars could easily be retrofitted once the battery technology is ready. It would not be hard to add batteries to a car later. These means that consumers would not have to be scared off by the "there will be a better technology in five years" thing.
  • Detroit would be able to start preparing for the future today. If it could get a headstart on the basics of the electric car, it could be the leader once we make the inevitable switch.
  • We could gradually change our infrastructure. The first people to buy the cars would use them exactly as we use our current gas cars. As the cost of batteries goes down, the wealthier will replace them first (the batteries will still be expensive, but less so). We could produce a little infrastructure to support the early adopters, and gradually add more as more people get the batteries.


Basically, this seems like it could be the stepping stone to electric cars, and an awesome opportunity for GM (or Ford). They should do this.

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